Yes, but they seem to include the 'slots' joining the holes which I mentioned earlier ... or was that your point??
Kind Regards, John
POTW - pointless trunking
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Kind Regards, John
yes that was the point, im sure its something we all know about but rarely see it.
Oh, fair enough.
All other than mwatsonxx, that would be
Well, I certainly haven't, but I've seen very little in the way of commercial/industrial installations, and metal CUs have been pretty unusual (unless they were very old) in domestic environments until recently.
So, if you're only rarely seeing the slots, what do you see - all tails through the same hole?
Kind Regards, John
Mostly see slots, or bushes and locknuts but a majority of the switchgear usually sits on 100mm or bigger metal trunking so plenty of room for supply cables to sweep straight in with at least their pairs in same hole.
Sometimes you do see just the tails through a 50mm bush and coupler, unrestrained, though, in my work its usually 3 phase and Neutral boards .
I recall one board sitting on 3 couplers on trunking, for the outgoing cables the installer put Reds through one hole, blacks through the 2nd hole and all the earths through the 3rd hole
Sometimes you do see just the tails through a 50mm bush and coupler, unrestrained, though, in my work its usually 3 phase and Neutral boards .
I recall one board sitting on 3 couplers on trunking, for the outgoing cables the installer put Reds through one hole, blacks through the 2nd hole and all the earths through the 3rd hole
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Given that we know that "high" earth currents are possible in PME installs in non fault conditions, if we use the CU earthing bar as the MET, by this logic we should also make sure any bonding cables go through the same hole as the main earth cable.
I've never thought of that, but I suppose what you say is theoretically true. I'm not sure whether the currents can be "high" enough under non-fault conditions for it to be a significant issue, but I certainly can't see any reason for not doing what you suggest, 'just to be sure'.
Kind Regards, John
Should we be very surprised that a man with his qualifications and experience has never even heard of it?All other than mwatsonxx, that would be
Or should we read his question as a Socratic one, designed to make us go and find out at what conductor currents eddy currents need to be considered?
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it seems to me that slotting is taken very seriously in commercial and industrial installations, but often doesn't get a thought in domestics.
My guess it's because domestic is (was) usually in insulated boxes, and the currents are so low that it would mostly not be significant. Lots of domestic installs were done by people with little training, and often many years ago.
p.s.
I don't know (does anyone?) that passing an earth or bonding connector through a hole in a metal enclosure that is itself earthed or bonded can produce eddy currents. I'd have thought not.
My guess it's because domestic is (was) usually in insulated boxes, and the currents are so low that it would mostly not be significant. Lots of domestic installs were done by people with little training, and often many years ago.
p.s.
I don't know (does anyone?) that passing an earth or bonding connector through a hole in a metal enclosure that is itself earthed or bonded can produce eddy currents. I'd have thought not.
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I can't say that I'm particularly surprised. Maybe you know something I don't, but I don't really know anything about his qualifications and experience (if any). If I recall correctly, the only thing he's told us is that he is not a 'domestic electrician', or something like that.
Kind Regards, John
Indeed. As I said, that's the main reason why I have personally seen very little of it, since my limited experience is almost exclusively of domestic installs (and nearly all with insulated CUs).
It's an electromagnetic phenomenon, and so, as far as I can see, should occur regardless of the potential etc. of the metal. In other words, if a single ('unpaired') current-carrying conductor passes through a hole in a ferromagnetic material, it will inevitably result in eddy currents in the metal around that hole - regardless of whether the metal is earthed, 'floating' of anything else.
Kind Regards, John
IIRC I read once that in a domestic context eddy currents won't be a problem.
Your quote overlapped my "on second thoughts" edit.
OOI, how many people here would consider making good the slot having cut it? Bit of epoxy, a can of spray paint....
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I don't know, but I can well believe that the magnitude of eddy currents would be such as not to be particularly significant in most domestic installations.
I suppose the 'energy-obsessed' might be concerned about the energy 'wasted' in slightly warming the CU, at least in summer!
Kind Regards, John
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