Ok to ground to gate post instead of driving a rod? (pic)

[Edrrt]

Electrician ran a GFCI outlet into driveway gate control box to charge the 12V battery that runs the gate.

As 120v is now in the metal enclosure it should be grounded. The soil is very rocky and I'm unsure if it will take a grounding rod. However the gate post right next to it is 5x5" steel set into about 4 feet of concrete.

Could I just weld a stud onto it and ground the box to the post? Would this risk electrifying the gate in the event of a short?

Should I just drive a rod?

(This is not being inspected. Conduits with PVC contain low voltage control wires only. Comments welcome, I'm learning.)

Thoughts?

 

[wwhitney]

If the gate structure has just one 120V circuit run to it, then the NEC does not require a grounding electrode at the gate. It would suffice to bond the metal box to the EGC that was run with the 120V circuit. Also, grounding electrodes are not generally useful in the event of a short circuit at utilization voltages; bonding to the EGC is what allows a short circuit to complete a circuit to trip an OCPD.

How far is the gate control box from the electrical panel, and what size conductors were run? What wiring method was used, how deep was it buried, and was it GFCI protected at the electrical panel?

Cheers, Wayne

 

[Sponsor]

 

[Jadnashua]

From a technical point, not code, if the receptacle is GFCI protected, ground is just a secondary protection point...the GFCI should trip if there's a mismatch between the power on the line versus neutral regardless of ground.

 

[LeakyBoat]

How is it a two-wire 120VAC feed to the control box, I would expect 3-wire. Where did the (incoming) ground wire go?
I would say you can use a local ground (gate post) but ensure it actually isn't in dry soil and the stud doesn't corrode.
A GFCI does not actually measure current to ground, it only looks at difference between line and neutral currents to see if their is a difference.

Lightning strikes can cause utility ground to spike up and jump to the nearest best ground (gate). So some people have troubles with their gate controller boards getting damaged. I'm not sure about your motor/sensor wiring, if anything is grounded. Example the motor housing/gearbox is likely conductive to the gate hardware?

 

[Edrrt]

If the gate structure has just one 120V circuit run to it, then the NEC does not require a grounding electrode at the gate. It would suffice to bond the metal box to the EGC that was run with the 120V circuit. Also, grounding electrodes are not generally useful in the event of a short circuit at utilization voltages; bonding to the EGC is what allows a short circuit to complete a circuit to trip an OCPD.

How far is the gate control box from the electrical panel, and what size conductors were run? What wiring method was used, how deep was it buried, and was it GFCI protected at the electrical panel?

Cheers, Wayne

The EGC was bonded to the box. The electrician commented he wanted me to ground the box 'instead of running a wire all the way back to the panel.' Which confused me. No GFCI breaker at the panel.

This uses #8 wire about 300 feet to an existing circuit in an out building which is an additional 200 feet from the breaker.

Amperage is low. It only needs 1.5 amps for a trickle charger.

Manual calls for grounding the box if AC power is run to it. Wire Guage is also within spec of the manual for the distance I'm presuming due to the low draw.

I'm wondering if I can just bond the lug with the green wire to the gate post and have that serve as the grounding for the box or should I go get a rod?

 

[wwhitney]

The EGC was bonded to the box. The electrician commented he wanted me to ground the box 'instead of running a wire all the way back to the panel.' Which confused me. No GFCI breaker at the panel.

So the term "grounding" can mean either earthing or bonding. Earthing means connecting to earth, and bonding means connecting conductive metal parts together in order to reduce the possibility of a fault energizing isolated metal.

The EGC being present in the supply conductors, and being bonded to the box, is the most important part. Bonding the gate post to the EGC as well is fine and possibly useful. Earthing the EGC via bonding it to the gate post is allowed and may or may not be useful.

The EGC is earthed 500 feet away at the service panel, via the grounding electrode system there. If you earth it at the gate post, there's a possibility that if there's an earth potential difference between these points 500 feet apart, you will get a small current flow along the EGC that is not supplied by your service conductors. That's a side effect of acceptable practices that is often fine but could cause obscure problems.

Cheers, Wayne