New CU in Loft

[Shaunoffshotgun]

Had an electrician around yesterday to look at some wiring for my loft conversion. The wiring will be 1 circuit for sockets ( TV, Hairdryer,Hoover ) , i circuit for smoke alarms, and one for lights ( about 7 or 8 bulbs )

I have a 6 way CU at the moment, 4 ways are being used. He told me i had 2 options :

1) Break into the existing upstairs light and power circuits and run the smoke alarms to the existing CU. He said that this is ok to do but it would mean more testing than the following option.

2) Install a new 3/4 way CU in the loft and run all the loft circuits from there. He suggested a 10mm cable from the existing CU protected by a 40A MCB, then a 32A ring for loft power and 2 x 6A for the lights/smoke alarms. He originally said he would use a 6mm cable with a 32A MCB but was concerned about discriminating so therefore recommended 10mm.

Does anyone have any comments ? Does the option suggested sound right ?

PS. He said he is registered with the competent persons scheme

 

[Pensdown]

How many and what type of rooms in your loft conversion?
How many rooms and what type on the 1st floor?

 

[Adam_151]

I'd recommend a couple of 20A radial circuits for the loft if you go for the submain idea, reason being, I don't think a 32A breaker would discriminate with a 40A one, though it might if the 40 was a C and the 32 a B , though I can't garentee that you could use a C40, the Z's required for it is getting pretty low at about 0.48 (80% rule of thumb fiqure)

 

[Shaunoffshotgun]

Hi Pensdown. Loft conversion is :

1 bedroom which will have 3 or 4 double sockets running not much more than hairdryer, TV and hoover. Lighting if all on would be around 500W.

1 ensuite , 200W lighting max ( with shower light ) , 12V extractor.

First floor = 3 bedrooms , 1 bathroom - 60W lighting each bedroom, 150W bathroom. Power points mainly for hoover plus combi boiler.

Hi Adam. He did mention possibly one 20A radial but said he'd use 4mm cable for that so that's another option i guess.

Does the 10mm cable sound right ? I thought this was used for 10KW showers , wouldn't be using anywhere near 10KW all in ??

The run from the existing CU to the loft would be about 15metres.

Thanks for your input

 

[Steve]

10mm² is used for submains, not just showers. if he puts a new CU in the loft, supplied by the main CU, thats called a submain. I would go for the submain route, myself. gives more scope for expansion later on.

Time was, you would have a 60w bulb on the ceiling of the bathroom. do you really need 200w of lighting?

 

[Pensdown]

1) Break into the existing upstairs light and power circuits and run the smoke alarms to the existing CU. He said that this is ok to do but it would mean more testing than the following option.

If this new room was on the first floor the ring and lighting circuit would be extended and unless you have got money to burn I would do the same. I can see no reason for over complicating this with a new CU for 1 extra bedroom and en-suit. Yes, the existing ring & lighting circuit will need testing but thats less testing than a new CU, although it is new works. The smoke alarm can also be fed from the existing lighting circuit.

Unless your existing wiring is old, I cannot see a problem

 

[ban-all-sheds]

I have a 6 way CU at the moment, 4 ways are being used. He told me i had 2 options :

So you have 2 spare ways, and he wants to put in a new CU....

He said he is registered with the competent persons scheme

Which one, and as what sort of "electrician"?

How did you find this guy?

How many quotes did you get?

 

[Pensdown]

He said he is registered with the competent persons scheme

Which one, and as what sort of "electrician"?

How did you find this guy?

How many quotes did you get?

<<<<needs to toughen up a bit and get to the point

 

[Shaunoffshotgun]

Time was, you would have a 60w bulb on the ceiling of the bathroom. do you really need 200w of lighting?

Maybe not - will have a seperate shower light 60W , maybe a couple of wall lights 60W each total 180W - just trying to give some idea of maximum.

So you have 2 spare ways, and he wants to put in a new CU....

That was something he suggested yes. He said that would leave a spare way if i ever wanted to run power outside , would only mean running one cable to the loft, and if i had a 4 way board in the loft i'd have a spare way there as well if i ever needed it. He said it would probably be cheaper in the long run .

Which one,

Dunno. BCO said i needed someone registered with competent person sceme. He didn't have any preference or at least he didn't say he had any preference. I asked if he was registered and he said yes he was and he could do my certificates etc for BC.

and as what sort of "electrician"?

Quite a nice one actually. He did some testing first , took an Ohm(?) reading then asked about my earth rod , disconnected another earth lead and took another reading. Said the reading was acceptable and asked if the ground was chalky , tripping the RCD quite a bit ( from upstairs sockets and downstairs) said he was testing for milliamps , 5 different tests ??? Then he went through the options and said if i wanted i could run the cables but he'd need to see the runs first before anything was covered up - told me about zones for running cable etc.

After about 2 hours he said i didnt have to use him he just wanted to make sure if i didn't use him it was all safe and to be wary if anybody i may use other than him did anything different.

How did you find this guy?

He was recommended to me by somebody i work with so i picked up the phone and called him.

How many quotes did you get?

None - i didn't ask him for a quote either as he was recommended and i was told he was honest. As far as i'm concerned if i get a good safe job its worth paying for.

<<<<needs to toughen up a bit and get to the point

.... eh ?

 

[dingbat]

I think the idea of running a new submain from the old board to a new consumer unit is the ideal way for all involved. And it certainly won't cost any more to do - what you pay in material costs you will more than make up for in time.

Only one cable run to consider and no disruption to (or from) existing circuits. New circuits can be installed with virtually no loss of power to the rest of the house. Not having to run all the way downstairs to reset a breaker whan a lamp blows. Lots of advantages.

And from your description of the time spent with him he sounds like exactly the sort of electrician we'd like all customers to use.

 

[Shaunoffshotgun]

Well dingbat i certainly got the impression he knew his stuff and was a decent chap - i was just wondering if he was going OTT .

But if 10mm is standard and the submain gets your vote thats good enough for me.

Thanks again

 

[Adam_151]

You could probably go down on the size of the submain, but when installing such things, its best to leave room for expansion, you'll never be able to put an electric shower on it (well maybe a small one if you really had to), but if you want to add things like air conditioners, medium sized heaters, etc you've got the capacity there

 

[ban-all-sheds]

If it were me I'd supply the 2nd CU via split tails and a switchfuse, not from a position on the first board.....

 

[Pensdown]

10mm cable, new CU new MCB's all for 1 bedroom and en-suit? I still cant see the logic in going to all that trouble and expense

 

[TeesdaleSpark]

Not many Electricians would be as thorough with their pre work inspection as this one. He could do it a number of different ways it's difficult to comment without seeing the installation.