strange earthing problem (lighting)

[Neon Vagabond]

Right, so its been one of those long days.

swift breakdown:
top floor flat.
lighting cable is single cores in a conduit system.

was employed to install downlights in 2 rooms.

Really bizarre one for me, ive never encontered nything like this before.

So i tested the original fittings in these rooms to establish an earth path, all was well.
1.16 zs.

wired all my downlights and then crimped onto the switc and neutral at the original fitting.
zs was 1776.

disconected my wiring, still 1776 ohms.

this was the same for both rooms.

ran a new earth from the MET (10mm)
the done a zs with that new earth and across the switch/neutral at the light.
still getting 1776.

Really confused as the ze on the property is really low (0.25ohms)

this problem is only happening on this lighting circuit.

Any ideas on this?

i had plan to wrap up for the big quarantine but ill need to go back out tomorrow

 

[SparkyChick]

Is the conduit being used as the CPC? Any RCD protection on the circuit? If no RCDs, is it possible the high current Zs has damaged the earth path?

Is it possible there is a crappy joint in the line conductor somewhere? I might check a few other light fittings just to check.

 

[Neon Vagabond]

the conduit has flying leads from the end boxes but connected with them appears to be dedicated earths through.

its an old board and the circuit is on the no rcd side of the board.
think its 3036 mcbs

i'll definetly look into the possible crappy line conductor.
its got be surely?
new earth ran in off a proven good met and still getting the bad reading.

there have been only a couple of noticable alterations to the original wiring
(lowered bathroom ceiling/ spots)
and a horrible looking cupboard light wired from another dimension where it appears bs7671 is not high on the agenda

 

[davesparks]

If a new continuous conductor back to the MET is giving such a poor Zs, and assuming the circuit works, then the logical answers are either a failure of the external earth or a problem with the tester or test leads.

 

[Neon Vagabond]

If a new continuous conductor back to the MET is giving such a poor Zs, and assuming the circuit works, then the logical answers are either a failure of the external earth or a problem with the tester or test leads.

Yeah everything seems to work fine.

I don’t think it’s the meter because why would I get good readings on the other circuits and when doin the ze?

 

[westward10]

If you have installed additional lights it will now require additional rcd protection. Sounds like you have disturbed something with your new works.

 

[Neon Vagabond]

If you have installed additional lights it will now require additional rcd protection. Sounds like you have disturbed something with your new works.

I thought you only had to install an rcd on a new circuit?
Not an an alteration of an existing circuit that doesn’t run through a bathroom?

yeah I’m goin to review the works I’ve done when I get there :/
Goin to bypass the dimmers I’ve put in as well.
Struggling

 

[westward10]

If you have installed additional points it must comply to current Regulations, your part at least and this means additional rcd protection. All lighting circuits in a dwelling now require additional rcd protection this applies to new circuits and additions to existing.

 

[Neon Vagabond]

If you have installed additional points it must comply to current Regulations, your part at least and this means additional rcd protection. All lighting circuits in a dwelling now require additional rcd protection this applies to new circuits and additions to existing.

right I’ll just move it onto the rcd side of the board then.
This also might tell me more if it starts tripping out

 

[Pretty Mouth]

Just a thought - is it possible that the earlier Zs tests were made with the tester in L-N mode, and the later ones L-PE?

 

[Neon Vagabond]

Just a thought - is it possible that the earlier Zs tests were made with the tester in L-N mode, and the later ones L-PE?

nah I’ve tried both on the new wiring and old

 

[davesparks]

Goin to bypass the dimmers I’ve put in as well.

You didn't carry out the Zs test through the dimmers did you?
If you did then that's your answer.

 

[Neon Vagabond]

Right!!!!!
I’ve took out the dimmers and put the connections in block.
Now getting 1.37.

could it bdd red faulty dimmers?
Cknndctions were good on these.

 

[davesparks]

Right!!!!!
I’ve took out the dimmers and put the connections in block.
Now getting 1.37.

could it bdd red faulty dimmers?
Cknndctions were good on these.

No, they're not faulty, they're dimmers, they are designed to restrict the flow of electricity so of course they will restrict the flow of the test current and give a high reading.

 

[Neon Vagabond]

You didn't carry out the Zs test through the dimmers did you?
If you did then that's your answer.

Haha, surely the max zs applies wether you’ve got a dimmer or not

 

[DPG]

Haha, surely the max zs applies wether you’ve got a dimmer or not

Yes but you cant test Zs through a resistor and expect sensible results!

 

[richy3333]

right I’ll just move it onto the rcd side of the board then.
This also might tell me more if it starts tripping out

I doubt a 3036 consumer unit will have an RCD side to it?

 

[westward10]

A dimmer switch isn't a resistor as such and under fault conditions the triac will close allowing fault current to flow.

 

[DPG]

A dimmer switch isn't a resistor as such and under fault conditions the triac will close allowing fault current to flow.

Ok, I simplified things, but you get my point. You certainly won't get a good Zs!!

 

[Timbo]

I doubt a 3036 consumer unit will have an RCD side to it?

Ah, but this is special - 3036 mcb's!!!! ???