40v on circuit after isolating at the RCBO.

[Ely Sparks]

Hi,

Hopefully someone can help me with the following:-

Having recently carried out a Inspection on a installation I came across the following problem-

After isolating a ring main at the RCBO, I still have approx 40v at the socket outlets. There is another ring main, where after isolating that circuit, the 40v clears at socket outlets. I assumed it was something like a shared neutral between the circuits, but after checking for continuity on the neutral between the two separate rings, they don't seem to be interconnected.

My Megger 1552 won't carry out a No Trip Zs test or RCD test on the socket circuits either, I'm assuming it's related to the above problem. My tester is fine, I checked it on another installation.

Any advice to point me in the right direction of solving the problem would be appreciated.

Thanks.

 

[telectrix]

try the Zstest with the other circuit isolated. try measuring the 40v with an analogue meter. this should tell you whether it's an induced voltage or if there's a problem. OH, and double check connections esp. the earthing and bonding.

 

[rich.250]

Sounds like a single pole rcbo. ( have a look at the diagram on it ) and a leakage on the other ring final circuit.
Also it the touch voltage is too high your megger will not test. So id check your Earthing conductor.

 

[andekoch]

could be an induced voltage.

 

[Farmelectrics]

Had a similar problem last year and it was induced voltage pressure on cables near trunking this was on commercial job but sounds very similar

 

[johnboy6083]

try disconnecting the cables from the breaker and neutral bar. this would highlight induced voltages as the course, if your IR test has proved that the circuits are not interconnected. Also test the MCB, with cables removed, just to be sure its not faulty.