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My direct bury feed is a little over 200 feet. I used 4/0 4/0 4/0 4/0 wire. I understand I need to isolate the ground from the neutral. This requires a grounding bar addition to my 200 amp QO sub/service panel. What lug kit should I use for this big 4/0 ground wire?

2 Answers 2

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Pull the green screw and fit a PK18GTAL

Assuming your subpanel is a QO as your post seems to imply, you need to pull the green bonding screw from the mains section of the panel and install a PK18GTAL (or PK23GTAL, if you need more holes) ground bar kit into the panel enclosure. (The L variants have a 4/0 lug attached to them.)

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The neutral bar is not the ground bar.

If you have 2 neutral bars, you cannot convert it to a ground bar. It's not set up to do that, and if you do, you'll run out of neutral spaces - neutrals cannot be double-tapped like grounds can!

The spotter's guide is this: If it's on insulated standoffs so it doesn't touch the panel enclosure, it's a neutral bar. If it is directly bolted to the panel enclosure, it's a ground bar.

Most panels don't come with ground bars; they must be bought separately and they're cheap. Get the largest available and it may contain the 4/0 lug you need. If not, try my second option below.

Why don't they provide ground bars? Because very few users need them - most are either service equipment (i.e. the first disconnect past the meter) or are installed with solid metal conduit where the conduit carries ground and no ground wires are needed. QO is an industrial tier panel, after all. Almost all industrial installations use metal conduit.

If the ground lug isn't 4/0, you can just bolt a lug to the metal enclosure

You can cheaply buy a bare lug made for 4/0 wire, and bolt the lug to the interior of the subpanel with a bolt and nut. Scrape the paint a little where it contacts the subpanel metal. Drilling a hole is OK, but do not drill it into a knockout!

You can also buy a bare 2-port splice lug (you don't need the costly insulated Polaris) and splice from 4/0 down to #4 aluminum or #6 copper and then go to your ground bar.

Beware 4/0 for 200A feeders from larger services

The service wire is the wire from the meter to the first disconnect. Service wire is 3-wire and doesn't have ground yet. A feeder is wiring past the first disconnect to any additional subpanels. It must be 4-wire.

Code allows an entire residential service to use a slightly smaller wire than normal. Thus, even though 4/0 is only 180A wire, it may be used for a 200A service from the utility. The same rule also says that feeder never needs to be larger than the service wires themselves. Thus a 200A subpanel feeder coming off a 200A service is also allowed 4/0 wire since the service wire is allowed to be 4/0.

However, if the entire service is larger than 200A, then 4/0 falls to its normal 180A limit. The Load Calculation is not permitted to exceed 180A (43,200 VA). Since 180A breakers are not sold, on a feeder you can round up to the next available breaker size, 200A. This is NOT permission to load it beyond 180A.

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  • So if I remove the green screw/bolt dose this sufficiently isolate the ground from the neutral, allowing me to put the ground wires in the built in grounding bar. If I understand simply bonding the ground wire directly to the inside of the sub panel is just as good as the kit, attached to the (add on) grounding bar? Thanks! Commented Oct 26, 2022 at 4:27
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    @Huckleberry NO! The "built in bar" is the neutral. Grounding bars need to be added for grounds. Removing the green screw isolates the neutral bars (built in) from the case (grounded, if wired correctly) and the accessory grounding bars (add-on kit, easily available for the panel, required if it's a sub-panel with isolated ground) need to be connected to the case.
    – Ecnerwal
    Commented Oct 26, 2022 at 12:51
  • @Huckleberry edited. The neutral bar is not insulated. Insulated bars are the neutral bars and must be reserved for neutral use (otherwise you'll run out of neutral slots). You need to buy accessory ground bars (they're cheap) and those bolt directly to the case metal. That's how you tell a ground bar from a neutral bar. Commented Oct 26, 2022 at 22:57
  • Thanks all, much help! Commented Oct 27, 2022 at 17:18
  • BTW I have a permit and an Electrician is coming by to do a deep dive on all my work 👍 Commented Oct 27, 2022 at 17:23

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