Bonding Metallic Bench with EGC Inside Receptacle

jlee405

Member
Location
Seattle
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

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
IMO there is no reason to bond the bench but there is nothing in the NEC that would prohibit it.
 

jlee405

Member
Location
Seattle
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

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
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.
 

Buck Parrish

Senior Member
Location
NC & IN
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

Member
Location
Seattle
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

Senior Member
Location
NC & IN
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

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
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

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
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?
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
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?
 

jlee405

Member
Location
Seattle
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

Senior Member
Location
NC & IN
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

Member
Location
Seattle
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

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
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
 
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