pscc

[fog]

Hi can you refresh my memory!
I am downstream from an RCD, trying to obtain PSCC do not wish to use meter as will trip RCD, can someone remind me of the calculation to obtain PSCC, to complete PFC.
230v, 45.9 ohms on TT stake.
Many thanks

 

[Sintra]

No point using the 45.9 ohm value from the rod. What you need to do is carry out a loop test between L & N which would be a lot lower. Then use this figure to work out the PFC.

 

[fog]

No point using the 45.9 ohm value from the rod. What you need to do is carry out a loop test between L & N which would be a lot lower. Then use this figure to work out the PFC.

Hi yes, the problem i have is i do not wish to knock out the RCD which is upstream of the sub board, would it be possible to calculate, the RCD is in main house which i dont have access to, and even if i did surely this test would not be possible as the RCD would trip out?

 

[telectrix]

dead test R1+Rn. then PSCC= 230V/( R1+Rn).

 

[fog]

Yes many thanks that makes sense, will use that method. Thankyou telectrix

 

[Octopus]

Can't you use the no trip setting?

 

[telectrix]

with most MFTs, the no-trip is 3 lead test and gives you the pefc. seems OP wants pscc, so that should be do-able using 2 leads. the RCD should not react as you are not connecting to E.

 

[Sintra]

dead test R1+Rn. then PSCC= 230V/( R1+Rn).

Yes many thanks that makes sense, will use that method. Thankyou telectrix

Surely to do this you still need access to the RCD to isolate.

 

[telectrix]

i'd trip it with MFT and let the silly arse that stopped access worry about resetting it.

 

[fog]

Surely to do this you still need access to the RCD to isolate.

hi have access to the fused connection unit, that the supply comes from in utility room, but the lovely.... householder would not allow access into main house, must of thought i was an electrician who is also a burglar ho ho, we cant choose are customers, well we have a bit of lee-way. all done now using R1 + Rn method
230/(R1+Rn)
Thanks for all the help

 

[SirKit Breaker]

OHMS law

 

[Geordie Spark]

OHMS law

Something to do with George Lazenby (remember him?) in the starring role wasn't it???

 

[tidyboiler]

Something to do with George Lazenby (remember him?) in the starring role wasn't it???

Not as good as Rog...........:94:

 

[Geordie Spark]

Not as good as Rog...........:94:

No pet ... there's nothing like a good Roger is there?

 

[telectrix]

p'raps that's why he's called roger MORE.

 

[ipf]

Lazenby had a bloody big FRY

 

[Geordie Spark]

Lazenby had a bloody big FRY

That's good.

Tidyboiler enjoys a bloody big fry up first thing in the morning.

 

[tidyboiler]

No pet ... there's nothing like a good Roger is there?

As in "Roger the cabin boy".............. :ninja:

 

[ipf]

Aye, thought she'd be up for a bit of Turkish Delight with her sausage and scrambled.

 

[Geordie Spark]

As in "Roger the cabin boy".............. :ninja:

Stoppitnow .... before you go any further. :38:

 

[telectrix]

awwww. just because it's your turn in the barrel.

 

[ackbarthestar]

dead test R1+Rn. then PSCC= 230V/( R1+Rn).

I can't see how that will work, IMO, as the OP will need access to the front end of the cct. So its a guesstimate.

Since you'll need Zline ext. + R1 +Rn of the sub-main and as the OP doesn't have access to either then its going to be a calculated value based on assumptions about the supply cable type, size, length and the same for the sub-main cable.

We're not even sure whether the supply earthing arrangement is TN or TT, only that the far end supply is TT'd so we might struggle to get a reasonable supply voltage off and on load and calculate the resistance from the volt drop at the far end....

I'd just go for the 'drive-by' calculation if I was you.

that is:
Guess one + guess two + Variations in terminal resistances through various in line connections = 0.5 Ohms

This calculation is only for advanced users only - not recommended for the barn stormer

 

[telectrix]

as OP said he had access to switch fuse supplying his installation, i assumed he wanted the pscc for that point.

 

[Jdsparky]

My suggestion is do the live "no trip" test, or normal one and hope for the best,if it trips knock the door and say can you reset the Rcd please, then resort to other methods....how can you do all the other tests you may need to do at the origin of supply?

 

[ackbarthestar]

hi have access to the fused connection unit, that the supply comes from in utility room, but the lovely.... householder would not allow access into main house, must of thought i was an electrician who is also a burglar ho ho, we cant choose are customers, well we have a bit of lee-way. all done now using R1 + Rn method
230/(R1+Rn)

Ok, so R1+ Rn from the utility room to the outside installation which can be measured.
We still have R1 + Rn from the DB to the Sw Fuse, Zline ext plus a bit for terminal resistances.....

Just a few thoughts