Electric Conductor Size Vs. Distance

[User3]

Sorry if this is not the right forum for this question, please feel free to flame me or move it to correct one if need be.

We are expanding our kitchen and installing more electrical appliances.

The additions will be a) Electric wall oven, Dishwasher and c) multi-point water heater for

My breaker box is full.

My questions are:

1- is it possible to install a new breaker box in parallel with the existing one so that I can get them to add the circuits for the heater/oven/washer?

2- Is there somewhere (besides the manufacture's info) that gives wire size vs. power use? These units will consume around 6kws. It is about 7m from the existing breaker box to the ceiling, across the ceiling then down the wall to grade level where the oven connection will be made and then the water heater and dishwasher will be a bit further into the room (installed in island).. But the longest run will be from water heater to breaker box, about 7 m. or so.

3- Would it be better to install the new breaker box in a cupboard closer to the oven/heater? This can be done and put the breaker about 3m from the users, but would be a lot more work.

If that is the best solution, what sort of wire size would I expect them to use??

Thanks

[Crossy]

1. Yes, no problem, but feed your second distribution board from the switched side of your existing main switch. Not required by law but it gives you a single point of isolation.

2. The oven and water heater should each have their own feed sized to suit their power consumption (post the consumption and distance here and we will oblige with wire and breaker sizes) dishwasher should be ok on a regular outlet (but can have a dedicated circuit if you want). Some cable sizing guidance here http://www.crossy.co.uk/wiring/Circuit%20types.html actually a bit conservative so do come back with the info on your loads.

3. Keep it all together if that's easier, means no hunting for the open breaker.

[electau]

You can install a additional load centre unit adjacent to the existing one. There should be one main switch (MCB) to isolate the whole electrical installation.

You should check the size of your incoming consumers mains size ( in sqmm) to make sure it can carry the extra load.

All equipment should be permanently connected to their own final subcircuits, each circuit protected by an MCB or RCBO.

The size of protective device (MCB/RCBO) depends on the current rating of the cable it protects.

You will require the rating in amps of each of the items you wish to connect.

All equipment should be earthed with a PE conductor to the earth bar of your switchboard.

A switch board should be installed in a readily accessible position from floor level eg no more than 2 metres to the top of the switchboard.

[User3]

Thanks for the info guys!

I've decided to go with a 50 amp breaker to feed the second breaker box from the existing breaker box. This way there will be the existing 100 amp incoming breaker (2 x 50amp ganged) and then the feed to the second breaker will have a 50 amp outgoing breaker. This should take care of concerns with the incoming feeder cable. I think my idea of the parallel breakers is not so good, as it could overload the feeder from the meter to the house, with all the attendant smoke, melted insulation, crispy critters (me) that would result.

The 100 amp protects for the incoming wiring, and the 50 amp (essentially in series really) protects the downstream users connected to the 2nd breaker box.

Thanks for the info, and I will check out the wire sizes in a day or so.

The thoughts on grounding are excellent, but I am not likely to find anyone to do that, and am not able to explain it to anyone likely to be sent to do the wiring. I'll give it a try, but don't expect much in the area of grounding. It's a shame as these are major power users... but...

Once the contractor has started the demolition and 'remolition' I'll have more time to get data together.

Cheers!

[Crossy]

I'm not sure what you are saying when referring to "100 amp incoming breaker (2 x 50amp ganged)" as this would be a very unusual configuration, do you have photos please?

What size is your meter? What size is the incoming cable from said meter?

Grounding of Class-1 appliances is VITAL for your safety!

[electau]

It is assumed that your supply is single phase L and N.

The main switch should be a 2 pole MCB 63A for 16sqmm consumers mains and 50A for 10sqmm mains minimum. (Your metering will generally be 45A)

ONE main switch should control ALL the electrical installation. It would be advised that all circuits be protected by RCBOs. This MCB provides short circuit protection on the load side of the device. Service protection on the line side of the metering is not used in Thailand.

A 50A protective device for a sub board if installed on 10sqmm cable but if load is not large a 32A on 6 sqmm would suffice.

To install a compliant earthing system you will require a 10sqmm main earth and earth electrode to PEA requirements, 16sqmm HD copper or copper clad steel 2.4 metres in the ground, and PE ( protective earth) conductors to all equipment including the earth terminal of 3 pin socket outlets. Earth conductors terminate on the earth bar of the switchboard.

It would be recomended that the earthing system complies with the current requirements of the PEA, ie TT or TN-N-S (MEN)

You should contact them before commencing upgrading your electrical installation.

[User3]

Here is the actual breaker box as installed by builder. Size of meter? no idea- whatever is put in for the average housing development.

Not sure if this photo is correct size....What I am thinking is removing the two unused 20a breakers and inserting 2 x 25amp then using that to feed second box.

[electau]

Here is the actual breaker box as installed by builder. Size of meter? no idea- whatever is put in for the average housing development.

Not sure if this photo is correct size....What I am thinking is removing the two unused 20a breakers and inserting 2 x 25amp then using that to feed second box.

The switchboard appears to be a Square D ( Schneider) load center. The Main Switch (MCB)will be 2 pole and the individual MCBs single pole.

There appears that no provision has been made for RCDs/RCBOs. This is normal for most electrical installations in Thailand unless you specify them.

You should check to see if a main earth and electrode is installed and any protective earth conductors. You should check this with the electrician.

As you have 2 spare 25A MCBs you could replace one of them with a 32A MCB for the additional load centre adjacent to the existing one.

[User3]

Here is the actual breaker box as installed by builder. Size of meter? no idea- whatever is put in for the average housing development.

Not sure if this photo is correct size....What I am thinking is removing the two unused 20a breakers and inserting 2 x 25amp then using that to feed second box.

The switchboard appears to be a Square D ( Schneider) load center. The Main Switch (MCB)will be 2 pole and the individual MCBs single pole.

There appears that no provision has been made for RCDs/RCBOs. This is normal for most electrical installations in Thailand unless you specify them.

You should check to see if a main earth and electrode is installed and any protective earth conductors. You should check this with the electrician.

As you have 2 spare 25A MCBs you could replace one of them with a 32A MCB for the additional load centre adjacent to the existing one.

Sigh.

Me again.

A couple of weeks ago I had given the "electrician" the diagram from Crossy's info page and a list, in Thai, of what I wanted for the second breaker box. Most specifically that it be fed from the first one and not in parallel with it. Yesterday I asked for clarification of that fact (the new box isn't connected yet) and was told that it would be put in and wired in parallel with the existing box. When I argued (via my wife) we were told that the "electrician's" way was better because you would not loose the kitchen power if you lost the house power. This was a bit puzzling so I asked why would I want to have a live dishwasher if the entire house had had a power failure. Blank looks all around......

So given that this "electrician" is not going to do anything that I suggest, and is going to do things his own way, the only way he has ever done things, I'm wanting to just let him go ahead and wire it is parallel then find a REAL electrician to fix it. But- how the hell does one find such an animal? I live in Bangkok- Surely to God there must be someone here who has a clue about this stuff that can be hired to fix it. But how to find them? I've got my wife looking at her University but I'd guess that the people doing the actual wiring are not going to be any good to me, I'll likely need someone that understands electricity. How do you find these people? There are ads by various 'contractors' that claim to specialize in renovations and the like and specialize in dealing with expats but in 3 emails and 2 phone calls I've never received a response.

Any ideas??

PS- am I correct that it would be a relatively simple thing to change the wires feeding the second breaker box from parallel to series with the first one's main breakers?

And am I right that with the two breaker boxes in parallel, there is a chance of overloading the service meter (never mind the wiring) to the point of damage??

[Crossy]

Running the two boards in parallel has the following characteristics;-

No single point of isolation, not illegal but could pose a hazard.

Possibility of overloading the supply meter, you can bet that both boards will have 50A incoming breakers.

Useful to be able to maintain power to some outlets whilst working on others.

It should be easy to re-wire so that board 2 is fed from a spare way in board 1, but your local sparks may well splice into the incoming cables making the job far more difficult to make neat and safe afterwards.

[bankruatsteve]

Here is the actual breaker box as installed by builder. Size of meter? no idea- whatever is put in for the average housing development.

Not sure if this photo is correct size....What I am thinking is removing the two unused 20a breakers and inserting 2 x 25amp then using that to feed second box.

Not sure you really need a second box. If you have 2 unused positions (nothing attached to the breakers, yah?) you could use one of them to service the oven and dishwasher and the other for the heater. You really should implement proper grounding but if that's not going to happen, at least use RCBO. Size will be determined by equipment draw and related cable.

BTW: 2x25a does NOT = 50a if that's what you were thinking.

[wayned]

I have three switchboards run in parallel from the same meter (15/45) due to the different locations of the installations, one a second house and two a workshop. PEA would not install seperate meters since the address of the locations were the same and there was only one blue book. Hooking them in series from the first switchbox would have been a cabeling nightmare, so I have three feeders from one meter tapped into the line on the pole closest to the next switchboard. Seperate ground rods at each location. Due to the utilization of the different locations, there is no chance of overloading the 15/45 input.

Not the best, but where I live they run romex in pvc water pipe under the dirt road to get power to the houses across the street since they are illegally built on government land and PEA won't set meters, grounding rods don't exist.

[electau]

One main switch ( MCB) rated to your mains size, this controls both load centres, one 32A MCB for each board, remove the 50A MCBs. A MCB will carry 1.2 rated load current.

[electau]

If you use more than one main switch (MCB) make sure that the total max demand is equal to or less than the current rating of incoming mains. eg. 2 x50A = 100A. 2 x40A =80A.

[Crossy]

A thought. since our OP currently has no earth leakage protection he could install one of the Safe-T-Cut stand alone RCBOs as a main incomer and then use it to feed both his old CU and the new one.

Single point of isolation and earth leakage protection in one easy step

[User3]

A thought. since our OP currently has no earth leakage protection he could install one of the Safe-T-Cut stand alone RCBOs as a main incomer and then use it to feed both his old CU and the new one.

Single point of isolation and earth leakage protection in one easy step

An excellent idea! Thanks so much for that.

I have a line on a company with 'certified' electricians and will be talking to them in a day or so but suspect they only do industrial jobs and my little house would be not worth their while. We'll see.

Indeed, yesterday when I was wandering through Home Pro I saw those main circuit breakers and they looked interesting. Never occurred to me to add one upstream of the whole mess I have now and 'Somchai's Your Uncle'....

Speaking of which- when we gave the general contractor the specifications for the job, we insisted on grounding on all the new box connections. This was agreed to, and the guy did run the ground wires (green?) but so far I see no grounding connection in the secondary breaker box nor any sort of ground rod outside....

Thanks again for all the info here. It's MUCH appreciated. One of the many things I am confused about is the incoming breaker. My old box main breaker is two separate breakers, tied together with a pin through to reset switches. (I put a photo of it here a while ago) I had assumed this would be a 100 amp feeder. Now I am seeing people talking about me having 63 amp and also one poster said that 2 x 50 amp did not equal 100 amp.

I looked at my meter and don't see any obvious markings to relate to it's capacity.

I have a meeting with the contractor day after tomorrow and will talk to him about the install of the RCBO at that time.

Thanks again you guys !!

[Crossy]

That incomer is a two pole 50A. It looks like two units tied together but only one will have the current sensing gubbins, the other is simply a switch so that both live and neutral are opened when the device trips.

On your meter will be figures like 5/15, 15/45 or 30/100 which indicate the rating, take a decent close-up photo and post here if you can't work it out Since you have a 50A incomer chances are you have a 15/45 meter, but best to check.

[User3]

That incomer is a two pole 50A. It looks like two units tied together but only one will have the current sensing gubbins, the other is simply a switch so that both live and neutral are opened when the device trips.

On your meter will be figures like 5/15, 15/45 or 30/100 which indicate the rating, take a decent close-up photo and post here if you can't work it out Since you have a 50A incomer chances are you have a 15/45 meter, but best to check.

Yup, it's a 15/45 all right. So now all I need is an RCBO with a trip current of...er...50A???

Then I need to get Somchai and Son's Electrical Contract, Dog Polishing and Nasal Irrigation Company (Inc) to agree to install it, and hope like hell they do it correctly.

Well, nobody ever said life was easy here...

[Crossy]

Yup, a 50A Safe-T-Cut will do the job, comes with installation instructions in Thai. assumes the sparks can read of course.

[bankruatsteve]

My comment that 2x25a not = 50a was in reference to what I think was the OP's thought to somehow combine two 25a MCB's in the current box and deliver 50a to a downstream box. Which cannot do.

[electau]

Yes, installing a RCBO as a main switch will provide earth leakage protection for the whole installation and a single isolation point (main switch).

A 50A or 63A, 2 pole 30mA RCBO. Note: The 50A or 63A will now be the max demand of your installation.

Your peak demand in amps in practice will be less than the actual max demand (MCB rating). For example I have a max demand ( MCB) rating of 63A. but in practice it is never over 25A ( peak load). It is the peak load that is the important figure. It must not exceed the max demand.

[User3]

Yes, installing a RCBO as a main switch will provide earth leakage protection for the whole installation and a single isolation point (main switch).

A 50A or 63A, 2 pole 30mA RCBO. Note: The 50A or 63A will now be the max demand of your installation.

Your peak demand in amps in practice will be less than the actual max demand (MCB rating). For example I have a max demand ( MCB) rating of 63A. but in practice it is never over 25A ( peak load). It is the peak load that is the important figure. It must not exceed the max demand.

Hmmm.. Is it better to get a 50A RCBO and have it and all main breakers the same or would there be any advantage to getting a 63A RCBO as sort of a last line of defense if the 50 amp breakers in the boxes don't trigger? I guess what I'm asking is what is the danger of having a 63A RCBO given that the initial installation was a 50A main breaker? And what about the meter (15/45) does that have any vulnerability if the RCBO is uprated to 63 A?

I do have a meter somewhere that measures current draw, and I used it last year to see how much current the two downstairs aircons were drawing (wanted to see the effect once the inverters kicked in and started ramping the units down) and it peaked out around 19 amps if I remember correct. Once the temp was reached the draw dropped to around 7 amps, if I remember correctly. They are 18,000 and 12,000 btu's

So add the oven, cooktop and kitchen air con to that and I'd guess it would be still safely below the 50 amp. area.

According to my calculations there are 37,800 watts of power consumption in total in the house, but that is higher now due to kitchen appliances.

[bankruatsteve]

You might want to re-check your calculation for max watts "consumption". If max demand is even close to that, you will probably need to start over from the beginning. Otherwise, I'm guessing that you would never even approach 50a peak (which is about 11KW).

[User3]

You might want to re-check your calculation for max watts "consumption". If max demand is even close to that, you will probably need to start over from the beginning. Otherwise, I'm guessing that you would never even approach 50a peak (which is about 11KW).

That was for installed electrical draw, that is- all the electrical items in the house. Does not mean, of course, that they would all be functioning and using at the same time. I couldn't afford that. That number was derived from looking at the nameplate consumption for each piece of equipment in the house, then adding them all up.

[electau]

You rate the main MCB in amps not to exceed the rating of the current capacity of the mains, What is the size of the incoming mains? 10sqmm or 16sqmm.

[electau]

An MCB must trip at 1.45 x rated line current. The convential tripping time is 1 hour. On short circuit conditions the MCB must trip is less than 0.4secs. An MCB will carry short time overloads quite safely with no undue temperature increase on the protected cable.

[electau]

post deleted due to duplication.

[User3]

You rate the main MCB in amps not to exceed the rating of the current capacity of the mains, What is the size of the incoming mains? 10sqmm or 16sqmm.

I would not have even a 1/2 a clue about the wire size. would it be written on it?

Can I get it from the meter? Here is a photo at the meter, but it doesn't show much.

The actual box(es) are covered with plastic at the moment due to ceiling and wall mudding and taping, so won't get them uncovered for a while.

In any case, sounds like the 50A is the safe way to go.

[User3]

An MCB must trip at 1.45 x rated line current. The convential tripping time is 1 hour. On short circuit conditions the MCB must trip is less than 0.4secs. An MCB will carry short time overloads quite safely with no undue temperature increase on the protected cable.

Here is a better photo of the wires.

[Crossy]

You need to look at the lettering on the cable jacket, it will indicate the size in mm²