PFC and PSC

[councillor]

Im a little confused as to what to record for Ze and PFC on a test form:

Its not that Im an idiot or anything its just what is meant to be recorded that gets me so here goes:

When measuring a Ze at origin Im using the meter set to L-PE (3 wire) and I record the result as my Ze value, the meter also displays the PFC value. But of course the PSC L-N should also be tested and the higher of PFC or PSC should be recorded on the test sheet right even though the test sheed says PFC?

Can you confirm that this is the correct procedure.

 

[oharaf]

Ze is the external loop impedance. This is tested by removing the main earth from the earth bar of the CU and connecting phase, neutral and the earth appropriately.

Select EFLI (non trip)

Your Meter will give a reading in Ohms.

The forms I use require only PFC to be measured. Replace the earth, change your meter to PFC and test as before, you are quite correct you should test for PSC also.

I was also taught to record the higher result

 

[bongos]

Ze - with the protective bonding removed (L/PE).

PEFC - is the L/PE reading with the protective bonding in place.

PSCC - is the L/N reading.

PFC is the higher of PEFC and PSCC (nearly always the PSCC figure).

They are all three wire methods on my tester, I just switch between LOOP L-N and LOOP L-E.

Hope that helps...

 

[councillor]

so what do you put in the PFC box?

The actual PFC or the PSC if higher,

its seems barmy that the forms say PFC but when taught all the litrature says put the higher in the box

 

[bongos]

Did you read my post?

PFC is the higher of PEFC or PSCC.

You record the higher of the two readings.

 

[councillor]

Bongos

Yes mate I read your post I was replying to oharaf then read your post just after , Thanks very much for the clarification

 

[Taylortwocities]

Select EFLI (non trip)

Why? Does the DNO have an RCD between the cable head and the transformer?

 

[STI]

b*gger slow typing again. I withdrawer my original clarification.

 

[ericmark]

I look at why we measure ELI and PFC.
For ELI we measure to ensure the MCB/RCD will open and so measured to earth.
For PFC we measure to insure the MCB/RCD is able to handle the current so highest reading which should be lower than the marking on the MCB/RCD or let through value of other protective device. (Fuse)

I do remember going to work for one firm and getting some high readings for the PFC and as a result looking back to see previous results all were high and it seemed person before me had taken readings but done nothing about them and I had to retro fit fuses to circuit to comply with regulations.

I do sometimes wonder how many people work out the results after testing? In some cases I can see the electrician will send result to his firm and expect the firm to write the report when passing on to the client. But often it seems this does not happen.

 

[STI]

ericmark,

So just to confirm if in a domestic situation with type B mcb's marked at 6k,the PFC comes in at 6.1k this is a problem. Its the CU breaker you compare to not the DNO breaker/fuse at 33k.

 

[bongos]

ericmark,

So just to confirm if in a domestic situation with type B mcb's marked at 6k,the PFC comes in at 6.1k this is a problem. Its the CU breaker you compare to not the DNO breaker/fuse at 33k.

If you measure the PFC across the main switch in a CU at 6.1kA and they're M6 breakers then i guess it could be a problem?

 

[flameport]

If you measure the PFC across the main switch in a CU at 6.1kA and they're M6 breakers then i guess it could be a problem?

No.
A fault at or before the main switch won't result in any current flow through individual circuit breakers.
After the breakers, the fault current will be lower, due to the added impedance of the circuit cables.

Even if still too high for the individual breakers, assembled consumer units are rated for fault levels of up to 16kA, provided a suitable fuse is installed before it (the DNO fuse in most cases).

Further, a PFC exceeding 6kA on a domestic single phase supply is somewhat unlikely.

 

[STI]

Thanks Flameport i thought i had read somewhere that its the DNO fuse that prevents this being a problem.

But if the reading was lets say 6.1Ka what would need to be done.

 

[dingbat]

Thanks Flameport i thought i had read somewhere that its the DNO fuse that prevents this being a problem.

But if the reading was lets say 6.1Ka what would need to be done.

Read regulation 536.1, paragraph 3 and related reg 434.5.1.

The IEE say that if the main fuse is a BS 1361 cartridge fuse, then you can consider your circuit overcurrent devices to okay up to 16kA. (Mad, isn't it?)

 

[STI]

i just tried the formula too. I need a drink