When Are grounding Bushings Needed


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Old 06-03-15, 09:26 PM
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When Are grounding Bushings Needed

I will admit I have answered this question bur have been corrected also. Doing a search I'm getting conflicting answers. Is it only a service panel? Is it only over 250 volts. Is it concentric or eccentric? Washers?

I'm helping a member in thread http://www.doityourself.com/forum/el...cabinet-2.html.
 
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Old 06-04-15, 03:17 AM
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Ray, I may not understand completely, but if the two panels are connected via metal conduit, no grounding bushing is needed, only the plastic chafing bushings where the wires pass through.
 
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Old 06-04-15, 07:24 AM
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In a residential situation the only places you'll need to worry about grounding bushings is on the live side of a service entrance when using metal conduit and on both sides of the conduit or protection sleeve the GEC runs through if it is metal. Other than those two fairly rare situations, a metal fitting and lock nut to the electrical box is a sufficient ground. The plastic bushings should be used on any fitting that has sharp edges, such as threaded pipe nipples. Most cast fittings are smooth enough to not need one.
 
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Old 06-04-15, 08:21 AM
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Thank you. .
 
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Old 06-04-15, 03:11 PM
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Ray,

I think it is just assurance that you have a solid bond on your conduit. Let's say you have a pipe run that ends in a compression coupling and two reducing washers, or a run of liquid tight flex. Can you ensure there is enough connection between your connector and box/panel tub to carry fault current through the pipe run?
Some of the places I've worked at in the middle of nowhere spec'd bonds and ground bushings everywhere just for assurance. Less chance for injured employees 2hrs from the nearest hospital and expensive service calls.
Not saying this is a common problem, but a guess as to why the rules are there.
 
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Old 06-04-15, 06:36 PM
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Is it only a service panel? Is it only over 250 volts. Is it concentric or eccentric? Washers?
The only place inspectors in my area look for them is on services when metallic conduit is used; heavy wall or EMT. The usual places you'll see them is between meter socket (sometimes CT cabinet) and service panel or disconnect. When concentric knockouts are present and at least one ring remains, a bonding or grounding bushing is required. When all rings have been removed or if you punch your own knockouts (eccentic K.O.s) a grounding locknut is used rather than a bonding bushing. Some engineers will spec bonding bushings on all conduits entering a panel or box through concentric knockouts, but it's rare to see a spec like that. As far as I know, voltage is not an issue on whether bonding bushings are required.
 
 

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