Eddy current clarification

[dave992]

hi all,

What are your thoughts on how the 6231 cables been terminated? Will aluminium cause eddy currents? Thanks

 

[Avo Mk8]

Yes aluminium is a good conductor, so eddy currents will be greater than if it were steel.

Whether in practice anything bad could happen I'm not sure

 

[pc1966]

There might be some eddy current effects but far less than for steel (or anything other exotic material that is ferromagnetic). See 521.5.1 for that.

Ideally you always would take the whole set through a single hole, it also helps preserve circuits when several are present so less connection errors (i.e. L1-3, N & E kept to same MCB, etc, etc) than if they are going via different holes.

 

[nicebutdim]

Yes aluminium is a good conductor, so eddy currents will be greater than if it were steel.

Whether in practice anything bad could happen I'm not sure

Unless I'm very much mistaken the issue of eddy currents only materialise in ferrous materials. Gland plates are often made of aluminium where large singles are brought into an enclosure.

 

[Avo Mk8]

Unless I'm very much mistaken the issue of eddy currents only materialise in ferrous materials. Gland plates are often made of aluminium where large singles are brought into an enclosure.

Seems I am mistaken - thanks

 

[westward10]

The first picture I assume is steel in which case it is wrong. The aluminium panel in the second picture is fine but the lock nuts assuming they are steel are not.

 

[nicebutdim]

The first picture I assume is steel in which case it is wrong.

I was assuming aluminium in the first image, but the two plates are separated by part of the steel enclosure which would be less than ideal.

 

[Julie.]

Seems I am mistaken - thanks

You are not mistaken, eddy currents (Foucault currents) will be induced in any conductor within the presence of a changing magnetic field.

However the ferrous material tends to enhance the effect.

I have to say though, we designed MV and HV switchgear for typical currents of circ 630 - 3000 A and using 1/4" steel plate we used separate apertures for each phase, and only added around 5-10 deg C temperature rise!

So in my opinion it doesn't matter at all whether the cables go through the same hole or different holes.

However if it is ferrous material, regulation 521.5.1 mandates that all current carrying conductors go through the same hole.

 

[IAmSparkytus!]

Has anyone found much difference in temperature when it’s only the CPC which goes through a separate hole? Line and neutral conductors going through together.

 

[Julie.]

Has anyone found much difference in temperature when it’s only the CPC which goes through a separate hole? Line and neutral conductors going through together.

Won't add any heating effect, unless it is carrying current.

 

[IAmSparkytus!]

From memory though doesn’t the reg also say “and the appropriate earthing conductor” should enter through the same hole?

 

[davesparks]

From memory though doesn’t the reg also say “and the appropriate earthing conductor” should enter through the same hole?

Yes it does, I think this is down to the fact a lot of current can flow through it under fault conditions.

 

[davesparks]

I have to say though, we designed MV and HV switchgear for typical currents of circ 630 - 3000 A and using 1/4" steel plate we used separate apertures for each phase, and only added around 5-10 deg C temperature rise!

This is interesting, but I believe the eddy current problems get worse the thicker the steel gets.

The eddy currents become an issue if the conductors don't just pass through separate holes but also separate couplers or even conduits.

I've been meaning to experiment with this for a while, maybe I'll get some time in the workshop soon.

 

[Avo Mk8]

I've been meaning to experiment with this for a while, maybe I'll get some time in the workshop soon.

I hope you have many 100's amps available in your workshop!
From Mr Ward rather a long time ago:

 

[mainline]

Beat me to it

 

[Avo Mk8]

Snap
And other words..

 

[davesparks]

I hope you have many 100's amps available in your workshop!

Nope, and shouldn't need much current either.

I recall Lucien mentioning that he made a simple square of conduit with a lampholder in the middle of one side and a mains input opposite it which got very warm with the live routed through one side and the neutral through the other with just a 100W lamp in it.

 

[Avo Mk8]

Nope, and shouldn't need much current either.

I recall Lucien mentioning that he made a simple square of conduit with a lampholder in the middle of one side and a mains input opposite it which got very warm with the live routed through one side and the neutral through the other with just a 100W lamp in it.

Not borne out by John Ward's video, or Julie's experience. I'm just perplexed now!

 

[pc1966]

Yes it does, I think this is down to the fact a lot of current can flow through it under fault conditions.

I guess the other side of that is it might add some impedance to the system due to inductance, making the AC R2 a bit higher than the DC one measured during dead testing to verify conductors are properly speced and installed.

 

[IAmSparkytus!]

Just annoying when you’re a bit of a neat freak with a distribution board and know that taking the earths through their own hole at the top of the board makes it look so much better