Never heard of this one before

[Maddison]

Had a three phase set and neutral conductors (120mm).. I was cutting out the holes on the gland plate etc 32mm for each conductor, 25mm for earth..one of the other sparkies said as the gland plate was steel not alluminium I would need to cut links between all of the holes in order to reduce inductance... Never came across that one before... Maybe if the glands were metal I would have seen some method to his magners but I couldn't... Anyway if someone could put me out my misery it would be appreciated thanks..

 

[telectrix]

eddy currents heat up the steel. the slots between the glands prevent the eddy currents from circulating.

 

[Engineer54]

Your colleague is correct you will need to slot between the gland entries or remove gland plate and replace with a non ferrous or insulating plate, such as Bakalite or similar....

 

[Pete999]

Not done anything like this for a long time, but yes your mate is correct running single cores through single hole in a ferrous enclosure will cause eddy currents to flow, causing the metalwork to heat up, if you have to use a ferrous enclosure cut slots between the holes, better still use a non-ferrous plate, I.m sure if you Google your question you will come onto some good diagrams. I have heard of the enclosure actually coming apart due to the heat, but never seen it myself.

 

[Spoon]

As above. Just in case you need another opinion...

 

[telectrix]

Had a three phase set and neutral conductors (120mm).. I was cutting out the holes on the gland plate etc 32mm for each conductor, 25mm for earth..one of the other sparkies said as the gland plate was steel not alluminium I would need to cut links between all of the holes in order to reduce inductance... Never came across that one before... Maybe if the glands were metal I would have seen some method to his magners but I couldn't... Anyway if someone could put me out my misery it would be appreciated thanks..

what has cider got to do with eddy currents?

 

[Pete999]

what has cider got to do with eddy currents?

Yep I wondered about that but put down to sausage fingers by the OP, or tapatalk

 

[Darkwood]

You missed that day in college then ... a very important point that requires observing at all times but at least your been looked over by someone in the know and its just a pre-commission alteration to save the day and a notch on your learning curve belt... Ive seen this set-up been ignored before with a nasty outcome ... everyday a school day as they say

 

[Andy78]

what has cider got to do with eddy currents?

Induced magners-tism causing the eddy currents obviously....

 

[Andy78]

Have a look at the diagrams in this link Madison... explains it very simply. As DW says this gets covered in magnetic theory in college.
The choice of wiring systems Page

Either slots between the holes to interupt any induced currents, rule of thumb is the width of the slot is equal to the thickness of gland plate, or use a non metallic gland plate as others have said. Paxolin is quite good as it is rigid but also very easy to work with.

 

[Engineer54]

Have a look at the diagrams in this link Madison... explains it very simply. As DW says this gets covered in magnetic theory in college.
The choice of wiring systems Page

Either slots between the holes to interupt any induced currents, rule of thumb is the width of the slot is equal to the thickness of gland plate, or use a non metallic gland plate as others have said. Paxolin is quite good as it is rigid but also very easy to work with.

That's the material i meant to state, just couldn't think of the bloody name!! lol!! There are many resin based ply boards available these days most of which are suitable for use as replacement gland plates and the like....

 

[Silly Sausage]

Am I right in saying that you can't use Ferrous glands/locknuts whathaveyou as well?

 

[Knobhead]

Something that hasn’t been mentioned, don’t use steel locknuts or you’ll be back where you started with a continuous ferrous ring around the core. Brass or plastic will be OK.

I had a 1000KVA transformer fail due to a contractor deciding the brass locknuts I provided were too nice to fit inside a box. No one will ever know, or so he thought.

 

[Pete999]

Am I right in saying that you can't use Ferrous glands/locknuts whathaveyou as well?

Archy don't that,s a problem

 

[Engineer54]

Also, aluminium gland plates don't solve the problem completely. which is why i always use insulating gland plates (eg, Paxoline or the like)

 

[Pete999]

Also, aluminium gland plates don't solve the problem completely. which is why i always use insulating gland plates (eg, Paxoline or the like)

Me also never bothered to cut a slot, always paxoline or some other insulating material

 

[Knobhead]

Also, aluminium gland plates don't solve the problem completely. which is why i always use insulating gland plates (eg, Paxoline or the like)

That’s OK if you can use plastic, we couldn’t.

 

[Pete999]

That’s OK if you can use plastic, we couldn’t.

I'll risk it, why couldn't you use plastic??

 

[telectrix]

perhaps for earth continuity between glands?

 

[Knobhead]

M&Q regulations and company policy.

That’s one I’d forgotten Tel. We always used brass stuffing glands so you could find yourself with a live gland.

 

[shanky887614]

this is one of the reasons why people struggle with multi core cables, it saves a lot of hastle having to either replace the gland plate or cut slots

 

[Knobhead]

this is one of the reasons why people struggle with multi core cables, it saves a lot of hastle having to either replace the gland plate or cut slots

I’ve installed two 750KVA 11/.55KV transformers. We couldn’t use our usual 600mm PVC/PVC 4 sector Al singles as the switchroom was in the middle of the plant and the transformers outside. ATA was no good as our product rotted aluminium, so SWA it had to be.

I was terminating the 11KV feeds but I got dragged around to the LV side. I don’t know who designed the terminal box but they had a sense of humour. No way were two 300mm 3½c SWA going in that.

Being the helpful sort that I am, I left them to it. My mate on the MV side was wetting himself with laughter at the cursing and swearing emanating from the LV side.

 

[Bobster]

Just a note, stainless steel will pass eddie currents. Just because it's not magnetic, doesn't mean it's safe to use.