grounding for junction boxes

[dave726]

250.110 says "exposed", normally non-current carrying metal parts... that are "likely to become energized" shall be connected to equipment grounding. We're in the process of doing an electrical refresh on a portable crane. There are several limit switches that run off 120 that are contained in specialized junction boxes. How is "exposed" defined? If we were to cover the interior of the junction box cover with an insulating material - does that meet the intent of not having "exposed" metal? And... how is "likely to become energized" defined? There are no moving parts in these junction boxes. The boxes are not routinely opened and are only opened by specially trained and qualified technicians. So what's the likelihood that any of these covers would ever become energized?

 

[jap]

Rather than trying to insulate the inside of the Junction boxes with an insulating material it would be best to bond any and all exposed normally non-current carrying metal parts to the equipment grounding conductor to clear a fault should one occur. Any frayed cable or conductor could energize the normal non-current carrying parts of the crane at any time, making it very likely that any and all exposed metal parts could become energized.


JAP>

 

[Jim1959]

250.110 says "exposed", normally non-current carrying metal parts... that are "likely to become energized" shall be connected to equipment grounding. We're in the process of doing an electrical refresh on a portable crane. There are several limit switches that run off 120 that are contained in specialized junction boxes. How is "exposed" defined? If we were to cover the interior of the junction box cover with an insulating material - does that meet the intent of not having "exposed" metal? And... how is "likely to become energized" defined? There are no moving parts in these junction boxes. The boxes are not routinely opened and are only opened by specially trained and qualified technicians. So what's the likelihood that any of these covers would ever become energized?

Grounding is one of the most important things an electrician does to promote safety.
What motivation would you have to not do so?

 

[Coppersmith]

250.110 says "exposed", normally non-current carrying metal parts... that are "likely to become energized" shall be connected to equipment grounding. We're in the process of doing an electrical refresh on a portable crane. There are several limit switches that run off 120 that are contained in specialized junction boxes. How is "exposed" defined? If we were to cover the interior of the junction box cover with an insulating material - does that meet the intent of not having "exposed" metal? And... how is "likely to become energized" defined? There are no moving parts in these junction boxes. The boxes are not routinely opened and are only opened by specially trained and qualified technicians. So what's the likelihood that any of these covers would ever become energized?

It's a portable crane. It's going to shake around and wires can come loose. Will the insulating material cover every bit of the metal box and cover? Will it be puncture proof from the pointy end of a loose strand of copper banging against it every time the crane turns? This sounds like a lots of if's and a lot of work to insulate. Why not just put in a bonding wire and call it a day?