Bonding Metallic Bench with EGC Inside Receptacle

[jlee405]

We are planning on installing exterior receptacles mounted on posts/poles near a metallic bench screwed to a concrete base (not mobile) for the sitter to be able to plug in their mobile devices. Is it a good idea for the metallic bench to be bonded for equipotential bonding? Can I use the ground screw and wire in the receptacle to bond the metal bench?

 

[infinity]

IMO there is no reason to bond the bench but there is nothing in the NEC that would prohibit it.

 

[jlee405]

Thank you for the reply. Just wondering how likely it is someone can get shocked while touching the metal portion of the bench and the receptacle post at the same time.

 

[LarryFine]

Better to bond it and be wrong, than not bond it and be wrong.

 

[LarryFine]

Just wondering how likely it is someone can get shocked while touching the metal portion of the bench and the receptacle post at the same time.

In theory, little. The receptacle box is more likely to become energized than is the bench, and its EGC should handle faults.

 

[ptonsparky]

Ground and bond, just don’t forget the GFCI.

 

[Buck Parrish]

You're taking a copper wire and attaching it to some ones metal seat then putting it into a box with 120 volts. Not a good idea.

You mentioned equipotential bonding. That would not require it to brought to a 120 volt panel. You only bring it to the pumps equipment. The equipotential bonding is only connected because the equipment it is attached to has an equipment grounding conductor.
But even then the equipotential bonding lug is on the outside of the equipment not in the 120 volt areas.

 

[jlee405]

Thanks for your reply Buck. My thought was that since the metallic bench/chair is conductive and has a different ground potential than the receptacle post (connected to EGC in receptacle box), someone could get shocked by touching the metal portion of the receptacle post and the bench at the same time.

 

[Buck Parrish]

IMHO That wire between the outlet and bench poses a greater danger. As small as a chance either might be.

The scenario you have described is the same in millions of areas in the world today. I don't think any one else has had a problem.

I agree with others about bonding metal parts. But not in this scenario, it would not be prudent.

 

[infinity]

Thanks for your reply Buck. My thought was that since the metallic bench/chair is conductive and has a different ground potential than the receptacle post (connected to EGC in receptacle box), someone could get shocked by touching the metal portion of the receptacle post and the bench at the same time.

IMO not likely besides the GFCI protection will keep someone from getting hurt.

 

[Dsg319]

Thanks for your reply Buck. My thought was that since the metallic bench/chair is conductive and has a different ground potential than the receptacle post (connected to EGC in receptacle box), someone could get shocked by touching the metal portion of the receptacle post and the bench at the same time.

Are you concerned about Neutral to earth voltage or just 120v faults?

 

[jlee405]

Neutral to earth. The gfci would take care of the phase to ground fault.

 

[Dsg319]

Neutral to earth. The gfci would take care of the phase to ground fault.

I could be wrong (hopefully someone else chimes in). But unless there’s some other issues leading up to an extremely high NEV. I wouldn’t think there being much of a concern being it should be around 2-3volts at normal?

Even once you bond the bench seat to the recep box wouldn’t that same amount of NEV be there from their “bum” to the ground where there feet would be?

 

[Buck Parrish]

Neutral to earth. The gfci would take care of the phase to ground fault.

The gfci uses the neutral to open the circuit. GFCI's utilize the neutral not the equipment ground to operate.

 

[Buck Parrish]

See here - Some where here Mike says the last thing you want to do is to tie something to the electrical grid that is not required to be.
Equipotential Bonding, 2017 NEC - [680.26] (20min:51sec) - YouTube

 

[jlee405]

Thanks, yes I did watch those videos. I’m going to plan on using non metallic receptacle posts. The benches will be covered with wood slats on top, but the metal framing is exposed on the side.

 

[Buck Parrish]

Yes , you betcha... Uncle Mike describes the equipotential bond about as good as any one ever has. Believe me their have been books written about it.
One thing to help you remember. If a utilities loose their neutral, wow that leaves all of what was an equipotential bond to now be a method to a return path for the utilities power.
If you're not wiring a pool, than just emphasize equipment grounding you'll be fine. Say if you want to utilize metal poles for the outlet. That becomes equipment. That's why their is an equipment ground. You can utilize equipment bonding jumpers if so desired.
I admire your wanting to be extra safe. I'm the same way... Let me tell you.. try doing several pools in a jurisdiction that does not have any "none, no " inspectors. I have to explain to these contractors why it is necessary to do certain things.
They say , were not getting an inspection. I say well be glad you hired me...

 

[jlee405]

I could be wrong (hopefully someone else chimes in). But unless there’s some other issues leading up to an extremely high NEV. I wouldn’t think there being much of a concern being it should be around 2-3volts at normal?

Even once you bond the bench seat to the recep box wouldn’t that same amount of NEV be there from their “bum” to the ground where there feet would be?

Yes, I believe you are right since the floor probably won't have any bonded rebars.

 

[hbiss]

We are planning on installing exterior receptacles mounted on posts/poles near a metallic bench screwed to a concrete base (not mobile) for the sitter to be able to plug in their mobile devices.

I have a better idea. Let people with cell phones find other ways and places to charge their phones. Why does every table and chair have to have provisions for charging?

-Hal

 

[jlee405]

I feel ya, but it ain't up to me.