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Article 250.97 Ground Bushing question

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Hi all,

I just want to find out when circuits of over 250 volts to ground DONT need ground busing connectors. I know Article 250.97 gives the following exceptions

(a) Threadless couplings and connectors for cables withmetal sheaths
(b) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(c) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(d) Listed fittings that are identified for the purpose


A job i'm on came with a factory installed 277/480v service panel feeding a factory installed 480v VFD. The 480V HAS a ground bushing at the service feeders but none of the loads coming out of it do. its my understanding is that 480v EMT or sealtite load circuits coming out of the panel would require a ground bushing. Any input much appreciated.

See pics below one is from 480 feeder panel other is where it lands at VFD

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I have seen product pictures of grounding bushings that can be added on after conductors were pulled into conduits. I have no idea if such animals exist any longer it was a fair long time ago .
Hi all,

I just want to find out when circuits of over 250 volts to ground DONT need ground busing connectors. I know Article 250.97 gives the following exceptions

(a) Threadless couplings and connectors for cables withmetal sheaths
(b) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(c) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(d) Listed fittings that are identified for the purpose


A job i'm on came with a factory installed 277/480v service panel feeding a factory installed 480v VFD. The 480V HAS a ground bushing at the service feeders but none of the loads coming out of it do. its my understanding is that 480v EMT or sealtite load circuits coming out of the panel would require a ground bushing. Any input much appreciated.

See pics below one is from 480 feeder panel other is where it lands at VFD
 
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You bring a question I have never considered.

Which UL listing does the assembly have? Have you looked it up?

You do not tell us if the load wires are in metal conduit or in seal tite.
I would question the bond bushing on seal tite.
Where I live seal tite is not considered a ground path any more. You must run a ground wire.

I gave up racing to minimum code several decades ago. I use Myers hubs, and ground wires
a lot. If the connections do not have teeth on one side and a lock nut on the other I put a bond bushing on them and press on.
 

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You answered your own question. All the loads leaving the service meet the exceptions. There are no exceptions like this for services, even at 120/240.
 

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All wires larger than #4 need a bushing. I believe 60 amps and up you need an EGC with a bonding bushing if you use seal tight or greenfield. LFMC or FMC. Code book is in the office.
 

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Discussion Starter · #7 ·
You answered your own question. All the loads leaving the service meet the exceptions. There are no exceptions like this for services, even at 120/240.
So you would think the loads pertain to part (c). Just curious because people interpret it different?

(c)Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
 

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Discussion Starter · #8 ·
All wires larger than #4 need a bushing. I believe 60 amps and up you need an EGC with a bonding bushing if you use seal tight or greenfield. LFMC or FMC. Code book is in the office.
I have heard this before, do you know what article this is? I hear from others seal tight does not require a ground bushing?
 

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So you would think the loads pertain to part (c). Just curious because people interpret it different?

(c)Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
There are bonding requirements for services, and bonding requirements for over 250v.

The requirements for services don’t have exceptions, so you are going to use bonding locknuts or bonding bushings.

The requirements for over 250v have exceptions. The conduits leaving do not contain service entrance conductors, even though they might be leaving the service enclosure, so they would follow the rules and exceptions for bonding over 250v.

I’m not sure where your part “C” comes from, the 2020 code? Here is 2017. Since I’m using my phone, I can’t see the picture too clear. Sealtight was mentioned, but I didn’t notice it. If there was, the connector would also meet the exceptions. I don’t know why it wouldn’t? You would have to get rid of any sealing gasket though.


Font Electric blue Number Document Screenshot
 

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Discussion Starter · #10 ·
I’m not sure where your part “C” comes from, the 2020 code? Here is 2017. Since I’m using my phone, I can’t see the picture too clear. Sealtight was mentioned, but I didn’t notice it. If there was, the connector would also meet the exceptions. I don’t know why it wouldn’t? You would have to get rid of any sealing gasket though.

OK you are making valid points but what section of 250.97 does my pics pertain to?
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I have heard this before, do you know what article this is? I hear from others seal tight does not require a ground bushing?
It needs an equipment grounding conductor as per the following.
2017 NEC 250.118. 5 Is for FMC or Greenfield.. You need listed fittings approved for grounding. 20 amps or less. No larger than 1 1/4 inch. Total length not to exceed 6 feet.
NEC 205.118. 6 Is for LFMC or liquid tight. Basically the same except this allows for up to 60 amps if larger size. I am still looking up bonding bushings.
 
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