PFC test

superspark · Sep 2, 2009

Hi.

When you said mcb tripped, did you actually mean it physically tripped or the word " trip " came up on the screen, I just brought a 1552, having some teething problems, if you do not have a good connection during the " test time " it will come up trip, try again using clips or a better physical connection.

Andywyatt · Sep 12, 2009

iceman said:
i just know when i go for me assesment the guys gona ask me y we test for pfc and ze do all the breakers have to fall with in the pfc value???

would i record 3500Ka on both parts of the eic cert???

The breaking capacity of the MCB has to be greater than the PFC of the installation.
Yes you record your pfc and Ze of forms
Andy

zupos40 · Sep 12, 2009

Andywyatt said:
The breaking capacity of the MCB has to be greater than the PFC of the installation.
Yes you record your pfc and Ze of forms
Andy

Hope you do not mind but your statement is only partially correct.

With reference too G.N.3 if the Consumer unit complies with BS 5486-13 or BS EN 60439-3 and the consumer unit is supplied through a type 2 fuse to BS 1361:1971 rated at no more than 100A. It also states that the current rating of the devices do not exceed 50A.

I investigated the above statement and found that all CCU to BS EN 60439-3 are type tested using 16kA fault current, also main switch is tested as well, both closing and opening underfault whether C.B are 3kA 6kA or 10kA.

With reference to the BS1361 type II 100A cartridge fuse that it 'let through energy' (thermal energy that could cause damage to the cable insulation) which is 27,000 A2 S ( 2 represents squared) is less than the let through energy that 6kA mcb can withstand which is 29,700 A2 S, so the fuse will melt before damage can occur to Circuit Breakers thus complying with Reg. 434.5.1

So as long as K2S2 (2 representing squared) of the smallest conductor feed from the C.B. must be greater or equal to I2t (A2s) of the C.B. Reg 434.5.2

See page 76, 77 BS7671:2008.

mikeymoo · Sep 12, 2009

If your using the probes to do the zs test, then use the croc clips instead. The smallest of movements whilst doing this test with the megger will display trip. If its rcd protected. use all 3 leads and plug red cable into no trip port on the side.

ian.settle1 · Sep 13, 2009

solavie said:
I have just changed the consumer unit and was doing all the nornal test. I thought that I had to do a PFC test to check the MCB capacity to withstand. I am fairly new in this field.

My Other problem was the ze where I keep getting trip on my MFT 1552. I can work it out but would really know why the meter trip. I was using the 3 test lead and setting the meter on no trip as suggested by the instruction.

Cheers.

The MCB will tell you what short circuit current it will take no need to test it.

This is why before designing a installation you need to know the Ze and thus the PFC so as to make sure the correct MCBs or other protecive devices are fitted as if you fit 6KA MCBs and the PFC can be greater then if the MCB trips it may be damaged and need replacing.