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!

 

[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.

 

[Fin170]

The part I'm not sure about...is who bought that wylex board over the superior Schneider ones?

 

[D Skelton]

The part I'm not sure about...is who bought that wylex board over the superior Schneider ones?

I ripped it out and replaced it with a Hager.

Client spec.

 

[D Skelton]

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 -

Distance
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.

Damaging or not, you'd still get Eddy currents though would you not?

What if it's a SP conversion board? That's a lot of potential neutral current! Not 200A worth, but enough for it to get warm surely?

 

[Darkwood]

Damaging or not, you'd still get Eddy currents though would you not?

What if it's a SP conversion board? That's a lot of potential neutral current! Not 200A worth, but enough for it to get warm surely?

I think we are all getting a bit over sensitive to the subject, no disrespect at first it got me thinking and think its one of those rare decent threads we get that the forum used to be about. The only time where I've witnessed <200 amp been a issue was 2 conduits feeding a multi-gang metal clad switch where the phases were split between the conduits and at only 40amps load the circulating local eddie currents made the conduit too hot to touch - with regards to your query here even a single phase at 200amps should not generate enough heat to cause problems because the circumstances are not right - we have no sheath currents so the currents have to be very large for it to even be a concern.

Yes!.. you're correct they still will exist but will not rise the temp' as the plate would disperse any small heat generated faster than it could ever build up or as known as the runaway effect.

PS - I edited distance out of my posts but will still exist in any the quoted format - this is becasue on read-up it gets complicated and generally for our discussion it is irrelevant.

 

[davesparks]

Damaging or not, you'd still get Eddy currents though would you not?

What if it's a SP conversion board? That's a lot of potential neutral current! Not 200A worth, but enough for it to get warm surely?

Yes eddy currents will occur, but will be minimal. By the same token the field around the busbars will have induce something in the steel plate, but it will again be so small as to be immeasurable.

If converted to SP and if all of the load is connected to the right hand side of the board you'll have ~125A max flowing through that bar. Something in the back of my mind is saying that in an experiment the temperature rise of a steel enclosure when tails are passed through seperate holes and 100A flows is around 1/2 degrees C.

It would be good, if you have the time, to actually put a decent current through that bar and see what happens.