Adding Ground Bus to 1960s Panel

[xguard]

I have an office building that was built in the 1960's with a 225 amp GE panel, panel looks to be original. We're adding a subpanel off of an existing 100 amp breaker. I'd like to run a wire type EGC to our subpanel but have nowhere to land it in the upstream 225 amp panel. I'm wondering if there's any consensus (or a standard) on the best way to add a ground bus to a panel that didn't come with one. I've seen people say drill and tap the enclosure or put a bolt through it with a nut on the other side. Any preferences? Thanks

 

[LarryFine]

That's about it; the enclosure is your EGC.

There's a bare wire up top that needs to land on the can, too.

 

[infinity]

I prefer nut and bolt directly to the existing can.

 

[gene6]

When I was sent to do this exact task recently I was supplied with and 8-32 drill tap to mount the ground bar and these 'bonding wedges' to put under the lock-nut of the EMT feed. I am not sure the reasoning but they did not want to rely on the can, it was also an older building. Then I ran a #6 green from the wedge to the ground bar.

 

[jaggedben]

DeWalt High Speed Steel SAE Drill and Tap Bit 10-32 1 each - Ace Hardware

Drill and tap holes in one application and deburr and countersink in a single step with DEWALT IMPACT READY® Tap & Drill Bits. Designed for impact drivers, each bit is equipped with a speed tip to penetrate materials quickly. Crafted for extreme durability to withstand tough jobsite...

www.acehardware.com

Plus the two screws that come with the ground bar.

(Just one example, pick your favorite vendor.)

 

[suemarkp]

I'd drill and tap as that seems easier than gaining access to the backside of the panel to use nuts. But if the enclosure isn't thick enough that two threads are fully engaged, then you need further bonding of that ground bar. You could run a jumper from the neutral bar to the ground bar (sized per 250.122). You can probably free up one of the larger neutral lugs if you move most of the grounds off to a separate bar and clean things up on that neutral bar.

 

[Eddie702]

You don't need access to the back of the panel to nut and bolt a lug to the panel. You can bolt it to the top bottom or sides even if you have to cut a small opening in the wall. Those old panels are usually pretty thick I would think a tap would be fine. I would use a fine thread 10/32 0r 1/4/28

 

[suemarkp]

The panel looked like it had wood framing all around the sides, so side mount approach didn't seem any easier.

 

[LarryFine]

You could run a jumper from the neutral bar to the ground bar (sized per 250.122). You can probably free up one of the larger neutral lugs if you move most of the grounds off to a separate bar and clean things up on that neutral bar.

Only if this is the service panel.

 

[TwistLock]

Just curious, are those 60+year old breakers even reliable at this point?

 

[david]

When I was sent to do this exact task recently I was supplied with and 8-32 drill tap to mount the ground bar and these 'bonding wedges' to put under the lock-nut of the EMT feed. I am not sure the reasoning but they did not want to rely on the can, it was also an older building. Then I ran a #6 green from the wedge to the ground bar.

I would have never thought of using a wedge in that way. It seems the OP could use a wedge and land his equipment ground on that.
Interesting.

View attachment 2572688

 

[ptonsparky]

Just curious, are those 60+year old breakers even reliable at this point?

Cycle them a few times if your worried about it. Go home. Sleep well.

 

[electrofelon]

I'm with the ground bar with 2 8-32 screws crowd. Do it all the time .

 

[Little Bill]

I'm with the ground bar with 2 8-32 screws crowd. Do it all the time .

I think the grounding screws that you buy are 10-32. Not sure that matters much as long as they are tight.

 

[electrofelon]

I think the grounding screws that you buy are 10-32. Not sure that matters much as long as they are tight.

Might vary by brand, but most ground bar screws are 8's

 

[jaggedben]

Might vary by brand, but most ground bar screws are 8's

Not it my experience, they're 10s. If we're talking about the ones supplied to attach to the can.

 

[electrofelon]

Not it my experience, they're 10s. If we're talking about the ones supplied to attach to the can.

I have a Siemens here and you are correct it's a number 10. Pretty sure the square D ones are number 8 (hope I don't eat crow a second time )

 

[suemarkp]

The Eaton ones are 10-32, and SquareD ones I've seen are 8-32. I like the #10 ones better since a normal green ground screw for a box is 10-32 threads. This lets you use a ground bar in its place if it also uses 10-32 mounting screws.

 

[Greentagger]

I have a Siemens here and you are correct it's a number 10. Pretty sure the square D ones are number 8 (hope I don't eat crow a second time )

I like my crow with a slice of humble pie.

 

[kwired]

Only if this is the service panel.

Yes, I think some might be confused a little, I think this is the panel the feeder will originate in to the panel the OP wants to run an EGC to. If this is the service panel then he can land his EGC on the neutral bus of the panel in the picture.