Checked out some work on a shop today that had 240 Volt 60 Amp, 4 wire feed coming down from the 200 Amp main service disconnect at the house. The lighting for the yard around the shop was wired into a smaller sub-panel off the shop sub with 10 AWG 3 wire. I noticed the lighting panel had the bonding screw connected,and started to second guess the wiring. I feel this is correct since there is no neutral in a 240 circuit, but just wanted to know if there is a safer way to do this?

Most lighting, either 120 or 240 volts use 3 wires, 2 hots and a ground, or a hot, neutral and a ground.

If the feeder to the sub-panel is a 4-wire then the bonding screw should NOT have been used.

Would not the NEC requirement that the only place that Neutral and Ground are to be bonded together is the Main Service Panel apply?

You have piquéd my interest.

You have a 200 Amp Main Service Panel at the house. Off the Main Service Panel, you have a 60 Amp feeder to a sub-panel in the Shop.

This is made up of a four conductor cable. Just guessing, but that should be a #4/3 UF feeder or a different cable could have been used.

Whichever, that means that you are bringing 120/240 VAC over to the Shop's sub-panel. The sub-panel should have an isolated Neutral from ground. There also should be ground rods set at the Shop.

Now, comes the serious questions, On the sub-panel, how many branch-circuits are installed. If there are more than six, then you must have a disconnect switch at the Shop sub-panel to kill the entire panel or a main circuit breaker <60 Amp> at the sub-panel.

Off the Shop's sub-panel you feed a 2nd. Sub-panel that in turn feeds the lighting. That sub-panel is fed by a 10/3 cable which suggests a 120/240 VAC - 30 amp feed. This is also a four conductor feed that is providing 2 hot conductors, a Neutral and a Ground. There should be no bonding screw between Neutral and Ground. Again, if there are more then six circuits installed on this sub-panel you will need a kill switch or a main circuit breaker, no larger than 30 amps because that is all your 10/3 feed cable is listed for.

You have peaked my interest.


Now, comes the serious questions, On the sub-panel, how many branch-circuits are installed. If there are more than six, then you must have a disconnect switch at the Shop sub-panel to kill the entire panel or a main circuit breaker <60 Amp> at the sub-panel.

I have 3 circuits in the shop, 2x 120v @ 20 amp, and 1x 240v @ 30 amp (the lighting circuit in question). The 30 amp breaker feeds 10/3 into the 240v lighting sub-panel. Inside this panel there are 2 hots and a ground. The ground is connected to the neutral bar and bonded to the panel. The 2 hots go through a 2 pole 40amp relay and then feed the backplate of the lighting subpanel. They then feed 2x 240v @ 15 amp breakers hard wired to 2x 240v 1000w hps ballasts each (4 lights in the yard.) The coil on the relay is activated via a 120v timer.




Off of the Shop's sub-panel you feed a 2nd. sub-panel that in turn feeds the lighting. That sub-panel is fed by a 10/3 cable which suggests a 120/240 VAC - 30 amp feed. This is also a four conductor feed that is providing 2 hot conductors, a Neutral and a Ground. There should be no bonding screw between Neutral and Ground. Again, if there are more then six circuits installed on this sub-panel you will need a kill switch or a main circuit breaker, no larger than 30 amps because that is all your 10/3 feed cable is listed for.



If there is no 120 vac circuit in the lighting subpanel, is a 3 wire feed with bonding safe?

Thanks in advance,
Cjonezz

CJ - since Neutral is not being brought over to the lighting panel, I would not connect it.

If the Neutral is in the cable, I would cap it off at both the Main Service Panel and the Lighting sub-panel.

DO NOT BOND NEUTRAL AND GROUND AT THE LIGHTING SUB PANEL.

The 30 amp breaker feeds 10/3 into the 240v lighting sub-panel.
The coil on the relay is activated via a 120v timer.




If there is no 120 vac circuit in the lighting subpanel, is a 3 wire feed with bonding safe?


The above statements imply that there is a 120v circuit (for the relay).

Separate neutral and ground, remove bonding screw, ground sub panel.

Hank,

There is a feed from the main panel (at the residence) to a sub-panel in the shop to a sub-panel for the yard lights.

Since the second sub-panel (lights) is in the same building as the Shop's sub-panel. The sub-panel for the yard lights can use the same grounding system as the shop sub-panel. A second grounding system is not required at the Lights sub-panel, correct.

Don

Not saying a second grounding system required. Just saying sub panel should be grounded and that the neutral and ground should be separate at sub panel.

Hank,

Sorry, I misread your comments. Nice pick up on the 120 V / 40Amp relay. I have no idea where that came from.

CJ - We could really use some pictures of the wiring inside the Shop Sup Panel and then some pictures of the Lighting sub-panel, please.

"The 30 amp breaker feeds via 10/3 cable into the 240v lighting sub-panel."

10/3 cable should contain a Black, Red (Ungrounded or Hot conductors), White (Neutral) and either a bare copper wire or green insulated ground wire. Is that what you have between the Shop sub-panel and the lighting sub-panel? The correct connections to the shop sub-panel would be Black to one terminal / Red to the other terminal on the breaker. White will go to the Neutral bus bar on the Shop Subpanel and Ground will go to the ground bus bar. The Neutral has to isolated from ground. Therefore, no bonding screw is allowed.


"Inside this panel there are 2 hots and a ground."


10/2 cable consists of 1 Black ungrounded conductor, 1 White (Neutral) grounded conductor and a bare or green insulated ground wire.


If this is what you have, step one would be to color or mark the White conductor at both ends with any color ,other than gray or white, electrical tape or a Sharpie pen to flag this conductor as being retasked to a ungrounded conductor. Again, there can not be a bonded connection here either. The Ground conductor will have to be moved to the Ground bus bar and the bonding screw removed. Neutral and ground have to be isolated from each other.

Then I would expect you have a 240V30Amp breaker in the Shop sub-panel that has both the Black and White conductors connected to the terminals on the (DPDT) breaker and the ground conductor going to the ground bus bar.


The relay has two terminals, correct are they fed by the Black and White conductors?