Discuss High PFC in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Andy,

Ohms Law.

I=V/R

Thanks for the lesson in electrical theory guys but as I said in an earlier post I got the pfc across live & neutral and I have not posted the live neutral loop reading.
I think I will have to use cartridge fuses and not mcbs.
 
My 11Ka came from my tester, I will go back tomorrow and do a line neutral test.
The pfc is definately 11Ka, my meter is calibrated and the reading is correct.
My op was about how to overcome this, and as I said in an earlier post it probably just needs a cartridge fuse.
 
My 11Ka came from my tester, I will go back tomorrow and do a line neutral test.
The pfc is definately 11Ka, my meter is calibrated and the reading is correct.
My op was about how to overcome this, and as I said in an earlier post it probably just needs a cartridge fuse.

It doesnt matter, as you record the highest of the 2 anyway. I would hope the PSCC is not higher!

All we are saying is that, by calculation, the reading you are getting from your meter seems remarkably high, which is very concerning.

Let us know how you get on tomorrow!
 
It doesnt matter, as you record the highest of the 2 anyway. I would hope the PSCC is not higher!

All we are saying is that, by calculation, the reading you are getting from your meter seems remarkably high, which is very concerning.

Let us know how you get on tomorrow!

11Ka is my pscc, across line & neutral. As I've been saying all allong.
 
Fair enough.

Im sure i have read somewhere that its ok to have a higher PFC than the breaking capacity of the CPD.

Reg 434.5.1.
 
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Yes I read that.

The first paragraph tells you that the rated short circuit breaking capacity of each device shall not be less than the maximum pfc at the point at which the device is installed. Easy.

The second paragraph then goes on to say that a lower breaking capacity is permited if another protective device having the necessary rated short circuit breaking capacity is installed on the supply side.

I'm not sure I understand this, if it means that a bs88 main fuse with a breaking capacity of 80Ka makes it ok, then there is never any need to worry about pfc. Or have I misunderstood the paragraph?

Had a quick look today, the L-N loop is .02 ohms, the supply voltage is 250v (another issue)

Looking in the osg page 56, the final paragraph seems to say that consumer units complying with BS EN 60439-3 are ok for fault currents up to 16Ka.
 
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Why can't a BS88 switch fuse be installed before the consumer unit in this case?
Its breaking capacity of around 80kA will safely clear any fault, as a backup to the MCB's.
 
The house is close to the sub station,
The Ze was what made me do a pfc test because it is a t-n-s supply and the earth is just a bit of 10mm connected to a clamp on the lead sheath, (I think the last electrician fitted this, it's not right but i'm not going to touch it)
I did the pfc test across live & neutral.

Hold on you said you did a PFC between Live and Neutral??? PFC is between Live and Earth You have measured a PSC which will be different on a TN S system. try it again on between Phase and Earth
 
Hold on you said you did a PFC between Live and Neutral??? PFC is between Live and Earth You have measured a PSC which will be different on a TN S system. try it again on between Phase and Earth

Hang on chaps, we seem to be suffering from a difference in terminology.

PSCC = L-N fault current measurement
PEFC - L-E fault current measurement
PFC - is the highest of the two above readings noted on the test cert.
 
Lenny i just remember it as

PSC Prospectice shortcircuit current L-N
PFC Prospective Fault Current L-E

never used PESC

but agreed biggest on sheet.
 
Hold on you said you did a PFC between Live and Neutral??? PFC is between Live and Earth You have measured a PSC which will be different on a TN S system. try it again on between Phase and Earth

The maxium prospective fault current is the current that would flow in the event of a fault either between live & earth (maxium prospective earth fault currrent) or between live conductors (maximum prospective short circuit current), whichever is the greater.
 
Had a quick look today, the L-N loop is .02 ohms, the supply voltage is 250v (another issue)

Andy,

You will measure 250v as this is the open circuit voltage across the sub-station windings esp as it sounds like you are sitting on the transformer! lol
It may be worth phoning the manufacturer of the CU; if they build to BSEN 60439-3 then this makes allowance up to 16k using 10k mcb's ~ speak to their tech dept. Remember IEE regs defer to manufacturers instructions.

I hope this is useful ;0)
Gaz.
 

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