Sub panel on a sub panel question

[machsnell]

House main panel 200 amp. Attached garage with unbound 100 amp sub panel (no main breaker type).

In the attic of garage I ran 6/3 for a few 240 runs for lift welder bandsaw planer etc. And maybe a 120 run in the future.

Anyway i bought a 100 amp (no main br) panel at local electric supply house and it only has 3 lugs?

2 hot legs and what I assume a ground bar? I didn't know a panel could only have 3 connections other than your main service feed.

It is correct that I want a panel for 4 wire?



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[pattenp]

Most panels only have the two hot connections and a combined neutral/ground bar. You need to buy a ground bar kit for the panel and isolate the existing neutral bar from ground to have the 4 connection points.

 

[machsnell]

This is the panel.

That stinks because I could have probably just gotten on with ground bar on it.

So I need to go find ground bar kit.

Got it. Thanks

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[pattenp]

Most panels come set up as the primary main panel where the neutrals and grounds are bonded. This is why ground bar kits are sold separately. Go back to where you bought the panel and purchase the kit. Make sure the bonding screw that grounds the existing bar to the panel is removed. Those small holes in the back on either side of the panel is where the new bar will mount.

 

[mdog892001]

Why bother? Just hook it up the way it is 2hot and ground/neutral


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[pattenp]

Why bother? Just hook it up the way it is 2hot and ground/neutral


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Wrong. This is a subpanel and the neutrals need to be isolated from ground.

 

[Ji m]

Why bother? Just hook it up the way it is 2hot and ground/neutral


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It's a bad idea,

you should only have one single connection between Neutral and Ground per electrical service.

Parallel paths to ground are bad for lots of reasons,

one being:
imagine the N to G connection at the service fails,


with a second connection at the sub-sub panel, electrically you'd never know the Neutral's main reference to ground was now open.

Now everything that gets accidentally shorted to ground in that system has to travel on the ground system all the way to that sub-sub panel, to find that sub-sub panel's connection to neutral.

Good luck having a dead short to ground trip a breaker when it travels that far to find it's reference to neutral.

Runs that long can have so much resistance they can turn into heating elements that don't quite draw enough power to trip the breaker.

 

[wyliesdiesels]

Why bother? Just hook it up the way it is 2hot and ground/neutral


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That is horrible and potentially life threatening advice.

Theres a reason the code was changed in 2008 forbidding the practice.

 

[finn]

How about if the entire shop is wired using emt. Is it ok to not run a separate green ground wire and not install a ground bar in the sub panel, or is it ok to rely on the metal conduit, which runs from the main, grounded panel, all the way to the sub panel, and ultimately the outlet?

 

[wyliesdiesels]

How about if the entire shop is wired using emt. Is it ok to not run a separate green ground wire and not install a ground bar in the sub panel, or is it ok to rely on the metal conduit, which runs from the main, grounded panel, all the way to the sub panel, and ultimately the outlet?

If metal conduit is used then yes.

However, metal conduit corrodes underground so PVC is superior.

Still need a place to bond the GEC from the electrodes as well as any water lines gas lines etc. Neutral needs to be isolated as well.

The outlets would need to be self grounding(some are not) and all j boxes need to be metal.

 

[finn]

In my case the sub panel is on the wall in the shop lean to, fully enclosed from the weather.

Sounds like I’m ok, as long as all of the emt fittings are secured properly.

I used the green ground leads screwed to the outlet ground and metal box at each outlet.

I do have to go back and install a gfi outlet at the beginning of each outlet circuit.