3 Phase Conection Cable

[Greenside]

Our contractor's electrical person wants to re-lay our 100m underground 3 phase connection to the road at a cost of almost 130,000 baht. The supply is to feed one large(ish) 4 bedroom house which will have 5 aircons, three multi-point bathroom water heaters, a small pool and the usual kitchen and domestic appliances. He's quoted for NYY 4x35mm² which of course costs an arm and a leg. He says the previous one we had put in is under specified (without looking it up I think it was 25mm²).

Can anyone tell me if this really is the appropriate cable size - I've seen so many over engineered things here (as well as plain badly engineered!) so some outside advice would be really helpful.

[bankruatsteve]

Do you already have 3-phase and they just want to replace? If you can estimate your max demand in watts or amps that would define the cable size you need. But 3-phase on 25mm2 seems like it would handle your home (and more).

[Forkinhades]

100m is a long way to go with a main cable, and all depends how 'strict' you want to be with volt drop 2,3,4, or 5%. If you wanted 2% then you would probably be looking at a 70mm sized cable! whereas 5% you would be ok 25mm. So you can ask to see his calcs, and what percentage VD he has used. 4% would suggest a 35mm cable.

Also ask him what factors he has allowed for his calcs 'ambient temp', 'grouping'. If he can give an instant reply, then I would say he was genuine, if not, then up to you as they say.

[Crossy]

What size meter is being proposed? The biggest that MEA/PEA will put on a 25mm² cable is a 15/45 (45A) supply, which should be more than adequate for your home anyway.

Assuming it is a 45A meter you'll be looking at a voltage drop of around 5% at full load (IMHO acceptable although outside UK regs).

25mm2 NYY is rated at 116A buried direct in-ground according to Bangkok Cable http://www.bangkokcable.com/catalog/BCC_CATALOG/NYY3EN.HTML but MEA/PEA still insist on 35mm² on a 30/100 supply.

[Greenside]

Thank you all for the information. I'll be able to look at his calculations more closely over the weekend and let you know the outcome.

[Forkinhades]

OK done some cable calcs for you

TV002.pdf

although its based on a single phase supply, it will suffice in this instance, I am sure crossy will confirm.

Calcs based on load of 45A , 4% VD, ambient temp 40c which gives factor (Ca = 0.87), Grouped circuits (3 for 3 phase) factor 0.70, even with these factors, and the length of run your original install of 25mm will suffice.

This is JUST on the information that you have given, there are many factors!!

but to be honest I think you are possibly ok with what you have.

[Crossy]

I concur with Forky.

Unless there's some other factor we don't know about I see no issue with the 25mm² cable.

[IMHO]

As Crossy noted a 15/45 meter will take max. 25mm2 and a 30/100 meter will take max. 35mm2

If you run >25mm2 to a 15/45 meter, the PEA *will not* allow it to be hooked up to the grid, same for >35mm2 with 30/100.

So your answer lies in the type of meter you're going to have, simple as that

These limits are the primary reason why we have a 30/100 meter (80M from meter to load centers).

Edited June 29, 2013 by IMHO

[IMHO]

130K Baht is way up there BTW - for that price I can only imagine it's copper, but even then a 100M roll of 35mm copper from Bangkok Cable only runs around 17K Baht, so 68K Baht for a 3 phase run.

35mm Aluminium cable is only 2,xxx per roll if you can tolerate a little more voltage drop, and a >= 55K Baht saving

As for labor costs, even if they have to dig 100M of new trench 60CM deep, and lay all new PE conduit, I would not expect to pay more than 80 Baht/meter - have paid as little as 20 Baht/meter for similar in the past, but price will vary depending on the difficulty.

It sounds like you're paying a big price premium for the parts - maybe you're better off buying the cable, PE pipe, connectors, and silicon yourself and just getting a labor only quote?

Edited June 29, 2013 by IMHO

[Crossy]

IMPORTANT NOTE: PEA will not allow aluminium cable underground.

If you need to use a cable bigger than will fit in the meter terminals (for volt drop reasons), no problem splicing on a short pigtail that will fit the terminals.

[IMHO]

IMPORTANT NOTE: PEA will not allow aluminium cable underground.

If you need to use a cable bigger than will fit in the meter terminals (for volt drop reasons), no problem splicing on a short pigtail that will fit the terminals.

Hrmm, I don't disagree that was your experience, but I can tell you they had no problem doing it at the house I'm talking about - in that case the run from meter to house was actually done by PEA electricians (the only real sparkies in the area), and it was 4x 35mm2 aluminium

They were adamant about cable size though - nothing more, nothing less than 35mm2 for a 30/100 meter.

[Greenside]

Thank you all for the advice. I'm meeting with the engineer and our architect early next week - I agree that it does look OTT. I'm getting hold of a copy of the load calculation he based this on and when I do I'll post it here. Meanwhile, the merits of different brands of reflective foil is overwhelming what's left of my brain!

[Pib]

Here in my Bangkok moobaan for single/three phase runs underground the developer uses copper 35mm wire...that's what I have along with a 30/100A single phase meter.

[doglover]

Here in my Bangkok moobaan for single/three phase runs underground the developer uses copper 35mm wire...that's what I have along with a 30/100A single phase meter.

Good to hear it's being done right (underground) somewhere. I had no idea developers in Thailand were choosing not to install electrical eyesores throughout their projects. Hopefully that forward thinking comes to Khon Kaen.

EDIT - I suppose it is only from your meter to your CU's underground and the distribution lines for the project remain above ground as an eyesore.

Edited July 1, 2013 by doglover

[Pib]

Here in my Bangkok moobaan for single/three phase runs underground the developer uses copper 35mm wire...that's what I have along with a 30/100A single phase meter.

Good to hear it's being done right (underground) somewhere. I had no idea developers in Thailand were choosing not to install electrical eyesores throughout their projects. Hopefully that forward thinking comes to Khon Kaen.

EDIT - I suppose it is only from your meter to your CU's underground and the distribution lines for the project remain above ground as an eyesore.

Yeap, the power lines still run up and down the soi's...and then come down the pole to the meter and then from the meter are run underground in metal or PVC conduit (mine is metal) to the CU/main circuit box in the house. The phone line also comes down off that pole and runs underground through a separate half-inch PVC pipe (right next to the electrical metal conduit) to the inside of the home.

[Forkinhades]

any updates greenside?

[Greenside]

Got the load calculation today but haven't had time to study it. Discussed issue at site meeting with the contractor and agreed that I'd review the likely loading again and then we'd talk to the PEA to see what they have to say. The electrical people turned up on site yesterday to start first fit so I'm full time checking that the placement of switches and outlets still works, given that built in furniture was planned after the elec specs were done. Power sockets in wardrobes aren't that useful I've found .

Edited July 6, 2013 by Greenside

[IMHO]

Got the load calculation today but haven't had time to study it. Discussed issue at site meeting with the contractor and agreed that I'd review the likely loading again and then we'd talk to the PEA to see what they have to say. The electrical people turned up on site yesterday to start first fit so I'm full time checking that the placement of switches and outlets still works, given that built in furniture was planned after the elec specs were done. Power sockets in wardrobes aren't that useful I've found .

The only real decision is whether your need a 15/45 or 30/100 meter - that then dictates the wiring run required to the house.

Sounds to me like you're making this all much more complicated than it needs to be.. if in doubt, just go the biggest for residential - 30/100 - no matter what your calcs might end up saying, there no option to go bigger than 35mm2 cable to a house.

[Crossy]

Greenside's issue is that there is already a 25mm² cable running to the house, this dictates that PEA won't couple a 30/100 (they insist on 35mm² for that).

To be honest, a 3-phase 15/45 should be enough for a small factory.

[IMHO]

Greenside's issue is that there is already a 25mm² cable running to the house, this dictates that PEA won't couple a 30/100 (they insist on 35mm² for that).

To be honest, a 3-phase 15/45 should be enough for a small factory.

Maybe easier in a factory where you have more constant/predictable loads to balance the phases.. In a house, 3 phase is always difficult to balance as you really only have one heavy consumer - hot water heaters - and they have pretty short duty cycles..

Unless you're running water heaters > 6kW, or airconditioners > 30K BTU, I can't see why you'd need 3-phase in a house. And if you are running multiple high kW heaters, you probably should be looking at going solar, and if running > 30K BTU air, you should probably consider other ways to cool things down - do these and the rest of your electrical system is now probably single phase and a whole lot simpler

[Crossy]

No real need to worry about balance in a domestic environment. The neutral current will never be greater than the largest phase, so with equally sized conductors no issue with overload.

[Forkinhades]

Here in my Bangkok moobaan for single/three phase runs underground the developer uses copper 35mm wire...that's what I have along with a 30/100A single phase meter.

Thailand being over engineered? Hard to believe that, unless fralang involved, and Hey lets rip him off

Sent from my GT-I9300 using Thaivisa Connect Thailand mobile app

[Naam]

I concur with Forky.

Unless there's some other factor we don't know about I see no issue with the 25mm² cable.

why replacing the existing cable instead of adding another one with smaller diameters connected accordingly and saving a bunch of Baht? or is this against any "code"?

[Forkinhades]

I concur with Forky.

 

Unless there's some other factor we don't know about I see no issue with the 25mm² cable.

why replacing the existing cable instead of adding another one with smaller diameters connected accordingly and saving a bunch of Baht? or is this against any "code"?

Very good idea, not seen it done in practice with different size cables. Not against any code that I'm aware of.

Sent from my GT-I9300 using Thaivisa Connect Thailand mobile app

[Greenside]

Here is the last load calculation and I've got to admit that I don't really understand it well enough to do much beyond point out some errors such as the size of a/c units which should be 4 x 12,000 and one 18,000. The most worrying factor is that it seems to indicate the need for a 30/100 meter and the 35mm² cables as previously discussed.

My architect is going to go and discuss this with the PEA very shortly but your thoughts on the attached would be welcome as would any advice as to how to reduce the loading.

Load Calc 2 LP1.pdf

Load Calc 2 LP2.pdf

Load Calc 2 Profile.pdf

Load Calc 2 Table.pdf

[Forkinhades]

yeah maximum demand looks quite scary, but you need to take into account diversity. Also 'we' wanted the cable calcs of the supply cable, not the loadings.

I will give you some pointers, you do the math for the diversity, then I will redo the calcs for the cable

lighting 66% of total current

AC / Water Heaters 100% of largest appliance, + 100% of second largest, then 25% of remaining appliances (quite a drop here of the full load)

standard arangement of final circuits - 100% of largest circuit + 40% of every other circuit

Sockets - 100% of largest circuit + 40% of every other circuit

before you had around 60Kva full load, with diversity you should be looking at less than half.

If you need the 30/100 meter, I still think you are ok with 25mm,

I also see you have 2 DB's, so if the PEA insist on 35mm cable, then just run another 10mm in parrallel, as already suggested, and connect the 10mm to the smaller board, and 25mm to the larger. Regs permitting

I hope crossy will add some comments to this

[Crossy]

Agree Forky ^^^. With diversity a 15/45 should be well capable.

You have a lot of outlet circuits, many of which will have zero load for much of the time, bedrooms for example, the biggest load our bedroom ever sees is Wifeys hair dryer, for about 10 minutes. I'd remove the bedroom circuits from the calculation.

PEA certainly won't connect a 30/100 to 25mm² cable, they insist on 35mm² for that service, no idea if they'll go for a parallel cable.

If I were in the OPs place I would go for a 15/45 on the existing cable, fused at 50A incoming and see how things went.

How long is the incoming cable so we can verify no volt drop issues?

[Greenside]

Thanks, both of you. I'll have a go at that calculation today.

I've had the conversation about the outlets to try to get them to understand that it's about convenience and not that we have hundreds of appliances waiting to be plugged in. I have 6 in every bedroom, one either side of the bed for a nightstand light and one more or less in each corner of the room: the actual load not likely to be more than a couple of energy saving bulbs and the proverbial hair dryer. Their response (or what they tell me the PEA will say) is that if the outlets are there you might use them all when you have a party.... hmmmm. Likewise with lights - with the exception of 12 (which I'm working on) they are all ES or LED and there are about 50 outside around the deck that will be 3w maximum.

What is making things a bit more delicate is that the Load Calculation was done by an ajarn at CMU and he refuses to fiddle it to understate anything that is really there on the basis that he has to protect his reputation, which I guess is understandable. I don't have any direct dealings with him so it's a little difficult to know if a donation to university funds would make things easier!

It looks like the line from the road to the load centre is close to 110m give or take 5m. Aren't I right in thinking that a 30/100 meter is going to be more expensive?

Must go. After having a quiet day yesterday with only the bricklaying crew on site, no less than 20 people have shown up this morning and I'd better get out there and find out exactly what they are doing!

[bankruatsteve]

I am constantly amazed at how maximum demand becomes theoretically possible to some and how more than one outlet per room is a curious western extravagance whilst not even considering that daisy chaining cheap extension cords is less than safe.

[Greenside]

I am constantly amazed at how maximum demand becomes theoretically possible to some and how more than one outlet per room is a curious western extravagance whilst not even considering that daisy chaining cheap extension cords is less than safe.

Not to mention stringing them across doorways and the exciting extensions that terminate in 3 pin outlets and have a three pin plug cleverly joined by two wire cable.

I'm going to have a party! Bring a bottle and a hair dryer...

Edited July 12, 2013 by Greenside