Required Grounding Bushings??

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K1GMB

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North Chesterfield, Virginia 23236
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Telecommunications Engineer (Master Electrician)
I am installing a new sub-panel for my Ham radio room. It is a 100 amp 240/120 Square D QO panel. I am running less than 25 feet of metallic liquid tight 1" conduit between the main electrical panel and new sub-panel. Question is regarding the need to install grounding bushings on each end of the liquid tight conduit connectors? I have searched the 2020 NEC and I cannot find anything. I thought at one time it was required for ampacity OVER 100 amps. Any thoughts on this?? Thanks
 
There is not an XXX.46 for article 350 (like 344.46), so you need to refer to 300.4.G.
 
K1GMB said:
I thought at one time it was required for ampacity OVER 100 amps. Any thoughts on this?? Thanks
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For a feeder the condition that would require them is with concentric or eccentric KO's and a voltage over 250 volts to ground. As Tom stated you'll need a wire type EGC run with the feeder because for 100 amps the metallic raceway cannot be used as the EGC {250.118}.
 
infinity said:
For a feeder the condition that would require them is with concentric or eccentric KO's and a voltage over 250 volts to ground. As Tom stated you'll need a wire type EGC run with the feeder because for 100 amps the metallic raceway cannot be used as the EGC {250.118}.
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What is/was the reasoning for that?
 
It use to be if there are concentrics then a ground bushing is needed even with a ground wire within the same pulled circuit.

No concentrics did not require a ground bushing, point was that the connection of connector to enclosure typically is much less likely to break apart as a concentric KO could.
 
Another C10 said:
It use to be if there are concentrics then a ground bushing is needed even with a ground wire within the same pulled circuit.
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When was that? The NEC only requires a bonding bushing around concentric or eccentric KO's when the voltage is over 250 volts to ground. Boxes listed for bonding over 250 volts would not require the bonding bushing even when the voltage is over 250 volts to ground.
 
Another C10 said:
It use to be if there are concentrics then a ground bushing is needed even with a ground wire within the same pulled circuit.

No concentrics did not require a ground bushing, point was that the connection of connector to enclosure typically is much less likely to break apart as a concentric KO could.
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Sorry, but you are incorrect.
 
Another C10 said:
It use to be if there are concentrics then a ground bushing is needed even with a ground wire within the same pulled circuit.

No concentrics did not require a ground bushing, point was that the connection of connector to enclosure typically is much less likely to break apart as a concentric KO could.
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Interesting, I am running a #6 THHN grounding conductor within the same liquid tight. Grounding the new sub-panel to main panel grounding. Electrically, the metallic liquid tight connectors are attached "bonded" to each electrical panel with the tightening of the retaining nut. I'm sure if I ohmed it out, I would have a good electrical connection between the metallic flex within the liquid tight and system ground. But I will ground each bushing at both the main electrical panel and the sub-panel. It's probably a good idea after all to ground the metallic flex in the liquid tight to help provide some "RF" shielding of the feeder when I eventually fire up the 1 kW amateur radio amplifier. Hopefully some RF shielding of the liquid tight, and good grounding will help reduce and or prevent RF interference within the house. My only regret is that I should have probably used 1 1/4" liquid tight. While the calculated conduit fill is less than 40%, I will say that it was a challenge (#$%^&) to pull. I had it on hand from a previous project and wanted to save some bucks.........no good deed goes unpunished....................Thanks again for the feedback!!!!
 
K1GMB said:
Electrically, the metallic liquid tight connectors are attached "bonded" to each electrical panel with the tightening of the retaining nut. I'm sure if I ohmed it out, I would have a good electrical connection between the metallic flex within the liquid tight and system ground. But I will ground each bushing at both the main electrical panel and the sub-panel.
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The NEC does not require bonding bushings for this installation. That doesn't mean that you cannot use them.
 
Another C10 said:
It use to be if there are concentrics then a ground bushing is needed even with a ground wire within the same pulled circuit.

No concentrics did not require a ground bushing, point was that the connection of connector to enclosure typically is much less likely to break apart as a concentric KO could.
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In this area, IF bond bushings were required to provide adequate grounding (ie: concentric, etc) without a wire type ground AND a wire type EGC was used, the bushings would still be required. In this case, with the flex involved, bond bushings would not provide the required grounding and they would not be required.
 
jimport said:
Interesting to see ground bushings on many panels at the Trade Hounds website. Seems some think they are required everywhere.
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I see them needlessly installed all over the place. Almost all of the sparkies that I work with have no idea when they are or are not required so they just install them everywhere.
 
infinity said:
I see them needlessly installed all over the place. Almost all of the sparkies that I work with have no idea when they are or are not required so they just install them everywhere.
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I see a lot of what I call "defensive" installs. With some portions of the NEC being a bit confusing, inspectors interpretations varying lack of training, etc., a lot of shops adopt "standards" they find less expensive than re-dos. Install grounding bushings on all services and 480v systems, always insrtall (2) ground rods, use anti-short bushings on MC, use HCF cable where not required, always use deep 4" sq boxes, etc.......
 
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