Ze - zs = r1 + r2?

[telectrix]

you can bypass the RCD to do a high current loop test. richard burns posted an excellent diagram of how to do it a couple of weeks ago.

 

[Pete999]

Hi I'm new here, I'm a second year apprentice.

When we do domestic testing such as a eicr my boss says that he can 'work out' R1 + R2 by taking the ZE from the ZS however i don't think this is correct as everyone would just do it?? I just wanted to confirm that this isn't correct as i do need to learn the correct way to test new installations for the future and for my college exams.

THANKS

No mate your boss is talking out of his back passage, unfortunately some unscrupulous practitioners of our beloved trade, think they are called cowboys, do this, sad really

 

[dcwuk]

Sorry to drag this up again and I always measure R1+R2 but why do some testers like the MFT1730 have the facility to measure R1+R2 using Ze as a reference. Or have I had a bit of a mental block?

 

[TJ Anderson]

Sorry to drag this up again and I always measure R1+R2 but why do some testers like the MFT1730 have the facility to measure R1+R2 using Ze as a reference. Or have I had a bit of a mental block?

I have a 1720 myself. I know there are sparks who do calc Zs (Zs-Ze=R1&R2), but it can potentially be very inaccurate when you take into account parallel earth paths. The megger is basically doing this for you and it encourages the bad practice.

 

[dcwuk]

I have a 1720 myself. I know there are sparks who do calc Zs (Zs-Ze=R1&R2), but it can potentially be very inaccurate when you take into account parallel earth paths. The megger is basically doing this for you and it encourages the bad practice.

Indeed so why do the manufactures include this facility ?
Surely there is some consultation between the manufacturer and the relevant bodies at the design stage.

 

[TJ Anderson]

They do it cause some people want it and it is an extra feature that other testers don't have.

 

[DuaneMHunt1976]

Zs

Ze + R1 + R2

dont know why they bother with breckets () dosnt do any thing for it
not keen on using = symbol as it is not pure

 

[dcwuk]

They do it cause some people want it and it is an extra feature that other testers don't have.

So at the end of the day even though its bad practice its still acceptable to the powers that be?

 

[TJ Anderson]

So at the end of the day even though its bad practice its still acceptable to the powers that be?

No not really, if you had a gun you dont have to shoot someone with it. At the end of the day, as a qualified electrician, you can put whatever you deem fit in the R1 + R2 box, it is only a model form taken from non statutory regulation.

 

[dcwuk]

Thanks for your replies, I'm in a protracted discussion about this subject and the people involved are using the fact that the meter
has the facility makes it acceptable practice. I disagree for all the reasons given in this thread.

 

[HappyHippyDad]

Thanks for your replies, I'm in a protracted discussion about this subject and the people involved are using the fact that the meter
has the facility makes it acceptable practice. I disagree for all the reasons given in this thread.

I measured a Ze on a TT the other day and it was 197Ω, Zs on the ring was 73Ω so by using Ze - Zs = R1 + R2 I get an R1 + R2 of -124Ω that's a damn fine conductor!

I can't see how it could ever be acceptable to calculate R1+R2 this way.

 

[hightower]

I measured a Ze on a TT the other day and it was 197Ω, Zs on the ring was 73Ω so by using Ze - Zs = R1 + R2 I get an R1 + R2 of -124Ω that's a damn fine conductor!

I can't see how it could ever be acceptable to calculate R1+R2 this way.

Is the title in this thread wrong? Shouldn't this (unacceptable) practice be Zs - Ze = R1 + R2

 

[telectrix]

Is the title in this thread wrong? Shouldn't this (unacceptable) practice be Zs - Ze = R1 + R2

well spotted, hawkeye.

 

[hightower]

well spotted, hawkeye.

YES! I FEEL LIKE A GOD! Pfft, all you puny humans replying to an equation that doesn't even make sense. I pity you all.

(DISCLAIMER: For those that don't know me too well, yes, this is obviously said in massive jest. I am not obnoxious enough to class myself as a God. If you forced my hand, I would say demi-God at best.)

 

[LeeH]

I have a 1720 myself. I know there are sparks who do calc Zs (Zs-Ze=R1&R2), but it can potentially be very inaccurate when you take into account parallel earth paths. The megger is basically doing this for you and it encourages the bad practice.

Do you disconnect all the parallel paths when measuring then??

Bad practice my arse.