The regs&OSG say you should get max PFC and Ze by enquiry rather than measurement. The Electrician's Guide says that suppliers are required to provide, amongst other things, the PSC, Ze (actually say Zc - missprint?), earthing type and cutout rating.
But how do you actually get the 'supplier' to cough up any of this lot? I've been passed around several numbers and all claim ignorance.
Alex
On Thursday 07 March 2013 10:06 Alexander Lamaison wrote in uk.d-i-y:
Ask for their technical department - worked for me with EDF (now UK Power in the SE). However, all they did was quote me the legal worst case values, so if you cannot measure, you might as well assume those (0.35 Ohm for TN-C-S and 0.8 Ohm for TN-S
They also told me I had a TN-S system when inspection in the cutout by the fuse puller chappie proved it was TN-C-S
So in short, don't bother... It's probably good practise to take te worst case values anyway as if their system drifts, yours will be in spec no matter. If theirs drifts past those limits, they are legally required to fixed it asap.
That's who I was speaking to apparently. They were very nice but said they could only help me if I'd measure Ze and it was too high. 'Too high compared with what' I though but kept quiet.
I could measure the Ze for a lower value but somewhere (can't find where now - probably the OSG) it says exactly what you just said: use the theoretical maximum because the supplier is free to change the actual value up to that max.
I'm pretty sure this is TN-S so will assume 0.8 Ohm. Was hoping to get away with less, hence the enquiry.
Alex
If you design so that it works in the worst case, then there is less to worry about later. If you must use a lower value, then I would always go with measurement rather than enquiry. I don't trust the record keeping of the supplier! (or for that matter that they are able to account for every change and extension to the network that may affect the results)
Ignorance because you are the fourth today to ask that but we don't keep that info as there is no call for it.. grin. Brian
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