Cord Grips

[Peter3355]

I found an unusual condition. The cord grips that support a 4/0 SOOW DLO single-conductor cord feeding a tap box are getting hot, but the SOOW Cords are not hot to the touch. I'm assuming an induced voltage causes this. What are your thoughts?

 

[TwoBlocked]

Huh, never thought of that happening, but yeah, I guess it could. A stainless steel or aluminum cord grip (instead of galvanized steel) shouldn't do that. Don't know if there is room left in the ole squash to remember that.

 

[don_resqcapt19]

How hot is "hot"? In general the inductive reactance heating is not a real issue until you have 300-400 amps of current.

Even though the manufacturer's tables will often show that conductor at 405 amps, that is in free air and at 90°C....very unlikely you are permitted to use the cable at that ampacity for any NEC application. There may be some applications where you could use it at 380 amps, but for most NEC applications, you will be limited to 230 amps, and that should not result in excessive heating where a single conductor is run through ferrous metal.

Note that both the enclosure and the cord grip, if made of ferrous materials will contribute to the inductive heating.

 

[Todd0x1]

ferrous enclosure with the conductors in individual holes?

 

[John A]

An 'old' trick was to cut a slit in the enclosure between the conduits.

 

[don_resqcapt19]

An 'old' trick was to cut a slit in the enclosure between the conduits.

300.20(B) talks about that method, but the cord grips would have to be nonferrous for that to work.

 

[Jraef]

An 'old' trick was to cut a slit in the enclosure between the conduits.

Assuming it didn't need to be NEMA 12 or 4...

 

[Jraef]

300.20(B) talks about that method, but the cord grips would have to be nonferrous for that to work.

Otherwise they bridge the gap that you just created...

Good previous discussion on this exact issue:

Single conductors passing through steel enclosures

I am being ask to install parallel runs of 373 DLO on a cable tray to feed a 4000 amp free standing breaker. The cables will be attached to the gear with aluminum gland connectors. Article 300.20 (B) requires aluminum or some other non ferrous metal for this application. Others are saying if...

forums.mikeholt.com

 

[Peter3355]

How hot is "hot"? In general the inductive reactance heating is not a real issue until you have 300-400 amps of current.

Even though the manufacturer's tables will often show that conductor at 405 amps, that is in free air and at 90°C....very unlikely you are permitted to use the cable at that ampacity for any NEC application. There may be some applications where you could use it at 380 amps, but for most NEC applications, you will be limited to 230 amps, and that should not result in excessive heating where a single conductor is run through ferrous metal.

Note that both the enclosure and the cord grip, if made of ferrous materials will contribute to the inductive heating.

How hot is "hot"? In general the inductive reactance heating is not a real issue until you have 300-400 amps of current.

Even though the manufacturer's tables will often show that conductor at 405 amps, that is in free air and at 90°C....very unlikely you are permitted to use the cable at that ampacity for any NEC application. There may be some applications where you could use it at 380 amps, but for most NEC applications, you will be limited to 230 amps, and that should not result in excessive heating where a single conductor is run through ferrous metal.

Note that both the enclosure and the cord grip, if made of ferrous materials will contribute to the inductive heating.

It is hot enough that I have to let go after 3 seconds.

 

[Todd0x1]

What exactly is the application. You said feeding a tap box. Are the cables supplying power into this box? Or is it something like a portable power hookup like used in entertainment where you have a disconnect switch and some cables coming out the bottom of it? Is this portable / temporary or is it part of a permanent installation? What is the actual wire type? There is no single conductor 4/0 SOOW afaik. DLO it might be, but are you sure its not SC, SCE, or W? Is the cable hardwired at each end or are there camlock connectors? What terminals does the cable land in and what are their temp rating?

 

[don_resqcapt19]

It is hot enough that I have to let go after 3 seconds.

How much current is flowing on the conductors?
Note that if you are flowing the 405 amps that would be permitted for 90°C free air conductors (very unlikely that the conditions of your installation would permit that amount of current flow, very likely that a code compliant application would limit the current to 230 amps), you could expect that the conductor temperature from just the current flow would be hot enough that you could not hold your hand on it very long. The OSHA rule is that equipment operating above 140°F (60°C) require protection so people cannot contact the equipment.