RCD Advice

[stidge]

hi all, Am i right in believing that if i install An RCD controlled garage cu fed from Dual RCD Cu i will cause problems with unwanted tripping???? It is not possible to come off unprotected side. Any advice much appreciated

 

[Hawk81]

Why put the rcd in the garage then? If it is already protected b a 30mA rcd then no need for a second one as you will have no discrimination.

 

[nickblake]

What you do is remove the RCD from the garage CU and install an isolator ,as it will be protected from the dual RCD board , it wont nesseseraly cause unwanted tripping but if the garage CU RCD trips it will trip the main RCD the other alternative is to have the main board as a hi integrety board this has 2 RCD's plus ways for RCBO's or MCB , which is used for circuits that may cause unwanted tripping and smoke detectors

 

[GrannySmiff]

would you not just put a 100mA rcd in? or do we need to know more info like har foar away the shed will be what it will be supplying etc?.

 

[nickblake]

would you not just put a 100mA rcd in? or do we need to know more info like har foar away the shed will be what it will be supplying etc?.

you couldnt put a 100ma RCD into the main board as all the other circuits would be protected by 100 ma when they should be 30ma

 

[Hawk81]

would you not just put a 100mA rcd in? or do we need to know more info like har foar away the shed will be what it will be supplying etc?.

Where is he going to put this 100mA rcd? He has stated his supply to the garage is coming for a dual rcd board and he has no other option but to come from here. Pointless putting the 100mA rcd in the garage as the circuit is already covered by a 30mA rcd.

 

[GrannySmiff]

don't know just trying to understand tbh, I thought if you have a outbuilding supply like that you are supposed to put in a 100mA rcd because of discrimination.

So its better to have the shed protected by the main DB's RCD instead of instaling an rcd for said shed?.

 

[Hawk81]

don't know just trying to understand tbh, I thought if you have a outbuilding supply like that you are supposed to put in a 100mA rcd because of discrimination.

So its better to have the shed protected by the main DB's RCD instead of instaling an rcd for said shed?.

No it is not better to feed the garage from the main DB's rcd in most cases. Its just this time the fella has no other option. In an ideal world it would come from its own rcd or be an armoured and not need an rcd at supply end

 

[nickblake]

in the Ideal world he'd have a hi integrety board mcb for the shed supply in armoured cable and its own cdu with RCd , agree with hawks comments

 

[GrannySmiff]

What I am not understanding is why cant he install a CU in the shed with an RCD that is configured so that any faults from shed will only trip the shed rcd? (discrimination). That way the RCD from main DB will protect the cable supplying the second CU and other RCD will protect those circuits.

Sorry if I have missed something obvious.

 

[Hawk81]

What I am not understanding is why cant he install a CU in the shed with an RCD that is configured so that any faults from shed will only trip the shed rcd? (discrimination). That way the RCD from main DB will protect the cable supplying the second CU and other RCD will protect those circuits.

Sorry if I have missed something obvious.

If he puts a 30mA rcd in the garage and the house db has a 30mA feeding the supply cable to the garage then there is NO discrimanation. So if a fault in the garage develops it can trip both rcds.

 

[nickblake]

i understand what you are saying appart from whats been mentioned the only other way would be to use a 30ma time delayed RCD in the main house this would then not trip if the RCD in the shed were to trip but realistically he wouldnt need the RCD in the shed as he has said it would be protected by a dual RCD board

 

[gregorabbott]

why not use rcbos in the shed for each circuit?

 

[Hawk81]

why not use rcbos in the shed for each circuit?

as has been explained in great detail already discrimination.

 

[Colin Integrale]

Discrimination with a 30mA at the supply and 100mA at the garage.. Eh?