Entertainment / Camlocks / Induced Currents 300.20(B)

Volta

Senior Member
Location
Columbus, Ohio
To install panel mounted camlocks for standard entertainment industry connections, I don't see any relief from cutting slots between the conductors passing through the ferrous enclosure wall.

NEC 300.20 said:
...(B) Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic
properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit.
Of course that wall section can be replaced with an insulating or non-ferrous panel, but that doesn't seem to actually happen much, or at least I've never seen it.

Has anyone witnessed overheating of panel walls from these connectors as they are commonly used?
 
Has anyone witnessed overheating of panel walls from these connectors as they are commonly used?
Hardly ever see the slots, not even all factory assemblies have them. Never noticed any heating, either, OTOH I don't check much. Most of the time, we have our tails going onto lugs (IMHO most facilities are too cheap to install panel-mounted cams).

It might be a good project for an Engineer-in-training to determine how much heating occurs in the panel given the current, panel material, and conductor spacing. I'm way too lazy to look up all the info needed.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I'd like to seem some hard evidence too that this hysteresis thing is even an issue, I'm guessing that it's not. I wonder why they wouldn't just make the bottom panel out of aluminum.
 

iwire

Moderator
Staff member
Location
Massachusetts
I'd like to seem some hard evidence too that this hysteresis thing is even an issue, I'm guessing that it's not. I wonder why they wouldn't just make the bottom panel out of aluminum.
It is a real issue if the current is high. Have you ever felt an amp clamp vibrate when measuring a heavy load? I think that is an example of it.

One of the companies I worked for was remodeling a operating TV station and they had run a heavy temp parallel feeder in PVC mounted with strut clamps. After some time the strut clamps started getting so hot they were melting the PVC. I did not go on on the repair but if I recall what I was told they had run A&B&G in one PVC and C&N&G in the other.
 

iwire

Moderator
Staff member
Location
Massachusetts
Hardly ever see the slots, not even all factory assemblies have them.
Here is a nice set up on a generator we use, here they used some sort of plastic to mount the cam locs.

bg3.jpg

This is one of two identical boards on the same trailer that contains two gensets that can be used separately or paralleled to supply this board or the other or both.
 

iwire

Moderator
Staff member
Location
Massachusetts
No manual, it is not ours. It belongs to a sub we hire.

It was made in CA by a company called Engines & Equipment LLC. But I think they went under or were bought out.
 

Volta

Senior Member
Location
Columbus, Ohio
Thanks guys, cut the slots yesterday as the facility had no shows on Sunday. Had 1/16" steel plates cut to reinforce the 3 existing cabinet bottoms which the slots would weaken. One of several steps to keep the roadies out of the disconnects and live equipment in this old building . . . .
 
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