Domestic Electrical Wiring

[elkangorito]

Coming soon........selecting a generator & "Transfer Switches".

[elkangorito]

Coming soon........selecting a generator & "Transfer Switches".

Attached is a paper about portable generators, the information of which I've gleaned from many sources. The paper includes an example of generator sizing.

Transfer Switches will be next to come.

[handyman321]

Coming soon........selecting a generator & "Transfer Switches".

Attached is a paper about portable generators, the information of which I've gleaned from many sources. The paper includes an example of generator sizing.

Transfer Switches will be next to come.

I wish to thank you all very much. I am planning to move to Thailand for my retirement years. I am a retired engineer and do minor building and repair. I was very happy to find this information about electrical wiring. I have learned that the contractors tend to use too much water in the concrete, now I find that they are all color (colour) blind to wiring standards too!!!

[Crossy]

I wish to thank you all very much. I am planning to move to Thailand for my retirement years. I am a retired engineer and do minor building and repair. I was very happy to find this information about electrical wiring. I have learned that the contractors tend to use too much water in the concrete, now I find that they are all color (colour) blind to wiring standards too!!!

to Thaivisa handyman321, just wait until you see what the locals define as 'plumbing'

[robint]

I think ive posted this before but forget wgere

quote

...but they can last 5 years, subject to a clean electrical supply & if only used at a greatly reduced duty cycle.

I always ignore claims that state 'years' & only recognise 'hours' as being truly representative of a lamps life.

unquote

AGREED

but you can improve your life expectancy 5 fold if you reduce your suppy voltage 10 % (say 200 volts ). If you have a commercial premises with 100's of lamps all on a dedicated light circuit(s) then its worthwhile considering an auto transformer (its a box with a handwheel and voltmeter). This enables you to reduce the voltage manually - its cheap (about 4K baht) and would pay for itself quickly with a 100 lamps say.

There are some auto changers but ive found them to be expensive

Funnily enough one might try using the readily available PC standby power supplies (UPC about 2K for a 1 kva unit), BUT one must try this carefully first because they may not like the capacitive load offered by a typical fluorescent tube (without proper equipment I cant quantify this, so it a may be a suck it and see job but you are not taking much of a financial risk and have the benefit of emergency lighting????)

I had a similar set up with auto changer in UK and had these long life lamps installed which give 3 times the light output compared with filament lamps.

some of my lamps were still going strong after 5 years 12 hours/day every day. this is 22, 000 hours

( cost saving 11 watt energy saver unit inital cost £2 , electrical unit 5p/kwatthour gives 90 hours for 5p gives £12 over 5 years

filament unit 40 watts cost £0.40 uses £44

so you save around £30 over 5 years

so its well worth looking after your fluorescent light units

NB

one of the significant problems is is the type of electronic cisrcuit used. If its a cheap and nasty type then it will produce a bad waveform with high induced voltage spikes. These spikes (which can be seen on a scope will seriously damge a tube and shorten its life to a matter of a couple of months.

This can be readily observed in the type of electronic ballast as used on 12v battery supplied fluorescent units

I was astonished how quickly the tubes burned out (an 11 watt unit for overnight lighting 8 hours per day - burned out in 6 weeks)

I will try to get a scope and investigate this nastiness

Edited January 22, 2007 by robint

[robint]

quote

Attached File PortableGenerators.doc ( 71.5k ) Number of downloads: 7

unquote

Although this is a worthy checklist, Im afraid you wont get much response if you offer this around to suppliers in the land of monkeys.

To cut to the chase I can personally recommend DANYO, which is a well known Japanese supplier of portable diesle welders and generators (they are practically the Ford Truck of the genny world - Ive got one and I love it)

You can find 2nd hand ones around the many machinery traders in bkk. look to pay about 708-80k baht for a 6kva jobby. Check on the net for specs

Of course you can buy a honda 4 stroke genny 3 kva, 60k but it cost twice as much to run.

the running cost of a danyo will be 5 times the cost of utility supply

Remember you cannot expect to run electric induction motors easily, such as air cons.

you will manage a small unit such as a 12000 btu unit but will need a 6kva genny - its an expensive way to get standby ac.

you caneasily run small power tools less that 1 hp (about 1kva)

[chownah]

I'm considering adding an approximately 200 metre circuit out to my pond so I can install an electic pump. For now I'm considering that the maximum load I would run would be a 3 horsepower motor that is rated at 15.4 amps at 230V or 15.1 amps at 220V. I am considering using 50 sq mm stranded aluminum wire...two strands so the full circuit has a length of 400 metres. I used an online calculator that shows for a 400 metre circuit drawing 15.4 amps a "0" sized wire which is 53.5 sq. mm has a voltage drop of 2.03V for copper and to convert to aluminum you multiply by 1.64 so for aluminum the voltage drop would be about 3.3V.....and for size "1" (42.4 sq. mm) the drop is 2.56V for copper which is about 4.1V for aluminum....so............if I run this wire and supply it with 220V the motor will only actually have 215V....or....if the good old Thai supply system is only delivering 215V then the motor will only be getting 210V......or there abouts. I'm not wanting to be too exact with these numbers...I'm just wanting some opinions about whether the 5V of voltage drop is a reasonably acceptable thing or does it mean that I should buy a bigger guage wire? I don't know for sure that I will ever actually run this motor at full load for any length of time (probably only at start up) but for now this is the load that I want to anticipate. In the future I might want to build a small shed at the pump site with a refridgerator, some lights, etc....so 15 amps is probably adequate for this purpose as well.....also, don't worry because I can turn off the fridge and the lights and the etc. whenever I run the pump!!!

Chownah

Edited January 22, 2007 by chownah

[elkangorito]

I'm considering adding an approximately 200 metre circuit out to my pond so I can install an electic pump. For now I'm considering that the maximum load I would run would be a 3 horsepower motor that is rated at 15.4 amps at 230V or 15.1 amps at 220V. I am considering using 50 sq mm stranded aluminum wire...two strands so the full circuit has a length of 400 metres. I used an online calculator that shows for a 400 metre circuit drawing 15.4 amps a "0" sized wire which is 53.5 sq. mm has a voltage drop of 2.03V for copper and to convert to aluminum you multiply by 1.64 so for aluminum the voltage drop would be about 3.3V.....and for size "1" (42.4 sq. mm) the drop is 2.56V for copper which is about 4.1V for aluminum....so............if I run this wire and supply it with 220V the motor will only actually have 215V....or....if the good old Thai supply system is only delivering 215V then the motor will only be getting 210V......or there abouts. I'm not wanting to be too exact with these numbers...I'm just wanting some opinions about whether the 5V of voltage drop is a reasonably acceptable thing or does it mean that I should buy a bigger guage wire? I don't know for sure that I will ever actually run this motor at full load for any length of time (probably only at start up) but for now this is the load that I want to anticipate. In the future I might want to build a small shed at the pump site with a refridgerator, some lights, etc....so 15 amps is probably adequate for this purpose as well.....also, don't worry because I can turn off the fridge and the lights and the etc. whenever I run the pump!!!

Chownah

Chownah,

How are you going to install these cables? Buried direct, in conduit or aerials? I can't do a calculation without knowing this. Also, if you are going to bury the cables, I can only calculate if Thai electrical conduit is used (it's yellow). BTW, the voltage drop will mean nothing if your cables are under-rated due to temperature rise.

Edited January 22, 2007 by elkangorito

[chownah]

I'll be going overhead.....and what is the suggested seperation between strands by the way....also, what happens if they are under-rated due to temperature rise? I don't know what "under-rated" means but the 50 sq mm wire that I'm proposing is the same stuff that is used for the supply to my house from the meter which is for a 100 amp service....it is difficult for me to believe that the suggested 15.4 amps (probably go with a 20 amp breaker) would overheat them so that they would be "under-rated due to temperature rise"...but of course since I don't know what this means...........

Chownah

Edited January 22, 2007 by chownah

[S3Iraq]

Gents,

This is my first visit to ThaiVisa.Com having just registered. I had been searching the internet for information about Thai Residential wiring codes.... ok, control your laughter please... but was pleasantly suprised to find such an in depth discussion related to wiring issues in Thailand. I am not an electrician, although have worked as a building contractor in the past, so have a better than average knowledge of general construction related issues. You may have already covered this in the 21 pages of posts submitted so far, but I have as yet not had time to plough through them... I am up in the sticks, NE of Khon Kaen and although I know that Thailand has a 220v service, but the house I'm staying in, close to the area I am going to build, has a 60v 250v Inter Fuse box fed by one black and one white wire... if they are both hot, where's the neutral... any ideas? or perhaps an explanation as to why this may be the case?

Thanks in advance for taking the time to respond...

John.

[Crossy]

Gents,

This is my first visit to ThaiVisa.Com having just registered. I had been searching the internet for information about Thai Residential wiring codes.... ok, control your laughter please... but was pleasantly suprised to find such an in depth discussion related to wiring issues in Thailand. I am not an electrician, although have worked as a building contractor in the past, so have a better than average knowledge of general construction related issues. You may have already covered this in the 21 pages of posts submitted so far, but I have as yet not had time to plough through them... I am up in the sticks, NE of Khon Kaen and although I know that Thailand has a 220v service, but the house I'm staying in, close to the area I am going to build, has a 60v 250v Inter Fuse box fed by one black and one white wire... if they are both hot, where's the neutral... any ideas? or perhaps an explanation as to why this may be the case?

Thanks in advance for taking the time to respond...

John.

John, to the madhouse we call Thaivisa

OK, your intermediate box (I assume it's a 60A 250V fuse) has two wires, Thailand tends to use the US colour codes, BLACK is Live (or Hot), WHITE (or grey) is Neutral. With luck you should have a nice GREEN ground wire

Have a look here http://www.crossy.co.uk/wiring it's not been updated recently (been way too busy) but lots of good information from myself and our tame certified sparks (Elkangorito).

Edited January 22, 2007 by Crossy

[S3Iraq]

Thanks Crossy,

yeah, that was a slip of the finger, 60A not 60V of course.. common sense really that the black is carrying 220v and white is neutral, I'm just used to seeing two hot wires carrying 110v a piece and a neutral... no sign of a ground though, cant say I'm suprised, but will certainly entertain the idea of adding a good solid grounding rod to my new build... will take a look at your site, thanks again for the advice and the welcome...\

John.

Gents,

This is my first visit to ThaiVisa.Com having just registered. I had been searching the internet for information about Thai Residential wiring codes.... ok, control your laughter please... but was pleasantly suprised to find such an in depth discussion related to wiring issues in Thailand. I am not an electrician, although have worked as a building contractor in the past, so have a better than average knowledge of general construction related issues. You may have already covered this in the 21 pages of posts submitted so far, but I have as yet not had time to plough through them... I am up in the sticks, NE of Khon Kaen and although I know that Thailand has a 220v service, but the house I'm staying in, close to the area I am going to build, has a 60v 250v Inter Fuse box fed by one black and one white wire... if they are both hot, where's the neutral... any ideas? or perhaps an explanation as to why this may be the case?

Thanks in advance for taking the time to respond...

John.

John, to the madhouse we call Thaivisa

OK, your intermediate box (I assume it's a 60A 250V fuse) has two wires, Thailand tends to use the US colour codes, BLACK is Live (or Hot), WHITE (or grey) is Neutral. With luck you should have a nice GREEN ground wire

Have a look here http://www.crossy.co.uk/wiring it's not been updated recently (been way too busy) but lots of good information from myself and our tame certified sparks (Elkangorito).

[Crossy]

yeah, that was a slip of the finger, 60A not 60V of course.. common sense really that the black is carrying 220v and white is neutral, I'm just used to seeing two hot wires carrying 110v a piece and a neutral... no sign of a ground though, cant say I'm suprised, but will certainly entertain the idea of adding a good solid grounding rod to my new build... will take a look at your site, thanks again for the advice and the welcome...\

That's why we're here

At least you're aware that we are 220V 50Hz. It's about now when the "I plugged my ????? in and smoke came out, is the electricity different in Thailand" posts start appearing. Easily done though, the outlets are just too similar to the US.

[elkangorito]

I'll be going overhead.....and what is the suggested seperation between strands by the way....also, what happens if they are under-rated due to temperature rise? I don't know what "under-rated" means but the 50 sq mm wire that I'm proposing is the same stuff that is used for the supply to my house from the meter which is for a 100 amp service....it is difficult for me to believe that the suggested 15.4 amps (probably go with a 20 amp breaker) would overheat them so that they would be "under-rated due to temperature rise"...but of course since I don't know what this means...........

Chownah

Hi Chownah.

I got your requirements too late but I did calculate for underground, which is listed below. BTW, temperature rise is critical & has little to do with load current. It is, however, all about short circuit current, which has the potential to destroy cables & anything that comes into contact with the cables.

I'll re-calculate tonight for an aerial installation & I'll see if I can give you solutions for both insulated & uninsulated aerials. One other question, will the aerials be in direct sunlight?

The following cable sizes were calculated using AS/NZS 3008.1.1:1998, which is a mandatory & legislated Australian Standard. This standard was used as it closely relates to temperature conditions in Thailand & also electrical characteristics (voltage, frequency, etc);

Minimum Aluminium cable size - 70mm squared, 1 per phase & neutral.

Minimum Copper cable size - 35mm squared, 1 per phase & neutral.

Minimum cable bending radius - 8 times the the total cable diameter.

Assumptions.

15 Amp single phase motor, 20 Amps mixed power (35 Amps total).

40 degree ambient temp, 25 degree ambient soil temp.

Power Factor greater than or equal to 0.8.

Supply Voltage equals 220 volts.

Max allowable voltage drop (AS/NZS 3000) equals 5% of supply voltage.

Frequency equals 50 Hz.

Supply transformer no greater than 150 kVA @ 4% impedance. Prospective Fault Current less than 6kA.

Cable run no greater than 200m.

Cable buried direct at a depth of no less than 0.5m.

Cable type - 2C + E flat TPS V75 (Copper), single double insulated PVC V75 (Aluminium).

Re-wireable fuses shall not be used as cable protection.

Exclusions.

Motor start duty (starts per hour).

Cable passing through thermal insulation or enclosures.

Size & type of circuit protection.

Notes.

For safety reasons, the motor must be assumed to operate at full load.

For safety reasons, it must be assumed that all other loads can be connected simultaneously with the motor.

Induction motors are normally designed to tolerate a voltage drop of no greater than 10% of rated voltage.

Thai electricians tend to have sharp bends in their cables when installed on bends corners etc. This will cause a debilitation in electrical insulation under short circuit conditions.

[chownah]

Elkangorito,

Your analysis is for 35 amps total load....I'm wanting advise for a 15.4 amp single phase motor. I do not want to design my circuit for 35 amps.

Also, your analysis shows a cable run of no more than 200 metres...I want to be sure that you understand that the overall lenght of the wire used will be 400 metres...two strands running a distance of 200 metres.

Also, you posted "BTW, temperature rise is critical & has little to do with load current. It is, however, all about short circuit current, which has the potential to destroy cables & anything that comes into contact with the cables." All I get from this is that you think that my way of thinking about this issue is inappropriate...but it doesn't really help me to understand just what the problem is....can you explaing the mechanisms involved here?

Also, since the wires will be overhead, they will have direct sunlight on them. No need to analyse uninsulated cables....unless its fun to do so.

Also, your report contains: "Max allowable voltage drop (AS/NZS 3000) equals 5% of supply voltage." This seems like the allowable voltage drop has been set at 5%. Does this mean that a single phase motor can run just fine at full load with a 5% voltage drop....without tripping the thermal overload protector or otherwise sustaining short or long term damage? The bottom line information that I am actually looking for is about how the motor will be affected by the voltage drop.....just how much voltage drop is acceptable generally speaking. It seems that your report assumes that 5% is acceptable....is this the standard for single phase motors? Do you know of an internet reference where I can read about this? Your report is great in that it helps me to see what all goes into determining the performance of a circuit run and I'm looking forward to your aerial analysis.

Chownah

Edited January 23, 2007 by chownah

[elkangorito]

Elkangorito,

Your analysis is for 35 amps total load....I'm wanting advise for a 15.4 amp single phase motor. I do not want to design my circuit for 35 amps.

...I don't know for sure that I will ever actually run this motor at full load for any length of time (probably only at start up) but for now this is the load that I want to anticipate. In the future I might want to build a small shed at the pump site with a refridgerator, some lights, etc....so 15 amps is probably adequate for this purpose as well.....also, don't worry because I can turn off the fridge and the lights and the etc. whenever I run the pump!!!....

Chownah, if you don't allow for all of your possible future needs now, you may have to totally replace the cable(s) in the future, due to excessive voltage drop caused by the unallowed for extra load. This goes for the motor current as well. If it is rated at 15 Amps, then this is what you must use as the 'operating current'. But I guess this is up to you.

Also, your analysis shows a cable run of no more than 200 metres...I want to be sure that you understand that the overall lenght of the wire used will be 400 metres...two strands running a distance of 200 metres.

Sorry but I'm confused by what you say here. Are you going to join two 200m lengths of wire together to make a total of 400m? If so, why? Joining cables is not recommended. Cable is usually available in various roll sizes. Or are you putting cables in parallel?

Also, you posted "BTW, temperature rise is critical & has little to do with load current. It is, however, all about short circuit current, which has the potential to destroy cables & anything that comes into contact with the cables." All I get from this is that you think that my way of thinking about this issue is inappropriate...but it doesn't really help me to understand just what the problem is....can you explaing the mechanisms involved here?

Cable sizing is based on 3 things; 1. Current Carrying Capacity, 2. Voltage Drop & 3. Temperature rise (due to fault current). If you get the current carrying capacity & the voltage drop calcs correct but don't get the temp rise calc correct, all it will take is one serious fault & you will be replacing the complete cable run.

Also, since the wires will be overhead, they will have direct sunlight on them. No need to analyse uninsulated cables....unless its fun to do so.

Direct sunlight on cables, insulated or uninsulated, does affect their current carrying capacity & therefore must be taken into consideration.

Also, your report contains: "Max allowable voltage drop (AS/NZS 3000) equals 5% of supply voltage." This seems like the allowable voltage drop has been set at 5%.

Yes, it has...unless you want to spend more money on bigger cables to attain an even smaller voltage drop. Generally speaking, a 5% voltage drop is very acceptable in all domestic installations. This specified voltage drop is the maximum allowed as per AS/NZS 3000.

Does this mean that a single phase motor can run just fine at full load with a 5% voltage drop....without tripping the thermal overload protector or otherwise sustaining short or long term damage? The bottom line information that I am actually looking for is about how the motor will be affected by the voltage drop.....just how much voltage drop is acceptable generally speaking.

Most, if not all motor manufacturers, specify a max acceptable voltage drop of 10% of the supply voltage, as I did mention in my report. This is mainly related to large motors & their starting characteristics & to prevent damage on startup.

It seems that your report assumes that 5% is acceptable....is this the standard for single phase motors? Do you know of an internet reference where I can read about this? Your report is great in that it helps me to see what all goes into determining the performance of a circuit run and I'm looking forward to your aerial analysis.

Most energy authorities will guarantee +5% -10% supply voltage variation. The Australian Standard is therefore well within this range. I guarantee you that a 5% supply voltage drop is very acceptable. If you want to get some data on motors, try Toshiba. I'm sure they're on the web somewhere. I'll see what I can come up with tonight re your aerials.

Chownah

[robint]

My doctor used to tell me (cheeky sod) "Im here to give you my medical opinion, not teach you medical science"

So Elkangorito, you have my sympathies and respect for trying to do a professional (free) job

[elkangorito]

My doctor used to tell me (cheeky sod) "Im here to give you my medical opinion, not teach you medical science"

So Elkangorito, you have my sympathies and respect for trying to do a professional (free) job

Thanks Robin....you cheeky sod

[elkangorito]

Just one more question Chownah.

Exactly what cable do you plan on using? Does it have insulation? If so, what is written on the insulation? I need to know a temperature rating & the material of which the insulation is manufactured. If I don't have this info, I can't find out if the cable you plan to use is adequate or not.

[chownah]

I'm certainly not wanting to cause you more work.

I'm certain that the cable I intend to use is adequate in so far as it sustaining damage or causing damage to something adjacent to it and I'll give my rationalisation:

....it is the same type of cable used for my house service installed in the same manner and instead of supplying 100 amps it will only be supplying 20 amps The heat generated in a wire of constant cross section will be generated everywhere the same and if the wire is longer but carrying the same current then the heat generated will be the same per unit length. If the wire to my house is carrying 20 amps then a one metre length of it will generate a certain amount of heat.....if I use the same wire for 200 metres and it is carrying 20 amps then the heat generated in a one metre length will be the same as for my house. The heat dissipated depends on the insulation and the environment in which the wire is constructed....these will be the same as for my house so the dissipative capacity for my wire installation will be the same as for my house. The heat generated will be the same (per unit length) for the same amp current and the heat dissipated (per unit length) for the same amp current will be the same in both cases...it is independent of the wire run length......every portion of both wires should heat the same given the same current. Since my house wires do not overheat with a 20 amp load then my 200 metre run installed the same way with the same wire should ot overheat.

Is there something I have gotten wrong or am missing?

I have one question which is central to my query: If a power company guarantees +5% to -10% supply voltage and the motor manufacturor allow for -10% from the supply...does this mean that the manufacturor allows for about -20%? Example: Thailand voltage is 220V....if they are running at -10% then I'm getting 198V at my metre (or panel...whatever)...does the motor manufacturor assume this 198V as my supply voltage and then deduct 10% so that their motors should run at 178.2V?....or do they design to the -10% allowance of the supply guarantee and then allow nothing extra for voltage drop?

Chownah

[elkangorito]

I'm certainly not wanting to cause you more work. Don't worry about it. If I didn't want to do this, I wouldn't.

I'm certain that the cable I intend to use is adequate in so far as it sustaining damage or causing damage to something adjacent to it and I'll give my rationalisation:

....it is the same type of cable used for my house service installed in the same manner and instead of supplying 100 amps it will only be supplying 20 amps The heat generated in a wire of constant cross section will be generated everywhere the same and if the wire is longer but carrying the same current then the heat generated will be the same per unit length. If the wire to my house is carrying 20 amps then a one metre length of it will generate a certain amount of heat.....if I use the same wire for 200 metres and it is carrying 20 amps then the heat generated in a one metre length will be the same as for my house. The heat dissipated depends on the insulation and the environment in which the wire is constructed....these will be the same as for my house so the dissipative capacity for my wire installation will be the same as for my house. The heat generated will be the same (per unit length) for the same amp current and the heat dissipated (per unit length) for the same amp current will be the same in both cases...it is independent of the wire run length......every portion of both wires should heat the same given the same current. Since my house wires do not overheat with a 20 amp load then my 200 metre run installed the same way with the same wire should ot overheat.

Is there something I have gotten wrong or am missing?

Yes there is. Please bear in mind that there are either few electrical rules in Thailand OR nobody follows the few rules. As a consequence & disregarding what state your Consumer Mains are currently in, I will only do this calculation 'by the rules'. Is the length of your Consumer Mains cable the same as that of your prospective new cable run? Anyway, I don't keep all this info in my head...there is simply too much info to keep. The cable size has to be calculated from consulting with the Standard, which takes about an hour to do. In order to perform the calculation, I need to know 1. the prospective load, 2. The prospective cable length in metres & 3. How you want to run the cables (aerial, buried etc). If you have existing cable OR a preference for a certain type of cable, I need to know it's insulation type & temperature rating so that I can incorporate this info into the calculation.

I have one question which is central to my query: If a power company guarantees +5% to -10% supply voltage and the motor manufacturor allow for -10% from the supply...does this mean that the manufacturor allows for about -20%? Example: Thailand voltage is 220V....if they are running at -10% then I'm getting 198V at my metre (or panel...whatever)...does the motor manufacturor assume this 198V as my supply voltage and then deduct 10% so that their motors should run at 178.2V?....or do they design to the -10% allowance of the supply guarantee and then allow nothing extra for voltage drop?

A motor designed to NEMA Standard MG1 (most motors), can tolerate a voltage variation of + or - 10% "OF IT'S RATED (NAMEPLATE) VOLTAGE. So, if the nameplate on a motor says that the rated voltage is 240 volts, then it can tolerate as high as 264 volts & as low as 216 volts.

Chownah

[chownah]

I just finished a long reply with the data you requested and didn't notice that my connection had expired so I threw it all away....I'll do it again later...thanks for you reply

Chownah

[chownah]

I'll try again:

1. Prospective load 15.4 amp single phase motor but since I'll probably put a 20 amp breaker if its not too much trouble can you do the calcs for 15.4 amps and 20 amps?

2. Point A is the power source and Point B is the Load and the distance between them is a bit under 200 metres so lets call it 200 metres to allow for sag in the overhead installation. This means the I will install two wires each being 200 metres long for a total circuit length of 400 metres. I'm going to buy 400 metres of wire (single conductor) and then I'm going to cut it in half so that I have two 200 metre pieces and then I'm going to string them up side by side on the poles...one will be the hot wire and one will be the neutral wire. I'm being overly descriptive here (I think) because I have had difficulty getting this idea across before and want to make sure. The total circuit length is then 400 metres....correct?

3. I will install the cables overhead on poles in direct sunlight. I'll assume that the type of cable will be the same as my house supply. The house supply cables have the following printed on them: "Bangkok Cable 750V 70 deg C PVC THW-A TIS 293-2541 Table 1." I intend to use 50 sq. mm cable. Could you do this analysis for 35 sq mm while you are at it since my voltage drop analyser seems to think that it might work too....or will your program determine the smallest acceptable wire?...because its looking like even a 25 sq mm should work....at least form the voltage drop standpoint.

Chownah

Edited January 24, 2007 by chownah

[elkangorito]

I'll try again:

1. Prospective load 15.4 amp single phase motor but since I'll probably put a 20 amp breaker if its not too much trouble can you do the calcs for 15.4 amps and 20 amps?

I'll do the calc for 20 amps.

2. Point A is the power source and Point B is the Load and the distance between them is a bit under 200 metres so lets call it 200 metres to allow for sag in the overhead installation. This means the I will install two wires each being 200 metres long for a total circuit length of 400 metres. I'm going to buy 400 metres of wire (single conductor) and then I'm going to cut it in half so that I have two 200 metre pieces and then I'm going to string them up side by side on the poles...one will be the hot wire and one will be the neutral wire. I'm being overly descriptive here (I think) because I have had difficulty getting this idea across before and want to make sure. The total circuit length is then 400 metres....correct?

Incorrect. The length of the cable run is 200 metres. Each conductor will carry the same current - the 'active' carries current TO the load & the 'neutral' carries the same current FROM the load.

3. I will install the cables overhead on poles in direct sunlight. I'll assume that the type of cable will be the same as my house supply. The house supply cables have the following printed on them: "Bangkok Cable 750V 70 deg C PVC THW-A TIS 293-2541 Table 1." I intend to use 50 sq. mm cable. Could you do this analysis for 35 sq mm while you are at it since my voltage drop analyser seems to think that it might work too....or will your program determine the smallest acceptable wire?...because its looking like even a 25 sq mm should work....at least form the voltage drop standpoint.

Chownah

I always calculate for the smallest size cable. I use the maximum allowable voltage drop (5% of supply volts) in the calculation. BTW, I wish I did have a 'program' to work this stuff out but unfortunately, what I've got is a 100+ page document full of clauses, tables & formulae.

[lingling]

1. Prospective load 15.4 amp single phase motor but since I'll probably put a 20 amp breaker if its not too much trouble can you do the calcs for 15.4 amps and 20 amps?

A 20 amp breaker for a 15.4 amp motor sounds to me like you are going to trip the breaker when the motor starts.

[elkangorito]

1. Prospective load 15.4 amp single phase motor but since I'll probably put a 20 amp breaker if its not too much trouble can you do the calcs for 15.4 amps and 20 amps?

A 20 amp breaker for a 15.4 amp motor sounds to me like you are going to trip the breaker when the motor starts.

It might if it is not a motor start breaker...but the maximum size of the breaker will be determined after the minimum cable size has been calculated.

[lingling]

Minimum Aluminium cable size - 70mm squared, 1 per phase & neutral.

Minimum Copper cable size - 35mm squared, 1 per phase & neutral.

Minimum cable bending radius - 8 times the the total cable diameter.

Hmm, am I missing something here..?

The incoming domestic supply cables here are usually 6mm² copper. 35mm² copper is for 300 amps... ...or...?

[elkangorito]

Minimum Aluminium cable size - 70mm squared, 1 per phase & neutral.

Minimum Copper cable size - 35mm squared, 1 per phase & neutral.

Minimum cable bending radius - 8 times the the total cable diameter.

Hmm, am I missing something here..?

The incoming domestic supply cables here are usually 6mm² copper. 35mm² copper is for 300 amps... ...or...?

Yes, you are. Those figures related to an estimated total load of 35 Amps.

As far as consumer mains cables are concerned, it depends upon where you are. In many rural areas, the supply cables are 35 - 50 square mm insulated Aluminium (for longish cable runs).

Edited January 25, 2007 by elkangorito

[chownah]

I'll do the calc for 20 amps.

I guess then that should be for a 20 amp single phase motor then.

Incorrect. The length of the cable run is 200 metres. Each conductor will carry the same current - the 'active' carries current TO the load & the 'neutral' carries the same current FROM the load.

I would like to clarify this. I have consulted voltage drop charts many times in the past and I have noticed that some say that they calculate for the entire circuit based on two identical conductors so in my example you would use the distance from Point A to Point B (200 metres) as the length to use in the calculations.....and some tables state that they calculate based on the voltage drop in one strand of wire of the type specified and that you must use the total length of the wire in the circuit to calculate the voltage drop so that in my example the entire circuit goes from Point A to Point B and then from Point B to Point A which for my example would be 400 metres and this is the way to use the table. My experience is that you must know which kind of table you have and use it appropriately.

There is an online voltage drop calculator I use:

http://www.stealth316.com/2-wire-resistance.htm

For my circuit I must use 400 metres to calculate the voltage drop. If you enter 400 metres and 20 amps you will find that for a #1 wire (approximately the same as a 50 sq mm wire) the voltage drop shown is 3.32 which is for copper wire and to adjust this for aluminum you multiply by 1.64 as per their instructions and you get about 5.5V of voltage drop. Does this agree with the way you are calculating it?

Also, doesn't the length of the circuit only affect the voltage drop and not any of the other considerations?

Chownah

[elkangorito]

Chownah,

My standards state that distance 'L' is the distance from point 'a' to point 'b'. Therefore, I must use 200m & not 400m.

The reason that I calculated the cable size for a 20 Amp load is that it is not realistic or practical to calculate for the exact load requirements since circuit breaker sizes are fixed ie 15 Amp, 16 Amp, 20 Amp, 25 Amp & so on.

Installation parameters.

Phases - 1. Voltage (Ph-N) - 220 RMS. Frequency equals 50 Hz.

Max prospective fault current based on a Tx of less than or equal to 150kVA @ 4% impedance = 6kA.

Conductor characteristics - single core, single insulated, Black PVC V75, 0.6/1kV installed in an aerial configuration with both conductors strung side-by-side in direct sunlight.

Load - 1 x single phase motor (15 Amps). P.F. greater than 0.8.

Total load allowance - 20 Amps.

Cable length - 200m.

Wind allowance - 1 m/sec.

Max allowable voltage drop - 5% of 220v RMS (2.75mV/A.m).

Min cable bending radius - 8 times the cable diameter.

Ambient air temp - 40 degrees Celsius.

Protective device fault current clearance time - 1 second.

Provisions.

Cables will not be enclosed in any way for a distance (length) of no greater than 3 Metres.

The above parameters must be met.

No cable joins within the 200m length.

Re-wireable fuses shall not be used as protective devices.

Recommended minimum cable sizes in accordance with Australian Standards AS/NZ 3008.1.1:1998 & AS/NZ 3000:2000. These sizes reflect temperature rise as being the critical limiting factor.

Copper - 70mm squared.

Aluminium - 95mm squared.

PLEASE NOTE - If the fault current clearance time of the protective device can be reduced to 0.1 seconds (that is, if it can safely open under a 6000 Amp fault in 0.1 seconds or less), the critical limiting factor of the cable sizes will be voltage drop. In such a case, the cable can be reduced to the following sizes;

Copper - 25mm squared.

Aluminium - 35mm squared.

Exclusions.

Motor start duty (starts per hour).

Size & type of circuit protection.

Upon checking a general Time/Current curve for Square D Miniature Circuit Breakers, I discovered that they will safely clear a 6000 Amp fault in less than 0.1 seconds, so I recommend that the smaller cable sizes be used. This only applies if Square D Miniature Circuit Breakers are used. Other CB's may not comply to the Time/Current requirements.