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Joined: Sep 2003
Posts: 60
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From searching the code, I can find only three places where bonding bushings are required. Around concentric and eccentric knock outs are two of them. The other is on the line side of the service, so I plan to put a bonding bushing on the new transformer but do I need one on the line side of the feed to the new panel?
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Joined: Aug 2003
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Re-read that code section (250.97) and you will see that it only applies to over 250 volt systems. Perhaps that will answer your question?
By the way, one other area that you would need a bond bushing would be for a metallic raceway encasing a grounding electrode conductor.
Ryan Jackson,
Salt Lake City
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Joined: Sep 2003
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Thanks for the tips and additional information. Now when I am reading it seems to indicate that bonding bushings are only required on the line side of theservice entrance conductors coming into service equipment, so since I am adding a transformer that is far downstream from them, I take it to mean that one is not required. That is also considering that the transformer is not establishing a new service because there isn't a meter being added.
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Joined: Aug 2003
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Thats correct. I am assuming you have a transformer with voltages of 480/277 and 208/120, either on the primary or secondary. Whichever side the 480 is on will require bonding IF a concentric knock out is used.
Make sure you use a non-metallic raceway off your XO to the GEC, or you will have to bond it as well.
Ryan Jackson,
Salt Lake City
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Joined: Feb 2001
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Bushings or equivalent are required around concentric/eccentric knockouts that are formed to impair the ground path.
Are all concentric/eccentric knockouts formed to impair the ground path?
Do you require or install them on 4X4's with 1/2"-3/4" concentric kos?
Ahead of the service main they are required, but many people install more than is needed and add grounding conductors which violate 250-6(a) 1999 NEC. Be careful of this.
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Joined: Dec 2003
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Section V of article 250 starts at 250.90, where it is made clear that in any situation where the electrician suspects that grounding continuity is not too good, he will have to bond. Bonding bushings MAY be used for this purpose.
I teach my apprentices that we have levels of required bonding. The most restrictive level is " At the Service" (250.92), followed by "Over 250 Volts" (250.97), and then "Other Enclosures" (250.96).
Earl
Earl
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