3 phase RCB

[Deimos]

I'm going to get a 3 phase RCB for the house. In fact, I'm going to buy it and get the local plumber/electrician to fit it. However, they seem to be rated at 25 amps or 40 amps (not the RCD cut-out bit but I assume the breaker/switch bit). Thus, for e.g. the 40 amp version, is this 40 amps per phase or across all three phases ? When I asked in Leroy Merlin they sort of gave me "no confidence" in their response - they just said you need the 40 amp version.

The EDF supply says 20 amps (on their cut-out switch thing) which I assume is 20 amps per phase or 60 amps is all three phases are fully loaded. Maybe this assumption is wrong. I certainly the only times it has ever cut out are during a close by thunderstorm and never because of excessive loading (even when I have switched my main boiler to use electricity as well).

Many thanks

Ian

[Nick Trollope]

[quote user="Deimos"]

I'm going to get a 3 phase RCB for the house. In fact, I'm going to buy it and get the local plumber/electrician to fit it. However, they seem to be rated at 25 amps or 40 amps (not the RCD cut-out bit but I assume the breaker/switch bit). Thus, for e.g. the 40 amp version, is this 40 amps per phase or across all three phases ? When I asked in Leroy Merlin they sort of gave me "no confidence" in their response - they just said you need the 40 amp version.

The EDF supply says 20 amps (on their cut-out switch thing) which I assume is 20 amps per phase or 60 amps is all three phases are fully loaded. Maybe this assumption is wrong. I certainly the only times it has ever cut out are during a close by thunderstorm and never because of excessive loading (even when I have switched my main boiler to use electricity as well).

Many thanks

Ian

[/quote]

A 40A 3-phase breaker is 40A per phase, likewise the EDF breaker. You don't want a rating less than the EDF breaker, or you won't get your whole "allocation"! If you have a 20A supply, I'd use a 40A breaker (if you have only 1).

 

[Deimos]

The 20A EDF supplies the house (one box of breakers), plus the workshop(s) (another box of breakers), plus an unused flat box of breakers, plus what is going to be a separate box of breakers for an attic conversion. However, all except the house are going to be occasional and not much load (a few lights, etc.) so I sounds like I'd be best going for a 40A for the main house one and then a 25A one for the attic conversion (2 bedrooms and a bathroom, heated from main house gas boiler). The EDF master cut-out thing is actually in a barn (with the meter).

Am I right in thinking that the 25A RCB is a bit too close to the EDF 20A and thus might not be enough ?

Many thanks

Ian