eddy currents

sparkyt · May 30, 2010

carrying out a pir on an industrial installation and the first thing that i noticed upon removing the fuseboard cover was a potentil problem. Your thoughts on the following please.

Metalclad 36way tpn board with two 50mm bushes in the top spaced about 150mm apart. one bush has live and earth conductors passing through and the other bush has lives, all the neutrals and the remaining earths passing through. now i know if they were completly split i.e all the lives in one and all the neutrals in another then we would have problems. what do you all think on this one? approx 50% of lives in each and 100% neutrals in only 1. do we have a problem with eddycurrents ? this installation was wired by a well known firm in brum about 9 years ago and hasnt been altered or inspected since.

Andy™ · May 30, 2010

do the circuits with only phase conductors in left have neutrals?

sparkyt · May 30, 2010

[quote name='Andy

ProDave · May 30, 2010

While I would always pair up live and neutrals of each circuit together, the old saying is if it ain't broke, don't fix it. So if it's worked for 9 years without problem, it's probably okay.

You talk about them just leaving the DB through different bushes. Where do they go? into the same trunking? in which case I can't see a problem.

If they both disappear off down separate lengths of conduit, then that may be more of an issue.

I guess if you are really concerned, try and re route them, but if there's not a lot of slack, or it's really congested, that may be more trouble than it's worth.

If you are going to re route them, then to avoid having to identify and pair up circuits, try and get all L and N through one bush, leaving the other bush just for E.

a1spark · May 30, 2010

Reg. 521.5.2

Evans Electric · May 31, 2010

As far as I know if you have a mixture of phases/lives/ neutrals in the bushes the eddy currents are cancelled out .

I think the worst senario is ,say, a metal plate with four seperate holes and a phase in each. The holes would need to be linked by a hacksaw cut to prevent the eddies.

Not quite the same but you may want search for this on here.

I have an earlier post ,if you are interested , concerning 200A meter tails which I installed seperately on a tray . This caused an induction field about 2-3 mtrs from the cables and destroyed the picture on a computer screen through a concrete block wall behind the meter position and another to the right .

The screen had to be moved 3mtrs for the interference to subside.

I had to return the tails to trefoil along with the neutral to reduce the field .

kme · May 31, 2010

I am of the opinion that you have a code 2 there, mate. If a phase doesn`t have its corresponding neutral ( or other phases of the same cct) through the same hole, an eddy current is generated in the metal between the bushes.

They should be re-routed, with each circuit`s conductors passing through the same hole.

KME

n.b. recently replaced a 9 way dimmer pack, supplying (yup, nine) lighting circuits; spread across the three phases.

When I stripped out the old one, there were nine phase conductors, and eleven neutrals. I could not determine what cct(s) the 2 extra neutrals were supposed to be part of, so they were left disconnected, rather than risk having them entering the (metalclad) unit through the wrong bush.

HTH

Chr!s · May 31, 2010

sparkyt

is the enclosure ferromagnetic? Use a magnet to determine

is there a plate of non ferromagnetic material or a non metallic material surrounding the cable entry points?

Are the holes in the enclosure slotted?

regards chris

sparkyt · May 31, 2010

sparkytis the enclosure ferromagnetic? Use a magnet to determine

is there a plate of non ferromagnetic material or a non metallic material surrounding the cable entry points?

Are the holes in the enclosure slotted?

regards chris

Hi enclosure is of steel construction

bushes are through top of steel enclosure i.e no non-metalic materials present

no slots

sparkyt

Chr!s · Jun 1, 2010

Hi sparkyt

if the entry points are of non ferromagnetic construction (eg plastic plate) then there shouldn't be a problem.

if they are just small bushes then yes there could be an issue with eddy currents

regards chris

eddy currents

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