Replacing one consumer unit with two

[raymie]

I am wondering if someone could give me some advice on the following.

My current consumer unit seems to be playing up more and more with the RCD (30ma) tripping fairly often now (including on occassion at night when nothing is being switched on or used all of a sudden). The power quality to the house is not that good being VERY rural and the RCD is covering all the load currently.

I cannot get a direct replacement for the RCD and so am considering switching consumer units totally and perhaps going with having two instead of one (but fairly near each other).

The mains power comes to the house via an external building which has a big isolator type of switch (allow allows me to switch to a generator). My idea of what is involved in the change is as follows

- switch of mains power to house.
- remove mains wires connected to exitsing consumer unit
- take mains wires and attach to 100amp DP supply connector box
- take two sets of meter tails and connect to same box
- one set of tails to be connected to each of the new consumer units
- rewire in existing house circuits splitting the load as is convient
(possibly cooker and lights on one box and ring mains on the other).

The existing unit has 13 MCB's in place and so this would allow me to have a greater possible number of circuits in the futire (which I will probably need due to some building work) and allow me to have some of the circuits terminating at a more convient location.

Am I misunderstanding what is needed here?

 

[breezer]

why not have a split load ?

but even then you are only solving the problem, not the cause

 

[raymie]

Not sure if I am not removing the cause. The manufacturer of the original RCD has implied that it might be going faulty.

"It may be that you RCD has received too many surges which has caused it's characteristics to change over time and just needs to be replaced" being the quote I was given.

Certainly the house can have a good few surges now and then and hence most items in it are behind surge protectors or UPS boxes.

 

[Steve]

It may also be that the RCD is responding to faulty electrical equipment / installation. Even new equipment can arrive faulty.

It is the norm, on TT supplies (which I suspect you have) to have a 100mA time delay RCD as the main, and a 30mA RCD protecting circuits that require it.

If you want ultimate reliability, you could use RCBOs on the circuits that need RCD protection, these are an MCB and RCD in one. But they are £40-50 each, as opposed to £5 each for MCBs.

RCBOman will be along soon, to tell you more.

 

[raymie]

Can't say if I have a TT supply or not but whatever it is it would be old and I am on the end of a spur from overhead cables (not unknown for the power co [Hydro electric]) to have to come out and reset something (fuse?) on a large grey box that is highish up on one of the power poles.

The power goes from overhead cables to run underground for 50 feet and then to a barn where there is a large switch alongside a huge set of fuses and then the power is split to the barn itself, another outbuilding, a pump house and the main house. It is only the main house that has an RCD and so that is the only place where the power periodically goes off.

Looking through the forum I am wondering now if this could be a cummulative effect from having a number of leaky appliances, there is always 1 computer and 3 servers on and the usual amount of electronic and kitchen stuff.

If this is the case would splitting the RCD protected circuits help, basically say I had the main switch on a consumer unit being 100ma and say two RCD's of 30a protecting two sets of circuits would this reduce the likelhood of a cumulative earth leak or would it still be effected since they are all still driven from the same power line?

Would there also be a difference if the two RCD's were in different boxes or a split load CU?

 

[Steve]

Splitting into seperate RCD circuits would almost certainly help. Computer power supplies are quite leaky. I'd recommend a 100mA time delay mainswitch, and individual 30mA RCBOs for the circuits that need 30mA protection. But RCBOs are pricy, as I said, so it depends how much you want to spend.

 

[JohnD]

RCBOman will be along soon, to tell you more.

Hee hee

RCBOs are great!

But a bit expensive

Time delay RCDs are also very expensive. Ask your electricity supplier if they can convert you to TNC-S (PME) which will make it unnecessary. It will probably cost in the region of £60-£120. There is a slim chance they will do it free.

You are aware this is notifiable work (except I think you may be in Scotland where I am not famiiar with rules).

You don't need to have two CUs just because you have lots of circuits. 20 ways or so are not uncommon in the better brands. See pictures in //www.diynot.com/forums/viewtopic.php?t=70551&start=0

 

[RF Lighting]

If you have loads and loads of circuits then you could always fit a TP distribution board with a single phasing kit fitted to it.

Then you could have a board with as many circuits as this

 

[sm1thson]

My idea of what is involved in the change is as follows................

some things you missed off your list: -you really need to test all the circuits before and after changing the CU. (-and to notify building control as changing a cu comes under part p of the building regs)

Can't say if I have a TT supply or not

you need to find out before you buy anything! -if you post a picture of where the electrics come into the house (ie the thing before the meter, and a pic of the whole lot would be good) we will tell you. as has been said the type of rcd protection you require is different with a tt supply, also (as johnd said) you may be able to get it upgraded from a tt to a pme.

 

[JohnD]

Then you could have a board with as many circuits as this

That's more like it!

 

[sparkyspike]

Do you have an earth conductor in the ground? Or does your earth supply come from the same cable as the neutral and phase?

I agree with sm1thson; get your circuits tested before changing your ccu, you may have dangerous earth leakage, beyond that expected from PCs. And you could save yourself all the trouble of changing the board if you do have a fault.

 

[raymie]

Little update....

Firstly I am working away from home at the moment but will add in some piccies when I get back (if I do with all the snow).

Part P does not apply, I am in Scotland.

Am still tending towards a low level general earth leakage rather than a specific one. Last night (I am told) that the RCD tripped again and this time several of the circuits had to remain off for a while before it would stop tripping as they were switched on.

These 3 circuits are all ring mains for different areas of the house, one had nothing attached but it seems a spur to the oil fired boiler, one was some sockets with only a light load and the other was for the main bedroom. On previously occassions neither of these circuits seems to be an issue and IF one MCB did seem to cause a trip it was a totally different one (normally however until recently the RCD simply needed to be switched back on (lever pulled clockwise)).

Last night it seems that leaving these circuits off at the MCB for a wee while did the trick and they went back on ok and have remained on for 12 hours and counting.


Thanks for the comments so far and if anyone has any other help to offer it would be apprecited. I will certainly investigate the earthing arrangements and so if hydro will come and amend it if needed. I don't know if I have an earth rod, certainly never seen such a thing but it could easily be under the barn or somewhere else on the property.

In case it is a known 'issue' the cu is a memera 2000 and the RCD is a A80H2.

 

[JohnD]

Memera 2000 will easily accept RCBOs. They fit in the same space as the MCBs but are taller. They are obtainable inexpensively (if you don't mind used ones) because the ones for MEM Memshield 2 (which is the Industrial and Commercial range, very good quality) also fit, and they are frequently removed during refits and changes. They are too good to chuck in the skip so are often seen on Ebay at £15 or less. (put your email address in your profile if you want to hear more).

This makes it an option, if you like, to RCBO each socket circuit or other circuit needing RCD protection, which can save you the inconvenience of losing several circuits due to a fault on one.

As far as I know, you can only fit single-pole RCBOs in Memera.
If the Memera CU has an RCD in it, this can easily be replaced with a 100A DP isolator which is the same size. You must of course isolate the supply before doing that.

 

[securespark]

There's a BESA box cover missing there Rob...!!

 

[Pensdown]

If you have loads and loads of circuits then you could always fit a TP distribution board with a single phasing kit fitted to it.

Then you could have a board with as many circuits as this

And if one's still not enough....have 3!

PS. I wonder who will be first to spot the deliberate mistake in the open board?