Testing Zs at Lighting switch's with no neutral

DanBrown · Feb 3, 2008

Could anyone just give me a bit of advice regarding a Zs test at a light switch, as the tester i have just baught is the ''Fluke 1653'' tester and it uses a 3 wire test earth, live, neutral to aquire the Zs.

Am i right in saying that you have to do it manually by shorting live / earth at C/U and do a ohms check then add this to your Ze test?.

Your thaughts would be appreciated, Thanks

ian.settle1 · Feb 3, 2008

The neutral is to allow the meter to work. So why not connect the neutral to earth to allow meter to work?

TonyM58 · Feb 3, 2008

Dan

connect line (used to be called phase) to earth bar at the cu (supply isolated obviuosly!)

and measure between line and cpc at the light switch on low resistance ohms. This is your (R1+R2) value, and when added to the Ze is your ZS. Its very unlikely this will be recorded on your schedule of test results, as the highest Zs value should be a the switched live conductor on the last light in the circuit.

If you measure Zs at the switch, you are (in theory) contravening the Electricity at Work Regulations

DanBrown · Feb 3, 2008

In response to your anwer ian.
What do you actually mean by saying put neutral to earth to make the tester work.
Thanks anyway

EasyFox · Feb 3, 2008

He means put the meters blue & green leads to the cpc at the light switch.
But why do the Zs at a switch?

TonyM58 · Feb 3, 2008

I agree with Easyfox

i would just confirm R2 at the light switch, and do my Zs at the ceiling rose (calaculated from the (R1+R2) value

Dan, i use a Megger. If we are on 'no trip loop' we use three leads, and normal earth fault loop is two leads (which connect to line and cpc). Cant recall how the Fluke carries out the Zs or Ze test, but do you have a two or three lead option? it wont be called 'no trip loop' but somenthing similar

DanBrown · Feb 4, 2008

Hi Guys,
Thanks for all your responses, The only reason i asked about testing at a light switch is to double check and make sure that the maximum Zs i recorded was actually the maximum Zs, seem s a bit stupid on my behalf but im kinda new to testing my work off. I am aware that with the theory and the actual Zs should be at the furthest part of the circuit as this has the highest resistance reading. Just wanted to 100% check and make sure my reading's were correct.

In response to you previous question tony, the tester uses 3 wire only, and it has ''non trip'', when you dis-connect the neutral lead from the tester it says ''lead''. You must be right in saying put neutral + earth leads onto earth terminal and live to live. I'll give it a try....

Thanks Guys

alan · Feb 4, 2008

All the leads in rotary sw to Z Tester should be on L-PE

At light put green crock to earth, blue to neutral and then red to phase.

TonyM58 · Feb 4, 2008

Alan,

but that was his original problem, he's at a light switch so doesnt have a neutral!!!!

alan · Feb 4, 2008

He tests at the light fitting, if there no neutral there ,patient the idea

Martin · Feb 5, 2008

For loop testing with the Fluke, choosing L-PE will do a low current "no trip" 3 wire test. Choosing L-P will do a high current 2 wire test. For this connect the L probe to live and N to earth. Remember that the 2 wire test will trip any RCDs.

TonyM58 · Feb 5, 2008

so the Fluke IS the same as the Megger

thought it would be

also think that two lead test will be virtually redundant under the 17th, all except PFC's at the CU

alex · Feb 8, 2008

ian.settle1 said:
The neutral is to allow the meter to work. So why not connect the neutral to earth to allow meter to work?

couldnt agree more.

Malcg · Apr 18, 2008

Hi
R1+R2 is only available at light drop / ceiling rose (also much easier to do).

Switch off main switch. Temp short MCB live to earth. at furthest rose, test using two leads (as L & E available).

Record result and remove temp link.

As shown on page 217/218 NICEIC Inspection, Testing, Certification and Reporting.

Hi

Also if you want to include switch drop, still test at ceiling rose with light switch on. Use Switch live, Neutral and earth. Then you get longest path of Live.

Shakey · Apr 19, 2008

Malcg said:
Hi
R1+R2 is only available at light drop / ceiling rose (also much easier to do).

Switch off main switch. Temp short MCB live to earth. at furthest rose, test using two or three leads (as L, N & E available).

Record result and remove temp link.

As shown on page 217/218 NICEIC Inspection, Testing, Certification and Reporting.

Hi

Also if you want to include switch drop, still test at ceiling rose with light switch on. Use Switch live, Neutral and earth. Then you get longest path of Live.

Malc,

how/why would you use three leads to test R1+R2

Malcg · May 5, 2008

modified

ian.settle1 · May 5, 2008

Shakey said:
Malc,

how/why would you use three leads to test R1+R2

Because some meters require L + N for meter to work

Shakey · May 6, 2008

ian.settle1 said:
Because some meters require L + N for meter to work

Not testing R1+R2 they dont, you are talking about Zs surely?

ian.settle1 · May 6, 2008

Shakey said:
Not testing R1+R2 they dont, you are talking about Zs surely?

Depends if your using a Megger (can't remember the model) as when you take the Ze reading and record it in the meter then when you take Zs at end of circuit it will calculate the R1+R2 for you when downloaded into computer.

Shakey · May 6, 2008

hmmmm, dont really like that Ian

R1+R2 is a resistance reading (as you know)

i.e dead

Zs and Ze are impedence (live) (yes, egg sucking and all that

)

We know that Zs = Ze + (R1 +R2) but adding R1+R2 to Ze does not automatically give the the same result as Zs (for many reasons which I know I dont need to explain to you!)

so taking Ze from Zs will not give an accurate R1+R2 either

Personally I would never do this, as Zs is the least preferable of the readings (due to the EAWR's)

Interesting that Megger use it though! Everyday is a school day......

my point was of course that you never MEASURE R1+R2 using three leads, what you saying is that you would measure Zs, and the meter would kick out an R1+R2 from it......... got a meeting with Megger soon, I will discuss it with them!

ian.settle1 · May 6, 2008

Shakey

It was a Megger LCB2500/2 meter but never used it that way. Took Ze & Zs readings as normal along with R1+R2 by continuity meter.

Shakey · May 7, 2008

ian.settle1 said:
Shakey

It was a Megger LCB2500/2 meter but never used it that way. Took Ze & Zs readings as normal along with R1+R2 by continuity meter.

Glad to hear it Ian, I would expect nothing less from you

good example to throw into my students though....

cheers

alancp · Jun 9, 2008

stop me if i am wrong but the certs ask for the MAX efli for that circuit, so if we have a pendant (end of line) at the top of stairs, and is 2 way switched, then obviously the max reading would be at the remote switch.

Shakey · Jun 10, 2008

alancp said:
stop me if i am wrong but the certs ask for the MAX efli for that circuit, so if we have a pendant (end of line) at the top of stairs, and is 2 way switched, then obviously the max reading would be at the remote switch.

if its done 3 plating at the pendant, then thats where the max Zs would be

johnosman · Jun 21, 2008

I would love to know what the megger rep says as some of the sparks I work with have been told that that particular test instrument does give you an r1+r2 reading. I have never used this reading myself as you are never asked to submit a ze reading that the machine can deduct the zs from ze to give you r1+r2 so as far as I can see it would be impossable for a tester to give a reading even if it was just deducting ze from zs. I probably have'nt explained it very well but according to the rep just by doing a test for zs the tester will give an r1+r2 just by doing this one test and nothing else.