3-phase Design Quandry

[bangkokumpalumpa]

ok the center pic is of the open door it is the back of the meters.

the right hand pic is the inside of the cabinate behind the meters, the blue units are the coils for measuring the amps, the mains wires go through these coils.

this is just some of the things we have in stock about the place, it is interesting what you collect over time, we have quite a lot of three phase stuff about.

[elkangorito]

Hi Zap.

You will not really save anything if you worry about socket outlets. Even if you halve the current of them, you will still end up with about 80 amps for your MD (27 amps per phase if you have 3 phase). You may save a little bit in the cable cost.

Let me reiterate the socket outlet part of the MD calc:

Upstairs <60 = 25 amps. Downstairs <40 = 20 amps. Under your circumstances, this seems to be quite resonable given that each socket outlet is rated at 10 amps. Your "after diversity calculation" arrived at a total of 45 amps for <120 socket outlets.

The method used to calculate your MD is one of 4 methods available (yours was "calculation"). The other methods are:

1] Assessment.

2] Measurement.

3] Limitation.

Assessment is the most difficult to do...especially in a domestic situation because people tend to change their habits etc. Also, when new family members arrive (babies etc), this causes yet another change.

Measurement is possible but it will only be of any use if the current used is monitored over a long period (months or better yet, 1 year).

The limitation method is simple but very expensive...even more expensive than your current calculation.

From the Standard;

Where more than one item of equipment is connected, the circuit current could be simply assessed as the sum of the individual equipment load currents. While this would provide a safe and conservative solution, it does not take account of the normal operating conditions during which all equipment is not operating simultaneously at full load or for long periods, e.g. submains to a distribution board associated with numerous socket outlet circuits. Under such conditions the circuit current is estimated using diversity factors and is often described as the 'after diversity maximum demand'.

The diversity factors applicable to any given circuit in an installation will depend on a number of features of the installation including—

[a] conditions under which the installation is expected to be used, e.g. residential compared with commercial; and

operating characteristics of the connected load, e.g. airconditioning load in tropical locations compared with heating loads in cold-climate regions; and

[c] number and physical distribution of points provided on the circuit, e.g. socket-outlets provided for convenient connection of portable equipment compared to dedicated or fixed equipment loads; and

[d] size and type of significant loads, e.g. large motors or industrial plant.

It should be recognized that the determination of diversity factors is not accurate for every installation and different installations of the same type may have significantly different load profiles which the designer needs to consider. The methods provided herein have been used over several editions of AS/NZS 3000 and, provided that care is taken to assess the

presence of unusual equipment loads, are considered appropriate for many typical applications.

When the load is assessed and the current-carrying capacity of the circuit is determined by allowing for diversity of operation of equipment, then the circuit should be protected by a circuit-breaker of rating to comply with Paragraph B3.2.

If you wish to gamble, that's up to you. When it comes to electrical, I trust a tried & tested standard. The 5 cents you might save today may cost you a lot more in the future.

BTW, electricians in Australia would end up with the same result as I did. The "not so smart" electricians tend to gamble (which means "guessing"). They do this to "win the job". Two important purposes of using "After Diversity Maximum Demand" are to avoid FUTURE situations of voltage drop & hot cables (fire).

If you have the notion of installing voltmeters & ammeters, it is not as easy as you think.

For a start, you will need a much larger switchboard. Then, "cutouts" will need to be made for the meters & rotary switches. BS88 (or BS1361) fuses will need to be installed for fault protection. There are no electronics involved but there is control wiring.

I think you have nothing to worry about. You have a valid MD calculation that has been tried, tested & otherwise proven to be safe & unproblematic.

I think you really need to concentrate on what the PEA are going to do about your MD, whether you take a short cut & make it 80 amps or use the present MD of 100 amps. You need to make sure that they will use the correct cable for your installation.

Also, don't get caught up in a battle with them (PEA) about paying money for transformers. Far too many foreigners fall for this trick. If you are in a "zoned" area for building, you need to find out what the electrical limitations are for your zone. I'll bet it's not a 15 amp meter! The PEA must supply you with electricity at their cost (if you are permitted to have a large supply). The exception is if you live a long way from power lines, in which case, you will pay for cable & transformer costs. FYI, typical transformer sizes in Thailand are from 20KVA for an individual installation to about 250KVA for local distribution.

Edited November 2, 2009 by elkangorito

[zapatero]

Hi Elk,

Regarding your below, let me assure you that I don't intend to try to "cut corners" here by presuming a lesser MD than you have calculated. I have already exhausted my questions regarding the possibility of reducing the MD, and you have addressed them satisfactorily.

The switchgear that I have already ordered complies with your MD. (From memory..., I think your arithmetic was): MD = 101amps, 101/3 = 34amps/phase, +20% for expansion = 40amps/phase, rounded up for conservatism = 50amps/phase. The switchgear that I have ordered complies with that 50amps/phase, and is consistent with our emails and posts.

In short, rather than gambling (your correctly chosen word) with a lesser MD, I prefer to be cautious and conservative. And indeed, I wish to use the appropriate main supply cable. But that's where the present confusion lies. I'll get to that in the next post.

Here I would just like to say that your extended discussion of the MD calculation makes this topic much clearer. Thank you.

Hi Zap.

You will not really save anything if you worry about socket outlets. Even if you halve the current of them, you will still end up with about 80 amps for your MD (27 amps per phase if you have 3 phase). You may save a little bit in the cable cost.

Let me reiterate the socket outlet part of the MD calc:

Upstairs <60 = 25 amps. Downstairs <40 = 20 amps. Under your circumstances, this seems to be quite resonable given that each socket outlet is rated at 10 amps. Your "after diversity calculation" arrived at a total of 45 amps for <120 socket outlets.

The method used to calculate your MD is one of 4 methods available (yours was "calculation"). The other methods are:

1] Assessment.

2] Measurement.

3] Limitation.

Assessment is the most difficult to do...especially in a domestic situation because people tend to change their habits etc. Also, when new family members arrive (babies etc), this causes yet another change.

Measurement is possible but it will only be of any use if the current used is monitored over a long period (months or better yet, 1 year).

The limitation method is simple but very expensive...even more expensive than your current calculation.

From the Standard;

Where more than one item of equipment is connected, the circuit current could be simply assessed as the sum of the individual equipment load currents. While this would provide a safe and conservative solution, it does not take account of the normal operating conditions during which all equipment is not operating simultaneously at full load or for long periods, e.g. submains to a distribution board associated with numerous socket outlet circuits. Under such conditions the circuit current is estimated using diversity factors and is often described as the 'after diversity maximum demand'.

The diversity factors applicable to any given circuit in an installation will depend on a number of features of the installation including—

[a] conditions under which the installation is expected to be used, e.g. residential compared with commercial; and

operating characteristics of the connected load, e.g. airconditioning load in tropical locations compared with heating loads in cold-climate regions; and

[c] number and physical distribution of points provided on the circuit, e.g. socket-outlets provided for convenient connection of portable equipment compared to dedicated or fixed equipment loads; and

[d] size and type of significant loads, e.g. large motors or industrial plant.

It should be recognized that the determination of diversity factors is not accurate for every installation and different installations of the same type may have significantly different load profiles which the designer needs to consider. The methods provided herein have been used over several editions of AS/NZS 3000 and, provided that care is taken to assess the

presence of unusual equipment loads, are considered appropriate for many typical applications.

When the load is assessed and the current-carrying capacity of the circuit is determined by allowing for diversity of operation of equipment, then the circuit should be protected by a circuit-breaker of rating to comply with Paragraph B3.2.

If you wish to gamble, that's up to you. When it comes to electrical, I trust a tried & tested standard. The 5 cents you might save today may cost you a lot more in the future.

BTW, electricians in Australia would end up with the same result as I did. The "not so smart" electricians tend to gamble (which means "guessing"). They do this to "win the job". Two important purposes of using "After Diversity Maximum Demand" are to avoid FUTURE situations of voltage drop & hot cables (fire).

I think you have nothing to worry about. You have a valid MD calculation that has been tried, tested & otherwise proven to be safe & unproblematic.

I think you really need to concentrate on what the PEA are going to do about your MD, whether you take a short cut & make it 80 amps or use the present MD of 100 amps. You need to make sure that they will use the correct cable for your installation.

[zapatero]

There are only three meter sizes available in our area: 5/15, 15/45, and 30/100. I have advised the PEA of your MD calculation and they have said that I would be able to have a 30/100 meter. The issue is that 3-phase is not yet available at our location. That leaves us with three options: 1) to pay for extending their 3-phase cables to our location, 2) to pay for a transformer at our location, or 3) "tough it out" with single phase until the PEA (inevitably) brings 3-phase past our location, to service all the new constructions downstream from us. But we cannot make this decision yet, because we don't yet know the costs of options 1) and 2)

The decision that we should be able to make at this time, however, is the specification for our main supply cable. I asked the PEA and they say, "16 mm^2 (copper) should be fine, but go with 25 if that makes you feel more comfortable". Sorry, but the precision of that answer doesn't make me feel more comfortable. Furthermore, the PEA's own endorsed table indicates that 35 mm^2 (copper) is the minimum size for a 100 amp service! But worse yet, that table includes no parameter for the length of the cable!

Furthermore still, I have tried at least six online cable-sizing calculators and get inconsistent answers from all of them. I am sure that much of this confusion is simply due to my own limited understanding. But for one thing their input forms don't appear to clearly distinguish between total amps and phase amps.

So my bottom line: Can someone out there please help me define the specifications for our main supply cable, based upon the following assumptions:

A 3-phase (30/100) meter

Elk's Maximum Demand = 101 amps, extended to 50 amps/phase for conservatism

100 meter run, 80 of this underground

Copper cores

**(If I've missed anything, please tell me)

If you use a calculator, that's fine with me, but please identify it so that I can get "grounded" with these things, and figure out why I can't get them to agree. If it is useful, here is my latest one, from an electrical engineering friend in the U.S.: **{http://www.csgnetwork.com/wiresizecalc.html}**

BTW, as a quick digression, for the first time today I have just fingered a sample of NYY 4-core 25 mm^2 copper cable. It is (to me anyway) a shockingly large hunk of hardware -- nearly 1-1/2 inches in diameter. And I was quoted a price of 366 THB per meter.

Also, don't get caught up in a battle with them (PEA) about paying money for transformers. Far too many foreigners fall for this trick. If you are in a "zoned" area for building, you need to find out what the electrical limitations are for your zone. I'll bet it's not a 15 amp meter! The PEA must supply you with electricity at their cost (if you are permitted to have a large supply). The exception is if you live a long way from power lines, in which case, you will pay for cable & transformer costs. FYI, typical transformer sizes in Thailand are from 20KVA for an individual installation to about 250KVA for local distribution.

[elkangorito]

Zap, I've calculated the type & size cable you need that allows for a voltage drop of not greater than 5% of the supply voltage (19 volts). It is made by Thai Yazaki http://www.thaiyazaki-electricwire.co.th/index_building.html

The size & type is 16mm squared copper, THW, MEA Type A - see the above link for pictures & other info.

Just to ensure perfect clarity, you will need four (4) conductors for your consumer mains. All of these conductors will be the size & type of cable mentioned above. I also recommend that you use a minimum size conduit of 40mm & that it be buried no less than 500mm deep.

This size cable will easily allow 46 amps as per the Aust Standard (AS3008.1.1:1998). The method I used is conservative so assume the cable is ok for 50 amps.

In case I didn't mention it, your Main Earth cable should be no less than 6mm squared copper. This is the cable that runs from the Earth Electrode (rod) to the Earth Bar in your consumer unit.

[zapatero]

Thank you, Elk,

I'm relieved to see that you are comfortable with 16mm^2 instead of that monstrous 25mm^2, 4-core that I mentioned.

Zap, I've calculated the type & size cable you need that allows for a voltage drop of not greater than 5% of the supply voltage (19 volts). It is made by Thai Yazaki http://www.thaiyazaki-electricwire.co.th/index_building.html

The size & type is 16mm squared copper, THW, MEA Type A - see the above link for pictures & other info. Check

Just to ensure perfect clarity, you will need four (4) conductors for your consumer mains. Check All of these conductors will be the size & type of cable mentioned above. I also recommend that you use a minimum size conduit of 40mm & that it be buried no less than 500mm deep.

For some reason I had pictured in my mind that I would need a single 4-core cable, whereas you are specifying four single-core cables. Can you please clarify the issues at play?

This size cable will easily allow 46 amps as per the Aust Standard (AS3008.1.1:1998). The method I used is conservative so assume the cable is ok for 50 amps.

In case I didn't mention it, your Main Earth cable should be no less than 6mm squared copper. This is the cable that runs from the Earth Electrode (rod) to the Earth Bar in your consumer unit. I should be O.K. here -- this cable is 25 mm^2!

Finally, I have searched, but cannot find, a table that defines the codes/ratings THW, VAF, NYY, etc. Can you please tell me where to look?

[elkangorito]

For some reason I had pictured in my mind that I would need a single 4-core cable, whereas you are specifying four single-core cables. Can you please clarify the issues at play?

Finally, I have searched, but cannot find, a table that defines the codes/ratings THW, VAF, NYY, etc. Can you please tell me where to look?

Four (4) individual cores may be cheaper than a multicore cable. Also, if you have an electrical problem with a multicore cable, the whole cable will need to be replaced whereas with individual cores, each affected core need only be replaced.

Ratings for the cable I mentioned are in the following link;

http://www.thaiyazaki-electricwire.co.th/p...hw_meatypea.pdf

[zapatero]

Thank you, Elk.

I keep thinking that I should be thinking about surge suppression. I'm aware that there are devices for this purpose but I know little about them. Do the HRC fuses that you recommend help with this concern? Or is their purpose completely different?

Also, since I am tied into the telco for DSL internet service, it would seem like I should have surge suppression on my phone line also.

If I am wrong on either or both counts, please tell me; or, if you agree, can you (or anybody) recommend any make/models of devices that you have had good experience with?

Thank you very much,

~~z

I have searched, but cannot find, a table that defines the codes/ratings THW, VAF, NYY, etc. Can you please tell me where to look?

Finally, if anyone is interested, after more searching the above codes are part of the Thai Industrial Standard (TIS) for the manufacture and testing of cables, (TIS. 11-2531). So, as best I can tell, they are particular to Thailand and not international.

[zapatero]

Hi David96,

Finally, in reply to your post below of some days ago. The PEA came out yesterday and affirmed that the local transformer is 50KVA. He said several things that just didn't make sense to me; (I have this trouble anyway , but the translation hash didn't help any.) I'll try to focus on just one point and see if you (or anyone) can clarify it for me.

He indicated that I could have the (expensive) 30/100 3-phase meter if I wanted it, but said that he felt that a 15/45 meter would be adequate. Well, I thought that 45 max/phase would be pretty close to Elk's 50/phase, so let's talk about this (as an example.) He affirmed that this meter would accept up to 45/phase. So, 3 x 45 = 135 doesn't it? This is 35% over Elk's MaxDemand calculation of 101 amps. So why not consider it? At this point he visibly pulled back and said, "Oh, no, the total maximum amps from this meter could not exceed 45." And this is when he cited his small 50KVA transformer.

Well, maybe I missed something in the translation, but I have been told more than once, by several different people, that I should be able to pull up to the full 45 amps/phase, (total 135), (at least for short periods), from this meter. Now I am completely confused. A complete contradiction. Can you, (or anyone), give me an explanation that hangs together with the above statements -- or am I completely misunderstanding something?

Strange that the PEA does not know the size in KVA of the distribution transformer it is usually

stamped on the side of the transformer and can be read from the ground. 50KVA and 100KVA

are common sizes for distribution transformers.

It is obvious that from your MD you may have to go to a 3 phase supply. Otherwise it is 22kw all on one phase or balance 22kw over 3 phases. ie approx 7kw per phase.

And if the PEA transformer is found to be too small it would have to be upgraded.

[faifa77]

Wow you guys are comprehensive!

May I sugest UN Electric in Bangkok as a cheap source of wire. Ask for K. USA ..she speaks English.

Make sure you get a high quality ground rod / copper encased steel 10' x 5/8" and if you can get someone with a ground resistance meter

check the soil..Should be 1 ohm. I f higher ..more rods or special gound soil..avail in BKk

Surge protect everything tv, phone lines , main panel.

These simple steps will protect the expensive componets in your home.

Jack

[david96]

Hi David96,

Finally, in reply to your post below of some days ago. The PEA came out yesterday and affirmed that the local transformer is 50KVA. He said several things that just didn't make sense to me; (I have this trouble anyway , but the translation hash didn't help any.) I'll try to focus on just one point and see if you (or anyone) can clarify it for me.

He indicated that I could have the (expensive) 30/100 3-phase meter if I wanted it, but said that he felt that a 15/45 meter would be adequate. Well, I thought that 45 max/phase would be pretty close to Elk's 50/phase, so let's talk about this (as an example.) He affirmed that this meter would accept up to 45/phase. So, 3 x 45 = 135 doesn't it? This is 35% over Elk's MaxDemand calculation of 101 amps. So why not consider it? At this point he visibly pulled back and said, "Oh, no, the total maximum amps from this meter could not exceed 45." And this is when he cited his small 50KVA transformer.

Well, maybe I missed something in the translation, but I have been told more than once, by several different people, that I should be able to pull up to the full 45 amps/phase, (total 135), (at least for short periods), from this meter. Now I am completely confused. A complete contradiction. Can you, (or anyone), give me an explanation that hangs together with the above statements -- or am I completely misunderstanding something?

Strange that the PEA does not know the size in KVA of the distribution transformer it is usually

stamped on the side of the transformer and can be read from the ground. 50KVA and 100KVA

are common sizes for distribution transformers.

It is obvious that from your MD you may have to go to a 3 phase supply. Otherwise it is 22kw all on one phase or balance 22kw over 3 phases. ie approx 7kw per phase.

And if the PEA transformer is found to be too small it would have to be upgraded.

A distribution transformer rated at 50KVA 220/380 volts will supply 76 amps per phase.

This has to supply all existing consumers supplied off this transformer.

When you add your max demand as calculated ( 34 amps per phase) it will be obvious

that the transformer will be overloaded.

The PEA will have to upgrade (replace) the existing transformer with a larger one eg,

100KVA. This will supply 150 amps per phase.

A 10/45 meter will carry 45 amps continuous, they are calibrated at 10 amps.So you could have 3 x 10/45 meters, one for each phase or 1 x 3 phase 10/45 meter. This would depend on the policy of the PEA.

Now whether the PEA want you to fund some of the capital cost of the upgrade is another matter. It would appear that you should not have to bare the cost except for the initial connection to supply.

[david96]

Just a note on energy metering.

The ratings of a kWh meter. eg 10/45. The first figure is the current in amps that it is calibrated at.

The second figure is the max continuous load current in amps that it will carry without affecting the accuracy of the meter. The revs per kWh is taken at a load of 10 amps or the first figure.

The first figure may be 5 ( 5/15 ) or 30 ( 30/100) for example.

Where the load is large eg 200A per phase or more current transformer metering is used.

The meters are rated 5/200, 5/400, etc. This means they have a max 5 amps though

the meter for measurement purposes, revs per kWh is taken at 5 amps.

Meters may be single phase or three phase.

The size of the meter in amps does not affect the total amps that one can use, this is dependant on the size of the distribution transformer, and your demand on the transformer in amps at any given time.

Energy meters remain the property of the supply authority, one does not "buy" a meter in this case the "connection to supply fee" covers the cost of supplying a meter.

[elkangorito]

Thank you, Elk.

I keep thinking that I should be thinking about surge suppression. I'm aware that there are devices for this purpose but I know little about them. Do the HRC fuses that you recommend help with this concern? Or is their purpose completely different?

Also, since I am tied into the telco for DSL internet service, it would seem like I should have surge suppression on my phone line also.

If I am wrong on either or both counts, please tell me; or, if you agree, can you (or anybody) recommend any make/models of devices that you have had good experience with?

Thank you very much,

~~z

I have searched, but cannot find, a table that defines the codes/ratings THW, VAF, NYY, etc. Can you please tell me where to look?

Finally, if anyone is interested, after more searching the above codes are part of the Thai Industrial Standard (TIS) for the manufacture and testing of cables, (TIS. 11-2531). So, as best I can tell, they are particular to Thailand and not international.

Hi Zap.

HRC fuses will not protect an installation from any electrical surges.

This page may shed some light on Surge Protection for you.

http://www.novaris.com.au/power/index.shtml

To protect your power, I'd recommend something like this;

http://www.novaris.com.au/Surge-Diverters/...ple_phase.shtml

To protect your phones etc, I'd go for something like this;

http://www.novaris.com.au/Telephone/RJ_Mod...rotection.shtml

The products shown are high quality & are probably not available in Thailand. The technical info on the pages can be used to source such equipment in Thailand.

In one of the Square D catalogs (Square D catalog 08 - page 11 to page 20), surge protection equipment is shown. Not enough information is shown to decide if this is what you need. The device is on page 6. Its part number is QO-SPD225.

David has done a pretty good job of covering your KWH meter questions

[david96]

Hi Zapatero,

One finds it unusual that the PEA does not look at and calculate the maximum demand in amps, and then see if the distribution transformer can handle the extra proposed load.

Supplying a 3 phase 45 amp energy meter (15/45) is correct if the MD is less than this figure and the distribution transformer can handle the extra load but supplying a 15/45 amp meter and then implying that you can have a load of 45 amps per phase when in fact the transformer cannot supply this extra load is misleading and the PEA is avoiding their responsibilities.

Your electrician should be capable of approaching the PEA on your behalf and be able to

advise them of the proposed loading (MD) and they should be able to advise what the actual

conditions of supply are for your installation.

In your case the MD has been calculated using AS3000/2007. How maximum demand calculations are made in Thailand may be completely different or more than likely in the case of residential installations ignored altogether in the case of the PEA or they just say that the MD is the max continuous rating of the meter (45A) and ignore the fact of the extra load on the distribution transformer and if it is capable of supplying it.

The standard meter for most Thai residential installations is single phase 5/15A.

[zapatero]

Hi David96,

Thank you for this, and for your previous post on energy metering -- that helped me clear up some misconceptions.

Hi Zapatero,

One finds it unusual that the PEA does not look at and calculate the maximum demand in amps, and then see if the distribution transformer can handle the extra proposed load.

Yes, I agree with you. I also am having to adjust to a number of things that I find unusual in the way such things are conducted around here. But, I guess, as Elk says, the PEA doesn't do MD calculations; they just guess, based upon their past experience...

Supplying a 3 phase 45 amp energy meter (15/45) is correct if the MD is less than this figure and the distribution transformer can handle the extra load but supplying a 15/45 amp meter and then implying that you can have a load of 45 amps per phase when in fact the transformer cannot supply this extra load is misleading and the PEA is avoiding their responsibilities.

Yep

Your electrician should be capable of approaching the PEA on your behalf and be able to

advise them of the proposed loading (MD) and they should be able to advise what the actual

conditions of supply are for your installation.

Would that it were so. Unfortunately, my ET and the PEA folks are equally enlightened on the subject of MD calculation. So they chat together, and then since both of their guesses are consistent (at 15/45), that then becomes the analytical conclusion

In your case the MD has been calculated using AS3000/2007. How maximum demand calculations are made in Thailand may be completely different or more than likely in the case of residential installations ignored altogether in the case of the PEA or they just say that the MD is the max continuous rating of the meter (45A) and ignore the fact of the extra load on the distribution transformer and if it is capable of supplying it.

IMHO, you have hit the nail directly on the head.

In summary, I guess it boils down to what Elk says: Advise the PEA of everything, including the proper MD calculation that was done. (And I have done this.) And make sure that my own wiring and main feed cables are consistent with that MD calculation, and then let PEA do what they wish. And if their meter burns out then it won't be my fault. (Side note: I should say, in the PEA's defense, that they have been very congenial and positive -- they just haven't been very rigorous in their conclusions, or precise in their recommendations.)

[zapatero]

Thanks for the edit, Crossy. It does look better. I didn't realize that there was such a rule. I need to learn how to better use this tool.

BTW, for some reason I cannot edit my own posts. The "Edit" button used to appear, but doesn't anymore. Does anyone else have this problem?

~~z

Edit: [Well, now it DOES appear again! Do other people have "intermittent Edit buttons"?]

Edited November 15, 2009 by zapatero

[zapatero]

This page may shed some light on Surge Protection for you.

http://www.novaris.com.au/power/index.shtml

To protect your power, I'd recommend something like this;

http://www.novaris.com.au/Surge-Diverters/...ple_phase.shtml

To protect your phones etc, I'd go for something like this;

http://www.novaris.com.au/Telephone/RJ_Mod...rotection.shtml

The products shown are high quality & are probably not available in Thailand. The technical info on the pages can be used to source such equipment in Thailand.

Thank you for your SPD post, Elk. I have been studying the links, but see that this is yet another topic that I need to learn more about.

In the meantime, if anyone has purchased such devices here in Thailand, that have performed well, I would appreciate knowing the makes and models.

TYVM, ~~z

[Crossy]

Thanks for the edit, Crossy. It does look better. I didn't realize that there was such a rule. I need to learn how to better use this tool.

BTW, for some reason I cannot edit my own posts. The "Edit" button used to appear, but doesn't anymore. Does anyone else have this problem?

Edit: [Well, now it DOES appear again! Do other people have "intermittent Edit buttons"?]

The 'edit' button only appears for a limited time (20 mins I think) after the post is made.

The rule in question

30) Do not modify someone else's post in your quoted reply, either with font or color changes, added emoticons, or altered wording.

is fairly new, there have been occasions that the quoted post has been modified and the meaning changed so Admin decided to prohibit any modification of quotes, you can still remove irrelevant bits of the quote just don't modify the wording.

I'm guilty as hel_l of adding coloured responses to quotes as in many cases it's a good way to respond, just go to get out of the habit

[elkangorito]

Zap, it appears that you are at a crossroads in your little project. What is your preference? Will you opt for;

1] a single phase supply (100 amp)?

2] a 3 phase supply using 3 single phase meters (15/45)? or

3] a 3 phase supply using a 30/100 3 phase meter?

The reason I ask is that the overcurrent protection for your consumer mains & KWH meter will be different, depending upon which one of the above you choose.

[zapatero]

Hi Elk,

Sorry for the delay in responding -- we have had some medical complications that needed attending to.

The PEA came out again yesterday; and, unless something unforeseen happens we are going opt for your first option -- a (30/100) single phase supply. This will save quite a bit of expense, and will (as I understand) end up with essentially the same result as would a 3-phase supply.

To recap things up to the present, we have a house that is fully wired for 3-phase, a 3-phase load center, and will have 3-phase (4-conductor) consumer mains to the PEA, with each core as you have recommended at least 16 mm^2 copper. (In fact, I am even considering 25 mm^2, for conservatism and expansion.) The three phase-conductors will be tied together just south of the (30/100) single phase meter. Both the PEA and my ET agree and are comfortable with this arrangement.

A single-phase (30/100) meter costs 12,383 THB, but a 3-phase (30/100) meter costs 38,754 THB. However, in our case, there would also be considerably greater expenses to bring 3-phase to our property.

I am presuming, (hoping is probably more accurate), that my 3-phase, 3-pole, 50 amp main circuit breaker will be satisfactory for this arrangement. If I am wrong, or if there are other flaws that need repairing, please tell me.

TYVM!, ~~z

Zap, it appears that you are at a crossroads in your little project. What is your preference? Will you opt for;

1] a single phase supply (100 amp)?

2] a 3 phase supply using 3 single phase meters (15/45)? or

3] a 3 phase supply using a 30/100 3 phase meter?

The reason I ask is that the overcurrent protection for your consumer mains & KWH meter will be different, depending upon which one of the above you choose.

[david96]

The 50kVA distribution transformer is rated at 75A per phase. This is 16.5kW at 220V.

You max demand is 22kW. It would exceed the rating for one phase of the transformer.

if connected all on one phase.

Even balanced accross 3 phases the transformer will be overloaded.

Your proposed load (MD of 100A ) plus the existing consumers loads already connected.

[elkangorito]

Hi Zap.

You will need a new Main Circuit Breaker. A 3 pole 50 amp circuit breaker used on single phase means a total current of 150 amps, which exceeds the maximum allowable current of the KWH. If you choose to use a 3 phase breaker for this application, it will need to have a maximum 30 amp rating (30 amps per pole). It's highly unlikely that you should suffer any nuisance tripping with this breaker. If the 3 supply cables are joined at the KWH meter, there is no need to join them again at the incoming side of the main circuit breaker...just connect each of the 3 cables to the main circuit breaker.

The price for the KWH seems odd after looking around on the web. You will most likely have a DD862 KWH. Look at the prices in the link below (remove the brackets). Even if import tax was high, the prices you were quoted still seem weird.

[http://www.alibaba.com/product-gs/224798075/DTS_DT862_3_phase_energy_meter.html]

Hi Elk,

Sorry for the delay in responding -- we have had some medical complications that needed attending to.

The PEA came out again yesterday; and, unless something unforeseen happens we are going opt for your first option -- a (30/100) single phase supply. This will save quite a bit of expense, and will (as I understand) end up with essentially the same result as would a 3-phase supply.

To recap things up to the present, we have a house that is fully wired for 3-phase, a 3-phase load center, and will have 3-phase (4-conductor) consumer mains to the PEA, with each core as you have recommended at least 16 mm^2 copper. (In fact, I am even considering 25 mm^2, for conservatism and expansion.) The three phase-conductors will be tied together just south of the (30/100) single phase meter. Both the PEA and my ET agree and are comfortable with this arrangement.

A single-phase (30/100) meter costs 12,383 THB, but a 3-phase (30/100) meter costs 38,754 THB. However, in our case, there would also be considerably greater expenses to bring 3-phase to our property.

I am presuming, (hoping is probably more accurate), that my 3-phase, 3-pole, 50 amp main circuit breaker will be satisfactory for this arrangement. If I am wrong, or if there are other flaws that need repairing, please tell me.

TYVM!, ~~z

Zap, it appears that you are at a crossroads in your little project. What is your preference? Will you opt for;

1] a single phase supply (100 amp)?

2] a 3 phase supply using 3 single phase meters (15/45)? or

3] a 3 phase supply using a 30/100 3 phase meter?

The reason I ask is that the overcurrent protection for your consumer mains & KWH meter will be different, depending upon which one of the above you choose.

[zapatero]

I keep learning from you David, thank you. I follow your arithmetic and it seems sound to me. My trouble is, I'm not sure what to do with it.

I'm not sure what is in the PEA's mind. Perhaps they are gambling that I won't reach that MD anytime soon. Or perhaps they are planning on upgrading their transformer themselves anyway. Or ... (?)

From my POV though, it seems like this now becomes the PEA's concern since they have endorsed this solution. What do you think?

~~z

The 50kVA distribution transformer is rated at 75A per phase. This is 16.5kW at 220V.

You max demand is 22kW. It would exceed the rating for one phase of the transformer.

if connected all on one phase.

Even balanced accross 3 phases the transformer will be overloaded.

Your proposed load (MD of 100A ) plus the existing consumers loads already connected.

[elkangorito]

Further about the quoted prices for the KWH meters, I have a faxed document (faxed from one Thai company to another Thai company), which is dated 2005. The prices for meters are as follows;

DD862 - 30(100)A - 1550 Baht. This is the single phase meter.

DT862 - 30(100)A - 5000 Baht. This is the 3 phase meter.

Even if these prices have had a 50% discount applied to them, it doesn't explain why the prices you were quoted are so high.

If I converted the prices that were quoted to you by the PEA to Australian dollars, this is what you get;

12,383 THB = about AUD$408.00

38,754 THB = about AUD$1277.00

Unless these meters are from NASA or are the latest thing with all bells & whistles, which is not necessary for a domestic installation, I think you're being ripped off.

Ask the PEA for the details of the meters...part numbers, functions etc.

Edited November 21, 2009 by elkangorito

[elkangorito]

Zap.

The attached drawing may help.

temp_single_phase_connection.pdf

[david96]

I keep learning from you David, thank you. I follow your arithmetic and it seems sound to me. My trouble is, I'm not sure what to do with it.

I'm not sure what is in the PEA's mind. Perhaps they are gambling that I won't reach that MD anytime soon. Or perhaps they are planning on upgrading their transformer themselves anyway. Or ... (?)

From my POV though, it seems like this now becomes the PEA's concern since they have endorsed this solution. What do you think?

~~z

The 50kVA distribution transformer is rated at 75A per phase. This is 16.5kW at 220V.

You max demand is 22kW. It would exceed the rating for one phase of the transformer.

if connected all on one phase.

Even balanced accross 3 phases the transformer will be overloaded.

Your proposed load (MD of 100A ) plus the existing consumers loads already connected.

HI zapeto,

Yes it looks like the supply problem is now the responsibility of the PEA. With regard to the costs regarding metering this may include the cost of connection of either a single phase or three phase supply and supply of metering. Remember the meters are the property of the PEA. The PEA should give you full details.

Connection fees may include labour and material costs.

http://www.pea.co.th/th/eng/page.php?name=FeeRates

[zapatero]

Elk, your perserverance is heroic!! Thank you very much!!

You will need a new Main Circuit Breaker. A 3 pole 50 amp circuit breaker used on single phase means a total current of 150 amps, which exceeds the maximum allowable current of the KWH. If you choose to use a 3 phase breaker for this application, it will need to have a maximum 30 amp rating (30 amps per pole).

I understand your conclusion and accept it. I am still trying to understand and learn however, so please indulge me for a moment. I presume that the 50 amp breaker would trip if the current exceeds 50 amps on any one of the three poles. Therefore, in order to reach 150 amps, wouldn't all three poles have to see 50 amps simultaneously? If this is so, I cannot picture the circumstances that would cause this to happen. Can you please give me an example(s)?

The price for the KWH seems odd after looking around on the web. You will most likely have a DD862 KWH. Look at the prices in the link below (remove the brackets). Even if import tax was high, the prices you were quoted still seem weird.

[http://www.alibaba.com/product-gs/224798075/DTS_DT862_3_phase_energy_meter.html]

I have looked at your link and agree. I see prices in there ranging from 8-15 $U.S. The inconsistency seems more than weird! These do appear to be mostly digital however; whereas everthing that I see around here is still analog, (with a disk that rotates at 400 revs./kWh.) Modernity is not one of the featured hallmarks of my location however, , so perhaps that accounts for some of the difference.

Another thought is that perhaps the high costs represent not only the hardware, but perhaps an additional local "tax" on the heavy breathers. (e.g., a 15(45) meter here is only 4,621 THB; and, as has already been noted, most Thais use even smaller meters, i.e., 5(15).)

Further about the quoted prices for the KWH meters, I have a faxed document (faxed from one Thai company to another Thai company), which is dated 2005. The prices for meters are as follows;

DD862 - 30(100)A - 1550 Baht. This is the single phase meter.

DT862 - 30(100)A - 5000 Baht. This is the 3 phase meter.

Even if these prices have had a 50% discount applied to them, it doesn't explain why the prices you were quoted are so high.

If I converted the prices that were quoted to you by the PEA to Australian dollars, this is what you get;

12,383 THB = about AUD$408.00

38,754 THB = about AUD$1277.00

Unless these meters are from NASA or are the latest thing with all bells & whistles, which is not necessary for a domestic installation, I think you're being ripped off.

Ask the PEA for the details of the meters...part numbers, functions etc.

I will enquire with the PEA and report back.

The attached drawing may help.

temp_single_phase_connection.pdf

Indeed, it does help. I'm not sure what the local customs are around here though, (i.e., who "owns" this connection and box -- the PEA or my ET), (or maybe they hold hands while working on it), but I will do my best.

Thanks again for all your help!

[zapatero]

Yes it looks like the supply problem is now the responsibility of the PEA. With regard to the costs regarding metering this may include the cost of connection of either a single phase or three phase supply and supply of metering. Remember the meters are the property of the PEA. The PEA should give you full details.

Connection fees may include labour and material costs.

http://www.pea.co.th/th/eng/page.php?name=FeeRates

Thanks, David. That table explains a lot.

[elkangorito]

Indeed, it does help. I'm not sure what the local customs are around here though, (i.e., who "owns" this connection and box -- the PEA or my ET), (or maybe they hold hands while working on it), but I will do my best.

Thanks again for all your help!

Zap, the connection box will belong to you as you will have to purchase it. Basically, anything after the KWH meter belongs to you.

About the KWH meter prices, I forgot about possible deposits

[zapatero]

I'm kinda slow sometimes. This thought just occured to me. The neutral conductor of the main feed cable has to carry the return current, right? If we are running a standard single phase, two conductor feed, that arrangement is pretty clear to me. But if we are running a "hybrid" 3-phase system driven by single phase, (as we have been discussing above), then it becomes not so clear to me. Specifically my question is this: if the three phase conductors are each 16 mm^2, then it seems strange to me that we can get away with the same size return (neutral) conductor. Shouldn't it be larger than the individual live conductors? Where has my thinking gone wrong?

Also, Elk, did you miss my question below?

You will need a new Main Circuit Breaker. A 3 pole 50 amp circuit breaker used on single phase means a total current of 150 amps, which exceeds the maximum allowable current of the KWH. If you choose to use a 3 phase breaker for this application, it will need to have a maximum 30 amp rating (30 amps per pole).

I understand your conclusion and accept it. (I have already ordered the 30 amp breaker.) I am still trying to understand and learn however, so please indulge me for a moment. I presume that the 50 amp breaker would trip if the current exceeds 50 amps on any one of the three poles. Therefore, in order to reach 150 amps, wouldn't all three poles have to see 50 amps simultaneously? If this is so, I cannot picture the circumstances that would cause this to happen. Can you please give me an example(s)?

Thank you very much, again...

~~z