Attached garage sub panel - adding ground?

[CrankyOldMan]

I have an existing 100A sub panel in my garage supplied by 3-wire NM cable (haven't verified the AWG yet but it's big). The neutrals and grounds are all mingled in the sub panel, which is OK from what I've read elsewhere since it's a 3-wire supply. I want to change the 240V outlet on that sub panel from a 3-wire NEMA 6-50 to a 4-wire 14-50 outlet. Can I wire the neutral and ground from the 14-50 outlet to the mixed neutral/ground in the sub, or should I separate the neutral and ground in the sub and run a separate ground back to the main panel?

Backstory: The 14-50 outlet will supply a rotary phase converter to power some small industrial equipment (208 3ph) and I want to be able to use the neutral at the machines for 120 lighting/power instead of running separate 120V accessory circuits to the machines--but keep the safety ground separate for fault protection. The plan is to use an appliance cord from the outlet to the RPC, then THHN stranded in conduit from the RPC to a 3-phase breaker panel and on to the machine outlets. I'm using 5-wire SO cable from the outlets to the machines as well, so the neutral and ground will be separate all the way to the machine panel.

I've considered hardwiring the RPC to the sub panel and eliminating the outlet, but the sub panel is recessed. I've looked at what's involved in making it surface mounted instead and it seems to be just a matter of running the NM cable into the *back* of the sub panel, patching the drywall and putting a sheet of plywood up for the panels.

 

[wyliesdiesels]

Thats completely wrong.

The 3-wire supply to a subpanel in an attached was the first mistake.

Where did you read that this is ok?

This is a prime candidate for shock potential.

When was this installed?

Can you post some pics here?

And read the electrical FAQ sticky for more info...

You cannot add a separate EGC due to the feeder being jacketed. Are you sure its 3-wire nm WITHOUT grnd? Post a pic of the wire.

The neutrals and grnds need to be separated. The bonding on the neutral bar needs to be removed and a separate grnd bar kit should be added.

 

[pattenp]

Since **/2 + ground NM was used (assuming the ground is serving as the neutral) you can't simply add a forth single wire. The NM cable needs to be changed to a **/3 + ground.

 

[teamextreme]

One exception; he didn't mention anywhere that I could see whether this garage is attached or detached. If it's attached, the comments above are correct. If it's detached, that's a different story as 3-wire feeds were allowed years ago (prior to 2008?).

 

[aka Larry]

One exception; he didn't mention anywhere that I could see whether this garage is attached or detached.

You mean like in the TITLE of this thread?

 

[Slednut]

This is my sub panel in my attached garage which was done in 2013. Washington State inspector.

BTW, I'm not happy with the neatness of the work.

 

[sberry]

As it looks there is a ground wire in the cable? If it is it needs to have some whites moved and the bond removed.

 

[wyliesdiesels]

This is my sub panel in my attached garage which was done in 2013. Washington State inspector.

BTW, I'm not happy with the neatness of the work.

Thats a 4-wire feeder...

 

[Norcal]

This is my sub panel in my attached garage which was done in 2013. Washington State inspector.

BTW, I'm not happy with the neatness of the work.

It's not horrible but could be neater seen a lot worse, BTW, it's a 4-wire feeder as mentioned above.

 

[sberry]

Looks better than mine,,, the electric doesn't know any different if its wired right. I saw a beautiful job the other day,,,,, wired wrong.

 

[Toothaker]

Since **/2 + ground NM was used (assuming the ground is serving as the neutral) you can't simply add a forth single wire. The NM cable needs to be changed to a **/3 + ground.

First off: I'm not arguing! I'm asking a question...

Given this situation: Let's go ahead and say the panel gets a new ground bar, there's no connection in the sub panel between the neutral and ground, and all the neutrals and ground wires are attached to the correct bus bar. And let's go on to say the existing **/2 + ground is the right size for the load and breakers and is in good condition.

Why couldn't a separate neutral be added? Does code mandate the feeder have all the wires encased in the same jacket?

 

[wyliesdiesels]

First off: I'm not arguing! I'm asking a question...

Given this situation: Let's go ahead and say the panel gets a new ground bar, there's no connection in the sub panel between the neutral and ground, and all the neutrals and ground wires are attached to the correct bus bar. And let's go on to say the existing **/2 + ground is the right size for the load and breakers and is in good condition.

Why couldn't a separate neutral be added? Does code mandate the feeder have all the wires encased in the same jacket?

Yes

 

[CrankyOldMan]

Wow, thank you all for the quick feedback!

Looks like I made some incorrect observations/assumptions about the setup. That's what I get for trying to post on lunch at work from memory. I went back this evening and actually inspected things. The cable is NM-B 6/3G. I didn't see the ground initially in the mess of the sub panel, but it's definitely bonded at the main panel in the basement. You can just see the ground in the lower left of the attached pic, behind the black lead. The sub is on a 50A breaker, so that should be fine for the 6 AWG.

The house was built in 1990, but there are no permits on file with the city from 1994 to last week (they don't have records before then) so who knows when it was installed. It's probably never been inspected, unless the initial run was done between 1990 and 1994. The routing is done in a way that didn't require removing interior finished drywall to get the NM to the garage wall, so it was very likely done post-build. If it had been done during the initial build, it would have taken a route about 15' shorter and more direct to the nearest wall.

I will DEFINITELY be separating the ground and neutral wires in the sub, and replacing the sub altogether if I can't get it sorted out with the existing panel. It's entirely possible that the mess of mixed ground and neutral was the handiwork of multiple previous owners and/or their agents.

Once that's sorted, is there any issue with the tight bend radius needed to get the cable in the back of the box for surface mounting? Is there a different way to get the cable from inside the wall into the sub?

Thanks!

 

[sberry]

We got messed up and looking at other pix. It looks like you need to add a ground bar.

 

[raco232]

As it looks there is a ground wire in the cable? If it is it needs to have some whites moved and the bond removed.

I’m not seeing the white wires and the bonding that needs to be moved. Can you point them out? Thanks!

 

[wyliesdiesels]

I’m not seeing the white wires and the bonding that needs to be moved. Can you point them out? Thanks!

He made that comment before the OP posted pics.

 

[teamextreme]

You mean like in the TITLE of this thread?

Doh, you don't expect me to read the titles?!

 

[CrankyOldMan]

Ok, looked over the sticky on 3- vs 4-wire. Makes sense.

There's a grounding kit available for my panel, gonna see if the local hardware store has it. If not, off to the big box store. The only place I can see in the panel to mount it is on the two dimples in the middle of the left side. They're threaded but painted over, so I might chase them with a tap to ensure good contact. The cover is also not for a flush mount, so it's a pain to remove.

Still looking for some feedback on running the NM cable in through the back of the panel. Is a standard clamp OK for that or should I get a 90° clamp?

 

[matt_i]

Easy solution for work lights on a 240vac machine (1ph or 3ph) is to use a 100VA dry transformer, 240:120vac. If you have LED lights it should be no issue. Even with incandescent you could still power a 100W bulb. Good idea to fuse the secondary side with appropriate glass fuse (or other overload protection).

 

[CrankyOldMan]

Aaah, much better! It's an ugly spaghetti mess, but I may need the extra length when I move the panel to the surface.

The smaller ground wires weren't even screwed in, just wedged in behind the neutral bar and held in by some spring clips. Is that an approved practice??

 

[theoldwizard1]

Thats completely wrong.

The 3-wire supply to a subpanel in an attached was the first mistake.

Wasn't there a time that even on an attached garage that a "local" ground (water pipe) was acceptable ?

 

[Norcal]

Wasn't there a time that even on an attached garage that a "local" ground (water pipe) was acceptable ?

Nope,been done but not acceptable.

 

[wyliesdiesels]

Wasn't there a time that even on an attached garage that a "local" ground (water pipe) was acceptable ?

No

But Youre mixing up concepts.

The issue is the bonded neutral. Not the EGC...

And a subpanel in an attached structure doesnt need grounding electrodes.

 

[CrankyOldMan]

Been a while, figured I'd come back with an update on the project.

I went and looked at the main disconnect for the house. It's only 100A! So the plan now is to have the service upgraded to 200A in the garage but keep the existing 100A panel in the basement and have a 100A breaker in the new main so we can use the existing cables there.

I'm getting a 30-slot panel and having it surface mounted so that I can do conduit in the garage more easily for all the 220 runs and 120 outlets. The sub panel from the original post might be reused but will be completely uninstalled from the basement panel to include the 6/3 NM cable.

 

[Rbreddin]

I bet that is going to be a pain! (bringing in new #4 service wire through the living space to the garage, then #8 from the garage to the basement)..

Is there an easy way to get from the basement to the garage?

 

[Augus7us]

I'm about to do something similar, though I already have 200amp service. For me, half my basement is unfinished so bringing 2224 across the basement will not be that bad. He may have something similar.

 

[wyliesdiesels]

Been a while, figured I'd come back with an update on the project.

I went and looked at the main disconnect for the house. It's only 100A! So the plan now is to have the service upgraded to 200A in the garage but keep the existing 100A panel in the basement and have a 100A breaker in the new main so we can use the existing cables there.

I'm getting a 30-slot panel and having it surface mounted so that I can do conduit in the garage more easily for all the 220 runs and 120 outlets. The sub panel from the original post might be reused but will be completely uninstalled from the basement panel to include the 6/3 NM cable.

Just because your main is only 100a doesnt mean you need to upgrade to support the new panel in the garage.

Have you done a load calc?

Does your house have all electric appliances?

 

[CrankyOldMan]

I bet that is going to be a pain! (bringing in new #4 service wire through the living space to the garage, then #8 from the garage to the basement)..

Is there an easy way to get from the basement to the garage?

The new panel is going on the other side of the wall from the meter, so it's only a few feet. The existing run of cable will just be pulled into the new panel.

 

[CrankyOldMan]

Just because your main is only 100a doesnt mean you need to upgrade to support the new panel in the garage.

Have you done a load calc?

Does your house have all electric appliances?

They're mostly gas, actually, but the original problem is that there's only a 6-3 NM cable feeding the sub panel in the garage. I want to have enough overhead to run more than 40A at once since I anticipate running a welder, compressor and a few hand tools at some point during racecar build parties.

 

[wyliesdiesels]

Have you done a load calc?

 

[CrankyOldMan]

Have you done a load calc?

I just did one on a generator company website. Only showed 55A (13.3 kW) for the house, so that's not as big of an issue as I thought.

I still want more than the 50A that the old sub panel will support and if I'm going to add a new panel in the garage, I might as well do the upgrade while we're at it. Not sure why I put 40A above. My current shop equipment can run on a 3 hp rpc but that may change in the future. I'm also planning to add heat and AC to the garage, not sure if I'm going to go with gas or electric for the heat in there to supplement the mini-split in the dead of winter, but I like having the option for either.