pfc testing

[james king]

hi all,

i have carryed out a pfc test at collage! i am confused about useing the 2 or 3 wire test. i have read that u put the megger on pfc high and test between L incomer and E with all earthing connected. but i spoke to another spark last night who said u need a 3 lead test to test between L,E and N ???

also while testing the megger came up with trip even though there is not a rcd

 

[Guest123]

The megger is a 3 lead test instrument when it comes to testing Ze, Zs & PFC.

 

[james king]

ok thnsks, can u please explains why i get the same reading with 2 lead or 3 lead test?

and does it only matter how many leads u use by what meter you are using?

 

[BlueToBits]

The more leads you have, the better the collage.

Ipsc is the prospective short circuit current and the highest theoretical value must be entered to ensure that protective device can break a current of this magnitude safely.

The fault current could be

• Phase to Neutral,
• Phase to Earth
• Phase to Phase for 3 phase supplies

The test should be carried out for all these, however most testers cannot cope with a 400V test voltage. It is therefore permitted to double the P-N result and use that as the Ipsc result for TPN supplies. The highest value of the three should be entered as this is the maximum current that could, in worst case scenario, flow.

A 3 lead tester may have a different range for P-E and P-N. If it only has one range, swap the earth and neutral leads to get the other result. You may have to calculate Ipsc from the "Zs" reading if there is no Ipsc range.

A 2 lead tester is easy, test P-N (double it for TPN supplies) and P-E and enter the highest value.

It should be established that earth continuity exists before carrying out P-E tests. Most modern testers have a way of warning you if this is not the case.

 

[BlueToBits]

Sorry, typing lag.
You will very likely get the same result for a TNCS supply because the E & N are bonded at the cut-out. You may get the same for a TNS, but very unlikely to get the same fo a TT

 

[telectrix]

megger testers wil show trip if there is a poor connection on any of the eads. mine did it ast week and it was a fuse in the neutral lead blown.

 

[james king]

a poor connection on the ends?

so am i corrent in saying PFC test is

L=red lead
N= black lead
E= green leed

and then take the resualt down in Ka?

 

[Guest123]

a poor connection on the ends?

so am i corrent in saying PFC test is

L=red lead
N= black lead
E= green leed

and then take the resualt down in Ka?

The test you describe there is the PEFC (Prospective Earth Fault Current)

You also need to measure PSCC (Prospective Short Circuit Current) measured between L&N (Red lead on Line, Black+Green leads on Neutral)

The highest of these two readings is then recorded as the PFC for the installation.

 

[james king]

sorry lenny u r confusing me u told me in your 1st post that its a 3 lead test. can u plz describe all 3 test to me? with pscc you put BOTH probes on the N? so you always use 3leads on those tests?

 

[Amp David]

Meggers use 2 leads when set to high loop test, 3 when doing no trip.

 

[Guest123]

Sorry, on the 'high' loop setting you can use the 2 leads for measuring the PFC, Red on line & Green on CPC for PEFC. Red on line & Green on Neutral for PSCC.

The highest of these two is recorded as the PFC.

 

[BlueToBits]

I don't know your particular meter and how, or if it displays Ipsc, so I can only say that this is not necessarily the case.
Your question suggests that you may be a little bit short of the level of experience or understanding to take this on your own without risking damage to your meter, your installation or most importantly, yourself. This is a live test and one of the potentially most dangerous at that. Most here will always try to help others where they can, and most would agree that live testing is not something you can learn to do over a forum like this. You really need someone to properly show you how to do it, how to interpret the results, and what precautions you need to take.

 

[BlueToBits]

Sorry. Typing lag and interuption again!

 

[james king]

sorry so u say

Red on line & Green on CPC = PEFC
red on line & green on N = PSSC

so there is no test for pfc?

 

[hillbillie]

The highest figure obtained for your PEFC and PSCC tests is the PFC, write that on the forms.