Recently saw where a panel screw in front panel embedded itself into a cable causing an arc flash. Is there a minimum distance of cables from font of panel? I've been told there are both NEMA and NEC violations but can't find a specific standard. Panel was being reinstalled after an inspection. Thanks for any help.
Clearance between 480V cables and dead front panel
- Thread starter Whangii
- Start date
- Status
rc/retired
Senior Member
- Location
- Bellvue, Colorado
- Occupation
- Master Electrician/Inspector retired
I don't believe there is. Common sense should kick in when making up a panel.
Confession time, I ran a screw through a wire once.
Confession time, I ran a screw through a wire once.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree with RC common sense is required, that a few cheap cable ties.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes, I have seen that too and it's always caused by a ugly, sloppy installation by a lousy electrician or worse, a DIYer.
- Location
- Illinois
- Occupation
- retired electrician
Most often that happens when the original screw is lost and field replaced with something different. However it does sometimes happen with the original screw and is just a workmanship issue. Look at where you have placed the conductors before you install the cover screws.
Thanks a lot
I really appreciate the answers. As to the screw, it was a blunt end panel screw and the installer was using an electric drill and slot head bit to install the screw. I think the drill RPM may have had something to do with possibly melting the insulation on the 500 MCM cable. Explosion was said to have been impressive...
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
That’s why I don’t allow my guys to use a drill to put covers back on! Doing it by hand has a better chance of burning the tip of the screw off and clearing, than driving a screw all the way into a cable. I hate it when people use drills to put covers on, they almost always over torque it, and strip out the clip.
SSDriver
Senior Member
- Location
- California
- Occupation
- Electrician
I have been using Electric drills or impacts for putting covers on for over 20 years without one single issue. I do check that wires aren't close to the screw holes. The time it saves on large panel's is huge. I also don't over tongue them. Common sense is all that is needed.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Yeah
Yeah, but unfortunately common sense has been dead for a while now.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
If you have any experience you know that you have to keep the areas behind the panel cover screws clear.
-Hal
-Hal
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Same here. Many of the commercial panels we work on can have up to 20 screws that need to be removed and reinstalled. I agree about the common sense, just check for potential problems before putting the cover back on.
It is important to secure your wiring. That’s what cable ties are for.
When terminating cable, cut the excess off. Leave 8” like you do in receptacles. The excuse I always hear from industrial electricians is that the 6 feet of extra wire they spent 20 minutes bundling up in the panel is so they have extra to pull in case the end is damaged. I have used up a couple inches and even had to use barrel connectors to extend some wiring that was all but “grouted” in. But those same coils are still in those panels 50 years later. It’s simply laziness on the part of the installer. Your wiring should look like factory wiring.
During a fault loose cabling will jump quite far. Also vibration is a big issue in motor peckerheads. If you don’t route and secure your wiring eventually something will happen. Murphy’s law says that the sharp end of the screw exerts a powerful attractive force that will cause loose wires to move towards the screw and impale themselves on it. If there is any question cut the end off, reroute the cable, or secure something over it like a wire nut, wood, plastic, rubber...but regardless...see point 1. Secure the wiring in the first place and nothing bad will happen.
Clearances between open (unshielded) should be maintained. You can see what this is by paying attention to “open” terminals without phase barriers. With 600 V rated equipment it’s about 3:4”. In UL testing they apply a surge voltage (BIL) of 200% of the nominal voltage plus 1000 V so 600 V class wiring is subjected to 2200 V. Thus the seemingly large gap. The tiny 5 mils of PVC over #14 survives up to around 2800 V when dry and not punctured by a screw.
This falls under the “workmanship” rule that is almost unenforceable, but if electricians had as much pride in their work as they do in other things it would never be a concern.
When terminating cable, cut the excess off. Leave 8” like you do in receptacles. The excuse I always hear from industrial electricians is that the 6 feet of extra wire they spent 20 minutes bundling up in the panel is so they have extra to pull in case the end is damaged. I have used up a couple inches and even had to use barrel connectors to extend some wiring that was all but “grouted” in. But those same coils are still in those panels 50 years later. It’s simply laziness on the part of the installer. Your wiring should look like factory wiring.
During a fault loose cabling will jump quite far. Also vibration is a big issue in motor peckerheads. If you don’t route and secure your wiring eventually something will happen. Murphy’s law says that the sharp end of the screw exerts a powerful attractive force that will cause loose wires to move towards the screw and impale themselves on it. If there is any question cut the end off, reroute the cable, or secure something over it like a wire nut, wood, plastic, rubber...but regardless...see point 1. Secure the wiring in the first place and nothing bad will happen.
Clearances between open (unshielded) should be maintained. You can see what this is by paying attention to “open” terminals without phase barriers. With 600 V rated equipment it’s about 3:4”. In UL testing they apply a surge voltage (BIL) of 200% of the nominal voltage plus 1000 V so 600 V class wiring is subjected to 2200 V. Thus the seemingly large gap. The tiny 5 mils of PVC over #14 survives up to around 2800 V when dry and not punctured by a screw.
This falls under the “workmanship” rule that is almost unenforceable, but if electricians had as much pride in their work as they do in other things it would never be a concern.
- Status