New Consumer Unit - not sure on configuration

[Jimbo]

Hi,

Bought a new CU, not sure what configuration to go for. It's a 100A Split load unit with 80A RCD, replacing a 6-gang fusebox.

What sort of things should be covered by the RCD? I'd like to, for instance, exclude the lighting circuits - but the downstairs circuit feeds a light in the conservatory, which I understand should be RCD-protected.

Could do with some advice as it's going in this weekend!

Thanks

Jim

 

[comms]

Non rcd side
Cooker ( if no socket on ccu)
lights
immersion
heating

RCD side
Socket circuits
Cooker (if ccu has a socket)


What earthing system do you have TN-s TNC-s or TT ?
Are you doing the cu swap yourself ?
The work you are planning is notifiable.
Dont forget all circuits will need to be tested after cu change.
Are equipotential bonds in place & correctly sized same for tails?
Is the supplimentary bonding in place?

 

[nozspark]

I would also put an electric shower on the RCD side of your CU..

However if you have a TT earth (earth rod) they you will have to have a 100A 100mA time delay RCD covering all circuits and a 30mA one for the sockets etc..

Also you will probably have the: main earthing, main equipotential bonding and supplementary bonding to upgrade...

This is a big job with lots of involved testing, which btw is part p notifyable, are you really going to DIY this??

 

[Jimbo]

Er... I was, albeit with a friend who has done this before (but admittedly is not qualified).

Not sure what earthing system I have, how do I find out? House is late 70s in a rural location, electricity is supplied underground. My guess is that it's TN[C]s, although I'll make sure before I proceed.

Am I okay to have the conservatory light on a non-protected circuit?

I also assume that my garage feed should go on the RCD side, as should any (IP-rated) external sockets I may fit.

 

[nozspark]

Firstly can you post a photo of your service head & meter and I'm sure that someone will have an educated guess at you earthing type.

Let's imagine that you do have a TNS or TNC-S earth.

All lighting should be run off the non-RCD side of the board. As should be a sub main to your garage, in which you should have a Garage CU which should have RCD protection (this does not need to be split load as you usually only have the 2 circuits!)

All sockets which could provide power for portable hand held equipment outdoors has to be RCD protected. You will find though that most pro-sparks RCD all socket circuits (except maybe for a fridge/freezer)

If you and your friend are going to do this work, how will you test it to make sure that it is safe for you and your family??

And don't say switch it on and see if it works!!

ELECTRICITY CAN BE LETHAL YOU KNOW!!

 

[Jimbo]

First of all, let me say that I'm not bothered about certification. Or more accurately, I'm not bothered about the expense of getting a certified sparky to do the job - I simply can't afford it.

I AM bothered about the work being safe, as you say, for my family and me. This is why I'm posting here, 'cos I know there are a number of professionals who will hopefully advise me so I can do this as cheaply as possible while not risking anyone's life!

The truth is, I don't know how I'll test it. But it seems logical that if the connections within the replacement CU are good, then there shouldn't be any more risk than there is at the moment.

That doesn't mean my current installation is safe so any advice on testing will be gladly taken!

I'll take the photo this evening and post tomorrow.

Thanks for the replies!

Jim

 

[comms]

so any advice on testing will be gladly taken

Purchase a meter (fluke 1653 or the like) £600 - £800

Undertake a few years of testing(if you like) or do the C&G2391 £200 - 300 (dont know the cost of course so educated guess)

Do the testing
Continuity
Ring continuity
insulation resistance
polarity
Earth rod resistance (if on TT system)
loop impedance
Pfc
RCD test.

Not forgetting you will have notified the work with BC £75 - £120.
And if you've done a quicky part P course £1500 you could also sign it all off.

So now £350 - £450 for a sparks to do it correctly isnt so expensive is it

The truth is, I don't know how I'll test it. But it seems logical that if the connections within the replacement CU are good, then there shouldn't be any more risk than there is at the moment.

It bugs the backside off me when I get told this by customers who think they know best & want a cheap job, my reply what price is the safety of your family & property.

But as already said theres alot to take into account when changing a cu.

 

[Cremeegg]

Have you thought about how you are going to connect up the tails? Have you any Henleys? Are you happy working live? - as I'd be amazed if you could get the DNO to disconnect at a weekend.

The more I think about you doing this the more I hope I dont buy your house off you or know you because you stand a good chance of being seriously injured.

 

[Jimbo]

So now £350 - £450 for a sparks to do it correctly isnt so expensive is it

Well, it's still £400 gone from my pocket for a job that I could possibly do some or all of myself. So yes, it is expensive. Comparing it to the price of getting qualified seems to have little relevance, unless you're effectively admitting that most pro electricians hold their customers to ransom, which I prefer not to believe.

It bugs the backside off me when I get told this by customers who think they know best & want a cheap job, my reply what price is the safety of your family & property.

I said "it seems logical". If it's not, fine. But why not? Most of the tests you list will have been done when the original house wiring was put in - or if they weren't it's at least stood the test of time. So why would a different CU change that? That's all I was asking. Seems like a fair question.

If I thought I knew best I wouldn't be asking for help. If I didn't care about my family, I wouldn't be asking for help. I don't know best and I do care about my family. But I also care about handing over 400 notes when I don't know what I'm getting for my money. The response, "Peace of mind" or whatever doesn't really leave me any the wiser or more willing to shell out.

I appreciate that there's a great deal of work that goes into getting qualified as an electrician, and I appreciate it ain't cheap. That doesn't mean I have no right to know what my £400 gets me, neither does it mean I have no right to try and find out whether I can do some or all of the work myself. If there's a safe and reliable way to test an installation on a DIY basis, then I'd like to know what it is. If there isn't, well then there isn't. I'm here trying to find out.

 

[Jimbo]

The more I think about you doing this the more I hope I dont buy your house off you or know you because you stand a good chance of being seriously injured.

You might know me but hate me!

I haven't really thought about it much at all yet, I wanted to get advice from here and then decide whether to proceed myself or fork out.

 

[MasterAbacus]

Nice one... someone actaully doing some DIY..... all be it a little naughty these days...

Everyone knows my thaughts on this kind of situation.....

DIY..... Do It Yourself....

Certification comes later.... .... if at all..

Must say, there are many ways and things that is frowned upon on this forum, so your not going to get much pointers to works that should be notified, or done by a qulaified electrician.... Shame really cos you proably could do with a little help too....

 

[Cremeegg]

I've no idea if I know you but I certainly dont hate you. Just hate people trying to do potentially fatal things.

Professional sparks will not hold customers to ransom - a great way to lose customers. Yes you get bad sparks just as you get bad ones in any other trade or profession but please dont tar us all with the same brush.

As you can see testing kit is not cheap and should be calibrated every year (another £100). Some of those tests may have been done when it was installed but things change over time. Only testing will tell how much. Any competent sparks will tell you with good reason and usually from much experteience that a CU change must be preceded by such tests.

 

[ricicle]

Is anyone else concerned?????

 

[electronicsuk]

Jim, fair play to you. I can understand your reasons for wanting to DIY the job, you may be a little short sighted in your reasoning behind not wanting to shell out for a qualified electrician but that's your choice.

It sounds to me as if you're going to do the job yourself either way, so rather than lecture you about part P testing and certification of which you are already well aware, perhaps we could offer some more constructive advice. This is, after all, a DIY forum, and there will be hundreds of people out there doing DIY work every day who aren't even remotely competent or aware of the regulations governing such work.

As we've already mentioned, it's important you determine what type of supply comes into your house. If it is TN-C-S (PME) then the neutral and earth tails to your CU should terminate into a single neutral block at the service head. A TN-S supply will have seperate incoming phase, neutral and earth at the service head, and a TT system will have some form of local earth, most likely an earth rod.

Assuming your supply is not TT and you understand how to wire a split load CU, things should be relatively easy for you. Before starting the work you should make sure the bonding in your property is up to scratch (see the WIKI). During the work you should at least conduct some very basic tests. For a DIY job I would feel a little happier if you at least check all your ring circuits and make sure there is L-L, N-N and E-E continuity between both legs of the circuit with a meter, and test all sockets with a martindale plug in.

If the information on the WIKI and this forum doesn't prove enough for you to do the job, don't even attempt it. All the above assumes at least some level of competency with regard to the task at hand, all the usual disclaimers apply. I don't condone those who don't go through the official channels and notify electrical work.

 

[Chri5]

I'm concerned, but at least Jimbo is being honest and straight with us.

Jimbo the cables in to the CU break down over X number of years due to various factors. I've just renewed a 5 bed house that had the same cabling for 25 years+ and virtually all of it was on or past it's sell by date.

Splitting TE to discover oxidised copper and individual cores within TE welded together where a few basic revelations. So the work was very necessary.

Now I don't know the age of your current cabling, fittings and CU. But putting a new CU on untested and unknown service life cable and fittings is like putting a new set of tyres on a rusty car (not exactly going to improve things).

Add to that the sensitive nature of the RCD and you could well find that the RCD trips out constantly due to aged kit terminated behind the RCD / MCB's

Right with the 16th edition your currently need to support a new CU with

25mm sq tails, double sheathed colours blue- neutral, brown live
16mm sq earth from main earth to CU
10mm sq earth from gas and water incoming points to the main earthing point by the DNO mains head

The general rule of thumb for RCD's is that are used to provide protection to any portable appliances (so all socket circuits should be on the RCD side).

To confuse things 17th ed due Jan 2008 requires all electrical circuits in a bathroom to be via an RCD. So you might want to put the 1st floor lights (if that's where your bathroom is) on the RCD side.
I understand this will replace the need for supplementary bonding of all metal in the bathroom to the earths of electric circuits in the bathroom.

Post if you need further advice, unlike the twisted lad who thinks we are all ****s I'd rather offer help and make the work safe that risk injury to you or your family by being stroppy about the regs, rules and Part P.

I would say, as a parting remark that DIY of this sort of level isn't for the faint hearted and is prone to issues and failures of circuits. RCD nuisance tripping is a constant post here, if such occurs post your work your get stung by a mtce / callout sparks for an unlimited number of hours to isolate the fault and fix it.

Such a qualified person might refuse to work unless you weigh out for a full system check and update to current standards- this isn't because they consider clients 'cash cows' but because they are duty bound by their registration scheme to do the work to the letter of the rules and regs.