Rcd's with High Resistance

[ElectricalAsh]

Hi, I recently installed a new c/u and was talked into a MCG board by my local wholesalers (which won’t be happening again!!!).

The problem I have is that the rcds are adding 0.51 to my zs reading. It’s a tnc-s system with a 0.04 ze. If I do an r1+r2 on a lighting circuit for example its 0.93 but my zs is 1.44. I have replaced the rcds but still getting the same reading. It is definitely the rcds as I have done a loop test either side of the Rcds there is a difference of 0.51. My question is are these readings acceptable as the zs is still within the limits or do I replace the board? thanks

 

[telectrix]

leave it. i had an rcd once pushing the Zs up by 349 ohms.

 

[Sintra]

One thing i will say is never use MCG they are absolute crap. So long as your Zs is below the maximum permissible then leave them in.

 

[telectrix]

One thing i will say is never use MCG they are absolute crap. So long as your Zs is below the maximum permissible then leave them in.

sintra, what's your view on BG ( british general ) CUs?

 

[Sintra]

TBH Tel I have never used them.

 

[ElectricalAsh]

I wont be using them again! thanks for the replies.

 

[telectrix]

TBH Tel I have never used them.

i've used 1. it had 3 decent N bars so was versatile and has a built in spirit level so even i could get it straight. good price as well. £65 fully loaded.( 2 RCD+10 MCBs) inc. VAT.

 

[malcolmsanford]

As your circuit is RCD protected then your Zs for that lighting circuit is 1667. As long as your R1 + R2 was what you expected it to be, and your RCD testing times were as they should enter 1667 on the SOTR