Bonding screw threads at panel stripped

T

thomasg88

New User
Location
Detroit
Occupation
Electrician
I have a Siemens SN series 200 amp load center which is the first point of disconnect. The bonding screw was over torqued and I cannot achieve the 45 in-lb torque spec’d. the screw itself is fine. It is the panel bonding tap hole that is not providing the necessary resistance. Any tips?

Thank you
 
Those are a 1/4-28 screw if I remember correctly they are also part of the neutral lug.
When I stripped one of those out I did not have the panel mounted so I was able to remove the paint behind the hole and use a longer 1/4-28 bolt with a nut behind it.
 
thomasg88 said:
I have a Siemens SN series 200 amp load center which is the first point of disconnect. The bonding screw was over torqued and I cannot achieve the 45 in-lb torque spec’d. the screw itself is fine. It is the panel bonding tap hole that is not providing the necessary resistance. Any tips?

Thank you
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Install a ground bar and run the MBJ from that to the neutral.
 
don_resqcapt19 said:
A lot of times the wall thickness it not enough to engage two threads if you drill a new hole. Often the factory hole is punched in a manner that metal is extruded out on the back side so that there is enough thickness for two threads.
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That is exactly what I was going to say. At least for SQD the bond screw hole and the ground bar mounting holes are this way.
 
don_resqcapt19 said:
A lot of times the wall thickness it not enough to engage two threads if you drill a new hole. Often the factory hole is punched in a manner that metal is extruded out on the back side so that there is enough thickness for two threads.
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I never realized that. I assumed the metal was thick enough. I have done it a half dozen times in my career.
 
Ever since we got these impact drills I often encounter stripped out machine screws, I recently tried to open a 4S box and the cover screws were so stripped out I thought they looked like nails. And when I finally got it open the ground screw had no threads left on it and just lifted out of the hole.
 
Dennis Alwon said:
I never realized that. I assumed the metal was thick enough. I have done it a half dozen times in my career.
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Take a look at the back side of the enclosure. If there is additional metal raised above the surface at the factory holes for grounding connections, the panel is not thick enough for two threads, so they use a special punch to "add" thickness.
 
don_resqcapt19 said:
Take a look at the back side of the enclosure. If there is additional metal raised above the surface at the factory holes for grounding connections, the panel is not thick enough for two threads, so they use a special punch to "add" thickness.
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Cabinet thickness is less than it once was as well. Maybe not as much of a change on typical load centers but commercial/industrial cabinets were generally thicker than they have been the past 30-40 years. If it were 1/16" thick then a 32 pitch screw would engage two threads. Not many load center cabinets or other general purpose enclosures have been that thick since at least ~1980.

A place I do work at has old I-line panels that have pretty heavy wall cabinets compared to most newer ones I have seen. And have front covers that just about need two guys to lift when installing them.

If you try to use a manual stud KO punch on one of those old panels, you easily know you have thicker material than what you are used to punching by how much harder your wrench is to turn.
 
don_resqcapt19 said:
Take a look at the back side of the enclosure. If there is additional metal raised above the surface at the factory holes for grounding connections, the panel is not thick enough for two threads, so they use a special punch to "add" thickness.
Click to expand...
I agree just tapping a hole in the flat metal is not going to provide enough metal to engage two threads of a 32 TPI screw. You could just use a nut and bolt to connect the MBJ from the enclosure to the neutral.
 
infinity said:
I agree just tapping a hole in the flat metal is not going to provide enough metal to engage two threads of a 32 TPI screw. You could just use a nut and bolt to connect the MBJ from the enclosure to the neutral.
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Would you need to have access to the nut after install? Could create problems for flush mounted or even surface mount if not close to the edge of the enclosure if you ever need to remove/reinstall that bonding screw or if you found it to be loose.
 
kwired said:
Would you need to have access to the nut after install? Could create problems for flush mounted or even surface mount if not close to the edge of the enclosure if you ever need to remove/reinstall that bonding screw or if you found it to be loose.
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You would need to find a way to install the nut and bolt. I would install the nut on the inside.
 
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