main breaker panel configuration

[wirenut]

i am wiring a new house and installing a square d 200 amp main service panel. out of the box the two neutral buses are joined. i plan to install parallel add on buses mounted directly to the panel for my separate ground. so the white would go to the neutral bus and the bare copper to the ground bus. is this correct.
second question. i plan to use 2/0 copper thhn entrance cable for the two hots and the neutral. what do i use for the ground wire and how do i get it into the box.
thank you.

[mdshunk]

With regards to ground wire size for service equipment, you need a #6 copper to the ground rod(s) and a #4 copper to the cold water pipe within 5' of where it enters the building (if one exists). I generally just bring them in a knockout hole. Most panels have a few real small knockouts for the ground wire.

You said this is a service panel. If this is in fact service equipment, then you need to install the green bonding screw that comes with the panel in the neutral bar, so that the neutral bar in bonded to the box. The grounds and neutrals all terminate on the same bar(s) in service equipement. You should have plenty of "holes". If you have a seperate service disconnect right after the meter, then this is not a service panel at all... it would just be a subpanel. In that case, neutrals and grounds must remain separated and the bonding screw left out and a ground bar kit(s) installed.

[wirenut]

thnak you for the clarification. the main disconnect is in the meter service panel on the outside of the house so i guess this is a sub panel. the two panels will be basically back to back. i plan on using the rebar grid in the fooring as the ground. from what i have pieced together in my readings, i would use the 2/0 copper for the two hots and the neutral from the load side of the main disconnect on the meter panel. i plan to use #4 copper bare ground from the grounding circuit (rebar) and bring this in to the main sub panel to the ground bus. i also plan on using a breaker in the meter panel as the main disconnect for my outside air conditioner unit since it is within 6 feet of the panel. is this okay. so much to keep up with. this site and the wonderful articles are so helpful. thanks for the reply

[mdshunk]

Do you really have rebar in your floor? Maybe in the footers. I'd have only thought you would have had #6 wire mesh. I have *zero* experience using rebar (or wire mesh) as the grounding electrode. I *think* these systems have to be engineered ahead of time with grounding in mind (extra tie wires and tie wires made up extra tight). I'm interested to see what develops in this thread from that thought. Is there some major objection to driving a couple of ground rods? I'm not sure what the approved connector for copper wire to rebar is. I would think you'd have to CadWeld it with a CadWeld kit. Since your panel and your service disconnect are so close, I'd put a breaker in the panel and feed the a/c through a breaker. I think that "just because it's allowed" is not a good enough reason to double lug the main disconnect to feed the condensing unit. I'm beginning to wonder in the back of my mind if this is a real post or not? Nearly every sentence sounds like "bait". Seems like you're gonna need at least 3/0 copper, also. The 2/0 you're wanting so badly to use is only okay for about 175 amps.

[wirenut]

the rebar is in the footing. fooring was my misspelling, sorry. yes the rebar was tied good with the anticipation of using it for the ground. in fact it is required in our local code because of the rocky conditions and people were not able to drive grounding rods far enough into the ground and would therefore cut them off when they could no longer drive them any deeper.
on the 2/0 copper for the 200 amp service, i read in mr. goodrich's article on wiring meters,etc. that 2/0 copper was the choice for 200 amp service. did i read this wrong.
on the air conditioner main breaker being in the meter panel maybe i wasn't clear but my meter panel is the type which has the 200 amp main disconnect and space for six breakers all of which can be accessed from outside the house. this is required here also so the fire department or emergency people can cut the power without having to enter the building. from what i know, the a/c can work off of a breaker installed in this outside panel if it is close enough to the unit.
no, i am not fooling you. i obviously don't know as much as you do and am asking for help and advice.

[mdshunk]

Sorry, wirenut. Sometimes I get thoughts and I'm better off biting my tongue (or keyboard finger in this case). It hasn't happened yet on this site that I know of, but sometimes folks will ask loaded questions that they know the answer to, in an effort to "stir the pot". As for the 2/0 and 3/0 thing. If Wg says 2/0, then 2/0 it is. I was just going off the top of my head on that one.

[Wgoodrich]

See NEC Table 310.15.B.6 for residential service conductors declaring 2/0 copper approved for 200 amp service in a dwelling.

HOpe this helps

Wg

[wirenut]

okay, thanks for the clarification on the 2/0 service cable. next step: i have run from the outside meter pan which contains the main disconnect into the main service panel for the whole house which is i guess is a sub panel by definition. in this sub panel do i run the white neutral wires to the neutral bus and the bare copper ground to a separate bus ( a ground bus). since the ground bus is screwed directly to the sub panel is there any other bonding that i have to do. do i run the # 4 copper ground wire to this bus only. thank you
oh, do i have to bring the ground wire into the meter panel?

[Speedy Petey]

All the grounding electrode conductors must go to the main panel. The outside panel in your case.
Do you have municipal water with a metal pipe entering the building?

[wirenut]

i have copper pipe in the slab but it will be pvc from the meter to the house.
all grounds to the main panel? do i then run them into the sub panel from there? thank you

[Speedy Petey]

The code for grounding electrode conductors is only concerned with how the water enters the building. Since it's plastic it's a non-issue. You do however have to bond the metal water piping in the house with #4 copper. This connection can be made anywhere accessible to a cold water pipe. This wire is to be run to the main panel also.

"do i then run them into the sub panel from there?" NO, these wires are run to the main panel only.

How are you feeding the panel inside the house? Cable or conduit?

[wirenut]

The code for grounding electrode conductors is only concerned with how the water enters the building. Since it's plastic it's a non-issue. You do however have to bond the metal water piping in the house with #4 copper. This connection can be made anywhere accessible to a cold water pipe. This wire is to be run to the main panel also.

"do i then run them into the sub panel from there?" NO, these wires are run to the main panel only.

How are you feeding the panel inside the house? Cable or conduit?
the house panel is basically back to back with the outside main panel. i would like to use the 2/0 copper for this short run inside conduit.

[suemarkp]

You'll need 3 pieces of 2/0 from the outside panel to the inside one (two hots and a neutral), and you'll also need a #6 copper for the equipment grounding wire. You don't need to bond anything else in the inside panel, so you need to make sure the green bonding screw that is sometimes installed in the neutral bus is NOT installed in the inside panel (neutral must be on isolated plastic feet with no binding screw). The grounding bus should be directly bolted to the inside panel chassis.

In the outside panel, you need to make sure that the neutral bonding screw IS installed in that meter/panel combination box, because neutral and ground are one and the same in only this panel.

Differentiate between grounding electrode conductors (GEC) and equipment ground conductors (EGC). The GEC's must be connected to your outside panel (the Ufer footing ground, and any ground rods). The only time a GEC can connect to a subpanel is when that subpanel is at a detached building. The EGC's of each branch circuit can terminate on the grounding bus of the inside panel.

If any of your interior water pipes are metal (except for short stubs), you must bond them with a #4 copper wire. However, I must admit I don't know whether this must connect to your outside panel ground, or if it is allowed to connect to the inside panel grounding bus. I would think that since we're just bonding the pipes and not using them for a grounding electrode, either panel would be allowed.

[wirenut]

You'll need 3 pieces of 2/0 from the outside panel to the inside one (two hots and a neutral), and you'll also need a #6 copper for the equipment grounding wire. You don't need to bond anything else in the inside panel, so you need to make sure the green bonding screw that is sometimes installed in the neutral bus is NOT installed in the inside panel (neutral must be on isolated plastic feet with no binding screw). The grounding bus should be directly bolted to the inside panel chassis.

In the outside panel, you need to make sure that the neutral bonding screw IS installed in that meter/panel combination box, because neutral and ground are one and the same in only this panel.

Differentiate between grounding electrode conductors (GEC) and equipment ground conductors (EGC). The GEC's must be connected to your outside panel (the Ufer footing ground, and any ground rods). The only time a GEC can connect to a subpanel is when that subpanel is at a detached building. The EGC's of each branch circuit can terminate on the grounding bus of the inside panel.

If any of your interior water pipes are metal (except for short stubs), you must bond them with a #4 copper wire. However, I must admit I don't know whether this must connect to your outside panel ground, or if it is allowed to connect to the inside panel grounding bus. I would think that since we're just bonding the pipes and not using them for a grounding electrode, either panel would be allowed.
next question: how does the main inside sub panel get the ground for its ground bus?

[Speedy Petey]

From the #6 mentioned in the previous post.

[Frank]

I'm not trying to hijack this thread, but why would #4 be required to bond the interior water pipe system when #6 is used for the service panel ground? Is this referenced specifically in chap. 250?

thanks

[suemarkp]

I know it doesn't make sense, but the water pipe bond must be per table 250.66 which is the grounding electrode table. Normally, bonding conductor size would be per table 250.122. I can only guess that they're afraid that somehow you'll convert your plumbing to have a metal pipe out into the earth. Then, you'll have a properly sized conductor if they forced you to use 250.66 from the beginning. You also have to use 250.66 when bonding a structural steel framework that is not intentionally grounded.

Here's the code:
250.104 Bonding of Piping Systems and Exposed Structural
Steel.
(A) Metal Water Piping. The metal water piping system shall be bonded as required in (l), (2), (3), or (4) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of ttachment
of the bonding jumper(s) shall be accessible.
(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and(A)(3).

One thing I did at my house which I wasn't sure if it was correct, was to run a conductor to the cold water pipe per 250.66 (which is 1/0 copper for my 400A service) but then I used smaller conductors sized per 250.122 to bond the hot water and metal drains.

[wirenut]

I know it doesn't make sense, but the water pipe bond must be per table 250.66 which is the grounding electrode table. Normally, bonding conductor size would be per table 250.122. I can only guess that they're afraid that somehow you'll convert your plumbing to have a metal pipe out into the earth. Then, you'll have a properly sized conductor if they forced you to use 250.66 from the beginning. You also have to use 250.66 when bonding a structural steel framework that is not intentionally grounded.

Here's the code:
250.104 Bonding of Piping Systems and Exposed Structural
Steel.
(A) Metal Water Piping. The metal water piping system shall be bonded as required in (l), (2), (3), or (4) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of ttachment
of the bonding jumper(s) shall be accessible.
(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and(A)(3).

One thing I did at my house which I wasn't sure if it was correct, was to run a conductor to the cold water pipe per 250.66 (which is 1/0 copper for my 400A service) but then I used smaller conductors sized per 250.122 to bond the hot water and metal drains.
mark, thanks for clearing things up. i didn't know i would have to hire a lawyer to interpret the code:)

[Frank]

Yes, thank you.

[Wgoodrich]

The grounding electrode or group of grounding electrodes are paths to ground listed in 250.50 all connected by a grounding electrode conductor to the main service rated panel. Everything after that main service rated panel must have separate neutals separated from the separate equipment grounding conductor. A point of confusion is the grounding electrode conductor is required to join with the main service neutral conductor either on the line side or inside the main service rated panel. The neutral service conductor located between the point of connection of the serving power company and within the main service rated panel may serve as a dual purpose wire being both grounding [grounding electrode conductor] and grounded [service neutral conductor].

Any grounding conductor after that or on the load side of that main service rated panel including any sub panels must be served by the grounding bar of that main service rated panel or disconnect.

The grounding and hte neutral are joined at that main service rated panel or disconnect and everywhere on the line side of that main service between the main service rated panel and the weather head including inside the meter base. All grounding electrodes in contact with earth must be connected to the main service rated panel or meterbase located between the power company connection and within the main service rated panel or disconnect.

All other grounding in that building must be served by the grounding bar inside that main service rated panel or disconnect as a green or bare equipment grounding wire in any feeder or branch circuit. Sub panels get their grounding by an equipment grounding conductor ran with the feeder from that main service rated grounding bar serving ground to that sub panel from within that main service rated panel providing power to that sub panel.

Water pipes now not in contact with earth may some day become in contact with earth thus the grounding wire bonding any metal water pipe in contact with or not in contact with the earth must be sized as a grounding electrode conductor. Metal water pipe in contact with earth used as a grounding electrode must be connected within 5' of contact with earth. Any metal water pipe not in contact with the earth must be made connected electrically with the grounding bar in the main service rated panel or disconnect.

Hope this helps

Wg

[wirenut]

WG and all, thanks for your preciseness and patience. i am finally recognizing the difference in terminology between the service entrance and the sub panel and the GEC. this is what i think i need to do now.
1. run #4 copper from the grounded electrode to the ground lug on the line side of the main disconnect which happens to be integrated into the meter panel enclosure.
2. run #4 copper from the ground lug on the load side of the main disconnect to the ground bus bar in my main sub panel inside the house.
3. run 2/0 copper from the neutral and 2 hot lugs on the load side of the main disconnect into the main sub panel in the house to the same respective lugs.
4. run #4 copper from the water pipe in the house to the ground bus bar in the main sub panel in the house.
is this correct?
5. the outside service panel and the inside sub panel will be mounted back to back using a 2 inch nipple passage. does this nipple need a grounding bushing. the line side neutral lug is attached directly to the cabinet so this would seem redundant.
thanks ever so much for sharing the expertise of you people answering these questions.

[suemarkp]

You're getting closer!

Item #1 is OK (except you have a groundING electrode, not a groundED electrode).

For #2, you can use #6 copper green or bare wire if you want, but there is nothing wrong with using the larger size.

Item #3 is correct.

For #4, the wire from the water pipe must go to the Service Equipment. The inside panel is a subpanel and not a Service rated panel. So it needs to go to the outside panel (can go through the inside panel and nipple to the outside panel if that simplifies things, you just can't terminate it at the inside panel). What you propose may be allowed since you have a #4 EGC to the subpanel. But the code says the pipe bonding wire must terminate in the service, and you're effectively putting a splice in this wire located at the equipment grounding bus in the subpanel. If you really want to do it this way, I'd check with your inspector or else he may make you run it outside (and you'll be a few feet short).

For #5, use a PVC nipple and there will be no questions that bonding is not required. If you use metal, normally this would not have to be bonded since Service Conductors are not going through this nipple (but you must either scrape the paint away or use locknuts with the twisted ears so they bite into the metal panel). However, if you expand the water pipe to go out into the earth, then that #4 to the water pipes becomes a grounding electrode conductor. This would require bonding of the conduit if it was metal. If you are just bonding your water pipe and not using it as a grounding electrode, then they shouldn't make you bond the conduit. Plastic conduit will save a lot of effort because getting the precise length is easy unless you have a conduit threader.

[wirenut]

:) Thank you mark. let me add that this house is on a slab so the copper water pipe is in the ground under the slab. the line from the water meter is pvc.

[suemarkp]

How far in the ground is it copper? If it goes 10' or more before transitioning to PVC, then it must be used as a grounding electrode. Don't know if you have to prove to inspector that it doesn't go into the ground that far or not.... If most houses in your area are built like this, and only a short stub is metal in the earth, then you may be fine.

You may just want to go ahead and pretend it goes into the ground. This means you must attach the #4 wire to the pipe within 5' of where it comes in from the outside. However, if this area is not accessible (the ground wire clamp must be accessible), then you'll need to consult with the inspector for what to do.

[wirenut]

mark, the cold water pipe is pvc from the meter at the street all the way to the house. at the house it ties into the copper line that runs all over under the house. all of this line is buried approximately one foot under the slab in the ground.
wally

[Wgoodrich]

This line will surface under a sink or tub coming out of the concrete floor. This copper if 3/4" size is in direct contact with earth [concrete] for more than 10' so some where where it comes out of hte concrete floor you must tap within 5' of it entering the house and used as a part of the grounding electrode system. Then a jumper must be connected between the hot and cold. A second grounding electrode [commonly a ground rod] must be also attached or installed to be a secondary grounding electrode when a water pipe is used as a grounding electrode.

Good Luck

Wg

[wirenut]

WG, something i just thought of. all of the copper pipe that is under the slab is encased in styrofoam insulation so none of it is in contact with the ground. that is code here that the pipe has to be enclosed in the slide on styrofoam tubing. in my opinion that removes the pipe as a source of ground. i do understand why you still need to ground the pipe in the event that a frayed wire came in contact with the pipe, correct. thank you

[Wgoodrich]

You are right this piping is isolated from contact with earth and must be bonded but can't be a source of grounding electrode in contact with earth.

Wg

[lingalls]

You said this is a service panel. If this is in fact service equipment, then you need to install the green bonding screw that comes with the panel in the neutral bar, so that the neutral bar in bonded to the box. The grounds and neutrals all terminate on the same bar(s) in service equipement. You should have plenty of "holes". If you have a seperate service disconnect right after the meter, then this is not a service panel at all... it would just be a subpanel. In that case, neutrals and grounds must remain separated and the bonding screw left out and a ground bar kit(s) installed.

This thread is what I have been endlessly searching the internet to find!!

We just tried for our permanent service inspection, (so that the inspector can call the elec. co. to let them know that we are ready for service,) and failed on one little item. He told me that the only thing we were missing was the little green screw that goes over the right bus bar (which I had assumed to be the grounding bus bar.) He was even going to put it in for us right there, but we couldn't find the little screw. The problem is that the place that he wanted us to put it is a non-threaded shallow hole, which doesn't even go through the box. It doesn't seem designed for a screw. The question is - should I be looking for another hole? or am I supposed to drill this hole so that I can put my screw in? This problem has been holding us up for so long! Any help is greatly appreciated, and please be patient with me - I am not so electrically savvy.

Laura

[suemarkp]

Hmmm. In the myriad of labels on your panel, does it say somewhere "Suitable for use as Service Equipment"? If so, that means it has provisions for the bonding screw. Perhaps the inspector was looking in the wrong place. There are many ways these screws can be done by the manufacturer. Did you buy this panel new? It should have come with the screw, either already inserted or on a little card labeled "bonding screw".

Do you know the brand and model of the panel? Is it recent or old? How large is it (100A, 200A)? Most newer 200A panels have a bar that connects the neutral and grounding bus together. There is a silver S hook shaped thing that connects the bar to a neutral bus terminal. There is a green screw that bonds the bar and hook to the panel chassis. Sometimes, screws like this need to cut their own threads, but the hole must be all the way through the sheet metal chassis in order for the screw to cut its own threads. See if the hole is just painted closed or if you can easily punch out the hole with a punch or nail set. Don't pound hard, as if this isn't where its supposed to go, you'll dent the panel. I would not expect most modern panels to require you to drill the bonding screw hole -- this is something that most installs require and the factory should have done it all for you.

If you have a smaller panel (like most 100A ones), they typically just have a long green screw that goes through the neutral bar and screws into a hole in the chassis. Again, the screw may need to cut its own threads, so it may be difficult to get this screw inserted.

If you've lost the screw and the panel is recent, you can probably buy a new screw from an electrical supply house (you'll need the panel make and model number). These must be green and they are usually hard (so they'll cut threads). You'll probably pay $5 for a stupid green screw though.

[lingalls]

Thanks for your reply. I had also posted something in the electrical repair forum because I found a similar thread about this same green screw again.

I am fairly sure that we have a Square D, 200 Amp panel - brand new. I read on Square D's website that the box should have a wiring diagram on the inside, which tells where the bonding screw should go. I am planning to go and take a look at this box tomorrow. Hopefully then, it will just be a matter of finding this type of screw. Ours was definitely lost. I am definitely going to try my local electrical supply co.

Thanks so much for your help!
Laura