testing 3 phase

[Ross Trician]

Afternoon all.

Can someone please tell me, when testing a 3 phase dis board for the Ze, PFC etc do you have to squarre route the reading or something, can't remeber what it is you do to it and can't find my testing book at mo, think i have lent it someone. ( can;t think who to and no doubt they wont return it)

thanx, Ross.

 

[acat]

Measure the pscc between each phase and neutral then double the largest reading.






Chris

 

[Jurasic Spark]

Afternoon all.

Can someone please tell me, when testing a 3 phase dis board for the Ze, PFC etc do you have to squarre route the reading or something, thanx, Ross.

Ze, same as a single phase board but you have 2 extra line conductors. Therefore you do each 1 individually and the higher 1 of the 3 is your Ze.

PFC, measure Pefc of the 3 individual lines to earth and the higher 1 is your Pefc.
Measure the 3 lines individually to N and the higher 1 is your single phase Pscfc. On a 3p DB the Pscfc between 2 lines will be higher than between 1 line and N. Some meters dont like 400v up 'em so this can be calculated by multiplying the highest L to N value by the sq root of 3. GN3 allows x2 as a rule of thumb which also errs on the side of caution.
The highest value is recorded as Pfc for the installation which will be the higher 1 between any 2 lines.

 

[johnnyb]

The highest value is the recorded one either it be L1/L2/L3 to E or L1/L2/L3 to N the highest is the recorded one you enter mate.

 

[Jurasic Spark]

The highest value is the recorded one either it be L1/L2/L3 to E or L1/L2/L3 to N the highest is the recorded one you enter mate.

The highest level of PFC won't be any of the ones you've mentioned.
It will be between any 2 lines which can be calculated as I said above or measured if your meter is safe to do so.

 

[johnnyb]

You don,t measure the pfc between 2 lines my mate its the highest value whether it be L to E or L to N thats it

 

[trix]

You don,t measure the pfc between 2 lines my mate its the highest value whether it be L to E or L to N thats it

PFC will be higher as stated between the phases rather than between any phase to earth or any phase to neutral. You could measure via tha latter method, then use rule of thumb and multiply by Two.

Or even better, get a decent meter, Meggar 1550's are brill.

PEFC is the potential between any phase to earth, it is different to PFC, and has been covererd ....

 

[D80]

PFC will be higher as stated between the phases rather than between any phase to earth or any phase to neutral. You could measure via tha latter method, then use rule of thumb and multiply by Two.

Or even better, get a decent meter, Meggar 1550's are brill.

PEFC is the potential between any phase to earth, it is different to PFC, and has been covererd ....

So the Megger 1550's actually can do the PFC between phases?

I was told they couldn't so have been using rule of thumb throughout

 

[Steve D]

It's always worth checking your instructions to see whether your meter can cope with 400V. Unfortunately mine can't.

If in doubt, don't. Just test between each line and N - then double the highest reading it to get your approx reading for 3ph PSSC.

(I actually read in a Scadden book that really you should be multiplying by 1.732, but after querying with a tutor at college this is wrong and you should be doubling it. A mistake in a Scadden book - who'd have thought it )

 

[Jurasic Spark]

You don,t measure the pfc between 2 lines my mate its the highest value whether it be L to E or L to N thats it

Ok my mate Johnny you do it the way you see fit.
But if you get a short between any of the 2 lines the amount of current will be much higher than L-E or L-N. And the OCPD must be able to safely clear the highest possible amount of PFC.

(I actually read in a Scadden book that really you should be multiplying by 1.732, but after querying with a tutor at college this is wrong and you should be doubling it. A mistake in a Scadden book - who'd have thought it )

Steve, I think Scadden is correct as the voltage between 2 Lines is 1.732 x greater than betwwen 1 Line to N:

VL = VP x 1.732

(1.732 is the sq root of 3 as I touched on in an earlier post. GN3 p52 allows 2x as a rule of thumb as it easier to remember and errs on the side of caution)

 

[Guest123]

Steve, I think Scadden is correct as the voltage between 2 Lines is 1.732 x greater than betwwen 1 Line to N:

VL = VP x 1.732

(1.732 is the sq root of 3 as I touched on in an earlier post.

Agreed.

 

[Ross Trician]

cheers for all your info, thanx