Main Panel Jumper

[Justin R. Ake]

I'm taking the required 25 Standards Every Inspector Should Know course. In it, it states that bonding bushings and jumpers are required for metal conduit entering the main panel through concentric or eccentric knockouts. Unfortunately, I'm pretty weak in electricity and I don't completely understand that statement. Anyone want to clarify?

[Frank P. Newman]

I'll try. The panels used in most residential work are pre-punched with knockouts that allow for easy creation of openings of various sizes. The holes can be concentric (all holes have the same center point) or eccentric (holes centered toward one side). All that doesn't really matter. The point is that because of the prepunched holes there is a concern that proper bonding may not be present. Therefore, a bushing has to be installed on the conduit that that permits a jumper to be installed between the condiut and panel thus insuring continuity.

[Justin R. Ake]

Mr. Newman,

Thanks for getting back to me. That does help. I'm pretty weak in electricity and need to get smart on it before I start inspecting homes. I was curious as to the reasoning behind the needed bonding but that makes sense now. Thank again.

Justin

[Frank P. Newman]

For those without an electical background, that area is almost always the weakest for a new inspector. For your own safety and knowledge, I would suggest taking every course you can find on the subject, then see if you can find someone who is willing to let you go around with them specifically to look at the electrical side of the business. Any other questions, please ask here - there are many who will be glad to help.

[Robert Meier]

The use of a metallic service raceway requires that the raceway be bonded by means other than standard locknuts. That means a bonding bushing, bonding locknut, hub or bonding wedge is required to bond that raceway. When no concentric or eccentric KO's are encountered a bonding locknut is permitted to bond the raceway. If concentric, eccentric KO's are encountered then a bonding bushing with the proper sized bonding jumper (NEC Table 250.66) is required. One other note, the bonding bushing, locknut, wedge or hub is only required on one end of the metallic service raceway.