ELCB- Garage

towbar

Quick question for the electricians,

When our house was wired the garage supply is taken from an MCB protected by the same ELCB covering sockets etc in the house consumer unit.

There is a seperate box in the garage that also has a local ELCB.

The problem is if anything in the garage trips it takes out the main ELCB.

Does the garage supply need to be protected by an ELCB in the main consumer unit or is the local ELCB in the garage sufficient?

Also the main ELCB has started tripping randomly when the house pc and TV is on together. Is there a limit to the number of devices on a single ELCB. Currently 3pc's, 1 TV quite a few transformers etc.

Don't plan to do the work myself but if the general opinion is it can be changed would get an electrician out to do it.

davelerave

The rules state that rcds in series should discriminate.To answer your question, the rcd should be in the garage only.
As far as the number of rcds in an installation goes .you have to take into consideration the overall size of the installation and avoid nuisances

Pcs have leakage current but 3 doesn't seem excessive but the overall leakage may be high(or there may be a fault).so you could test and split up into separate rcds and also separate garage

2011

Does the garage supply need to be protected by an ELCB in the main consumer unit or is the local ELCB in the garage sufficient?

To answer your question the ELCB in the garage is sufficient. BTW they are now better known as RCDs.

+1 to what Dave said.

As far as the number of rcds in an installation goes .you have to take into consideration the overall size of the installation and avoid nuisances

This is a very good point. Many people put too many circuits through 1 RCD. This increases the chances of nuiscense tripping.

It also means that more circuits are lost when the RCD operates.

2011

If the 3 PCs are on the same circuit you could put them on their own RCBO. This is an RCD and MCB unit that are combined into one. This would be the norm for computer socket circuits in offices.

towbar

Thanks folks good feedback

so if the RCD's should discriminate would that be something certain models may support or not


The Pc's are on seperate circuits but maybe use RCBO'S might be way to go.

davelerave

No. You don't need discrimination here.The rcds shouldn't be in series

eoghan.geraghty

There is nothing in the regs about discrimination of RCDs, as others have said though, the RCD in your shed will suffice so take the shed MCB in your house board off the RCD.
This will prevent any outside lights on your shed board tripping the RCD also.
While you're at it, replace the RCD, it may be too sensitive so at the very least get your sparks to test it's tripping current.

2011

so if the RCD's should discriminate would that be something certain models may support or not

Don't go down this road. As others have said simply don't put RCDs in series.

davelerave

eoghan.geraghty wrote: »

There is nothing in the regs about discrimination of RCDs, as others have said though, the RCD in your shed will suffice so take the shed MCB in your house board off the RCD.
This will prevent any outside lights on your shed board tripping the RCD also.
While you're at it, replace the RCD, it may be too sensitive so at the very least get your sparks to test it's tripping current.

You must discriminate in series(536.3).Although it's not relevant here.
They can be used as a main protective device for TT systems or to provide fire-protection (usually 300mA)
Horticultural installations and some temporary structures also have main rcds(740.411.3.01) which discriminate to prevent a 30mA trip knocking out the mains

eoghan.geraghty

Well corrected davelereave, i checked my regs when I was in the van this morning, serves me right for not going out to confirm last night. .
As a general rule though for domestic applications, do not put RCDs in series OP.

As a side note, has anyone used/seen an RCD/RCBO with a smaller rating than 30mA?

davelerave

Ya not much call for series rcd atm in domestic.The s-type 300mA 'main rcd' may come in eventually for leakage/fire in domestic? i wonder