Electric - Clarification Required!

[technocracy]

Firstly I am not in Thailand - but in Laos. I am currently at the phase of defining the electrical requirements for my house, well the requirements are there but now I am trying to sort out the bloody Laos Electric company to provide what I really need not what they want to give me!

Background - the house is a relatively large space 200+ sq meters with 3 bedrooms, living area, pool room, office kitchen, 2 en-suites and 2 bathrooms. However I aren't going overboard with the electrics!

In total there is 27 double sockets, lighting in each room (flourescent - will be of choice, although if standard no more than 60w), the 2 ensuites and 1 bathroom will have electric showers, there will be a single water pump providing the water (Grundfos - MQ I think is the model), there will be 4 air cons - two of which will be the small Mr Slim Mitsubishis and the other 2 be the one model up (dunno what the model is called). There is also will be a pump outside for a fountain (size to be confirmed - on waterflow) and one for occasional pumping from the well.

Now first off - as I am from the UK and I am more familiar with ring mains - this is the approach to be taken for the sockets, there will be 3 of rings one on each side of the house and one upstairs (each area downstairs is just with in the 105m2 limits - hence why two downstairs. As they don't enforce 'Electrical standards' and no checks are performed this is why I am so heavily involved - because also I have seen the 'Electricians' hand work over here (mix lighting, sockets and aircon on one radial - sure why not!!!!! ).

All the cable in the house will be earthed - which is connected to a 8m Earth rod sunk outside . . . I ready run 25mm2 cable run in conduit from the meter to the house (the house is 35metres from the meter). Don't know about Thailand but in Laos all the meters are outside of the property near the boundary usually on the nearest electrical pole.

Ready bought the Consumber Unit - with the require breakers 32amp for Rings, Aircon, 10amp lighting (couldn't get 6amp!), 15amp for the outside area - to be connect via a ELCB etc and the main breaker is 63amp. Normal living there will be 2 people this will occasionally swell to 4 or 5 folks.

NOW . . . today after a minor disagreement with the same 'Electrician' who arrange for the meter to be installed (as he wanted to install 3 phase at my wifes Aunties house - all to add a 2nd aircon unit ... all I wanted him do was change the size of cable into the consumer unit (current tiny.. same used to the rooms!)!). I looked at the meter at my wifes aunts house to see it is a 10A/40A which I believe is the nominal and max amp. In this argument we are talking about a house with 3 tv (1 barely used), 1 living room, 3 bedrooms with very few appliances, 2 hot water showers and 1 aircon ..... but that's a different arguement!

Back to my things . . when the meter was installed I was given option of a Small, Medium, Large type - so I plunked for a medium - since it was installed by this same above guy (who I assumed worked for the Electricity Company) after getting a pole installed for our meter (posh eh!). A bog standard breaker was stuck on the end by this guy to give power to the works for lights etc on the land working (which I later add a ELCB). Because of this I didn't really look or take much notice of the meter (mistake number 1) later I discovered that for some bizarre reason we had been provided with a 3 Phase supply. Oh well I thought I can just use a single phase - then maybe as I might be starting a company on another part of my land I'll use another phase so not money wasted.

Today following this argument that ensued I went down to the land to have proper look at the meter - to discover it is a 3 phase - 380v meter which has a 10A/40A rating (which I assume is 3 x 10A/40A).

As meter rating is something I have absolutely no knowledge of (the UK in a house they are just there. . .) the question is this meter sufficient to just use a single phase? I had a quick look around the local electrical supplies store today and saw a higher rated 3 phase amp meter so I know they exist here.

I know if I use all three I have 120A, I suppose I could put 2 in for 80A - but really I don't want to have run in more 25mm2 cable - firstly as it cost as bloody fortune also I don't want to put in a 2 or 3 pole main breaker in purely because of this bloody meter!

Can Anyone help answer this question?!?!

[Crossy]

I believe you are correct suggesting the 10/40 is nominal/max current.

I'd be concerned as to how your meter reacts to using just one phase, will it read correctly? If it were a modern electronic meter I would have no problem but the old mechanical type may under / over read with such a massive imbalance. Just get them to install what you originally asked for (or would that prove as easy as it would in LoS?).

Any meter specialists out there??

IMHO I'm not sure your use of rings with 32A breakers is sensible since you're not using UK style fused plug tops, may be an idea to drop to 20 or 25A (as if it were a radial installation), you're never going to pull anything like that anyway except maybe in the kitchen

[technocracy]

I believe you are correct suggesting the 10/40 is nominal/max current.

I'd be concerned as to how your meter reacts to using just one phase, will it read correctly? If it were a modern electronic meter I would have no problem but the old mechanical type may under / over read with such a massive imbalance. Just get them to install what you originally asked for (or would that prove as easy as it would in LoS?).

Any meter specialists out there??

IMHO I'm not sure your use of rings with 32A breakers is sensible since you're not using UK style fused plug tops, may be an idea to drop to 20 or 25A (as if it were a radial installation), you're never going to pull anything like that anyway except maybe in the kitchen

Cheers for that . . . very true on the 32A breaker . . it didn't actually cross my mind regards the fuseless plugs. The downstairs ring without the kitchen and upstairs will be lowered.

The meter is a 'new' one but mechanical style - I did think about the reading also which concerned me also. As you say it would be a big imbalance on the load. As for changing it - hmmmm as this guy so tells there is not a larger meter for Single Phase supply than a 10A/40A, you can probably guess the fun and games I would have! Obviously they must make more cash from installing 3 phase at any house that has a sniff of aircon!!!

Also today I am going to have a full look at the 'breaker' that has been connected - since this is a 3 phase (3 pole) breaker which has a 3 output each giving out approx 220v, well 217, 227 and 219 what I check yesterday. I'll report back what exactly it is later!

All very frustrating - the last thing I want to do is running in more 25mm2 and buying new main switches etc. Mainly as I'll need to change the conduit size and as the entire run is 50 odd metres it ain't fun!!

[elkangorito]

Since you already have 3 phase connected (it may be useful one day), it would be recommended that you divide your 3 phases with approximate equal load, at your consumer unit. This means that you would need to calculate the maximum demand & divide it equally (or as close as you can) over the 3 phases. This will also help to decrease any error in your KWH meter. Incidentally, "induction disc" (the aluminium disc that spins inside) KWH meters that are used to calculate 3 phase power are not as accurate as if you had one KWH meter per phase.

I would not recommend exceeding 20 amps for the circuit breaker that protects 2.5mm squared copper cable. If you wish to have a 32 amp power circuit, the minimum cable size should be 6mm squared copper cable, but this not recommended. 2.5mm squared is adequate.

[Khonwan]

Since you already have 3 phase connected (it may be useful one day), it would be recommended that you divide your 3 phases with approximate equal load, at your consumer unit. This means that you would need to calculate the maximum demand & divide it equally (or as close as you can) over the 3 phases. This will also help to decrease any error in your KWH meter. Incidentally, "induction disc" (the aluminium disc that spins inside) KWH meters that are used to calculate 3 phase power are not as accurate as if you had one KWH meter per phase.

I would not recommend exceeding 20 amps for the circuit breaker that protects 2.5mm squared copper cable. If you wish to have a 32 amp power circuit, the minimum cable size should be 6mm squared copper cable, but this not recommended. 2.5mm squared is adequate.

It appears that the OP does not have his own transformer so (apart from any effect on the meter readings) the issue of balance should not be important.

[technocracy]

Cheers for the replies guys.

I have already ditched the idea of attempting use a single phase and ran in an additional cable to use 2 of the 3 phases and increasing the main breaker to 80amp. Which obviously gives plenty of overhead if I wish to add more aircon or pumps at a later date. The third phase I will then use for my company plan on the rest of the land. All costing another 10,000+baht.

As for the 32amp breaker that has already been addressed - as I said I completely overlooked the fact that we don't have fused plugs unlike the UK. As they say two heads are better than one. Also elkangorito bear in mind I am using a ring main - rather than a radial so there will be more DPOs on it compared to a radial (which I believe the recommended max is 7?). Also 2 x 2.5mm will be connecting to the MCB so theorically giving a 5mm2 cable size.

Interesting to know though khonwan that balance on the meter wouldn't be an issue. Never having to deal with 3 phase before (never known 3 phase to be installed at a house in the UK - as 80amps is on tap from single phase) I am after bit of advice of how it is best to cable the unit. The options which I see are:

1) Use my existing single phase box and installing a three pole mains MCB, moving the main breaker to the middle of the box cutting the buzzbar for the MCBs in half and then spread the load on either side of the mains MCB.

2) Ditch the single pole consumer and buy a 3 phase consumer unit.

I am currently waivering between the two because I have a 14 way Siemens (single phase) consumer unit so would still have 11 usable circuits (only 9 to be used so having 2 spare). The downside is I find the idea of cutting the buzzbar etc a bit hokey although I know technically there is no reason why I can't do this.

As for number 2 I know really this would be the technically be the real way and correct way to go but a great whopping metal 3 phase unit stuck on the all doesn't exactly appeal!!

Thoughts gentlemen?

On the topic of the 3 phase it's very amusing (sic) here in Laos how they view 3 phase. They seem to see it as a fix all for when there is voltage drops on single phase (which is common here), they don't seem to grasp that the 3 phases will still be affected since they come off the same overheads! There standard installation seems to be stick a whopping sized industrial breaker (albeit 63amps and not weatherproof(!)) next to the meter then run from this I assume into the house consumer unit so have two breakers - but then again they might use this has the main breaker! I await the uproar when I tell them to remove the breaker and wire my consumer directly to the meter . . . but that'll be an argument for another day!

Thanks in advance.

[Khonwan]

Cheers for the replies guys.

I have already ditched the idea of attempting use a single phase and ran in an additional cable to use 2 of the 3 phases and increasing the main breaker to 80amp. Which obviously gives plenty of overhead if I wish to add more aircon or pumps at a later date. The third phase I will then use for my company plan on the rest of the land. All costing another 10,000+baht.

As for the 32amp breaker that has already been addressed - as I said I completely overlooked the fact that we don't have fused plugs unlike the UK. As they say two heads are better than one. Also elkangorito bear in mind I am using a ring main - rather than a radial so there will be more DPOs on it compared to a radial (which I believe the recommended max is 7?). Also 2 x 2.5mm will be connecting to the MCB so theorically giving a 5mm2 cable size.

Interesting to know though khonwan that balance on the meter wouldn't be an issue. Never having to deal with 3 phase before (never known 3 phase to be installed at a house in the UK - as 80amps is on tap from single phase) I am after bit of advice of how it is best to cable the unit. The options which I see are:

1) Use my existing single phase box and installing a three pole mains MCB, moving the main breaker to the middle of the box cutting the buzzbar for the MCBs in half and then spread the load on either side of the mains MCB.

2) Ditch the single pole consumer and buy a 3 phase consumer unit.

I am currently waivering between the two because I have a 14 way Siemens (single phase) consumer unit so would still have 11 usable circuits (only 9 to be used so having 2 spare). The downside is I find the idea of cutting the buzzbar etc a bit hokey although I know technically there is no reason why I can't do this.

As for number 2 I know really this would be the technically be the real way and correct way to go but a great whopping metal 3 phase unit stuck on the all doesn't exactly appeal!!

Thoughts gentlemen?

On the topic of the 3 phase it's very amusing (sic) here in Laos how they view 3 phase. They seem to see it as a fix all for when there is voltage drops on single phase (which is common here), they don't seem to grasp that the 3 phases will still be affected since they come off the same overheads! There standard installation seems to be stick a whopping sized industrial breaker (albeit 63amps and not weatherproof(!)) next to the meter then run from this I assume into the house consumer unit so have two breakers - but then again they might use this has the main breaker! I await the uproar when I tell them to remove the breaker and wire my consumer directly to the meter . . . but that'll be an argument for another day!

Thanks in advance.

Technocracy, let me first explain that I am not an electrician - just a guy like you who now has a three-phase supply. I would not dismiss elkangorito's concern that an analogue kWh meter with unbalanced loads will not be as accurate as a single-phase meter - I simply don't know. However, the issue of balance has more to do with the 'well-being' of the transformer (correct me if I'm wrong sparkies). I have my own transformer, so balanced loads should be important to me. I assume you do not (you'd have had to pay PEA around 160,000 baht if you do - I don't think you did); the issue of balance (in as far as it effects the transformer to which your supply is connected) is therefore of importance only to PEA. PEA 'balance' their transformer by assuming that the total loads on each phase-leg servicing the village will average out in equilibrium. Your now-planned actual use of the three phases makes the issue of the meter efficiency unimportant anyway.

With regards to installation, perhaps you should consider a third option. If you have already installed a single-phase distribution box, why don't you add a second similar box for the second-leg? That's the route I chose when I switched from a single-phase set-up (powered by my generator) to a 3-ph supply.

[elkangorito]

Technocracy, let me first explain that I am not an electrician - just a guy like you who now has a three-phase supply. I would not dismiss elkangorito's concern that an analogue kWh meter with unbalanced loads will not be as accurate as a single-phase meter - I simply don't know. However, the issue of balance has more to do with the 'well-being' of the transformer (correct me if I'm wrong sparkies). I have my own transformer, so balanced loads should be important to me. I assume you do not (you'd have had to pay PEA around 160,000 baht if you do - I don't think you did); the issue of balance (in as far as it effects the transformer to which your supply is connected) is therefore of importance only to PEA. PEA 'balance' their transformer by assuming that the total loads on each phase-leg servicing the village will average out in equilibrium. Your now-planned actual use of the three phases makes the issue of the meter efficiency unimportant anyway.

With regards to installation, perhaps you should consider a third option. If you have already installed a single-phase distribution box, why don't you add a second similar box for the second-leg? That's the route I chose when I switched from a single-phase set-up (powered by my generator) to a 3-ph supply.

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage drop can occur on any one phase.

BTW, I am an electrician.

[Khonwan]

Technocracy, let me first explain that I am not an electrician - just a guy like you who now has a three-phase supply. I would not dismiss elkangorito's concern that an analogue kWh meter with unbalanced loads will not be as accurate as a single-phase meter - I simply don't know. However, the issue of balance has more to do with the 'well-being' of the transformer (correct me if I'm wrong sparkies). I have my own transformer, so balanced loads should be important to me. I assume you do not (you'd have had to pay PEA around 160,000 baht if you do - I don't think you did); the issue of balance (in as far as it effects the transformer to which your supply is connected) is therefore of importance only to PEA. PEA 'balance' their transformer by assuming that the total loads on each phase-leg servicing the village will average out in equilibrium. Your now-planned actual use of the three phases makes the issue of the meter efficiency unimportant anyway.

With regards to installation, perhaps you should consider a third option. If you have already installed a single-phase distribution box, why don't you add a second similar box for the second-leg? That's the route I chose when I switched from a single-phase set-up (powered by my generator) to a 3-ph supply.

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage drop can occur on any one phase.

BTW, I am an electrician.

You have just described the HOW not the WHY. An unbalanced load can damamage the transformer! I know of no other reason to be concerned, do you?

[technocracy]

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage can occur on any one phase.

BTW, I am an electrician.

Any thoughts on my previous post?

I ain't a fully qualified sparkie just someone whose learnt from one - rewired numerous houses then my friend (who is a fully qualified sparkie and taught me) did the certifying checks to make it official and legal. So I am pretty well versed when it comes to putting it all together inside - however like I say this is the first time I had to deal with 3 phase (and having to check meter types etc!).

Khonwan in terms of installing a secondary single phase unit - I couldn't link the neutral between the two boxes since I am using 25mm2 cable and the 2/3 pole MCBs only accept a max cable size of 25mm2. Also running a neutral cable between boxes is even more hokey than just cutting a buzz bar in two!

I will be making a trip over to Udon to view some 3 phase units in the coming week (well once I've finished the cutting out and put the trunking in) as they don't have an homely styled ones here only industrial.

PS .. I noticed in the first post I put I have an 8m earth rod .. .. not really! It's 8 foot!

[Khonwan]

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage can occur on any one phase.

BTW, I am an electrician.

Any thoughts on my previous post?

I ain't a fully qualified sparkie just someone whose learnt from one - rewired numerous houses then my friend (who is a fully qualified sparkie and taught me) did the certifying checks to make it official and legal. So I am pretty well versed when it comes to putting it all together inside - however like I say this is the first time I had to deal with 3 phase (and having to check meter types etc!).

Khonwan in terms of installing a secondary single phase unit - I couldn't link the neutral between the two boxes since I am using 25mm2 cable and the 2/3 pole MCBs only accept a max cable size of 25mm2. Also running a neutral cable between boxes is even more hokey than just cutting a buzz bar in two!

I will be making a trip over to Udon to view some 3 phase units in the coming week (well once I've finished the cutting out and put the trunking in) as they don't have an homely styled ones here only industrial.

PS .. I noticed in the first post I put I have an 8m earth rod .. .. not really! It's 8 foot!

For the second s-ph box, the neutral would simply be connected to the incoming neutral (before it enters the 1st box). Connectors are available in most local DIY shops. A 3-ph box is tidier, of course, but I couldn't find any that were not expensive. BTW, if you do install a 3-ph box, I'd suggest you run the 3rd phase-leg to the house also since it may well prove useful to be able to run a 3-ph motor in the future (the cost of this third cable is almost negligible for your distance).

[elkangorito]

Technocracy, let me first explain that I am not an electrician - just a guy like you who now has a three-phase supply. I would not dismiss elkangorito's concern that an analogue kWh meter with unbalanced loads will not be as accurate as a single-phase meter - I simply don't know. However, the issue of balance has more to do with the 'well-being' of the transformer (correct me if I'm wrong sparkies). I have my own transformer, so balanced loads should be important to me. I assume you do not (you'd have had to pay PEA around 160,000 baht if you do - I don't think you did); the issue of balance (in as far as it effects the transformer to which your supply is connected) is therefore of importance only to PEA. PEA 'balance' their transformer by assuming that the total loads on each phase-leg servicing the village will average out in equilibrium. Your now-planned actual use of the three phases makes the issue of the meter efficiency unimportant anyway.

With regards to installation, perhaps you should consider a third option. If you have already installed a single-phase distribution box, why don't you add a second similar box for the second-leg? That's the route I chose when I switched from a single-phase set-up (powered by my generator) to a 3-ph supply.

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage drop can occur on any one phase.

BTW, I am an electrician.

You have just described the HOW not the WHY. An unbalanced load can damamage the transformer! I know of no other reason to be concerned, do you?

Assuming a standard distribution transformer (the same as used here in Thailand), which is a 3 wire primary Delta connected & a 4 wire secondary Star connected unit, an unbalanced load cannot damage the transformer, however, it's efficiency will be reduced. An overcurrent on a phase can damage a transformer but would only occur if the transformer is not adequately protected.

Energy Authorities try to keep the load across 3 phases balanced so that they don't waste money on cable & transformers are used more efficiently.

Addressing the issue of 'phase balance'; this has nothing to do with the transformer. What it is exactly, is how YOU distribute YOUR load over YOUR 3 available phases. For example, if your total load is 60 Amps, you must try to distribute it over 3 phases so that you end up with about 20 Amps on each phase. Of course, it will never be exact but the closer you can get this, the better off you'll be.

It is a fact that an induction disc KWH meter used to calculate power over 3 phases is not as accurate as if 1 of these meters was used per phase. This inaccuracy is exacerbated if there is a significant load imbalance.

Also, it is very possible that a voltage can occur on any one phase.

BTW, I am an electrician.

Any thoughts on my previous post?

I ain't a fully qualified sparkie just someone whose learnt from one - rewired numerous houses then my friend (who is a fully qualified sparkie and taught me) did the certifying checks to make it official and legal. So I am pretty well versed when it comes to putting it all together inside - however like I say this is the first time I had to deal with 3 phase (and having to check meter types etc!).

Khonwan in terms of installing a secondary single phase unit - I couldn't link the neutral between the two boxes since I am using 25mm2 cable and the 2/3 pole MCBs only accept a max cable size of 25mm2. Also running a neutral cable between boxes is even more hokey than just cutting a buzz bar in two!

I will be making a trip over to Udon to view some 3 phase units in the coming week (well once I've finished the cutting out and put the trunking in) as they don't have an homely styled ones here only industrial.

PS .. I noticed in the first post I put I have an 8m earth rod .. .. not really! It's 8 foot!

Having two separate distribution boards (consumer units) separately fed from the incoming supply, is not a good idea because you will need to operate 2 switches in order to isolate the whole installation from the incoming supply.

Inside the distribution board are 2 brass bars with lots of holes & screws. 1 bar is for the earth cables & the other bar is for the neutral cables.

My recommendations since your KWH meter has a maximum value of 40 Amps;

1. Use only one (1) 3 phase consumer unit.

2. The Main Switch in this unit could be anywhere from 40 Amps to whatever size will fit into the consumer unit. This main switch does NOT have to be a circuit breaker (since the KWH meter belongs to the PEA & it is up to them to protect their meter, something which they never seem to do in Thailand). No matter whether the Main Switch is a circuit breaker or an isolator, it should be rated to interrupt a minimum of 6kA (6000 Amps). All of your circuit breakers in the consumer unit should also be rated likewise.

3. Save cable - do not use a 'ring main'. A ring main is used essentially to decrease the risk of failure of supply & also to allow maintenance on circuits without isolating the whole circuit. Since your will not require to maintain such equipment as transformers in your ring main, & since there is a very tiny chance that the ring main cable can be cut, I can see no reason for using such a thing. Power outlets wired in parallel are more than adequate & this is also standard practice.

Anyway, all of this has been discussed ad infinitum in the thread "Domestic Electrical Wiring", which is summerised on

http://www.crossy.co.uk/wiring

Below is an example of balancing a 3 phase prospective load using maximum demand:

The domestic installation comprises of the following;

26 x lighting points

24 x 10 A single socket-outlets

1 x 15 A socket-outlet

1 x 16.6 kW range

1 x 4 kW air-conditioning unit

1 x 12.96 kW instantaneous water heater

1 x 3.6 kW clothes dryer

and arranged for connection across a three-phase supply as follows:

Red - 15 A socket-outlet, 5 kW hotplates, 4 kW air-conditioner, 4.32 kW instantaneous water heater.

White - 15 × 10 A socket-outlets, 5 kW hotplates, 4.32 kW instantaneous water heater, 3.6 kW clothes dryer.

Blue - 26 lights, 9 × 10 A socket-outlets, 6.6 kW oven, 4.32 kW instantaneous water heater.

Lighting - 5 Amps (Blue phase)

10 A socket-outlets - 20 Amps (10 Amps each for White & Blue phases).

15 A socket-outlet - 10 Amps (Red phase).

Range - 10.4 Amps (Red phase), 10.4 Amps (White phase), 13.7 Amps (Blue phase).

Air-conditioner - 12.5 Amps (Red phase).

Water heater - 6 Amps for each phase.

Clothes dryer - 7.5 Amps (White phase).

Total Amps per phase; - 38.9 (Red phase). 33.9 (White phase). 34.7 (Blue phase).

This is just a very broad example of how to balance a load over 3 phases using maximum demand.

[Crossy]

Elkangorito.

Just for interest have a look at this article in the IEE journal Wiring Matters, it goes in to the development of the UK ring-main system (which I believe is still unique in the world).

http://www.iee.org/Publish/WireRegs/Wiring..._and_socket.pdf

The ring in its original form, actually saved cable

[Khonwan]

Elkangorito.

Just for interest have a look at this article in the IEE journal Wiring Matters, it goes in to the development of the UK ring-main system (which I believe is still unique in the world).

http://www.iee.org/Publish/WireRegs/Wiring..._and_socket.pdf

The ring in its original form, actually saved cable

I can't see how that no longer applies today! According to the article, not only did it apply originally, but it still applied in 1994. The only reason I used the radial system in my home was the lack of fused plugs here in Thailand.

[elkangorito]

Elkangorito.

Just for interest have a look at this article in the IEE journal Wiring Matters, it goes in to the development of the UK ring-main system (which I believe is still unique in the world).

http://www.iee.org/Publish/WireRegs/Wiring..._and_socket.pdf

The ring in its original form, actually saved cable

A very interesting article Crossy.

But as for using this system without the prescribed 'fused plugs', I think it could be dangerous...especially if the protective device is say 32 Amps (3 times the current rating of standard appliance flexible cable) & if fault current limitation is not provided (if required) at the incoming supply of the installation (HRC fuse).

No doubt it can save on material & labour costs but I think if it is going to be employed, it should be done so according to the standard after the standard has been normalised to the country where the system will be installed.

[Crossy]

But as for using this system without the prescribed 'fused plugs', I think it could be dangerous...especially if the protective device is say 32 Amps (3 times the current rating of standard appliance flexible cable) & if fault current limitation is not provided (if required) at the incoming supply of the installation (HRC fuse).

No doubt it can save on material & labour costs but I think if it is going to be employed, it should be done so according to the standard after the standard has been normalised to the country where the system will be installed.

All points agreed 1000%, our OP has reduced his breakers to 20 or 25A

It may also be an idea for him to split each ring into two radials each on a separate breaker, that would avoid confusion later when a local sparks looks at the system ("wot's a ring main boss???").

Interestingly, the UK regs have recently (10 years or so) been changed to permit radial installations in industrial premises, 2.5mm cable on a 20A breaker or 4mm on a 32A (IIRC).

[elkangorito]

G'day Crossy.

Now that I've thought about it, the ring main sounds like a great idea. The only thing that I'd do would be to ensure the use of miniature HRC fuses in the plugs (or at least ceramic fuses) as well as ensuring that a fault current limiting HRC fuse was installed at the point of connection of the incoming supply.

The ring main I was referring to in a previous post is used in Australia in the distribution network to facilitate maintenance with minimal outages.

[technocracy]

Well I am now a new owner of a Square D 24 way 3 phase consumer unit (albeit a big ugly thing!) 24 way as it was only about 50 baht more than the 18 way. Complete with a 100amp mains breaker so I have sufficient overhead for any future aircon needs.

The ring mains are great - no doubt about it! But for the first time I have taken the decision to use radials on 20amp breakers .. .. all nice and standard. Although I am sure a local spark would be very confused in this install anyway as the aircon, shower, sockets and lighting aren't hanging off the same MCB!

Back to putting the trunking in tomorrow . . bloody poxy metal clips.

Cheers all for the advice much appreciated.