Cascaded RCDs

[thomP]

I'm having a new consumer unit wired in to replace a dated fused type. The current set up has a standalone RCD unit (rated 100mA) between the supply and the unit. The electrician is simply going to swap out the unit with a new split unit. This means that the circuits not RCD protected by the new unit will still be protected by the old RCD but those that are on the new unit's RCD will be protected by two RCDs in series (the new RCD rated at 30mA)

I dont have a problem with him wiring the new CU into the existing RCD just wanted some confirmation that an RCD running through an RCD wont cause any problems.

thanks

ThomP

 

[bongos]

There is discrimination between the two so it isn't a problem. For example an earth leakage of say 40mA on the RCD side would trip the 30mA unit but not the 100mA RCD. Items not on the 30mA RCD are still protected by the 100mA RCD.

As of 1st July all circuits need 30mA RCD protection if not buried deeper than 50mm. I'm assuming the CU change is happening soon?

 

[thomP]

Thanks bongos, yes it's due to be fitted next week.

 

[industryspark]

a 100ma rcd and a 30ma rcd dont neccesarilly discriminate with each other in all respects. what type is the 100ma? is it time delayed?

what earthing type is the installation out of interest? TT, TNS?