Heat marks at bond screw in sub panel

[srechkin (Simon Rechkin)]

If the conduit is PVC and there is no other metal connection between the subpanel and the service, it could all be correct except for loose bonding screw which could have arc’ed during a ground-fault.

[lkage (Larry Kage, CMI)]

@gmurray2

This house is in the city so it had to pass their inspections when built.

That doesn’t matter, Greg. They are why we have a job and not just donuts like them.

[dscott101 (David Scott, HI 10814)]

I think Robert is right the screw looks like they didn’t tighten it down, and failed to remove it.
So possible back feed from neutral.
This used to happen a lot and it’s why they put in the code to remove it or bars that some come with if the panel is a sub fed.

[rmeier2 (Robert Meier)]

Could also have arced during a ground fault as Simon suggested. Should be an easy fix.

[mparks2 (Michael PARKS)]

@rmeier2

Looks like the ground screw is loose, are there any neutrals connected to the EGC bus? If so the neutral current is flowing through the loose ground screw. Since this is pre-2008 NEC a 3 wire feeder is permitted.

Rob is correct!
DO NOT REMOVE THE SCREW.

@lkage

That doesn’t matter, Greg. They are why we have a job and not just donuts like them.

Donuts are trying to help you!

[lkage (Larry Kage, CMI)]

Ignoring…

[dscott101 (David Scott, HI 10814)]

Yep, if it’s a sub fed it will not pass inspection unless they remove the screw completely.
I used to have a box full of them!

[rmeier2 (Robert Meier)]

In this installation the green bonding screw is actually required to be installed because the sub-panel has only a 3 wire feeder. Although this is no longer permitted by the NEC it was permitted in 2005.