Zs test at a light switch.

[s1m0n]

Hi,
Just started 2330 level 3, and on practical assignments,
at the stage on a test rig, one circuit is for lighting.
there is only a Light switch to test at for Zs.

I just lloking for comfirmation that I can (using a 3 lead tester) put the Red lead to the Phase with the switch in the closed position and put the black and green lead on the CPC connection,as there will not be a neutral available.

I read some where that this cant be done if the circuit is protected by an RCD.

Any views Welcome.

 

[ian.settle1]

Hi,
Just started 2330 level 3, and on practical assignments,
at the stage on a test rig, one circuit is for lighting.
there is only a Light switch to test at for Zs.

I just lloking for comfirmation that I can (using a 3 lead tester) put the Red lead to the Phase with the switch in the closed position and put the black and green lead on the CPC connection,as there will not be a neutral available.

I read some where that this cant be done if the circuit is protected by an RCD.

Any views Welcome.

Why would you want to do a Zs at the light switch because the futhest point away from the DB would be the light fitting after the light switch.

As to the part about tripping the RCD you would need a meter that has a setting which will not trip RCD such as D-LOK on robin meters.

 

[Shakey]

which meter are you using?

I use Meggers, they have two lead (hi-loop) measurements or three lead (no-trip loop for RCD protected circuits)

To be honest i have never tried connecting both black and green to Earth on a three lead measurement, but it wouldnt surprise me if this did trip the RCD - are you not able to do a two lead measurement, or is the lighting circuit RCD protected?

But anyway, (As Ian said) Zs should never be at a light switch, the furthest electrical point has to be the switched line and CPC at the luminaire.

 

[hodgey1972]

yep,you can piggy back,green and black test lead,but you shouldnt need to,just use the green,you are also testing,that the earth in the switch is connected to the circuit,and you can also verify weather common is in correct terminal at switch,a earth loop impedance test should be carried out at every point within a circuit,testing at what you think is the furthest point,can lead to problems,especially if your registered with a relevant organisational body,and are showing them how you test

 

[s1m0n]

Thanks, guys, gives me some food for thought,
I would test at the cieling rose myself, it is just on this test board there is only the Light switch.

Our lecturer likes to make us think !!

 

[greekislandlover]

You can always do the Zs by measuring R1 and R2 and adding that to Ze on radial circuits provided there are no socket outlets. That would be acceptable for the purpose of the test rig exam I think.

 

[ian.settle1]

You can always do the Zs by measuring R1 and R2 and adding that to Ze on radial circuits provided there are no socket outlets. That would be acceptable for the purpose of the test rig exam I think.

That would technically not be testing when you do the practical exam would it?

 

[jibspark]

maybe they are trying to get you to fill in the limitations box on the test sheet?

 

[ian.settle1]

maybe they are trying to get you to fill in the limitations box on the test sheet?

Maybe but also to see if you know how to use the meters and are testing correctly before they give you the qualification.