Is it just me, or have Wylex made a blunderous error?!

[D Skelton]

Anyone notice anything odd about this board, in particular the main neutral linking bar?!

And before anyone asks, both the enclosure and mounting plate are steel.

This has really got me questioning both my basic electrical theory, and Wylex's, because if I'm right (which I'm certain I am), I shouldn't be, and if I'm wrong, I shouldn't be!

 

[davesparks]

Id ask Monsieur Foucault about that one!

 

[davesparks]

I guess it's not been a problem as the current actually flowing through that link will be pretty low. Plus the phenomenon to which you are referring doesn't really manifest itself at currents under 200A

 

[ipf]

Did it come with blue heat shrink and gun ?
:4:

 

[sparkdog]

Like the gloves.

 

[D Skelton]

Like the gloves.

It's a cast lol

 

[Darkwood]

Looks cheap and tacky...

Not sure on this one - very poor design with lack of sheath to the rear ... an area you may run your cables thus easy to accidently create a N/E issue.
As for Eddie and his currents...hmmmm a good point, as you have only the N passing through the slots I can't see how it would create an eddie current large enough, if it had one or more phases passing through separate slots/holes then you have a possible circulating eddie current path...

 

[Lucien Nunes]

Current is current, no matter which conductor is carrying it. I'd call it poor design but as mentioned I bet it doesn't notice in normal use with mixed loads. Neutral currents can be unusually high in some applications, such as theatre lighting, because loads are often heavily unbalanced. Under some conditions they can even exceed phase currents due to the 3rd harmonics which add in the neutral rather than cancel. Would be interesting to know if they did tests to prove it wasn't a real problem...

 

[davesparks]

I can't see a problem with the insulation of the bar, all Wylex boards of that age use that same enamelled copper bar and I've not heard of any problems with it. It's the same bar they use for the live in their 100A single phase sw fuse.

 

[Geordie Spark]

It's a cast lol

I was thinking that hand looks too clean to belong to an honest hard-working man. :laugh:

 

[Darkwood]

Also to note here is the cable has no metallic sheath so Sheath currents will not be an issue which is one big influence of the eddie current effect especially enforced if grounded by metallic glands to the steel plate although not grounded won't stop the issue .... I'm on the 'It should be ok' camp on this one tbh at these low currents and lack of sheath currents too.

I've only ever had Eddie current issues on jobs I've been to if the single core cables were metal sheathed or in steel conduits and then even small loading can see significant heating.

 

[Darkwood]

I can't see a problem with the insulation of the bar, all Wylex boards of that age use that same enamelled copper bar and I've not heard of any problems with it. It's the same bar they use for the live in their 100A single phase sw fuse.

If thats just a see through insulating laquer then Ill retract my concerns over the N/E issues.... I always use Scheider gear and a lot better by design.

 

[Darkwood]

Reet had a good think and look at the pics and we all have missed the obvious..

In order to create an Eddie Current you will need to have a flow and return between 2 x AC current carrying cables entering through separate glands/holes where a closed loop between glands can exist, looking at the picture the 3phases will be as expected totally insulated from all other metalwork except its busbar and pins. This means the N going through the back plate is of no concern regardless of its loading etc.

Eddie currents are more pronounced and expectant on metal sheathed single core cables as you get sheath currents induced.
Grounding of this sheath through a ferrous metal plate with say a gland or conduit will re-inforce the issue.
Eddie currents can flow not just between two adjacent glands but any situe where a closed loop has been created to allow the eddie currents to flow.

Thats how I see it ... now when looking at much bigger currents >200amps say you may get problems regardless of a metallic sheath or conduit, also very large currents and even Non ferrous metals can circulate Eddie currents.. but I'll leave that those that deal with the big stuff.

 

[davesparks]

But the neutral passes through the plate twice, with the current effectively going from front to back the first time and back to front the second time.

 

[Silly Sausage]

But the neutral passes through the plate twice, with the current effectively going from front to back the first time and back to front the second time.

There'll be a caveat in the instructions somewhere, "Only to be used on a near balanced system".

 

[Adam W]

deleted

 

[Darkwood]

But the neutral passes through the plate twice, with the current effectively going from front to back the first time and back to front the second time.

Ok point taken but given this is small load in the stance of things and as mentioned we have no metallic sheath here to create opposing magnetic flux we only have the weak field of the conductor itself and its not grounded either so I think there's no real concern... I trust the many years these boards have been in service is justification on that.

 

[D Skelton]

Reet had a good think and look at the pics and we all have missed the obvious..

In order to create an Eddie Current you will need to have a flow and return between 2 x AC current carrying cables entering through separate glands/holes where a closed loop between glands can exist, looking at the picture the 3phases will be as expected totally insulated from all other metalwork except its busbar and pins. This means the N going through the back plate is of no concern regardless of its loading etc.

Eddie currents are more pronounced and expectant on metal sheathed single core cables as you get sheath currents induced.
Grounding of this sheath through a ferrous metal plate with say a gland or conduit will re-inforce the issue.
Eddie currents can flow not just between two adjacent glands but any situe where a closed loop has been created to allow the eddie currents to flow.

Thats how I see it ... now when looking at much bigger currents >200amps say you may get problems regardless of a metallic sheath or conduit, also very large currents and even Non ferrous metals can circulate Eddie currents.. but I'll leave that those that deal with the big stuff.

Why a flow and return between two AC conductors?

It's AC, isn't that the point. The change in magnetic flux is what mimics motion, hence the eddy currents that could circulate in the flat sheet.

This is why motors are laminated.

My understanding is that eddy currents can flow in a ferrous material that is next to an AC conductor unless there is another AC conductor with an opposing change in magnetic flux to cancel it out.

I'm thinking induction coils here.

 

[davesparks]

Ok point taken but given this is small load in the stance of things and as mentioned we have no metallic sheath here to create opposing magnetic flux we only have the weak field of the conductor itself and its not grounded either so I think there's no real concern... I trust the many years these boards have been in service is justification on that.

Proximity also plays a role in eddie currents relative to field strength so with all factors considered I still can't see anything for concern.

As I said earlier it's unlikely to ever be a problem as eddy currents don't have an appreciable effect with conductors under ~200A and the actual current flow through that bar will be small

 

[Darkwood]

Why a flow and return between two AC conductors?

It's AC, isn't that the point. The change in magnetic flux is what mimics motion, hence the eddy currents that could circulate in the flat sheet.

This is why motors are laminated.

My understanding is that eddy currents can flow in a ferrous material that is next to an AC conductor unless there is another AC conductor with an opposing change in magnetic flux to cancel it out.

I'm thinking induction coils here.

Principle are similar and maybe my wording could have been better, I was discussing damaging eddie currents relating to the theme of this thread, you would require 2 opposing magnetic flux around the conductor to create a eddie current now as I see this this cannot be achieved due to limiting factors mentioned above which are -


Lack of sheath to boost the effect
No grounding of said sheath
Small nature of the currents discussed with these boards, usually <200amps

Yes you can create the effect to damaging results even in thes boards but you would have a lot of the above points involved.