To make my wiring job easier and more polished, I’ve added a neutral bar to a 200A subpanel. In order to keep the neutral and ground unbonded, I mounted the neutral bar with nylon screws threaded into tapped holes in the subpanel can. Then I jumped the new neutral bar to the existing neutral bar with 2 #4 THHN. By my investigation, a #4 THHN single conductor (not in romex or conduit) is good to 140 amps at 86 F . So I figure 2×140 = 280, so I have some room for derating if necessary. Not sure how hot a main panel gets. It resides in conditioned space.
Before I call the inspector, I thought I would check here to see if anybody could think of glaring issues that I overlooked. I’ll probably call inspector on Monday morning.
MERC.
Replies
I've used extra bus bars for grounds only- never nuetrals. Besides, you said you used nylon screws?, but it's still in contact with the panel itself.
Bottom line, I would not add ANYTHING to a panel that is not supplied by the panel manufacturer.
Jim
It's not in contact with the panel itself. The bus and both the ground and neutral bars are isolated from the panel because they are all mounted on plastic that snaps into the metal panel housing.
MERC.
1) Why weren't there enough terminal positions in the original neutral bar for the number of breakers in the panel? Are you using one hole per wire when the manufacturer expected each hole to serve multiple wires?
2) What size is the neutral from the subpanel back to the service entrance? I can't see any reason for the bond between the two neutral bars to be any bigger than that. But I can't see any convincing reason for it to be any smaller, either.
inspectors do not like anything added to a box, that did not come with the box. also the tie must be with a solid bar not a wire.
The wire from the subpanel to the service entrance is 4/0 Aluminum.
Most major manufacturers of panels can provide additional neutral bars that are designed, when correctly installed with supplied screws, to be used within their panels.
It is not unknown for main panels to become sub-panels as buildings are remodeled and being able to obtain a neutral bar to allow segregation of neutral from ground makes this a lot easier. It also maintains the design rating and safety margins originally design.
You will need to note the specifics of the panel in question. Make, model, rating and number of breakers should be noted. Take this to an electrical supply house which carries the brand. If the panel is a common one they should be able to get the right neutral bar for you.
I would be careful trying to use any site built additions. These bars under fault conditions are exposed to high stresses under fault conditions. Residential panels and breakers are rated at 10,000 short-circuit amps and the stresses under these conditions are quite high. If they fail the panel can kit itself and lead to a cascade fault, greater damage and possibly a fire.
Worse case I grab a neutral bar from a salvaged panel, made a lot easier if you replace a lot of panels, of the same type and rating or, in some cases where the existing panel is old enough to justify it, replace the entire panel. Not a bad idea if it is an obsolete, hard to get breakers for or unreliable design or brand.
Good points about fault conditions. Thanks all for the responses.
This panel is a Siemens 40/40 200A main breaker panel from Lowe's (local supply house doesn't handle Siemens and I had a dozen or so spare Siemens breakers). My main panel is also a Siemens 200A 40/40 and I bought it about 4 years ago. It had a full length ground and neutral bar with 50+ screws on each one. This last pile of junk has a neutral and ground bar that is less than half the length of the panel and each one has about 32 screw slots, but 4 of the slots have no screws (why...I don't know). I called Siemens about getting a matching neutral and ground bar kit and they played dumb. Gave me some SquareD part number and told me good luck.
I don't see anything with the panel that allows me to put two neutrals under a single screw (and it is my understanding this is not allowed), so how is this panel supposed to ever be full?
MERC.
First I wouldn't worry too much about doubling up on a couple of slots on the neutral or ground bars. Just make sure the wires are the same gauge so one isn't loose while the other is nearly cut in two. This is analogous to a piece of stranded wire.
Not the preferred method but usually not an issue. One thing people commonly fail to do with bar connections is to treat, clean and then brush some in, and evenly recoat with anti-oxidant when aluminum conductors are used.
The other consideration is that both the neutral and ground in some panels remain insulated from the enclosure until the bonding screw is installed.
Concept being that if an insulated run of conductor, sized to match the neutral as the feeder, or, in some cases, the bonding bar can be run from one bar to the other and the bonding screw left out. Effectively this makes the two bars a single neutral isolated from the enclosure.
The ground that is now missing is easy to replace off the big box shelves as they are commonly stocked. One or more can be, using the includes screws, mounted inside the panel. The bars being electrically connected through the enclosure. You can add a jumper, sized like the ground feed, if you wish.
If you get the same manufacturers bars they should fit those odd holes in the panel. If not drilling, be sure to use the right sized drill and under sized being better than over sized, and tapping, even though most included screws are self-tapping, are best to guarantee good conductivity. Don't use sheet metal screws. Only fine threads have enough contact area to make a good connection.
Grinding the paint off under the location of the bar and a dab of anti-oxidant compound also helps but this is only really necessary for critical applications. No harm in a belt and suspender approach if you have the time and energy. Be sure to use all the screws required. Even if they say one I recommend using at least two as it keeps the bar from rotating.
There was indeed a bonding bar that attached the two bars...but Siemens also attached a big lug to the top of both bars (one for neutral and one for ground). I guess we could have put a big lug in somewhere else for grounding conductor and then installed a couple of other ground bars, leaving one of the Siemens provided lugs empty. But what a poor design this thing is.
Will multiple neutrals under one screw pass inspection? I almost always run 12 gauge to the panel so all the wires will be the same size.
Thanks for the response. MERC.
Those lugs mounted to the bars are removable if you remove the set screw and remove the mounting screw. Usually a torx screw. You can usually remount them to any bars of a similar design.
I hear stories about it not passing because of multiple conductors in a single hole but I have done many and never had a problem. Used only where necessary and neatly done I cannot imagine any problems but it will depend on the inspectors.
If they see you busting your hump to find out what is right and do things right because they should be done right, not just because the inspectors are looking, they are more likely to be understanding. If they think your trying to put one over or treat them like the enemy they are more likely to be sticklers and to follow strict procedures.
By rights a thirty breaker panel should have at least thirty holes available so there should be no issues.
Think of it in terms of legal liability. If you design and install a neutral bar, the finger points squarely at you. If you install the panel manufacturer's bar per their instructions, they're on the hook, not you. Inspectors also have a much easier time saying yes to something done the manufacturer's way than a home brew.
-- J.S.