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?
Cord Grips
- Thread starter Peter3355
- Start date
TwoBlocked
Senior Member
- Location
- Bradford County, PA
- Occupation
- Industrial Electrician
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.
- Location
- Illinois
- Occupation
- retired electrician
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.
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.
John A
Member
- Location
- New Jersey
- Occupation
- Inspector
An 'old' trick was to cut a slit in the enclosure between the conduits.
- Location
- Illinois
- Occupation
- retired electrician
300.20(B) talks about that method, but the cord grips would have to be nonferrous for that to work.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Assuming it didn't need to be NEMA 12 or 4...
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
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
It is hot enough that I have to let go after 3 seconds.
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?
- Location
- Illinois
- Occupation
- retired electrician
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.