Consumer Unit Wiring Question

[Wired1]

You need to ensure that the cable supplying the garage CU is meaty enough

a. to take the load you intend putting on that cable AND

b. to exceed the value of the device supplying the cable.

The RCD is not a current limiting device. It will not trip if you exceed 40A. But it must not be used to supply more than 40A.

But it can be used for circuits under 40A.

Very little load actually.

From memory, 1kw = just over 4 amps

Total load is a freezer at a @200W, a pond pump at 150W then the odd tool one at a time eg lawn mower or tool at say 2KW max (allowing for a heat gun) with most probably a few hundred watts only.

So never likely to exceed 2.5KW or 11 amps or so.

Lighting circuit - 2 fluorescents @ 58W each.

 

[ban-all-sheds]

It will be Part P tested don't worry.

What do you mean by that?

It would be helpful if you would explain what you think you're going to do about notification, testing, Electrical Regulations compliance certification and Building Regulations compliance certification, in case you have some major flaws in your plans....

The incoming mains breaker (RCD) is 40 amp although the current through this is limited as its a spur taken off the main consumer unit and is on a 20 amp MCB.

So no discrimination between the 16A in the garage unit and the 20A in the house. Fail.

What about an RCD in the house - is the 20A breaker on one? If so, chalk up another fail.

Depending on what you think you are doing about "Part P testing" you may find you crash and burn here because of your incompetence at design.

The incoming wire is 2.5mm 2 therefore - nothing to do with me, existing wiring / arrangement which I don't intend to touch.

If it's not suitable you can't use it.

Not sure what diameter should be using though for a 40 amp breaker - 6mm 2, 10mm 2?

You believe that you are competent to design and install a CU connected to a sub-main. Why don't you already know how to size cables?

• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  

One of these:

http://www.toolstation.com/shop/Ele...ex+Garage+Kit+IP65/d190/sd2917/p27838[/QUOTE]
And that came without an internal cable to the neutral bar?

I'm 99.99% certain it should have done - complain.

 

[viewer]

BAS : Knowledge relating to electrical matters 99.99%
BAS : Knowledge of the way human beings behave ???

There is nothing wrong with any of the advice given by the people who replied, but did any of it alter the situation? Is there anybody reading this who needs to be told that smoking is not a healthy option? Nobody; so why are you smoking?
Given the choice between just getting the job finished and having another flaming row with a spouse; do you really want a divorce?
I'd suggest that a pragmatic answer followed by advice and offers of help is more likely to work than a "You Idiot" response.

 

[ban-all-sheds]

Nothing wrong with any of the advice?

What about this cr***y advice to do a substandard bodge by making do with inappropriate materials, rather than using the correct cable, correctly terminated as per the maker's original design?

I'd suggest that, in the absence of "blue" wire s/he should use a piece of 6mm or 10mm (as available) Y/G and sleeve it with blue.

This is good though:

may be easier, and safer to get an electrician...

"just getting the job finished" is not acceptable - it has to be done properly, not that you would appear to understand that.


The pragmatic answer is to get an electrician, because the OP simply does not know enough to be tackling a job like this, either from an electrical point of view or a regulatory/legal one.

But if he does want to DIY then you'll find that I have helped him to do that by pointing him at the information he needs to assimilate to be able to work out for himself the answer to the question he asked.

Testing etc will have to be put on hold until he tells us what he thinks his route to compliance will be.


And nowhere have I called anybody an idiot, but I reserve the right to call you one if you think that you should encourage Wired1 to work on things he does not understand.

 

[RF Lighting]

As the OP will have got so far and will (have to?) continue whatever, I'd suggest that, in the absence of "blue" wire s/he should use a piece of 6mm or 10mm (as available) Y/G and sleeve it with blue.

I'm sorry but that's disgraceful advice. You ought to be ashamed of your self for even suggesting that.

As for the OP, am I missing something? Why do you think you need to install a consumer unit in your garage at all?

 

[viewer]

Whilst sleeving as suggested may not be ideal, exactly what is wrong with it? The OP is quite likely to have Y/G bought for the earthing/bonding.

It isn't a bodge as it would be more than adequate for the 40A continuous load, structurally sound and clearly identified. The original Volex supplied connector is just that - a short length of 6mm. The connections are screw compression with no special terminations.

Does he need a separate CU at all? That was in my first question (is it an external garage? which was dismissed) - if integral why is it needed?

I would never encourage anybody to start on the wrong foot, but it was clear that the OP had almost completed the work. Whilst BAS pointed him at links, it would I suggest be better to set out to the OP a "let's step back, check where we are and make it safe" story rather than the confrontational language used.

I, RF, BAS and others would not end up in the situation described by the OP, however, the truth is that many otherwise sensible people do end up working in an area they do not understand because a succession of DIY articles and TV programmes tell them that anybody can do the work. Many times in this forum we hear cries from people who have been caught out in this way and are stuck. I suggest that without thoughtfully worded replies, many go away and do "whatever makes it work". Do these people "have to" continue once out of their depth? In their world they do. This doesn't make it right of course, but a combination of pressures and "You don't know what you don't know" means that they are likely to ignore all advice if they feel that they are being demeaned.

Understanding people is key to making a DIY advice forum useful.

If you want to call me an idiot then go ahead

 

[PrenticeBoyofDerry]

To be honest if I were the OP, I would go out and buy type tested unit that has all the component required, all ready fitted.

 

[securespark]

It may be that he did.

More and more consumer units are supplied SKD.

Perhaps this one was just missing the part required?

 

[ban-all-sheds]

Whilst sleeving as suggested may not be ideal, exactly what is wrong with it? The OP is quite likely to have Y/G bought for the earthing/bonding.

It's not ideal, that's what's wrong with it. It's a way to avoid getting the right component.

The original Volex supplied connector is just that - a short length of 6mm. The connections are screw compression with no special terminations.

So the supplied cable has no ferrules crimped to it?

Does he need a separate CU at all? That was in my first question (is it an external garage? which was dismissed) - if integral why is it needed?

Why would a detached garage make one necessary?

I would never encourage anybody to start on the wrong foot, but it was clear that the OP had almost completed the work. Whilst BAS pointed him at links, it would I suggest be better to set out to the OP a "let's step back, check where we are and make it safe" story rather than the confrontational language used.

Almost completed or not - the OP is clearly insufficiently competent and should be advised to stop and learn or stop and get an electrician, not helped to do things he does not understand.

I, RF, BAS and others would not end up in the situation described by the OP, however, the truth is that many otherwise sensible people do end up working in an area they do not understand because a succession of DIY articles and TV programmes tell them that anybody can do the work.

Then it falls to us to tell them that they can't.

Many times in this forum we hear cries from people who have been caught out in this way and are stuck.

And when you force them to confront the facts, those inevitably include that they decided to fiddle with something which they knew they did not understand.

I suggest that without thoughtfully worded replies, many go away and do "whatever makes it work".

Another failure on their part.

Do these people "have to" continue once out of their depth? In their world they do.

No they don't and if they think they do then they are delusional.

This doesn't make it right of course, but a combination of pressures and "You don't know what you don't know" means that they are likely to ignore all advice if they feel that they are being demeaned.

If people feel demeaned by it accurately being pointed out that they are ignorant then that is another failing on their part.

Understanding people is key to making a DIY advice forum useful.

People learning to read is what makes receiving advice useful.

 

[ban-all-sheds]

It may be that he did.

More and more consumer units are supplied SKD.

Perhaps this one was just missing the part required?

And that came without an internal cable to the neutral bar?

I'm 99.99% certain it should have done - complain.

 

[SimonH2]

It will be Part P tested don't worry.

It doesn't work like that.

To be legal, the work must be notified by one of two routes :
1) The electrician doing the work can notify through his registration scheme - if he isn't in a scheme then he must use option 2.
2) The person doing (or commissioning) the work can notify before starting the work his LA Building Control department and pay their fees, and then notify when the work is complete.

There is no process for you to do the work and then get someone else to inspect and sign off the work. Only LABC are in a position to sign off someone else's work.

 

[Wired1]

As I understand it a "Skilled" person can undertake work provided it is then checked and Part P certified by a qualified electrician.

I have been doing small scale electrical work for over 30 years and as such understand fully how to safely install lighting circuits using loop in, switched circuits using open loop and both radial and ring main circuits. The only thing I've never done is install a consumer unit before, hence the reason I wanted to check on the correct diameter of cable I should use as in a consumer unit its fittable size vs minimum safety diameter. I know a consumer unit installation would be illegal on a house unit as only a competent person can attach something to the incoming mains. However, as I pointed out before, this is fed as a spur from a breaker in the main consumer unit (existing wiring) and so doesn't involve any connection to incoming mains supply.

In any case, a friend of mine whos an electrician is now going to do it to ensure there's no legal ambiguity and also replace the link from the existing unit with 6mm cable to remove that issue, so matter closed. Thanks for the help.

 

[ban-all-sheds]

As I understand it a "Skilled" person can undertake work provided it is then checked and Part P certified by a qualified electrician.

Your understanding is flawed.

Either you are qualified and registered to self-certify Building Regulations compliance of work you do or you are not.

A registered electrician may not "sign off", as in certify Building Regulations compliance, work which he did not do.

The legal route for notifiable work not done by a registered electrician is to apply for Building Regulations approval in advance. Different councils have different policies on charging, inspection, testing etc - the only way to find out what you would end up doing is to ask your council. One thing they all have in common though is that none of them will let you fetch up after the event saying "I did this work and here's a certificate from an electrician I got to look at it."

I have been doing small scale electrical work for over 30 years and as such understand fully how to safely install lighting circuits using loop in, switched circuits using open loop and both radial and ring main circuits.

I'm not sure you do understand it because you appear not to know how to do the calculations to size cables.

I know a consumer unit installation would be illegal on a house unit as only a competent person can attach something to the incoming mains. However, as I pointed out before, this is fed as a spur from a breaker in the main consumer unit (existing wiring) and so doesn't involve any connection to incoming mains supply.

The installation of a CU is notifiable whether it's the main one or not, whether its supplied directly, or via a switchfuse, or from another CU, and whether it's in the house or in an outbuilding.

 

[SimonH2]

As I understand it a "Skilled" person can undertake work provided it is then checked and Part P certified by a qualified electrician.

Then you understand wrongly.

The system doesn't allow for <random person> to do the work, and then <random qualified person> to "sign it off". When it's notified through a scheme, that person doing the notifying is making a statement that he (or she) has designed, installed, and tested the installation to whatever standards. If some random other person has done the work, then that statement is false. Not to say it doesn't happen
Speaking personally, I too would find it very useful if there were scope in the system to legitimately do work and then have a qualified person inspect and "sign it off".

There is a mechanism to deal with teams of electricians - in this case I assume the employer is the scheme member, and the individual electricians will be working under the responsible person's instruction and oversight. In the same way, an individual electrician can employ others to assist with any installation - but he still has to sign it off as his own work.
If someone is prepared to work with you assisting, and then sign it off, then that will work - of course, how much he does and how much the assistant does is down to the judgement of the person who has to put his name to it. This is your best way of doing the work legally - work with the person who is going to have to put his name to it, and you can do as much of the work as he is prepared to let you.

 

[SimonH2]

One thing they all have in common though is that none of them will let you fetch up after the event saying "I did this work and here's a certificate from an electrician I got to look at it."

Actually, mine does. If notification is to regularise work already done, then you still need to give them the same information as you would if notifying properly in advance of starting work. But they charge an extra 50% on top of the already eye watering cost of notifying minor electrical works.

But having the electricians test report (all he could legally do would be a PIR) would allow you to pay a lower rate as BC wouldn't then need to pay someone to do the testing.