Hi, new guy here & some help needed with RCDs

[westward10]

Not spoiling - just educating....

Yeah I know was in jest, took 13 posts for it to raise its ugly head though

 

[mickfred]

If values permit fit a c type MCB in the first board , therefore a overload should trip the b type in garage unit fist

The earthing arrangement and installation method doesn't require 30mA RCD protection for the distribution circuit. The final circuits will be covered by the RCD in the garage board. Having a high integrity board means you can feed the distribution circuit from a non RCD protected way. Doing it this way means you wont have RCD's in series with lack of discrimination. The only discrimination issue you would have would be having to circuit breakers in series of a similar current rating but you'll have to decide if that's going to be an issue and if it is look at a way of providing over current protection for the distribution circuit with a fuse or similar. Are there any extraneous conductive parts within the garage that will require bonding?

 

[westward10]

A circuit breaker is not going provide good discrimination but a type C, assuming fault protection is maintained is the best option and they are not critical circuits should the wrong one trip.

 

[Leesparkykent]

If values permit fit a c type MCB in the first board , therefore a overload should trip the b type in garage unit fist

That will not provide short circuit discrimination.

 

[mickfred]

No it won't but it will solve overload problems and if plugging in transformer in the garage only the b type will have to be reset not walking back to the house every time

That will not provide short circuit discrimination.

 

[Leesparkykent]

No it won't but it will solve overload problems and if plugging in transformer in the garage only the b type will have to be reset not walking back to the house every time

What over load do you envisage? Surly the circuit should be designed for the intended use.

 

[mickfred]

Well it's not my garage , so i don't know . But you agree not to put it on rcbo (two RCDs in series ) so where back to mcbs around the same size . So why not try a c type , for all i know the op could have full set of 110v tools ( plug a transformer in a b type and its 50/50 it will trip ) . Maybe he going to start his own private disco and with the laser light and smoke machine running at the same time OVERLOAD

 

[Leesparkykent]

Well it's not my garage , so i don't know . But you agree not to put it on rcbo (two RCDs in series ) so where back to mcbs around the same size . So why not try a c type , for all i know the op could have full set of 110v tools ( plug a transformer in a b type and its 50/50 it will trip ) . Maybe he going to start his own private disco and with the laser light and smoke machine running at the same time OVERLOAD

 

[Sooby2]

Are they actually extraneous conductive parts tho? Where have the bonds been connected to? If they've been connected to the earth marshalling terminal in the garage board that is using the TNS earthing arrangement then the CPC of the 4mm armoured cable is not of an adequate CSA to form part of a bonding conductor.

Sorry for the delay in replying. At present they are connected to the metal case of the fusebox, to its earthing point and is using the armour of the old 2 core 2.5mm SWA. There is T&E cabling running along some of the frame to the lights, but the earth system seems to work ok as I had one cable pull out of a junction box and touch the frame (clearing out old timber) which tripped the RCD in the house instantly.

The bonds will be connected direct to the new consumer unit as and when I fit it as the old box will be going. But if 4mm isn't enough, I could go up to 6mm.

All the old cabling will be going as well and being replaced with conduit. Actually, everything old is going and will be replaced as this is very much a project.

And this is notifiable under part p

Thanks, but I was aware of that.

 

[davesparks]

Sorry for the delay in replying. At present they are connected to the metal case of the fusebox, to its earthing point and is using the armour of the old 2 core 2.5mm SWA. There is T&E cabling running along some of the frame to the lights, but the earth system seems to work ok as I had one cable pull out of a junction box and touch the frame (clearing out old timber) which tripped the RCD in the house instantly.

The bonds will be connected direct to the new consumer unit as and when I fit it as the old box will be going. But if 4mm isn't enough, I could go up to 6mm.

All the old cabling will be going as well and being replaced with conduit. Actually, everything old is going and will be replaced as this is very much a project.



Thanks, but I was aware of that.

If they are extraneous parts then they will need main bonding of the correct size for the incoming main, what size bonding does this installation require?
Being TNS the minimum is obviously 6mm, but it could be larger