PEFC & PSCC

[Mr T]

Evening All

Can someone pls clarify the test procedures for the above tests as I have witnessed various methods of obtaining this result and some very high readings logged on test sheets..

test kit is a megger 1552 , my understanding and testing method is

PEFC , 1 probe on L1 and 1 to earth , repeat with l2 to earth and L3 to earth and record the highest as your PEFC reading.

PSCC , 1 probe to L1 and 1 to Neutral , repeat with L2 to N and L3 to N and double the highest reading , whichever is the highest out of the PEFC and the PSCC is recorded as your result..

I have known people to double the PEFC but surely you only double the PSCC ???

What are your thoughts and methods ?

 

[jakecameron]

Yes on 3 phase double ur highest result. Test methods are correct

 

[Steve3948]

Or you could use a meter that does test phase to phase with no need to double.

Earth disconnected yes/no ?

 

[markyspark76]

+1

Your merger will test phase to phase safely

 

[NozSpark]

No need to double with the Megger 15xx MFT,,, just test across the phases

 

[apprentice87]

Hi There,

You are exactly right.. But if you are on about testing at the origin of an installation, as in testing Ze, you will have to isolate the installation completely, as you will have to disconnect the earthing conductor to remove the effect of parallel earth paths caused by bonding to extraneous parts, as you are trying to obtain a figure entirely EXTERNAL to the installation. This is why you are supposed to connect the earth conductor to the MET via a bolted link to make it easy to do this.

Anywhere else, i would leave the earthing and bonding arrangements exactly as they are, as you need to know what PEFC will be under actual fault conditions, when the earthing and bonding will obviously be connected. [not forgetting that it is perfectly possible for Zs to be LOWER than ZE] and hence PEFC will be higher...

Also

"I have known people to double the PEFC but surely you only double the PSCC ???"

Exactly....

But most meters will just do a phase to phase reading anyway. [Or at least mine will!!]

john...

 

[NozSpark]

And definately leave the earth connected

 

[Mr T]

I mentioned that to the lads at work and there words were ok try it , they basically believe the test kit will blow up if you tried it....so testing between phases then 1 probe to L1 and 1 to L2 then 1 probe to L1 and other to L3 , L2 to L3 ???? The lads seem to think this would be the same as going between phases i.e shorting out two phases and blowing a main fuse ???

 

[NozSpark]

I've got a 1502 and you can definately do PSSC between the phases, I couldn't vouch for the yellow MFTs though

 

[Mr T]

in this situation we have a mains room with parallel feeds to a number of section boards , from the section board we have a breaker feeding a DB , testing at the DB

 

[batty]

Don't do 400 volt tests with a Fluke they don't like it.

 

[PC Electrics]

I've got a 1502 and you can definately do PSSC between the phases, I couldn't vouch for the yellow MFTs though

I have a 1552 and have used it to test phase to phase. It's part of the meters spec that it is capable of this testing.

Surely they all ought to be?

 

[kme]

Don't do 400 volt tests with a Fluke they don't like it.

Depending on who you talk to (including Megger Mark ) , the Fluke either CAN, or CAN`T do phase-phase.

I have done, successfully, in the past, with a 1652. But I am reliably informed that it is the most stressful test you can do, and may not do the meter much good.

 

[batty]

They do have a strike through is it at 500 or 550 volts on the case maybe they are OK up to that voltage.

 

[apprentice87]

Hi All,

I got a Megger 1730, you can definitely do phase to phase with that..

Megger's own words.......[from the manual]

Overview of the LOOP IMPEDANCE test.

The MFT has two primary loop test options;

(a) Phase to Earth test mode

(B) Phase to Neutral (Phase to Phase) test mode.

When the rotary knob is changed from L-E to L-N (L-L) the tester automatically switches the test between the Phase/Earth terminals and the Phase/Neutral (Phase/Phase) on the instrument.

In addition, the test current changes from a non-trip test between L-E to a high current test between L-N (L-L).

Consequently there is significantly less risk of accidently testing a Phase-Earth circuit with a high test current and tripping the RCD.

(a) Phase to Earth testing:

The Phase to Earth test mode uses a non-tripping loop test. This will not trip RCDs.

(B) Phase to Neutral (and Phase to Phase) testing:

The Phase to Neutral (and Phase to Phase) test uses a higher current test. This is a more accurate test and should always be used in preference to the non-trip test where there is no risk of tripping RCDs.

Note: RCDs can still trip when performing a