PVC Cable Glands

This has been covered before on CR4 and this is the best response I could quickly find.

http://cr4.globalspec.com/comment/60648/Re-Trefoil-of-single-core-cables-for-3-Phase-AC-power

I am assuming you have multiple single core cables (3 perhaps) passing through a single mild steel gland plate. If this is the case you can either replace the gland plate with an aluminium one or perhaps cut a slot between each of the single core conductors (at right angles to the electromagnetic field created by the current passing through the cables) to break up the electromagnetic heating effect. You can seal up the holes with a filler or aluminium plate (as long as it isn't magnetic).

The slot option above may be able to be done with the cables connected, if you are careful (but you need to go all the way through the metal to the cable, which means moving the glands out of the way). If it were me I would replace the gland plate (you are MUCH less likely to accidentally damage the cable this way).

I've just got through the same drama, and it really is a pain. Yes, the answer is to break the magnetic circuit with a slot between the cables. I achieved this by drilling a series of small diameter holes, in line between the glands, I then slackened off the locknut securing the gland, leaving the gland body still in place on the cable, and drilled right up against the gland. With a series of holes now between the glands, "waggle" the drill so that the holes break into each other. In my case, I finished it off by inserting a flat bladed screwdriver, and levering, this will break any whiskers remaining. I then replaced the locknut. The enclosure integrity was restored by applying a bead of silastic along the slot. I used a 3mm drill bit, powered by a cordless drill.""IT GOES WITHOUT SAYING THAT EXTREME CARE SHOULD BE USED, AND THAT THE POWER SHOULD BE OFF!!"" I am assuming that there is room to get the drill in!

Good luck.

During detailed Engineering stage itself these issues should have been checked and the panel builder should havebeen instructed to provide Aluminium Gland plates of adequate thicknes of minimum 4 mm.

Dear Sridhar Ganesan,

May be you are getting confused with cable gland and Aluminium gland plate. Aluminium gland plates are used because they are non magnetic. whenever a current flows in a conductor( specially 200 A & above), magnetic field is created and eddy currents circulate around the metal where the cable enter the panel( it is true for any case, not only panels). Since steel is magnetic, eddy currents circulate and produce heat. the heat in this case is very high. if aluminium is used, due to non magetic nature, eddy currents WILL NOT BE INDUCED and heating of sorrounding metal will not take place. This concept is quite old and by default,panel manufacturers provide them during commissioning.

Thanks and Regards

Many responders are incorrect. Eddy currents are also induced in aluminium in a variable magnetic field. This is why AC induction motors work!

To prevent eddy currents flow in an electrically conductive plate (steel, aluminum, copper...) you need to balance the current flow in each holes to obtain a near zero difference. This means that balanced three phase conductors must use the same hole.

That being said, I have seen many installations (to my great surprise) in Mexico where each phase has its own hole in a steel cabinet. The loads were DC drives generating >30% THD. I didn't measure any temperature rise at the cabinet surface while drawing > 600A AC. That reduced my fear of conductors in different holes described above. The heating doesn't seem to be so important at low frequency.

Thank you for the better clarifications sir.