ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Air Conditioning?

Over here you're talking about going 3-phase once the demand goes beyond 63A at 230V.

100A supplies are only installed if the ESB (PoCo) approves them and generally they don't in urban areas as the distribution system is designed around 63A services. If you're in a rural area they might sanction a 100A single phase supply. In an urban area they're more likely to just hook you up to 3-phase and split the load over the phases.

Very easily achieved if the building is wired using radial circuits as you just decide which rooms go on which phase. Ring circuits tend to complicate matters! You're not allowed to have single phase wiring sourced from different phases within the same room. Incase someone somehow connects themselves across 2 phases.

You could have the air con unit sitting on a single phase or 3-phase supply or several small units all on different single phase supplies to split the load. Where 3-phase is used the wiring regulations suddenly become a lot more serious.


[This message has been edited by djk (edited 10-12-2003).]

Similar rules apply in British IEE Regs.

3-phase is rare in residential, but where it is employed in a very large house the regs. specify that all sockets in a room must be on the same phase.

djk,
Over here, we have the standard 63A single phase supply to most of our Residential dwellings.
Where this ends, is for new housing here that ask for a 3 Phase supply of 30A/phase, in that this is to run A/C gear or 3 Phase heating equipment.
Everything in the house is evenly Balanced over the 3 Phases.
Incidentally, you can have a supply out in the country of (3 Phase) 50A, 100A, but you pay more, because you are no longer on the Domestic Supply Rate.
Just as a question, to yourself and Paul, we have the same Regulation over here, about single phase points being on the same Phase within one room.
How on earth could this be a danger?, as it would be pretty rare, if two Phases did contact one another, in a situation like this, can either of you guys give an example of where this has happened?.
We have the situation here, where lighting circuits might be spread over 2 or 3 Phases, but you are required to mark on the sub-plate(of the switch), that there is 400V on the other side of the switch-plate.

As far as I know you can have sockets directly next to each other on different phases if you want. There was something about not mixing 1ph and 3ph wiring though, which would mean you have to run seperate conduits for each single phase and 3ph circuit right from the panel.

The argument is that somebody could end up with two appliances within arms reach of each other on different phases.

If you had two simultaneous faults which left each appliance casing live at 240V to ground, there would be a shock of 415V awaiting anyone who touched both at the same time.

It's always seemed to be a pretty far-fetched scenario to me, but the rule has been there a long time (not sure how long, but it's certainly in the 1955 Regs).

Paul,
Re sockets on different phases in the same room, please see Reg 514-10-01 of BS 7671 : 2001. There is no specific reg prohibiting such an installation, all that is required is a warning notice of the maximum voltage that exists between simultaneously accessible enclosures / equipment, before gaining access to such live parts.

Personally I would consider installing single phase sockets on different phases within the same room to be bad practice, although if the appropriate warning labels are fitted it is in accordance with BS 7671.

I think the actual regulation requiring sockets to be same phase was last in the 14th Edition IEE regs (1966 - 1981). I can't find it in the 15th Edition (1981 - 1991) or 16th Edition / BS7671 present edition.

Trumpy

Over here you get a very over-sized 3 phase system with each phase rated at 63Amps

Certainly won't have any problem powering a few air con units on one anyway

djk,
3 Phases @ 63A a piece?.
That's a HUGE supply!.
I'm guessing that you guys use 3x 16mm2?, to supply this?.
What sized Neutral accompanies this supply?.

David,
I hadn't realized that the rule had been gone so long, so I stand corrected. With 3-ph being so rare in residential work it's not a situation encountered very often.

I no longer have a copy of the 15th edition, but as that's when the regs went to international format and many rules changed, it sounds probable that that's when the requirement was dropped, unless it was an amendment to the 14th during its last years.

By the way, one thing those of you outside the U.K. might not realize is that each edition of the IEE Regs. often has more than one version. David mentioned the 14th edition, in effect 1966 through 1981, but there were running amendments issued, so if someone talks about the "14th edition" it could mean the original 1966 rules, or the amended version of 1968, or the 1970 rewrite into metric units, and so on.

Mike,
For what it's worth, here's the rule as it used to be in the 14th edition:
6 ft. became 2m in the 1970 rewrite.

Trumpy:

There is a smaller 30A 3-phase setup too. However, with 3-phase being relatively rare in domestic installations here it's not seen very often as most 3-phase supplies are for commercial premisis.

However, smaller 3-phase installations on farms and in small commercial installations are becoming much more common place.

3-phase in domestic situations can prove quite expensive to install, particularly if the service is relatively old and underground as there may not be an accessible 3-phase connection point near by. In more remote rural areas it can involve running cables cross-country to the nearest 3-phase connection point which again can cost a lot of money. However, farmers and rural businesses can usually get a government grant to upgrade the supply.

You could be talking €5000 (euro) +...

If you're in an area fed by overhead 3-phase cables it's VERY easy