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#78288 - 09/01/01 06:48 PM Overloaded U.K. circuits  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
The discussion about hair-dryers & the possible overloading of circuits has prompted me to explain what I see as a problem here.

As most of you now know, the majority of homes here have 30A ring circuits feeding receptacles. The original IEE Regs. on these specified that a ring may serve any number of outlets within a floor area of 1000 sq. ft. The change to metric measurements altered this to 100 sq. meters, which is 1076 sq. ft.

The average home is smaller here than in the U.S., so in many cases a single ring was used. In larger homes (or smaller ones built to a better spec.) it has been the norm to install two such 30A rings.

The IEE Regs. specify that the designer should ensure that the "anticipated load is distributed evenly, as far as is reasonably practicable, between the circuits." As with many IEE rules, the wording is somewhat vague, but I think the intended aim is fairly obvious.

So the designer/installer isn't a mind-reader and can't allow for the unusual use of general-purpose outlets, but he should be able to make intelligent guesses as to what types of loads are likely to be used.

When two rings are installed in a two-story house, the most common arrangement seems to be one ring for each floor. The result is that the downstairs ring feeds all the heavy kitchen/utility appliances, while the upstairs ring often has no greater load than a couple of clocks and bedside lamps. In my mind, that's not ensuring the "reasonable" distribution of load.

"OK," I hear you say, "but 30A at 240V provides 7200W. Surely that's enough for serving kitchen/ground floor outlets?"

I agree that it would be, except for the fact that it's NOT usual to provide separate dedicated branches for washing machines, dryers, or dish-washers.

British washing machines & dish-washers usually incorporate a 3kW heating element. Start both at the same time (not uncommon) and there's 6kW already. That doesn't leave much spare for toasters, microwave ovens etc. running on the same ring. 99% of British kitchens have an electric kettle, rated between 2 & 3kW (Gotta make that tea!).

Add a clothes dryer as well, & the potential for overloads & trips is even greater. (Some large dryers are wired separately, but most are 3kW & plugged into a standard 13A outlet.)

When the ring was introduced here, washing machines were much less common than today, and dryers & dish-washers were practically non-existent in the average home.

Now, all three are common, yet we still have new homes wired so that all the heavy appliances end up on the same circuit.

The IEE Guidance Notes for the current edition acknowledge the increased loads in today's homes, but then seem to suggest a "solution" which is of little help. Their advice is to "consider the provision of a separate ring circuit to feed kitchen sockets."

As 90% of British homes have all the aforementioned appliances in the kitchen, and not a separate utility/laundry room, I don't understand the logic behind this. We'll still end up with an overloaded kitchen ring, only this time there'll be TWO 30A cicuits each running just table-lamps, TV's, etc., plus maybe an occasional heavier load from time to time.

Sure, there's a vaguely worded rule about ensuring sufficient number & capacity of circuits to allow for the expected load, but I don't see too many installations where this has been applied intelligently.

My preference is to follow American/Continental practice, and install a dedicated circuit for each of these major fixed loads.

Your thoughts on this? (With apologies for the lengthy explanation!)


2017 / 2014 NEC & Related Books and Study Guides

#78289 - 09/01/01 07:54 PM Re: Overloaded U.K. circuits  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
well , it sounds as if your IEE regs at least feel the growing pains of modern usage, as non-commital as it currently stands.

our NEC has beaten the IEE in this respect only in our addiction to appliances & 120 V 20A circuitry.

Does the IEE have a method of updating ? If so , do you see a trend towards dedicated circuits?

I really can't imagine wiring a home with only 2 circuits. I've been averaging 25-35 lately for a single family [Linked Image]

[This message has been edited by sparky (edited 09-01-2001).]


#78290 - 09/01/01 11:47 PM Re: Overloaded U.K. circuits  
tdhorne  Offline
Member
Joined: Mar 2001
Posts: 345
Maryland, USA
Quote
Originally posted by sparky:
well , it sounds as if your IEE regs at least feel the growing pains of modern usage, as non-committal as it currently stands.

our NEC has beaten the IEE in this respect only in our addiction to appliances & 120 V 20A circuitry.

Does the IEE have a method of updating ? If so , do you see a trend towards dedicated circuits?

I really can't imagine wiring a home with only 2 circuits. I've been averaging 25-35 lately for a single family [Linked Image]

[This message has been edited by Sparky (edited 09-01-2001).]

Sparky
- Keep in mind that UK normal service voltage is 240 and their ring circuits are 30 Ampere. That gives 7200 watts per circuit as opposed to our US 2400 watt or 1800 watt circuits.


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

#78291 - 09/02/01 06:32 AM Re: Overloaded U.K. circuits  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
yes I understand, but do the math for the wattage of a typical US install here....


#78292 - 09/02/01 06:44 AM Re: Overloaded U.K. circuits  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Sparky,

I'm talkng aboot the circuits feeding 13A receptacles here. There will be other branches as well.

Remember that we usually wire lights on separate circuits: Most often one or two 5A branches. For homes with an electric range ("cooker" in British terminology) there'll be a 30A branch for that.

In many modern homes with central heating, the unit also heats water, but if an electric water heater is present - either a the sole water heating or as a backup - then this has its own 15A branch due to the continuous long-term load.

Instant electric showers are becoming popular nowadays, and these are rated between 7 and 9.5kW, so they get their own 40A branch when present.

So, the average older house panel has 4 to 6 circuits, while newer ones may be about 8. There may be a couple of extras if there's a sub-feed to a garage etc., although these are often fitted as a separate 1 or 2-branch panel with its own main switch. These small panels are also found where showers etc. have been added and the owner didn't want the expense of fitting a bigger main panel.

Going back to the rings, some older kitchens have a separate small water heater mounted over or under the sink. They're usually only about 3 gallons and were intended to provide hot water quickly without the need to heat up the big 40 or 50 gal. cylinder.

These units are typically 2kW and connected to the kitchen ring circuit, allowed by IEE due to the fact that they are likely to be on for only a short time.

Again, when originally installed there wasn't a problem, but with the extra kichen loads added in more recent years, it could be the last straw.


#78293 - 09/02/01 07:23 AM Re: Overloaded U.K. circuits  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Oops, forgot your other questions.....

I've not noticed a general trend toward separate circuits for washers & dryers, except where the dryer is a large 4 or 5kW type, in which case it will have a dedicated branch. But most domestic dryers here are only 3kW.

The IEE updates the "regs." every few years. There's no fixed schedule as with the 3-yr. NEC, but 10 to 11 years seems about average.

The last few new editions were 13th (1955), 14th (1966), 15th (1981), 16th (1992). There was a pretty drastic change in 1970 with the introduction of metric cables & measurements, but they still called it the 14th edition as little else had changed (except for the new color codes, mentioned elsewhere).

Between major new editions they publish various minor amendments, which are incorporated into reprints of the current edition.



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