eddy currents


Postby gav46 » Thu Oct 13, 2011 10:12 pm

Hello, can anybody shed some light on topic as not alot of information available. I have fitted a metal clad 60a isolation switch I had to run the 25mm tails through seperate knockouts as their not big enough for both, the question is will I have any trouble with eddy currents occuring ? Have looked through the regs book and on site guide but can find no regulations or notes on the subject.
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Postby ericmark » Sat Oct 15, 2011 3:21 pm

Saw a slit between the two holes. Only needs to be width of hack saw blade.
The amount of current drawn will make a difference we had a power factor connection unit fitted and the installers did not make the cut with hack saw and had to return to modify. The noise alone was enough to make one realise something was wrong. But talking about 300A with smaller current you may not notice the problem.
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Postby gav46 » Mon Oct 17, 2011 10:15 pm

Cheers for that, not noticed any vibrations but handy to know. Did you have any trouble with heat build ? Was told this would be a major problem but have seen hundreds of isolations switches installed in this way, is this guy wrong or just making a mountain out of a mole hill ?
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Postby ericmark » Mon Oct 17, 2011 11:11 pm

Oh yes it did heat up. But so easy to put a slot with hacksaw between to two holes then they are one hole.
I was a lot of power we were drawing around 300A three phase I was rather shocked that any electrician could have made that mistake they returned and cut slots.
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Postby sparx » Tue Oct 18, 2011 6:03 pm

This is a well known and documented problem.
Guidence note 1 says "live cables (inc Neutrals)of the same circuit may cause overheating if they enter a ferromagnetic enclosure through different openings"; & refers to reg sect 521.
Red book 521.5.2 ..."The conductors of an AC circuit installed in a ferromagnetic enclosure shall be so arranged that all line conductors and the neutral, if any, & the appropriate protective conductor are contained in the same enclosure.
Where such conductors enter a ferrous enclosure, they shall be arranged such that the conductors are only collectively surrounded by ferrous metal."

So it's in the regs; even if obliquely worded.
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