UK Earth to Live Voltage - 206v

Chrisknowlesuk · Mar 23, 2022

I've been fault finding an issue in a domestic property, the situation is as follows...

RCD spur that is protecting outside sockets,

This spur is on the downstairs 32A ring, the sockets directly on the ring pass RCD tripping test.

The cables coming into the spur won't trip when tested?

Voltage readings: L-N=240v; L-E=206v; N-E=34v

Can't find where the spur comes off the ring, have checked several of the nearest sockets and also the CCU. Although, there does look to be a blanking plate on the wall but it can't be reached.

Any thoughts what could be causing this??

Thanks

pc1966 · Mar 24, 2022

Sounds like a faulty E connection. Have you got a wader lead or similar to measure the resistance from the RCD spur back to the suspected CU ring connections?

timhoward · Mar 24, 2022

Chrisknowlesuk said:
The cables coming into the spur won't trip when tested?

Am I reading it right that the fact it's an RCD spur and outside sockets isn't the pertinent point?
For clarity, you are saying that there is a ring final circuit and generally RCD tests trip the RCD at the CU, but there is one point on a spur off the ring where RCD tests don't trip the RCD at the CU?

As above more testing needed. Live Zs would be quickest.
Assuming this comes back with a high number or even open circuit, trace the route by isolating circuit, joining live and neutral at the spur, and measuring resistance at sockets. It will tap into the ring at either of the two points with lowest numbers or somewhere between them.