High Zs on lighting circuit

[Maxstone89]

Hi all

I have a house where all the circuits meet the Max Zs for that circuit yet the lighting circuit is testing as 747 ohms Zs

It looks like it used to be a TT system and been converted to a TN-C-S system. As its also got an main tcd before the board. Could this somehow be causing this high reading, even though the lighting circuit is connected to the main pme where all other circuits are or is their other possibilities.

Thanks max

 

[Sintra]

What are the dead test continuity results for this lighting circuit? These readings will help determine why you have a high Zs.

 

[Maxstone89]

Ran out of time, so gotta go back to sort other problems out so i am going to dead tests then, any ideas to give me a heads up.

Would be appreciated

Regards Kurtis Randle

 

[Sintra]

Hi all

I have a house where all the circuits meet the Max Zs for that circuit yet the lighting circuit is testing as 747 ohms Zs

It looks like it used to be a TT system and been converted to a TN-C-S system. As its also got an main tcd before the board. Could this somehow be causing this high reading, even though the lighting circuit is connected to the main pme where all other circuits are or is their other possibilities.

Thanks max

Ran out of time, so gotta go back to sort other problems out so i am going to dead tests then, any ideas to give me a heads up.

Would be appreciated

Regards Kurtis Randle

Ok mate let's start with who you are. Post #1 you're called max and post #3 you're Kurtis Randle. View Profile: Kurtis.Randle@m - Electricians Forum | Electrical Advice Forum | An electrical forum for electricians in the UK This leads me to believe you have opened a duplicate which is against forum rules. Let me know which name you want to use and I will merge the 2 accounts.

 

[Farmelectrics]

do your dead tests first lets see the results for this lighting circut

 

[DuaneMHunt1976]

I was wondering if it had a earth. So I Google how to measure Zs without an earth, found a chat on ITE talking how...



John Peckham
"I think you can get a special meter for measuring Zs on a circuit without a CPC. I have not seen one of these meters and I do not know how they work however I have seen Zs readings on PIRs for circuits without a CPC! "

 

[telectrix]

this special meter he refers to is "make it up. client only wants a satisfactory report for £50."

 

[Maxstone89]

Will do dead test when there next, and yes it has cpc,s

 

[telectrix]

a R2 from CU to each point would help. easiest way is to go to each switch for starters.

 

[Maxstone89]

Yep will do further testing when their again, pretty much same reading was coming out on up and down stairs lighting circuit

 

[DuaneMHunt1976]

So what value you getting for R1+R2 And R2 if you can

 

[DuaneMHunt1976]

this special meter he refers to is "make it up. client only wants a satisfactory report for £50."

Maybe cash to be made there... Just a circuit with a timer to get a random number for Zs that is under what you need.
We could stick to probs on to make it look goos and a test button to set the random figure off

 

[Maxstone89]

Will be going back if customer will pay, but if he wont would any of you guys class this as unsatisfactory on a eicr even if there is an rcd protecting the full board?

If their was no rcd i wouldn't pass it but as there is and the result is below 1660ohms for a 30ma rcd cant remember exact figure would you pass it and add a note of recommendation?

 

[Richard Burns]

If you have 747Ω as the resistance of a domestic circuit then there is something very wrong, this is equivalent to a 60W light bulb connected through the cpc.
Even though it does meet the 1667Ω requirement for a 30mA RCD it is very likely that you have a very poor / corroded connection somewhere (or a major wiring error) and that this will get worse over time.
There is no sensible way this can be a result from a satisfactory circuit.
The fault needs to be identified and resolved.
However if the customer does not want to do it then you do have to leave it, but I would recommend putting an advisory of a faulty circuit in writing.

 

[DuaneMHunt1976]

I would guess.the problem is, did you measure some thing wrong and it looking daft on you

Maybe do.it for free to make sure you didn't cook up
If you did cook up some way it would look like your trying to con the person