Single core cables and a mild steel gland plate.

[SilverfoxUK]

I’ve got to take about 600A from a 500kVA transformer. The calcs are taking me to 300mm singles or 400mm 4c.

400mm I can’t accommodate the bending radius so that’s out. The gland plate on the transformer is mild steel so with the singles I’m on route to creating a large induction cooker.

My spec called for a non-ferrous gland plate but getting past an existing cable on the gland plate is proving problematic.

The smaller cable to the back of the terminal box will be disinvested.

My get out of jail is to run the 3 x phase cores as close as possible in the existing mild steel gland plate and then cut slots between the holes. Has anyone had experience with this?

Slot size, 1mm, 5mm, larger ??

Could you backfill the slot with mastic of lead?

Would welcome the benefit of your experience.

 

[che12345]

["#1... is to run the 3 x phase cores as close as possible in the existing mild steel gland plate and then cut slots between the holes.#2. Slot size, 1mm, 5mm, larger ?? #3. Could you backfill the slot with mastic of lead?"
I have the following suggestion for your consideration.
1. cut three holes say from left to right. The distance from hole to hole is NOT critical.
1.1 a)Cut a slot from left to right the whole length of the grand plate, or
b) Cut a slot between whole A and B, and another slot between hole B to C.
2. Slot size may be 1-2mm ...NOT critical.
3. Use any silicone sealant available from hardware shops, sealing off the gaps; to prevent any ingress of insects etc...
Che Kuan Yau (Singapore)

 

[Kiribanda]

Hello SilverfoxUK,
I am curious to know why only one cable is having the neutral (BLACK) conductor?

 

[waross]

I have cut the slot with a sawsall and had good results.
Filling the slot? Never done that but if I did I would consider RTV silicon.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

@ Kiribanda (Electrical)3 Feb 24 17:19
"...I am curious to know why only one cable is having the neutral (BLACK) conductor?"
I think it could be:
a) the bigger cable is a 3-core cable. It feeds 3-phase 3W loads, such as motor; where the Neutral is NOT required.
b) the smaller cable is a 4-core cable. It feeds 3-ph and 1-ph (3ph 4W) loads, where the Neutral is needed.
Che Kuan Yau (Singapore)

 

[waross]

By the way.
Spacing.
I have always use one cable diameter spacing.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SilverfoxUK]

All

Many thanks for your replies.

For Kiribanda the transformer is supplying to a large electric motor, through the 3c cable.
The smaller 4c cable is feeding some local distribution.

 

[Padlock01]

Hi SilverfoxUK
Cutting slots in a mild steel gland plate between single-core cables worked very well in the old days however, these days we use stainless steel or aluminium plates to prevent Eddy currents from circulating.

 

[che12345]

For general information.
cut-out hole spacing. In practice, the cut-out holes must be spaced > grand fitting that accommodates the tightening tool and have sufficient spacing for the lock-nut to turn around with the tightening tool. Caution: the lock-nut is always bigger in size than the grand fitting.
Che Kuan Yau (Singapore)

 

[waross]

Aluminum or stainless plates have always been an option.
If new switchgear may be ordered with non magnetic glanding plates that may be the best option..
For existing cabinats the slots are often the quickest and cheapest solution.
NOTE. LOCKNUTS SHOULD BE NON MAGNETIC.
I have seen an inspector reject an installation bacause of steel locknuts.
I told them but they didn't listen.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

I am not sure for single-core wire > say 200Aac 50/60Hz installation. Please advise me.
1. For single-core wire say >200Aac, the use of Aluminium , Brass or Glass-fibre gland-plate; instead of steel is widely recommended.
2. Aluminium gland mounted on Brass gland-plate or Blass gland on Al gland-plate is NOT acceptable.
3. Re lock-nut material
a) do Al glands come with Al lock-nut? Note: separate loose item Al lock-nut are not readily available on the market,
b) do Brass glands come with Brass lock-nut? Note: separate loose item Brass lock-nut are not readily available on the market,
c) there is NO mention in IEC, IEEE/ANSI, UL, NEC...that the lock-nut should be of non-metallic material.
4. Does the inducted eddy current on the metallic lock-nut would heat up with say >200Aac 50/60Hz.
Che Kuan Yau (Singapore)

 

[SilverfoxUK]

All

Thanks for responding to my question. Due to issues with an existing power cable I can't easily change the gland plate over to non ferrous.

It is possible to use the existing mild steel gland plate but you must saw cut between in this case the 4 cable entry points so 3 cuts.

Share your concerns with brass and aluminum. My understanding is if it is in dry conditions then unlikely to be an issues. For external application it can be protected.

Totally agree with comments about ferrous locking nuts.

 

[waross]

No mention of locknuts?
Did you look under 'Magnetic Encirclement'?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SilverfoxUK]

I've hung off the back of comments from others about the locknuts. Absolute no to ferrous lock nuts around the single core cables. Ferrous lock nuts would glow brightly!!