Neutral to earth voltage

[New guy 397]

Favour for a mate has turned into a nightmare. Really appreciate any comments on the below!

Was asked to look at some sockets which have apparently been "sparking".......

17th edition board. 100amp/30ma RCD as main switch and only additional protection for 11 circuits. Unsure if that conforms with BS EN 60947-3?!

Ze 0.32. TNS

Bonding appears good, only ohm tested across exposed metal work couldn't find actual straps, but it leaves from the CU.

Unable to perform a Zs at 4 sockets from 8, Error 4 on my fluke. >50v N->Earth. Rest of circuit tests no issue. 2.5mm radial.

L->E 240v
L->N 240v
N->E 30v(ish)

So i'm assuming we have a poor neutral joint somewhere between the good and bad sockets...why is the RCD not tripping when load is applied to these sockets?!

After taking the entire circuit apart i couldn't find the smoking gun, so now i'm working on the assumption a joint in the ceiling.... At which point I threw in the towel isolated the circuit and said i'd have to come back ASAP.

It also looks likely that that 2x B16 radials use to be a ring (flagging on cables with tape in CU). Would that change anything?

Am i missing anything here? neutral to earth faults always mess with my head.

Any advice will be helpful. Constructive or otherwise!!

 

[Pete999]

Favour for a mate has turned into a nightmare. Really appreciate any comments on the below!

Was asked to look at some sockets which have apparently been "sparking".......

17th edition board. 100amp/30ma RCD as main switch and only additional protection for 11 circuits. Unsure if that conforms with BS EN 60947-3?!

Ze 0.32. TNS

Bonding appears good, only ohm tested across exposed metal work couldn't find actual straps, but it leaves from the CU.

Unable to perform a Zs at 4 sockets from 8, Error 4 on my fluke. >50v N->Earth. Rest of circuit tests no issue. 2.5mm radial.

L->E 240v
L->N 240v
N->E 30v(ish)

So i'm assuming we have a poor neutral joint somewhere between the good and bad sockets...why is the RCD not tripping when load is applied to these sockets?!

After taking the entire circuit apart i couldn't find the smoking gun, so now i'm working on the assumption a joint in the ceiling.... At which point I threw in the towel isolated the circuit and said i'd have to come back ASAP.

It also looks likely that that 2x B16 radials use to be a ring (flagging on cables with tape in CU). Would that change anything?

Am i missing anything here? neutral to earth faults always mess with my head.

Any advice will be helpful. Constructive or otherwise!!

Bit of IR testing would be my choice for starters.

 

[New guy 397]

Bit of IR testing would be my choice for starters.

Didn't include sorry. Dead short N->E.

Why so confused about no RCD trip?!

Rest OK for service, around 8Ohms

 

[plugsandsparks]

Probably lost the earth somewhere

 

[New guy 397]

Probably lost the earth somewhere

That makes sense why the rcd not tripping.

Little confused about my ir readings though

 

[DPG]

That makes sense why the rcd not tripping.

Little confused about my ir readings though

Is that figure of 8 Ohms supposed to be 8 Megohms?

 

[pc1966]

Unable to perform a Zs at 4 sockets from 8, Error 4 on my fluke. >50v N->Earth. Rest of circuit tests no issue. 2.5mm radial.

L->E 240v
L->N 240v
N->E 30v(ish)

Can you use a wander lead and check for connectivity of both N & E back to the CU?

As already said above, it looks like an open E as if it were N-E short you probably would see the RCD trip.

N-E faults though are tricky as if you have a very low supply side N-E voltage, say TN-C-S, then you may only get enough residual current flowing when there is a big load on some branch giving enough volt drop on the neutral conductor to cause 30mA of stray current to trip the RCD at the location of the fault.

 

[Lucien Nunes]

Your observations are in conflict. If there is a dead short between N & E, there can't also be 30V between them. Or is the 30V at the sockets that don't have the short? It could be that the CPC is severed and one side of it is down to the neutral. Someone came along and discovered the break, turned the circuit into two radials without disconnecting the faulty leg, and the N-E breakdown has since developed.

 

[New guy 397]

Can you use a wander lead and check for connectivity of both N & E back to the CU?

As already said above, it looks like an open E as if it were N-E short you probably would see the RCD trip.

N-E faults though are tricky as if you have a very low supply side N-E voltage, say TN-C-S, then you may only get enough residual current flowing when there is a big load on some branch giving enough volt drop on the neutral conductor to cause 30mA of stray current to trip the RCD at the location of the fault.

I will be wandering leading as you suggested on my next visit. Thank for your response, very helpful.

Your observations are in conflict. If there is a dead short between N & E, there can't also be 30V between them. Or is the 30V at the sockets that don't have the short? It could be that the CPC is severed and one side of it is down to the neutral. Someone came along and discovered the break, turned the circuit into two radials without disconnecting the faulty leg, and the N-E breakdown has since developed.

Yes i am thinking i am at fault.

I didn't think to end to end at the time, only really made the connection as possible ring when closing up the CU. but having a faulty leg which has deteriorated further makes sense.

appreciate the help.