High PFC

[Spudnik]

Andy,

Your PFC does sound very high indeed and calculation gives nearer 6ka.

Would your meter be giving a false reading?

I dont think there are any MCB's rated over 10ka, unless there may be some specialised manufacturers.

 

[Guest123]

I know of no MCB above 10KA. Do you have a Fluke multifunction tester?? I've heard on the grapevine that these particular testers do have issues with fault current measurements.

 

[andyb]

Andy,

Your PFC does sound very high indeed and calculation gives nearer 6ka.

Would your meter be giving a false reading?

I dont think there are any MCB's rated over 10ka, unless there may be some specialised manufacturers.

Jason, what calculation have you used to get 6K?

 

[Spudnik]

Andy,

Ohms Law.

I=V/R

 

[Guest123]

230/0.04 = 5750.

 

[andyb]

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.

 

[Guest123]

Well where does your 11KA come from then???

 

[andyb]

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.

 

[Spudnik]

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!

 

[andyb]

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.

 

[Spudnik]

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.

 

[Guest123]

Hey Mark, I was trying to find the reg for you - 434.5.1, P76, I believe is the one.

Same as me then.

 

[andyb]

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.

 

[kkc35348]

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.

 

[scotsparky]

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