electromagnetic effects

[Robegginton]

Electromagnetic effects upon cables both single and three phase cables upon entering a metal distribution board. this was picked up on a periodic test and inspection on a small block of flats. This has caught me out and i cant think of what causes this or the implications, any ideas ????

 

[topquark]

Try looking up eddy currents.

 

[Darkwood]

Are you asking how it works or what you are looking how for to identify possible issue?

 

[tigerpaul]

Keep all the lines together with the neutrals going through the same metallic enclosure.
ie.. Don't take lines through one metal coupler neutrals through another and earths through another.

 

[Robegginton]

How to identify the problem and what to look for, that should enable me to sort it. and then for future ref refresh my memory on eddy currents. cheers

 

[spark 68]

As the others have said, you need all your supply cables going through the same aperture, and if that is not possible then a workaround is to cut a slot between all the holes and make sure you use brass glands, nut's and banjo's if fitted.

Another possibility is to use a suitable plastic gland plate, the brass fittings above also apply here.

 

[Knobhead]

If the gland plate that the singles pass through is steel (IE magnetic) you will get eddy currents. The eddy current will equal the current in the conductor.

There’s two ways around this:
Make the gland plate out of aluminium.
Cut a slot between the gland holes to break the circuit.

A word of warning, don’t use steel lock nuts for the glands.

This plate was for a 1MVA transformer. I usually fill the slots with epoxy resin to keep creepy crawlies out.

View attachment 13602

 

[Engineer54]

There’s two ways around this:
Make the gland plate out of aluminium.
Cut a slot between the gland holes to break the circuit.

Even aluminum.plates can allow circulating currents over a certain level/magnitude. I always use brass sealing glands in 10mm Paxoline (for want of a better name) board for multi entry single cables into Switchboards/TX's and the like. The slotting of standard steel gland plates is as good a method as any, for stopping circulating currents forming, but the finished installation can look a real pigs ear, if care isn't taken on sealing the slotted sections...