Damaged conductors in cramped boxes

[Hitchum]

Hey folks,

I was replacing a smoke alarm on a job and noticed charred insulation on some conductors in the (overfilled) ceiling box, and evidence of some arcing. I pulled a nearby luminaire and found the same thing - box was overfilled and two conductors were charred with compromised insulation. Neither circuits were protected by AFCI.

Curious to get folks thoughts on potential causes here, especially since these circuits are not carrying high loads. The cables are 12 AWG BX, originally installed in the early 90s, and were properly terminated (i.e., anti-short bushings were used). My best guess is that 30+ year old insulation has become brittle, and is easily cracked when bent or moved, which is made worse by the box overfill.

Some photos attached...

Neil

 

[roger]

The two pictures of AC (BX) are perfect examples of why anti short bushings and the correct connectors are required.

 

[infinity]

The 30 year old conductors have higher temp thermoplastic insulation so unless they were subject to excessive amounts of heat they should not be brittle. Looks more like they were damaged during installation.

 

[Hitchum]

The two pictures of AC (BX) are perfect examples of why anti short bushings and the correct connectors are required.

Ah, to clarify, there was an anti-short and connector originally installed. I removed them (second photo) so I could get a closer look at the condition of the cable.

 

[ptonsparky]

No supervision of poorly trained installers that are pressed for time to even breath.

 

[kwired]

The two pictures of AC (BX) are perfect examples of why anti short bushings and the correct connectors are required.

How much you want to wager that someone stripped sheath with a hacksaw or improperly adjusted strip tool and damaged the conductors with that? Anti short bushings won't protect from poor stripping methods.

The burn near the end of the conductor in first picture is probably physical damage as well and ended up faulting at some point?

 

[hbiss]

I think I see a connector that was opened up by breaking out opening in the end? Looks like sharp edges cut into the wire as it was moved around.

-Hal

 

[Hitchum]

@kwired not shown in the photos, but looks like a rotosplit was used to cut the armor.

@hbiss I don't think the connector was modified, but I'm thinking along the same lines .... i.e., the insulation was nicked by the edge of the connector opening. Unusual but if everything needed to be forced in to close the box it could happen. Good reason to use connectors with an insulated throat (and not overfill in the first place)

 

[LarryFine]

@kwired not shown in the photos, but looks like a rotosplit was used to cut the armor.

Actually, you can see that it looks like it in the center picture if you enlarge it.

@hbiss I don't think the connector was modified, but I'm thinking along the same lines .... i.e., the insulation was nicked by the edge of the connector opening.

Agreed. It looks the the connector is damaged from arcing in the right picture.

 

[Fred B]

You indicated a cramped box. Did you do a box fill calculation?

 

[SceneryDriver]

If you need to repair in place:

It appears that you have sufficient slack to remove a couple inches of sheath.
Once the sheath is removed, repair the conductor insulation with heat shrink tubing (don't use a torch or lighter - use a proper heat gun).
Install a new antishort fitting and box connector.

If the conductors themselves are damaged, Wago now makes an inline Lever-Lok that's perfect for these types of repairs:

Inline splicing connector with lever (221-2401) | WAGO USA

Inline splicing connector with lever; for all conductor types; 12 AWG (max.); 2-conductor; transparent housing; white cover (4066966120271) Online at WAGO USA!

www.wago.com

SceneryDriver

 

[ptonsparky]

If you need to repair in place:

It appears that you have sufficient slack to remove a couple inches of sheath.
Once the sheath is removed, repair the conductor insulation with heat shrink tubing (don't use a torch or lighter - use a proper heat gun).
Install a new antishort fitting and box connector.

If the conductors themselves are damaged, Wago now makes an inline Lever-Lok that's perfect for these types of repairs:

Inline splicing connector with lever (221-2401) | WAGO USA

Inline splicing connector with lever; for all conductor types; 12 AWG (max.); 2-conductor; transparent housing; white cover (4066966120271) Online at WAGO USA!

www.wago.com

SceneryDriver

These would certainly have been welcomed more than once.