new consumer unit

staffy · Posted: Tue Sep 14, 2004 12:31 pm Post Subject: new consumer unit

I was looking to install a new unit as the one that i have is forty years old.
I have run new ring circuit cables and new lighting circuit cable and they are ready to connect to the consumer unit, but i want to install a new con.unit.(10 mcbs)
Any info, on disconnecting the old one.
Please note that i am not an electrician and the quotes that i have received are a joke?

mingmong · Posted: Tue Sep 14, 2004 4:28 pm Post Subject:

How much have you been quoted?

plugwash · Posted: Tue Sep 14, 2004 4:34 pm Post Subject:

someone is going to have to pull the service fuse

technically you are supposed to get the rec to do it but in reality this is usually both expensive and impractical (or sometimes even impossible when everyone starts to pass the buck)

most electricians i know jup pull it themselves but this is not generally reccomended for diyers

if you are going to do it yourself bear in mind the following points
1: there may be exposed live parts during and after pulling so take care to only touch plastic parts

2: make sure there is no current flowing by turning off the main switch first to prevent arcing

dingbat · Posted: Tue Sep 14, 2004 4:54 pm Post Subject: Re: new consumer unit

staffy wrote:

... the quotes that i have received are a joke?

I usually charge in the region of £250-350, depending on the number of circuits, accessibility, etc. By the time you've disconnected, tested everything, sorted out any snags, mounted and connected up the new unit, done the live tests, written out certificates and tidied up it can easily be the best part of a day's work in some properties. Your electricity company may well quote £400-500. How far out are your quotes?

benjiman · Posted: Tue Sep 14, 2004 7:36 pm Post Subject:

plugwash wrote:

someone is going to have to pull the service fuse

A friend of mine said he done his one without pulling the service fuse. He needed new cables as the old ones were too short.

He took out the live (and neutral) cable that comes from the consumer unit and goes in a box with a lid on it. This has a seal, which he broke. Then he unscrewed the old live cable that goes into this box and pulled it out. Same with neutral.

Then first connected the new cables (L and N) into the new consumer unit. Then connected the ends of the new live and neutral cables into the box.

All this done while everything was still live.

Is this safe to do and should it be done like this? Or do most pros play it safe and pull the fuse so everything is dead?

BTW what is arcing?

kai · Posted: Tue Sep 14, 2004 7:52 pm Post Subject: arcing..

Arcing is where an electrical spark jumps across live metal.

Or when a cable gets hit by an JCB digger etc, and a mighty BANG results, as happened the other day where I worked.

fubar · Posted: Tue Sep 14, 2004 8:05 pm Post Subject:

benjiman wrote:

All this done while everything was still live.

Is this safe to do and should it be done like this? Or do most pros play it safe and pull the fuse so everything is dead?

It is not safe to work on live equipment. There is a common mis-conception that electricans always work on live equipment - in fact they rarely do and only when there is absolutely no alternative.

A pro would choose to pull the main fuse.

Quote:

BTW what is arcing?

Arching is when electricity jumps an air gap. The greater the voltage and current, the greater the distance that can be jumped.

--
Michael

Damocles · Posted: Tue Sep 14, 2004 8:55 pm Post Subject:

Breakdown voltage of air is about 1KV/mm (yeah,well I had to look it up, but thought that was about right).

So if you keep the live more than 0.5mm away from any other conductor, then it should not arc. But god help you if it gets any closer, because once the arc has started the air will ionise and then its arc welders-R-us.

Turn off the power.(by pulling fuse, or getting it pulled). Even if you have, still work on it as if it was live. One day it may be. Use insulated tools (screwdriver shafts!). Think about which wire to disconnect first. Disconnect the end feeding the power first.

If i was even remotely considering moving live wires capable of supplying 500A for a short period, I would be damn sure that if I was stuffing thick unbending copper cables through a small hole into a plastic box, that there was absolutely nothing else inside it which was connected to anything else. That way, even if the live end hit anything, it could not short out. That any switches inside the aforementioned plastic box were off.

You need to take care with thick tough cables that the screws are really pressing tight and holding the cables properly.

securespark · Posted: Tue Sep 14, 2004 10:09 pm Post Subject:

Yes. I agree with Fubar.

Please, DIY'ers, DON'T work live, and get your REC to pull the fuse. You can always have an isolator fitted so you don't have to get them back every five minutes.

Working live unprotected and untrained is absolute madness.

In 17 years, I have worked live 3 times, and NEVER on the main tails. Always wearing the proper kit, boots gloves, rubber mat etc.. and fully insulated tools.

Here is my isolator:

plugwash · Posted: Wed Sep 15, 2004 6:32 am Post Subject:

bad termination of those tails to the meter though

i see stripped sheath......

plugwash · Posted: Wed Sep 15, 2004 7:10 am Post Subject:

afaict the main reason for working live is to add a cuircuit in a situation where it would cause huge disruption to turn off the DB/CU

or for working on (spurring off attaching something to a spur etc) a cable outside when that cable is supplying lots of stuff and would cause hige distruption to isolate (this is afaict the main reason recs work live)

daveaspy · Posted: Wed Sep 15, 2004 10:04 am Post Subject:

How should tails be terminated/stripped? I am guessing you should have a little bit of the red/black showing inside the enclosure and only the grey outer insulation showing outside the enclosure?

breezer · Posted: Wed Sep 15, 2004 12:01 pm Post Subject:

that is correct

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staffy · Posted: Thu Sep 16, 2004 12:29 pm Post Subject:

Sorry for taking so long to reply WORK WORK WORK

I was quoted in the region of £600-£750 and when i asked how much to rewire the whole house, the quote was £2000-£3500.
Excuse me for being stupid but it is only a 3 bed-semi.
Do you recommend pulling the service fuse and if so what precautions can i take,and what safety precautions or checks to make sure that everything is in order before doing so.

[/quote]

ban-all-sheds · Posted: Thu Sep 16, 2004 2:02 pm Post Subject:

staffy wrote:

I was quoted in the region of £600-£750 and when i asked how much to rewire the whole house, the quote was £2000-£3500.

Not necessarily OTT - it depends a lot on where you are, and how easy it is to access the infrastructure in your house. But it is possible that the guy didn't want the job - it's fairly common for tradesmen to give daft quotes rather than say "no", for some reason...
How many quotes did you get?

Quote:

Excuse me for being stupid but it is only a 3 bed-semi.

I don't think you realise how much can be involved.

Quote:

Do you recommend pulling the service fuse

No, but...

Quote:

and if so what precautions can i take,and what safety precautions or checks to make sure that everything is in order before doing so.

Think about how you will fix a mechanically strong (i.e. not a polythene bag) insulating cover over the exposed fuse terminals while you're working
Make sure everything is off (i.e. main switch(es) on the CU(s))
Make sure that you have good access to the fuse, and that it will pull out cleanly when you go for it.
Having cut the seals and pulled the fuse, securely fit the cover you've made.
When putting it back in, again make sure everything is off.

I take it that you have done proper continuity, loop resistance and insulation tests on the new circuits that you've installed?

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