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Nominal size

Posted: Thu Jan 28, 2021 8:43 pm
by Dan L
Scenario...

120al mains with 50mm cu tails

160amp service fuse

What is the nominal size of active here?

Mains are not sized larger for vd

Re: Nominal size

Posted: Fri Jan 29, 2021 6:57 am
by Dan L
To put it simply for choosing the main earth size and the PE for switchboard can I work off tails?

( forget about PE selection by calculation in this question)

Re: Nominal size

Posted: Fri Jan 29, 2021 7:18 am
by DougP
IMO, according to the wording of "the largest active conductor of the consumers mains", you should go for the earth rated for the size of the 120mm² Al.
The 50mm² Cu, only has a suitable CCC for that service because it's rated as spaced within a switchboard. It's not big enough for the whole mains run. So if the mains was 70mm², you would be at the same 25mm² MEC anyway. So that's the size I would use.

Re: Nominal size

Posted: Fri Jan 29, 2021 10:13 am
by JamieP
Yeah I'd go with what Doug said and go by the largest part

Or attempt calculation 5.3.3.1.3 and see what happens haha

Re: Nominal size

Posted: Fri Jan 29, 2021 9:06 pm
by DougP
JamieP wrote:
Fri Jan 29, 2021 10:13 am
Or attempt calculation 5.3.3.1.3 and see what happens haha
ain't nobody got time for that :lol:

Re: Nominal size

Posted: Thu Feb 18, 2021 8:35 am
by AlecK
Agree with DougP that the tails may possibly be undersized.
Not enough info given to be sure; as CCC depends not only on conductor material;
but also insulation type, and installation conditions (for worst part of the run).
however as long as they do have CCC adequate for load to be carried, and are protected against overload;
then that's the size to apply when selecting MEC size from Table 5.1.

The rating of supply fuses is only relevant IF they are being used as the overload protection for the mains