Superfluous grounding screw in Square D main panel?

[Parke]

I am replacing an old Square D 200 amp 20 space panel with a new Square D 200 A, 42 space panel, both QO series. The new panel came with a large box bonding (green) screw with the comment "When it is required to bond the box to to neutral, use screw on this card."

My understanding is that panels with a main breaker installed, the neutral bars are bonded to the ground bars, and the ground bar is bonded to the box. This would make the box bonding screw superfluous in a standard installation, yes?

 

[Bert_]

The screw will bond the neutral to the can (ground).

It makes no difference if the panel comes with a main installed, the screw is always included but not installed.

If this panel is the first disconnect, or service panel, then the screw MUST be installed. If you will be using it as a sub panel then do not install the screw, in this case you may need to purchase a separate ground bus. Many panels do not come with a dedicated ground bus.

 

[Parke]

It is the main panel (which of course has the main breaker for the house). So I will install the screw.

So the silly question is where? It is not obvious as the screw doesn't appear to be long enough to reach the box from the neutral bar.

 

[zmaxmotorsports]

Right in the middle in the jumper connecting the 2 neutral buss bars under main,there's a hole for it.

 

[AntonLargiader]

It is the main panel (which of course has the main breaker for the house). So I will install the screw.

If you have an outside disconnect, the main panel is not the service panel and you do not use the screw.

 

[Parke]

There is an exterior meter box, which when the meter is pulled the house is de-energized. Does that count as an outside disconnect?

 

[Parke]

Zmax, are you saying under the screw hole is located under the main breaker?

 

[AntonLargiader]

There is an exterior meter box, which when the meter is pulled the house is de-energized. Does that count as an outside disconnect?

No. Sounds like you don't have one.

Around here, an outside disconnect typically looks like a tall box with one double breaker in it:

http://www.gordonelectricsupply.com/tsimages/SQAREDE53302_TWB_1_PE_Q22200NRB.jpg

They can be integrated with other things like the meter, though. Bottom line is, the first point of disconnect (not the meter) is where the neutral and ground are bonded. Downstream of that, they are separate so you would not use a bonding screw in the panel. If your main breaker panel is the first means of disconnect after the meter itself, then you do use the bonding screw there.

 

[zmaxmotorsports]

Zmax, are you saying under the screw hole is located under the main breaker?

Yes,in the middle of the jumper.
The hole in the bar is not threaded,it passes through the bar and threads into the back of the panel.

 

[i4ni]

What if your disconnect is on the pole?

 

[zmaxmotorsports]

What if your disconnect is on the pole?

Then the box inside inside of house is a,sub panel and you don't use the screw.
You'll need a 4 wire feed though.

 

[wyliesdiesels]

There is an exterior meter box, which when the meter is pulled the house is de-energized. Does that count as an outside disconnect?

NO. A meter is not a disconnect.

Post some pics of your inside and outside panels...

What if your disconnect is on the pole?

Then all downstream panels are subpanels.

With that being said, prior to 2008, panels in detached structures were allowed to be 3-wire with a bonded neutral bar...

 

[sberry]

With that being said, prior to 2008, panels in detached structures were allowed to be 3-wire with a bonded neutral bar...

Going along with this, any panel fed only 3 wire needs a bond to the box. Old fuse panels had a rivet in them and now are no good as subs for this reason. My neighbor used one in his garage but he drilled it out and added a bar. The previous owner had used 4 wire but used an old panel, I guess he didn't want to replace it which would have been as easy. Its now wired right but the problem with doing something like that is not everyone understands it.
I just did a follow up from a handyman type that did a neighbors garage. At least he used the right feed wire but left the panel floating and landed the ground on the N bar. I added a bar and a ground rod. Moved the egc over to it as well as the branch circuit grounds.

 

[Parke]

Pic of the new panel hopefully attached

 

[Parke]

Picture of the outside meter box

 

[Parke]

Close up of the neutral, ground buses and main breaker. There just isn't a hole to fit the screw that goes through to the panel on the junction bar or on any of the buses. I'm thinking the screw is for some oddball case if someone uses the panel for a sub panel and disconnects the existing ground buses and relocates them elsewhere in the box.

 

[sherrod624]

its the square hole just to the side of the feeder lug

 

[mm08822]

Close up of the neutral, ground buses and main breaker. There just isn't a hole to fit the screw that goes through to the panel on the junction bar or on any of the buses. I'm thinking the screw is for some oddball case if someone uses the panel for a sub panel and disconnects the existing ground buses and relocates them elsewhere in the box.

See attached pic:

You need the bonding screw installed at green circle
wrong lug used for neutral/grd on right side of panel
All Al connections look dry - no penetrox used
I would also pull all lug set screws and coat all threads with penetrox too.

 

[sberry]

See attached pic:

You need the bonding screw installed at green circle
wrong lug used for neutral/grd on right side of panel
All Al connections look dry - no penetrox used
I would also pull of lug set screws a coat threads with penetrox too

Yes, I put a fizz on all the treads in those. meter bases too.

 

[Parke]

Thanks for the observations.
You need the bonding screw installed at green circle

That hole bottoms out on the plastic base of the bus mount. There are no threads inside to hold a screw, and unfortunately, it is also to small for the green screw provided. There is a square hole above the round hole that does fit the screw, but again it bottoms out on the plastic base and has no threads.

wrong lug used for neutral/grd on right side of panel

Copy that. Will replace. For the record, wrong size or... what?

This stranded wire apparently runs to the copper piping after the well line enters the house. Not sure what its purpose is as there is a whole house filter on the water line between entry and the point of connection, and that the pipe coming into the house is plastic. But I figure this is the "backup" neutral ground to the box as the Al cable runs through a metal connector clamp exiting the panel box. In the old panel, it was doubled tapped with the incoming yellow neutral. As I reversed the new panel, it wouldn't reach the nice convenient additional neutral lug at the bottom, so I opted for the neutral bus.

All Al connections look dry - no penetrox used

I used Noalox on the main feeds and lugs at the bottom. I didn't use it on the smaller AL wires. I debated it but didn't do it, probably because I always lose debates.

 

[AntonLargiader]

I think you will find the lower left hole in that image to fit the green screw. That's roughly what it looks like on my SD panel. Can you see what's under it well enough to see if it would bond the box?

 

[Parke]

Anton, yeppers. The sheathing is visible at the back of that hole. I tried the screw there a couple of times with no luck. But, since you asked, I took another gander and even though it looks like some kind of interior lip at the panel, the screw just bottoms out on the sheathing without catching anything. Plus, this hole is actually on the left ground bus.

 

[mm08822]

Thanks for the observations.
You need the bonding screw installed at green circle

That hole bottoms out on the plastic base of the bus mount. There are no threads inside to hold a screw. Anton answered it right. see pic.

wrong lug used for neutral/grd on right side of panel

Copy that. Will replace. For the record, wrong size or... what?

Not listed for panel and can easily rotate. see other pic.

This stranded wire apparently runs to the copper piping after the well line enters the house. Not sure what its purpose is as there is a whole house filter on the water line between entry and the point of connection, and that the pipe coming into the house is plastic. But I figure this is the "backup" neutral ground to the box as the Al cable runs through a metal connector clamp exiting the panel box. In the old panel, it was doubled tapped with the incoming yellow neutral. As I reversed the new panel, it wouldn't reach the nice convenient additional neutral lug at the bottom, so I opted for the neutral bus. In the earlier days, that was your system ground with a jumper around the water meter out to the steel water distribution system. Now with all of the plastic pipe, ground rods or ufers are used and that same wire is now just used to bond the copper water pipe in the house to the electrical system for safety.

All Al connections look dry - no penetrox used

I used Noalox on the main feeds and lugs at the bottom. I didn't use it on the smaller AL wires. I debated it but didn't do it, probably because I always lose debates.

Ok, as long as you used it. I would still do them all - only 2 minutes and done.

 

[mm08822]

Anton, yeppers. The sheathing is visible at the back of that hole. I tried the screw there a couple of times with no luck. But, since you asked, I took another gander and even though it looks like some kind of interior lip at the panel, the screw just bottoms out on the sheathing without catching anything. Plus, this hole is actually on the left ground bus.

Is there a 3/16" -1/4" of thread left before the screw head would bottom out when you feel the end screw contact the sheathing? If so, just push harder to get the threads started in the enclosure housing as you "drill" through the sheathing..

 

[AntonLargiader]

If it is like similar panels that I have seen, both buses are neutral buses and you either a) put grounds on those buses and bond the panel, or b) add ground bars to the back of the panel and don't bond it. Aren't those two buses electrically connected by a bar under the neutral lug?

 

[mm08822]

If it is like similar panels that I have seen, both buses are neutral buses and you either a) put grounds on those buses and bond the panel, or b) add ground bars to the back of the panel and don't bond it. Aren't those two buses electrically connected by a bar under the neutral lug?

Yes but you still need a way to bond the neutral to the enclosure/ground.

OP, try this pic - pull the screw and see if it goes to the bottom of the enclosure to a threaded hole.


And what is the panel cat #?

 

[wyliesdiesels]

Its weird that the bond screw didnt come on the bar from the factory or the correct location wasnt identified.

OP- did you buy this new?

 

[mm08822]

Is the screw the correct one - as in correct length? Try a longer screw of same thread just to see if it bites into back of enclosure.

You definitely tried this location where the green screw is?

 

[Parke]

Ta Da!!!

mm08822 persistence has solved the problem. I finally did something smart and measured the depth of the recommended hole from the bar to the sheathing. It happens to be 1/8 inch deeper than the screw is long (1 1/2 vs ~1 7/16). So the next smart thing I did was get a bigger screw driver and put more ummphh into it. The screw finally bit and I drove it flush to the bus bar.

The bonding screw is self tapping essentially, which wan't what I was expecting. It apparently threads the panel. There is a "swelling" of the panel at the back but no threads present on the bus bar or the panel hole.

Lesson learned.

I have also gone ahead and applied the Noalox to the 2-2-2-4 Al SER sub panel feed cables. I'll pick up a new lug later today.

Regarding other questions, yes it is a new panel, picked up at HD, Square D Q0142M200PC.

Thanks everyone for all the assistance and patience for what seems like a silly little question, but I really appreciate getting things right.

 

[Parke]

So, before and after pics:

Old hot mess: 20 space panel with 19 occupied. 11" wide box which leaves no room left for the gutters.

The craziest thing is that once I removed the service cables, I found a sticker in the back of the panel identifying the box as a QON 20-40 MG200 Series L5 and to use QO, QOT, Q1 and Q1-A circuit breakers. I can't believe that this would be okay to run somewhere north of 30 circuits in this panel.

 

[Parke]

New happiness:

42 spaces with a generator interlock kit installed (and generator inlet plug installed outside) and plenty of room to permit remodeling a 43 year old kitchen and to add a few other lines.

 

[Parke]

Sorry, I have no idea why the pics are sideways.

 

[wyliesdiesels]

Good job.

Nice quality upgrade.

And the sideways issue with the pics is a bug.

Thx for reminding me to ask the admins to fix it.

 

[mm08822]

Sometimes trouble is where you least expect it!!