EICR help

[SaladFingers]

The only situation in which I can see that slots (joining the holes) would work would be if single cores (or, at least, separated L's and N) passed through separate holes in a metal enclosure through non-conductive grommets or glands. As I recently wrote, I suspect that the material is a bit of a red herring - one will get eddy currents in a brass plate (or, indeed, the brass body of a gland) just as one can in a steel enclosure, won't one?

Kind Regards, John

Eddy currents are not induced into non-ferrous metals as there are no magnetic fields in them.

Indeed, brass being one of those. I've got a lovely set of brass gland plates here to fit at some point. Very shiny, very nice looking, almost too nice to drill holes into!

 

[JohnW2]

Eddy currents are not induced into non-ferrous metals as there are no magnetic fields in them.

Indeed, brass being one of those. I've got a lovely set of brass gland plates here to fit at some point. Very shiny, very nice looking, almost too nice to drill holes into!

...and, I would imagine, designed for something (e.g. mounting metal glands in flimsy plastic enclosures) other than prevention of eddy currents.

Although, by not thinking clearly enough, I initially 'fell for it' myself, to suggest that eddy currents cannot be induced in non-ferrous materials is actually nonsense, and indicates a lack of understanding of what eddy (induced) currents are all about. As I responded to ricicle before, as I see it, if what you say were true, then motors, generators, transformers etc. with copper wire coils would not work, and induction hobs would not work with non-ferrous pans. The pattern, and probably magnitude, of eddy currents will differ between ferromagnetic and non-ferromagnetic materials (because of the influence of the ferromagnetic materials on the field), but the currents will be there in both cases.

Kind Regards, John

 

[SaladFingers]

Eddy currents are not induced into non-ferrous metals as there are no magnetic fields in them.

Indeed, brass being one of those. I've got a lovely set of brass gland plates here to fit at some point. Very shiny, very nice looking, almost too nice to drill holes into!

...and, I would imagine, designed for something (e.g. mounting metal glands in flimsy plastic enclosures) other than prevention of eddy currents.

They've actually been specified for prevention of eddy currents, which is the reason we're using them on these enclosures which are stainless steel. We haven't gone for plastic, or paxolin as we need to provide the strength and impact resistance for an industrial site - so went for brass instead of a stainless steel plate due to eddys, even though a wack there could possibly damage the cables anyway.

They mate with a gasket, so galvanic reactions ought to not occur.

 

[JohnW2]

They've actually been specified for prevention of eddy currents ...

As I've said, I find that a little odd, since by using a non-ferrous gland plate will alter the eddy currents, it won't AFAIAA prevent them.

...which is the reason we're using them on these enclosures which are stainless steel.

... which I find particularly odd, since most stainless steels are not significantly ferromagnetic! ...and I wonder how you plan to use these plates in a steel enclosure for the purpose you mention. Would you cut a hole in the steel and 'replace' it by the gland plate, or what? Even if it would, in itself, reduce eddy currents, any such benefit would preumably be lost if you attached it 'over' the steel - since the steel would still be there.

I'm getting very confused. If one Googles the topic of eddy currents, one finds two seemingly contradictory sets of assertions. It is a topic often discussed in various electrician's forums, and in information intended for electricians - in which case one repeatedly sees the assertion being voiced by some here, that you don't get eddy currents in non-ferrous materials. However, if you look at general educational/academic/scientific material, you will find a vast amount about eddy currents in a range of materials - most commonly steel, copper, brass and aluminium - which is what I have always understood. Indeed, a lot of what you'll find relates to use of eddy currents induced in aluminium and brass for crack/defect detection. Is electricians' Physics different from everyone elses?! Can anyone shed any light on this confusion?

Kind Regards, John

 

[SaladFingers]

They've actually been specified for prevention of eddy currents ...

As I've said, I find that a little odd, since by using a non-ferrous gland plate will alter the eddy currents, it won't AFAIAA prevent them.

...which is the reason we're using them on these enclosures which are stainless steel.

... which I find particularly odd, since most stainless steels are not significantly ferromagnetic! ...and I wonder how you plan to use these plates in a steel enclosure for the purpose you mention. Would you cut a hole in the steel and 'replace' it by the gland plate, or what? Even if it would, in itself, reduce eddy currents, any such benefit would preumably be lost if you attached it 'over' the steel - since the steel would still be there.

I'm getting very confused. If one Googles the topic of eddy currents, one finds two seemingly contradictory sets of assertions. It is a topic often discussed in various electrician's forums, and in information intended for electricians - in which case one repeatedly sees the assertion being voiced by some here, that you don't get eddy currents in non-ferrous materials. However, if you look at general educational/academic/scientific material, you will find a vast amount about eddy currents in a range of materials - most commonly steel, copper, brass and aluminium - which is what I have always understood. Indeed, a lot of what you'll find relates to use of eddy currents induced in aluminium and brass for crack/defect detection. Is electricians' Physics different from everyone elses?! Can anyone shed any light on this confusion?

Kind Regards, John

Actually, that's a good point, stainless isn't so ferrous! But still, brass ones have been specced, so brass is what's being used. I'll see if I can find out exactly why, since when used with stainless steel cabinets.

 

[SaladFingers]

Is electricians' Physics different from everyone elses?!

Kind Regards, John

Could be, an electricians cup of tea is different to a builders brew!

 

[333rocky333]

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• 333rocky333
• 27 Jan 2013
• 1

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• 333rocky333
• 27 Jan 2013
• 1

You slipped this in after I replied to your post!

Yes sorry john just added them for the Diyers who may not know whats being discussed.

Though as i said earlier the slots were commonplace as far back as the 14th when the single cores were usually copper pyro and Afaik single core Swa did not exist.
So i too am not sure this ferrous, non ferrous material factor realy alters the situation

 

[333rocky333]

Also where would Rf's situation stand regarding 521.5.2, oops spark 123 mentioned that earlier

 

[JohnW2]

Though as i said earlier the slots were commonplace as far back as the 14th when the single cores were usually copper pyro and Afaik single core Swa did not exist.

Indeed- and, as I've also said, I would think that the slots made (and still make) total sense in relation to single conductors (without any metallic sheathing or metal gland) passing through holes in metal. However, I would have thought that the whole situation changes dramatically if there is some sort of metallic sheath around a single core - since I would have thought that the entire length of such a sheath would present the mother and father of an eddy current issue (far more so than just passing through the wall of an enclosure. For that reason, I would not have expected single core SWA or pyro to exist (then or now). When you speak of pyro, do you mean a single core of multi-core pyro or literally 'single core pyro'?

So i too am not sure this ferrous, non ferrous material factor realy alters the situation

I've agreed that the nature of the metal will affect the eddy currents, but I still cannot understand how those currents would 'disappear' if the metal was not ferromagnetic.

Kind Regards, John

 

[333rocky333]

When you speak of pyro, do you mean a single core of multi-core pyro or literally 'single core pyro'?

Single core , im sure i have a picture somewhere

Heres some lead for you

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• 333rocky333
• 29 Jan 2013
• 1

Untitled

• 333rocky333
• 29 Jan 2013
• 1

 

[JohnW2]

When you speak of pyro, do you mean a single core of multi-core pyro or literally 'single core pyro'?

Single core , im sure i have a picture somewhere

Hmmmm. As I said, I woiuld that thought that, if eddy currents are an issue of concern, then any metal-sheathed single should invoke such concerns. I think that there still has to be something about all this that I don't understand, or am missing! Anyone?

Heres some lead for you

Again interesting, given that my comments apply to any sort of conductive sheathing..

Kind Regards, John

 

[Lectrician]

We fitted some 240mm copper conductor, aluminium armoured, single cores between a generator and it's automatic transfer switch.

The cable company also supplied us with aluminium glands and an aluminium gland plate to replace the steel end plates on the busbar chambers each end.

521.5.2 Ferromagnetic enclosures: electromagnetic effects.
Single-core cables armoured with steel wire or steel tape shall not be used for an a.c. circuit. The conductors of an a.c. circuit installed in a ferromagnetic enclosure shall be arranged so that all line conductors and the neutral conductor, if any, and 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
colletively surrounded by ferrous material.

 

[JohnW2]

We fitted some 240mm copper conductor, aluminium armoured, single cores between a generator and it's automatic transfer switch. The cable company also supplied us with aluminium glands and an aluminium gland plate to replace the steel end plates on the busbar chambers each end.
521.5.2 Ferromagnetic enclosures: electromagnetic effects.
Single-core cables armoured with steel wire or steel tape shall not be used for an a.c. circuit. The conductors of an a.c. circuit installed in a ferromagnetic enclosure shall be arranged so that all line conductors and the neutral conductor, if any, and 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 colletively surrounded by ferrous material.

Thanks. There's still something I'm missing. Whilst the above all makes total sense, what I don't understand is the implication that the issue only arises with ferrous metals - since one will get eddy currents in any conductor, including copper (e.g. with single-core pyro) and aluminium (such as the cables you describe). Is it perhaps that the eddy currents are lower, and deemed not to be a problem, with non-ferrous conductors?

Kind Regards, John

 

[SaladFingers]

It's because of the magnetic feild. The current is passing through the conductor, not the enclosure, so you'll get an eddy current in the conductor as that's what's carrying it. But with ferrous or magnetic enclosures, the magnetic fields of eddy currents will react with magnetic enclosures causing heat, non ferrous, or non magnetic metals won't have the magnetic attraction to excite the material.

 

[JohnW2]

It's because of the magnetic feild. The current is passing through the conductor, not the enclosure, so you'll get an eddy current in the conductor as that's what's carrying it.

That doesn't make much sense. We're talking about the eddy current induced in a surrounding conductor (e.g. a metal enclosure) as a result of current passing through the wire. I'm not sure what, if anything, would be meant by an eddy current induced in the current-carrying-conductor (wire) itself!

But with ferrous or magnetic enclosures, the magnetic fields of eddy currents will react with magnetic enclosures causing heat, non ferrous, or non magnetic metals won't have the magnetic attraction to excite the material.

I'm afraid that none of that makes much sense to me. Eddy currents will be produced in any conductor (regardless of material) surrounding a conductor carrying an AC current, and the passage of that current through the material will result in the generation of heat. "Reaction of a magnetic field with a ferromagnetic enclosure" (whatever that means) will not, in itself, result in any heat generation if heat is generated, taht would be the result of eddy currents flowing in the material.

Kind Regards, John