Flickering lights, tripping RCD and voltage at consumer unit...

[Marcus Vaughan]

Hi All,

I have just been to a property to fault find a tripping RCD. Lights are flickering. All a bit strange. Vacant property - no loads plugged in. TNCS.

The RCD protects socket circuits, CH, garage etc - but not the lights.

Anyhow, I tested the the RCD - no problem.

I turned off all the breakers for the RCD and turned them back on one at time. Garage circuit tripped the RCD - ah-ha I thought. But then it held. Tried the process again and then the kitchen ring tripped it. Tried again and downstairs ring tripped it. But now all holding. Not so straightforward now....

I tightened up all the connections in the CU and checked roses and switches. Nothing.

Soooooo. I then did something I should have done at the start - and checked the voltage at the tails to the consumer unit.

175 volts.

Just to make sure my kit was OK - went next door -247 volts.

So have called DNO.

The lights flickering I understand - but I am trying to relate this low voltage reading to the RCD.

Any ideas?
Any other advice?
It's a new one for me.....

 

[SparkyChick]

Could be a loose supply terminal. I've had a situation at a local hotel where I was getting 90v LN. Turned out it was a loose neutral on the supply pole (was overhead supply).

Without loads I wouldn't expect it to trip the RCD, but if there is a load it could also explain the random tripping.

 

[SparkyChick]

Should have added... I tend to work my way back from the final circuit to the supply head, giving all the tails a tug to check for secure connections.

 

[westward10]

It is possible there is a supply neutral issue especially with TN-C-S whereby the neutral is randomly floating causing voltage dips and peaks which will result in imbalances.

 

[Marcus Vaughan]

Thanks SC.

I’ll let you know how it pans out.

 

[Strima]

Another vote for loose supply neutral.

 

[DPG]

I'll have the same bet (£5 I think) I've had a few times before - loose neutral in a tee-off joint under the pavement.

 

[marconi]

Maybe you did it but did not report it - but you can gather more evidence by measuring L-E and N-E voltages and watching them over a minute (or longer).

 

[Pete999]

Another vote for loose supply neutral.

Yes agree another vote for a dodgy Neutral connection.

 

[Toneyz]

Yes agree another vote for a dodgy Neutral connection.

Something seems loose somewhere, BTW how are you, Pete? noticed you 've not been posting for a few days.

 

[Pete999]

Something seems loose somewhere, BTW how are you, Pete? noticed you 've not been posting for a few days.

Been rethinking something Ant, don't ask.

 

[buzzlightyear]

giving all the tails a tug to check for secure connections.

I loved to be on the end of that .

 

[Marcus Vaughan]

I was not onsite when the DNO turned up but they did phone me up and confirm a problem with the supply, saying voltage was ranging from 170 to 240 or so over time.

They also confirmed a high Ze of about 2 ohms.

I don't know much more than that at this stage but do know that a supply has been 'altered' recently in a house opposite, and that a smart meter has been recently put in. But I am only speculating what may have gone wrong.

I suspect I'll pop back when supply is repaired - just to carry out a few tests at the board - the RCD especially......

 

[KEV 1 N]

Nasty things, loose or lost neutrals on main supply.

I remember once there was a neutral fault on a 2 phase supply of a large HMO.
The fault was a bad joint on the DNO cable in the street (ancient PILC).
The underground joint went altogether and the neutral was lost, the fault was only noticed when all the rcbos tripped but not mcbs, so the lights and non rcd circuits still worked....only because one of the lighting circuits turned out to have a N-E dead short on it (no rcd) so when the supply neutral was lost the current found its way along the lighting neutral, across the short and back to earth! So the 1mm cpc back to the DB was carrying all the current and became extremely hot and melted the cable at the DB and and 2 feet back up the wall! Almost a fire!

 

[UKPN]

Could have been as simple as a loose neutral in the service head, but don't tighten them yourself!