EZ and spur

[the pict]

If a ring final is RCD protected, and a spur is taken outside the EZ need that spur be seperatly RCD protected, IE at point of use by a RCD socket or other method
Pict

 

[telectrix]

i would say no. e.g. if you are fitting an outside socket to an RCD protected circuit, by fitting a 2nd RCD you would have no discrimination.

 

[the pict]

I was thinking the same,But if the ring is prtected by a 80A/30mA and I use a 25A/30mA I know that discrimination is met at the current rating but does discrimination at the trip current have to be met.I cant see how unless I used a 100mA RCD at the board but that raises more issues
Pict

 

[telectrix]

you're correct. however , having no RCD discrimination is not a safety issue, more a matter of inconvenience. the only good way would be to feed the outside RCD socket from a non-RCD way in the board, but then you'd have to run the cable surface.

 

[the pict]

Problem is this is to a cold room outside and the cable is buried in plaster on the inside then the spur goes through a hole in the wall in 2.5 T&E
I feel that as it is part surface part buried any future issue will take out the whole kitchen and I would like to limit this by a RCD I suppose it's a judgement call at the end of the day, but your right if safety in not compromised it should be fine
Pict

 

[Engineer54]

Problem is this is to a cold room outside and the cable is buried in plaster on the inside then the spur goes through a hole in the wall in 2.5 T&E
I feel that as it is part surface part buried any future issue will take out the whole kitchen and I would like to limit this by a RCD I suppose it's a judgement call at the end of the day, but your right if safety in not compromised it should be fine
Pict

Again ...No!! The likelihood is that any fault will take out Both 30mA RCD devices, not one or the other!!! So it will take out the whole kitchen!!

 

[telectrix]

if the cable is already installed from the RCD protected RFC then you're shafted. as eng54 says, a fault in the cold room will take out the kitchen. having said that, at least they will know that it's tripped.

 

[Deleted member 26818]

Is there a requirement for the circuit to be RCD protected?
It sounds as if the installation is commercial?

 

[the pict]

Spin Yes commercial kitchen, Eng 54 But how then does one attain discrimination ??
Pict

 

[telectrix]

you could take the RFC off RCD or replace the RCD with a 100mA time delay one, but that would be leaving the installation less safe than it was before.

 

[Deleted member 26818]

Well at present, it would appear the spur is allready RCD protected.
Removing the RCD protection from the RFC would mean that the installation still complied with BS7671, however as Tel says, it would be less safe.
It looks like your options are to the leave the RCD protection as is, which would trip the RCD for the RFC if there is a fault on the spur.
Or run a new Radial circuit either with or without RCD protection.

 

[Deleted member 19807]

I was thinking the same,But if the ring is prtected by a 80A/30mA and I use a 25A/30mA I know that discrimination is met at the current rating but does discrimination at the trip current have to be met.I cant see how unless I used a 100mA RCD at the board but that raises more issues
Pict

you have no discrimination at all the 80a & 25a are just the max load they can switch not an overload rating such as an mcb.

you have no way of getting any discrimination with the setup as it is. You also can't get discrimination by changing the current rcd to 100mA, you would need to fit a s type rcd (time delayed) up front.

Personaly I would say they are better off having it on the 30mA rcd ring as you don't want the cold store tripping out and no one knowing about it until its all go warm. If they don't like that they will have to have a new circuit from the DB.