Help - Consumer Unit Argument ?

[the_constructor]

I have been advised to ask on this NewsGroup so here goes.

Been having an argument with a friend just lately over consumer units, or rather the placing fuses, yes I know modern day it's circuit breakers but principal is the same, within.

I was always told that next to the main switch, you start with the lower current, lighting circuits (6A) building to the larger Shower/Cooker circuits (32A) being farthest away. This is so that if the lights went out, you would be able to find lighting fuse in the dark.

Friends says higher current first next to switch.

Is there a rule for this or is it just personal preference.

[Ian Stirling]

IMO, personal preference. IMO also, you have in the CU box a torch that is charged from the mains, and goes on if the mains/lighting circuit fails.

As a cheap alternative, go to ebay, and search for keyring tritium, and put it next to a cheap torch with a lithium AA battery in in the CU cupboard.

[dcbwhaley]

The instruction sheet that came with the CU that I fitted a couple of months ago recommended your friend's way. Reduces voltage drop along the bus bar. And you can find the lighting breaker just as easily as it is the one furthest from the switch. Anyway you should have an emergency light (aka torch) by the CU.

Dave

[Jonathan Schneider]

If it's a traditional wired fuse you're better than me if you can locate your wire and change it in the dark. If modern MCBs anybody can check them from either end with their eyes closed.

Electrically yes your system might be .001% more efficient if high current loads are closer to the switch.

At the end of the day I believe it's just preference.

Jon

[Bob Eager]

Instructions with the last CUs I fitted (MK) said higher current next to switch. Presumably to reduce voltage drop along the busbar. And I've always done it that way.

I wouldn't want to be feeling around a CU in the dark, just in case something had melted and left stuff exposed (pessimist that I am!).

I'd fit a non-maintained light above the CU, that came on if the lighting circuit for that area had failed.

[David Hansen]

On Mon, 4 Dec 2006 20:22:15 -0000 someone who may be "the_constructor" wrote this:-

One traditional way to deal with this is to put a light near the consumer unit that is fed from another lighting circuit, eg the upstairs one if the consumer unit is downstairs. That deals with all but major failures.

Now that non-maintained emergency lights are so cheap these are another option.

Alternatively torches and candles, in places where everyone knows where they are.

[Alf]

Any way you like. If someone is telling you something - why not simply ask them why? They must know why they are giving you particular advice. Fuses are labelled and colour coded - circuit breakers are labelled. You can even write what each is for. For what reason would the lights go out and nothing else? Keep a torch handy and the phone number for your electric supplier. Don't rely on mains operated cordless phones either.

[HLAH]

"David Hansen" wrote

Got one on Ebay the other week, 3 hour, for a tenner. Haven't fitted it yet so I can't say how good it is but it looks fine.

H

[John Rumm]

I have always opted for the way your friend suggests - the highest loads nearest the incomer. This is to keep the high current loads near the start of the bus bar.

There is not alot in it either way.

I also always fit a maintained[1] emergency light above the CU powerd from teh lighting circuit that would normally illuminate it. So when there is a trip you can still see what you are doing.

[1] I use a maintained one so that you can manually switch the light as well - makes life easier if you want to see in the cupboard.

[Owain]

Got one in my local junk shop for £2 a few years back. I didn't know if it worked but I thought it was worth taking a chance on, as I'd had two power cuts in the preceeding two days.

It's been worth every penny I paid for it - I don't think I've had a power cut since.

I have mine in the kitchen.

Owain

[Andrew Gabriel]

I got a pile from work. The batteries are supposed to be changed every 5 years, but they change out the whole thing. Given that a new battery pack seems to cost considerably more than the whole thing, I'm not surprised. Batteries are 10 years old now, and still give over 3 hours.

I also picked up a couple from a builder's merchant. They were a quid each as they'd gone past their sell-by date (again, due to the batteries), although still brand new and sealed in their boxes. Likewise, they still work for over 3 hours.

One issue with all these is they are horribly inefficient as they have very dum chargers. They are required to charge quite fast so they are ready for use again reasonably quickly, but there's no intelligence in them to drop back to a trickle/topup charge when the main charge is complete -- they just carry on charging at high current forever. Although the batteries are designed for this, it does mean they consume around 3-4W continuously (which is more than they give off during a power cut!) In buildings full of them, this adds up -- it's probably another one of these wall-wart effects if you add up how many power stations are being used to keep the lights off ;-).

[nightjar]

Putting the high current stuff nearest the incomer reduces the average current flow in the bus bar, reducing the heating effect. I don't see that putting a lighting fuse next to the main switch makes it easier to find than putting it at the other end of the row.

My house has two separate lighting circuits on the ground floor, specifically so that one or other provides light at the consumer unit even though, with MCBs, you can find the one that has tripped by touch.

Colin Bignell

[David Hansen]

On 05 Dec 2006 08:29:17 GMT someone who may be [e-mail] (Andrew Gabriel) wrote this:-

In a large building the wise use a central battery system. The chargers for these are rather more sophisticated.

[the_constructor]

"nightjar .uk.com>"

My thanks to everyone who has replied.

[Andrew Gabriel]

I don't buy that explanation. I just measured the bus bar in a cheap SquareD CU, and it's 36mm², quite likely substantially thicker than the meter tails. In the previous generation MK ones, it measures 30mm².

The instructions I've seen with some MCB's say that high current rated ones which are run at high current for long periods should not be placed adjacent to each other. Also some single width RCBOs must not be placed next to high current MCBs.