Earth leakage - no load

[nowaypedro]

Called out today by new owners to a domestic 3 bed semi with history of nuisance RCD tripping from day 1 (lived there about a month). TNS. No dual supply. No regular pattern to tripping. Most appliances new.

First - Ramp Tested RCD unit with no loads = 25mA (can live with that). Popped leakage tester on earthing conductor =0.2A (yes AMP!). Opened MCBs one by one - no change - finally main incomer - but still 0.2A (see photo). Any thoughts? (please ignore the obvious other errors on the board).

 

[Deleted member 9648]

What was the Ze? It's possible the TNS sheath earth has gone missing and there is leakage from the sheath to a parallel path (bonding?) on the installation.

 

[The Ghost]

Have you disconnected the main earth and tested? As above kinda beat me to it.

 

[nowaypedro]

Visible TNS connection looks good (visible bit anyway). Disconnected EC from CU end and zero reading. Measured 0.1A on bonding conductor to gas though. Water not tested yet. Haven't carried out Ze yet (ran out of time) but will do on next visit.

Never experienced before on a domestic - I'm wondering if there's leakage from DNO running through from supply sheath to gas/water pipes via bonding? Or am i on the wrong track completely?

 

[Octopus]

What are the RCD tripping times like?

Occasional nuisance tripping is a pain! I normally ask the homeowner to keep a diary of when it happens....... to see if there is any pattern - sure they say no regular pattern but by making notes they may spot something.

Had a case recently where the "pattern" was when the misses got home - and plugged in her laptop charger!

 

[KEV 1 N]

Visible TNS connection looks good (visible bit anyway). Disconnected EC from CU end and zero reading. Measured 0.1A on bonding conductor to gas though. Water not tested yet. Haven't carried out Ze yet (ran out of time) but will do on next visit.

Never experienced before on a domestic - I'm wondering if there's leakage from DNO running through from supply sheath to gas/water pipes via bonding? Or am i on the wrong track completely?

You might be onto some thing with that last comment, your getting 0.2amp, but which way is it flowing?

 

[plugsandsparks]

might be better to clamp LN tails

 

[Wilko]

If I understand correctly, you have isolated the installation at the lovely Protek iso and you are still seeing 0.2A on the earthing conductor? So there must be a voltage on the DNO means of earthing that's causing the current flow. Possible poor earth at local transformer and your installation's bonding looks better ?

 

[Ian1981]

As above clamp the live and neutral tails
clamp round the line and neutral conductors only (Not the protective conductor) and will measure the difference between the line and neutral currents, which is the earth leakage.

 

[Deleted member 72666]

How far from the substation is the property? The reason I ask is that I've seen this before where there's possibly a ground fault current on the dno's network probably from the hv side of the tx. Try isolate the cu and check if there's still leakage if there is then you have the same problem as I've got, I even get leakage of approx 700mA (which fluctuates) when the whole area is down on the lv side during a power outage! The dno have been informed about it and are next to useless as they'll only check Ze and measure the input voltage.

 

[polo1]

Although the installation presents as TNS, chances are that the DNO will have created N-E bonds elsewhere on the supply network during repairs. Ze test may show similar figures on L/E & L/N tests. Small diverted neutral current on main earth is not that unusual in TNC-S.

 

[stevethesparks]

Had a similar problem yesterday, it ending up being an early design DTV of which is double insulated, causing problems through its aerial connection.

 

[telectrix]

what's a DTV?

 

[stevethesparks]

Digital TV

 

[telectrix]

arrrgh. thought it might have been a domestic transvestite.