consumer unit

[timmyquick]

I have in my home a mem consumer unit wich has a built in 80a 30 ma RCD which covers all the circuits but according to regulations you should not have a 30 ma RCD covering all the circuits but yet with TT system supplys ( thats what i think i have as the earth cable to CU goes into floor under floor boards) you have to have an rcd covering all the circuits which i think should be a 100 ma RCD but i wish to have a 100a CU fitted maybe split load to give sockets a 30 ma RCD protection so how do i achieve this as i have not seen a 100ma RCD which can support 100amp only 80amp can you buy a CU with a 100ma RCD built in but with also a separate 30ma RCD for certain circuits like sockets?

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[dw3101]

you could buy a split load cu, remove the main switch and replace it with a 100ma rcd and still retain the 30ma rcd if you wished, rcd would be between 7 - 10 quid.

David

 

[timmyquick]

the 30 ma RCD is built into the CU itself not split load the switch on the cu is itself is the 30 ma RCD

 

[andy]

rcd would be between 7 - 10 quid.

David

isolators are about that. RCD are more

 

[ban-all-sheds]

you could buy a split load cu, remove the main switch and replace it with a 100ma rcd and still retain the 30ma rcd if you wished, rcd would be between 7 - 10 quid.

David

£7-10 for a 100A/100mA Type S? What's the name of your wholesaler again??

PS - did anybody work out what timmyquick was on about? I kept running out of breath before I got to the end of his 100% punctuation-free "sentence".....

 

[timmyquick]

I got a GCSE in English so it just shows how crap they are!. I am still unclear about my tt electric supply, anyone wish to clarify what type of setup you need for this (CU setup). According to my electric wiring domestic book you should have on a tt supply a 100ma rcd protecting all the cu circuits as a 30ma RCD is no longer acceptable under current regs due to plunging into darkness, so if anyone can clarify?.

I will try to improve my punctuation why i'm at it maybe english to.

 

[L.Spark]

LOL, lets me completely clear about this Timmy

firstly there is nothing said about not having an rcd, you should have one!

on a TT supply first you would have a 100mA Time Delayed RCD (Type-S), this would protect everything, then somewhere further down the line you have another RCD, this is 30mA and this MUST protect EVERY socket outlet and anything else that should be protected by this, the lights would be placed after the 100mA RCD, therefore if there are any faults on socket outlets the lights won't go out and leave you in darkness.

Any questions?

 

[timmyquick]

Hi L.Spark

Just one more question. Can i achieve what i need to do from your last reply?, by just using 1 CU and not a separate RCD (space very limited). If so what equipment as i have only seen CU's for sale which are split load and do not have a 100ma RCD protection for all circuits bearing in mind that my current CU is rated 100A.

Thanks very much for you help, will be considering getting an electrician to do the work, would just like to know whats what and buy my own equipment. Not what a sparky supplys and charges if thats how i proceed.

 

[L.Spark]

Hey Timmy

Lets be clear about this, what I said in my post are the basic requirements, almost all Consumer Units are rated at 100A, It's what goes inside them thats important.

A Plastic/Insulated Split-Load board with a 100A/100mA Type-S RCD should be first, then a selection of MCB's appropriate to your circuits, then a 80A or similar 30mA RCD for protecting the socket outlets.

with regard to the work, yes it's essential this is done correctly and having an electrician do this is a must, however it is important to get the correct equipment for the job, and I would personally let the electrician get hold of it, if your persistent it's possible you may get the wrong things but it's up to you.

 

[L.Spark]

Thanks very much for you help, will be considering getting an electrician to do the work, would just like to know whats what and buy my own equipment. Not what a sparky supplys and charges if thats how i proceed.

Don't consider, it's essential the works all done correctly!

 

[dingbat]

Thanks very much for you help, will be considering getting an electrician to do the work, would just like to know whats what and buy my own equipment. Not what a sparky supplys and charges if thats how i proceed.

Most sparks tend to use the same kit time and time again. It means they know the quality and reliability and often it means they can get decent discounts for the quantities they buy. Familiarity with the layout also means they can often a do a quicker, neater job. On the odd occasion when I've [foolishly] let a client supply parts it's made my life harder and sometimes the kit supplied has not been entirely suitable for purpose.

These days, faced with a client who wants to supply, I load my estimate to allow for this. It may be a false economy to insist on purchasing yourself equipment which you confess to not know much about. If you're going to get a spark to do it, then let him get on with it.

 

[breezer]

put it this way.

you want a ford car, you ask ford for one, but tell them you are going to supply the parts, how far do you suppose you will get?

 

[Damocles]

Put it this way, you go to a ford garage, you get ford branded parts. You go to a different garage you get cheaper non-branded parts, but quite possibly made by the same company on the same production line.

 

[ban-all-sheds]

Just one more question. Can i achieve what i need to do from your last reply?, by just using 1 CU and not a separate RCD (space very limited). If so what equipment as i have only seen CU's for sale which are split load and do not have a 100ma RCD protection for all circuits bearing in mind that my current CU is rated 100A.

The problem is that all you have seen for sale will have been the packaged CUs from the sheds (Screwfix is just an on-line shed, except it's open for shorter hours). If you have a TT supply (still to be confirmed - you need to follow that earth cable) then you can use a split-load board, but instead of the normal main switch it will have a 100A/100mA Type S RCD.

100A is the overall load it can switch - that's what the figure on your current CU means, the main switch can safely pass, and interrupt, a 100A current, the busbar can safely carry 100A etc.

100mA is the RCD tripping current, i.e. the amount of imbalance that it has to detect before springing into action, in this case after a slight delay.

The other RCD you'd have would be a normal one, in roughly the same place it would be in a "normal" CU, and would typically be rated at 80A/30mA.

The idea of that setup is that if you get a fault on the socket circuit, the combination of a higher trip current and a time delay means that you get what's called discrimination, i.e. the RCD protecting the sockets trips, and the main one does not.

 

[timmyquick]

What seems strange to me is how that having all the circuits protected on the cu by a 30ma RCD is no longer deemed acceptable by the regulations, when surly that is safer than having a 100ma RCD protecting all the circuits on a cu.

why was it installed like this in the first place? what is so unsafe about a tt supply that all the cu needs RCD protection?. Unlike modern supplys in new homes?.

I mean who cares that when a bulb goes my whole electric cuts off. I have to get up in the dark in mornings to turn the light switch on any way seems silly to me. I feel when i have this work done to bring it to current regs my installation will be less safe due to having a 100ma RCD protecting all my cu rather than the 30ma RCD. The reason my CU needs replacing is that the cover has a very big crack (very big) which i think should be replaced i have left it for years and it got to be done sometime!