Another ground ???

[JKgrizzly]

Below my meter is a disconnect switch. In that panel a ground is connected to the neutral. Then 3 conductors run into my shop. Do I use a ground rod here also?

 

[pattenp]

If the feed to the shop is after the disconnect it should be 4 conductors unless the feed is old because 3 conductors were allowed some years ago. And yes the shop needs 2 ground rods.

 

[JKgrizzly]

The ground would go to the neutral bar again? Or am I supposed to add a ground bar in the breaker panel?

 

[Charles (in GA)]

The ground would go to the neutral bar again? Or am I supposed to add a ground bar in the breaker panel?

Yes, you do need to add a ground bar, and no, the neutral and ground will remain separate in your panel, since it is after the disconnect...... unless as already noted, this is old work that has three and not four wires from the disconnect to the panel.

The neutral needs to be insulated from the panel. The ground will screw directly to prepunched holes in the back wall of the panel.

 

[JKgrizzly]

It has three wires. So the ground goes where? If it had 4 wires from the disconnect, where would the ground be connected at the disconnect? There are only 3 wires from the transformer to the meter. I guess I don't understand why you would need 4 wires if it just connects to a ground rod at the disconnect.

 

[pattenp]

New code requires an equipment ground to run between the buildings. Since you have an old 3 wire feed the ground will be bonded to the neutral at the sub plus you still need the ground rods at the shop. Here's a diagram for a four wire feed and a three wire feed to a sub-panel.

View media item 16967

 

[JKgrizzly]

Thank you

 

[JKgrizzly]

but looking at the two diagrams I don't understand the purpose of the four wire. what does having the ground all way back to the meter loop do differently?

 

[Aceman]

There is potential for current to flow on any other metallic paths that may be added between the buildings in the future.

Say you have a gas furnace in the home and you want to add a gas furnace in the garage. So you tap off the house and run a new gas line out to the garage. The furnace in the house as well as the furnace in the garage would no doubt be attached to the ground wires from the circuits feeding them. Since both the ground wires both go back to their respective panels where the neutrals/grounds are terminated, that gasline is now in parallel with the neutral between both buildings. Current flow will now divide, some will be on the neutral, some will be on the gasline.

Not something you want.

A 4 wire feed takes this potential hazard right out of the equation.

 

[Steevo]

There is potential for current to flow on any other metallic paths that may be added between the buildings in the future.

Say you have a gas furnace in the home and you want to add a gas furnace in the garage. So you tap off the house and run a new gas line out to the garage. The furnace in the house as well as the furnace in the garage would no doubt be attached to the ground wires from the circuits feeding them. Since both the ground wires both go back to their respective panels where the neutrals/grounds are terminated, that gasline is now in parallel with the neutral between both buildings. Current flow will now divide, some will be on the neutral, some will be on the gasline.

Not something you want.

A 4 wire feed takes this potential hazard right out of the equation.

This is the best explanation I have read for the 4-wire sub panel scenario.
Thanks.

 

[JKgrizzly]

Makes sense to me now. Thanks