Overhead or underground electrical supply

[thaibook]

We are planning to build a house which will be some 250m from the current electricity supply and transformer.

 

We will need to decide whether to have 1 phase or 3 phase and whether to run the cable on poles to the house or bury it underground.  Is 9kVA the maximum for a 1 phase supply in Thailand?  There seems to be a limit to the distance a cable can be laid underground.  What is it and is it due to heating or power loss?  I have read that power loss of 3 phase is about half that of 1 phase.  Yes, there will be a cost difference but I am firstly interested in finding out the technical limits of the alternatives with the materials available here.  All comments and advice gratefully received.

  

[Kwasaki]

Depending where you are PEA may not allow you to put underground.

I run 5/15 200 meters on poles wouldn't know if there power loss.

Wait for Crossy to comment, I reckon 15/45 supply would do unless your installing industrial electrical equipment. 

[taninthai]

If the 250 m distanc is not your land ie public land the cable will be run on poles which you will be paying for ,,,if it’s on your land you can run it how you want.

[Crossy]

The usual maximum single-phase supply from PEA is a 15/45, 45A max = About 10kVA.

 

If you need more then it's 3-phase time.

 

A 250m run at 45A single-phase you are looking at 70mm² copper, you could get away with smaller cable (but 4 wires instead of 2) if you go 3-phase, say 50mm². Go one size bigger if you use aluminium cable (cheaper but not permitted underground)

 

For such a long run I would go aluminium on poles until you get near the house where copper underground may improve the look.

[Crossy]

Give us an idea what's on the end regular house or a mansion with a workshop and we can guesstimate a maximum demand.

 

Go with tank or gas water heaters and you can significantly reduce your demand.

[thaibook]

thank you for the responses.  There will be no workshop and no industrial equipment.  The building is likely to be a normal house (2 bedrooms, bathrooms, dressing rooms, kitchen, study, reception room, library plus a guest bungalow (max 2 bedrooms) so not huge demand although possible more than 10 kVA.  If that is the tipping point, I shall be more cautious in assessing our needs. 

 

From what you say, if PEA allows underground (yes it will be on my land) the choice of poles or underground is more a function of cost and aesthetics than technical considerations.  

 

Interesting what you (Crossy) say about tank water heaters as I had assumed they consumed more having to keep water hot all day but perhaps here the weather plays a role.

 

My additional questions are:

is the PEA is the best entity to ask to do the installation as I understnd there are also private companies that claim to do such work.

you write 5/15A and 15/45A is this because the cable has three strands each of 5A and 15A respectively?

[Crossy]

5/15 and 15/45 are the ratings of the meter, 15A max and 45A max (the first number is the calibration current). You would be looking at a 15/45 which is where the 10kW limit comes from. In some areas you can get a 30/100 but if you are heading that way then go 3-phase on a 15/45 (3 x 45A supplies).

 

Tank heaters have smaller heating elements (3kW) as opposed to the on-demand heaters (6-8kW) and place less strain on the supply by heating the water over a longer period. Yes, keeping the water hot all the time is slightly less efficient but modern insulation is very good and you can put the beast on a timer so the water temperature is boosted at shower time.

 

We have a 3 bed, 3 bath home on a 15/45. Whilst at times it's been close when we have visitors running all the aircon and taking showers our incoming breaker (50A) hasn't opened, yet! The acid test will be April when we have family over from the UK, I expect the aircon will be working overtime.

 

I reckon what you describe would be fine on a 15/45 if you have gas cooking and don't want a blisteringly hot deluge in the shower. 

 

Getting PEA chaps to do your poles and underground could be a good idea. Many of them moonlight (with the full knowledge of their employer). Our poles (which were installed on a cash basis) have PEA stamped on them, were installed by chaps wearing PEA uniforms, driving a PEA truck. Of course as it's their regular job they have all the kit and experience which a regular contractor may not.

 

[English Engineer]

We have just completed an ECO house and our water heating is direct solar. Ample hot water at zero cost. Single phase is fine. The problem with 3 phase is the voltsge between phases is 380v and not necessary for a small house. In any event you should ensure the system is bonded to earth and RCBO circuit breakers are used.

[English Engineer]

The size of cable is likely to be based on voltage drop not current rating. You mulitiply the maximum current by the cable resistance. Cable resistance can be found on google. I used a maximum voltage drop of 10v for the go and return. ie. 2 x calculated voltsge drop.

[bankruatsteve]

19 minutes ago, English Engineer said:

The problem with 3 phase is the voltsge between phases is 380v and not necessary for a small house.

That is not a problem or even an issue.  The advantage for domestic use is that 3-phase is essentially 3 separate single-phase supplies.  This can help for homes with higher than normal demand.

[Crossy]

34 minutes ago, bankruatsteve said:

This can help for homes with higher than normal demand.

 

I sometimes wish we'd gone 3-phase. Not for load reasons but because when we have a power failure it's invariably our phase. The rest of the village is still on whilst our genset is running ????

 

Sadly solar water wasn't an option for Madam, she won't allow anything to sully her feature roof.

 

[English Engineer]

1 hour ago, bankruatsteve said:

That is not a problem or even an issue.  The advantage for domestic use is that 3-phase is essentially 3 separate single-phase supplies.  This can help for homes with higher than normal demand.

Yes I would agree for high demand but not for a small house.

[bankruatsteve]

1 hour ago, Crossy said:

I sometimes wish we'd gone 3-phase. Not for load reasons but because when we have a power failure it's invariably our phase. The rest of the village is still on whilst our genset is running ????

 

Unless too tangential to the thread... is there equipment that can automatically share a live phase to a dead one and then back when things are normal?   Or, how would you work out a benefit for whatever is connected to the dead phase?  Just curious.

[English Engineer]

2 hours ago, bankruatsteve said:

Unless too tangential to the thread... is there equipment that can automatically share a live phase to a dead one and then back when things are normal?   Or, how would you work out a benefit for whatever is connected to the dead phase?  Just curious.

Yes it is called a phase failure. It can automatically swich to the live phase. The lines must be carefully segregated to ensure no access to the line voltage.

[khunPer]

20 hours ago, Crossy said:

Go with tank or gas water heaters and you can significantly reduce your demand.

Or a solar powered water heater, mine was about 40k baht with a 200 liter tank (that even came with build in electric heater for longer periods of clouds/rain, but I don't use it). I placed it on roof, with the tank on the attic with a 35W "Grunnfoss" circulation pump (made for heating system circulation, available in Thailand) to flow water from tank to solar heater panel; lots of nice hot water. However, it will depend of number of bathrooms, if one only an instant 3kW electric heater might be enough.

[Crossy]

2 hours ago, bankruatsteve said:

Unless too tangential to the thread... is there equipment that can automatically share a live phase to a dead one and then back when things are normal?   Or, how would you work out a benefit for whatever is connected to the dead phase?  Just curious.

 

Yes, and it's not really that difficult to do.

 

I did design one once to place "essential load" (and only the essential, load) automatically onto a working phase using a three voltage sensors, a handful of relays and three 50A contactors (a sort of giant relay). The hardest part was designing the control logic (using relays) to ensure absolutely that your load couldn't be connected to two phases at once (there would be an earth-shattering kaboom).

 

I never built it but I'm 100% sure it would have worked as advertised and since it used relays would have been infinitely reliable (no software bugs).

[shaemus]

On 3/27/2019 at 6:54 PM, Crossy said:

The usual maximum single-phase supply from PEA is a 15/45, 45A max = About 10kVA.

 

If you need more then it's 3-phase time.

 

A 250m run at 45A single-phase you are looking at 70mm² copper, you could get away with smaller cable (but 4 wires instead of 2) if you go 3-phase, say 50mm². Go one size bigger if you use aluminium cable (cheaper but not permitted underground)

 

For such a long run I would go aluminium on poles until you get near the house where copper underground may improve the look.

Mr Crossy.

 

I will going down this route myself soon as per my previous post about voltage drop on my supply.

 

I am just curious as to what standard/ cable selection chart you have used for the cable calculation you have given the OP?

 

 I did mine based on Australian standards and it came out a a much bigger CSA than wht you have proposed. the software i used is implementing the standards reqd for submains and not overhead supply.

 

Just curious if you have some PEA / thai  cable selection standard that you have employed here.

 

Thanks in Advance

 

Shaemus

[shaemus]

On 3/28/2019 at 10:21 AM, English Engineer said:

We have just completed an ECO house and our water heating is direct solar. Ample hot water at zero cost. Single phase is fine. The problem with 3 phase is the voltsge between phases is 380v and not necessary for a small house. In any event you should ensure the system is bonded to earth and RCBO circuit breakers are used.

Would you mind sharing what Solar hot water system you have installed and a rough cost.

 

thanks in advance

 

Shaemus

[Crossy]

10 minutes ago, shaemus said:

I am just curious as to what standard/ cable selection chart you have used for the cable calculation you have given the OP?

 

Being lazy I plugged the numbers into the Doncaster Cables calculator.

 

What sizes are you getting?

 

I used a 5% volt drop for meter to house. In reality you shouldn't be anywhere near max load for significant periods so the drop will be proportionately smaller.

[shaemus]

3 minutes ago, Crossy said:

 

Being lazy I plugged the numbers into the Doncaster Cables calculator.

 

What sizes are you getting?

 

hold tight i will dig it out. from memory it was about 150mm in Cu, i used cable calc pro. but as i said it is for submaain calcs rather that supply authority networks. it has allot of the necessary rating factors, like T amb, emthod of install, protection technique etc etc.

 

I did a little bit of fact finding from Aus and the sparks who do that kind of install there are all using Alu super flex.

 

I am still to go to the PEA to see what they can offer me and how much. Just as a point of interest did you buy your own transformer and what size?

 

Document to follow...

 

Shameus

[Fruit Trader]

Single 50 mm2 Cu/PVC mounted in air on poles

220 V single phase length 250 m total cable length 500 m

Load 45 A

Cable impedance 0.10585 Ω (R=0.10143, X=0.03028)

Voltage drop: 9.53 V (4.33%)

[Crossy]

14 minutes ago, Fruit Trader said:

Single 50 mm2 Cu/PVC mounted in air on poles

220 V single phase length 250 m total cable length 500 m

Load 45 A

Cable impedance 0.10585 Ω (R=0.10143, X=0.03028)

Voltage drop: 9.53 V (4.33%)

 

Yeah, I plugged 50A into the Doncaster calculator and it pushed it over the 5% drop.

 

70mm² (or even 95mm²) Al would be a lot cheaper (not underground) and less likely to wander in the night.

 

[lopburi3]

On 3/28/2019 at 5:30 AM, Crossy said:

We have a 3 bed, 3 bath home on a 15/45. Whilst at times it's been close when we have visitors running all the aircon and taking showers our incoming breaker (50A) hasn't opened, yet!

We have 6 bedrooms and 7 bathrooms (3.5kw heaters) on 15/45 and never had main trip.  Normally have 8 people and 5 air conditioners running at night.  If look at figures not good but when heaters are used air conditioning usage is low and vice versa. Showers are not used more than a few minutes and spread so often not the issue they may seem.

 

Got this guy on the brain today - used to be on the b/w converted radar Raytheon TV all the time when young.

[thaibook]

On 3/27/2019 at 10:21 PM, English Engineer said:

We have just completed an ECO house and our water heating is direct solar. Ample hot water at zero cost. Single phase is fine. The problem with 3 phase is the voltsge between phases is 380v and not necessary for a small house. In any event you should ensure the system is bonded to earth and RCBO circuit breakers are used.

would you mind sending me details (pm) of your solar water heating system and its cost as you have done to Shaemus.  What else constitutes an ECO house (references to outside sources are fine) and does it limit the design of the house? 

[Crossy]

On 3/28/2019 at 9:21 AM, English Engineer said:

We have just completed an ECO house and our water heating is direct solar. Ample hot water at zero cost.

 

If you feel like doing it (and have time) a thread on energy saving homes would be nice. Post a few photos and detail your energy saving features.

 

If you have an indication on ROI for each feature that would be great.

[thaibook]

Does the Thai grid buy excess electricity generated by individuals from solar?

[sometimewoodworker]

1 hour ago, thaibook said:

Does the Thai grid buy excess electricity generated by individuals from solar?

There is a new program accepting applications starting soon. Getting on it is often difficult or impossible, and the paperwork is significant 

 

So the answer is theoretically yes, practically unlikely.

 

Some people run the meters backwards so have lower bills. Never have a negative amount used as then it's quite likely that they will install a meter that can't run backwards.