Advice for a typical 400 amp residential service

[mark32]

Hello, having never had the opportunity to wire a 400 amp service, I was curious as to how I would do the install if I ever had to. Now living in FL, I see a lot of mains installed outside so I would do the same. I would mount two 200 amp main breakers in their own enclosures next to the meter pan. From there I would run a 4 conductor SE cable to the respective 200 amp panel. At this point I would then run a GEC to the water pipe from EACH of the 200 amp panels. Back outside I would run a GEC from each of the disconnects to the same ground rod. Does this configuration fly with anyone? I haven't done residential work in years and even when I did I wasn't exposed to a service of this size, so I hope this question wasn't dumb. Thanks.

 

[scrino]

Re: Advice for a typical 400 amp residential service

Typically, Ive seen parallels pulled from the meter base to two (2) 200 amp mcb panelboards in the basement. Why add all that cost, in addition, the outside wall of the residence wont look to pretty. Ever see a 400a meter base, quite hunky.

 

[mark32]

Re: Advice for a typical 400 amp residential service

Thank you scrino for your reply. I see your point in reference to maintaining the appearance on the outside of the house. However, in my scenario the main panels would be located quite a distance from where the meter would be located. Because of this, from my understanding, you'd want overcurrent protection on those feeder cables. Aside from that, in your scenario, how would you run your main and supplementary grounding electrode conductors? Would you run separate gec's from EACH panel, meaning, for instance, a #6 copper to a single ground rode and a #4 to the underground water pipe from EACH panel? That's (2) #6's and (2) #4's in total. Thank you for your insight, Mark

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

You have to run your GEC's and water pipe bond from the service side, not after the main disconnects. If you use two outside 200A disconnects as you suggest, you must ground from one of the two disconnects, or from the meter base, or from some other point along the service neutral. You can't ground the pipes from MLO panels inside the house. If they only have to be bonded as opposed to being a ground electrode, you may be able to do that from an inside panel as long as you have 1/0 copper EGC all the way back to the service neutral. Normally, your EGC wouldn't be nearly this large (a #6 for 200A would suffice).

The service neutral can do double duty and ground the second disconnect and remaining service equipment if you ground one of them (per 250.142). Note that if you're doing a full 400A service, you'll need a 1/0 copper to your water pipes -- takes a larger clamp than the typical #10-2 clamps. Your rods only needs to have a #6 copper.

 

[mark32]

Re: Advice for a typical 400 amp residential service

Hello suemarkp, thanks for your input. I can see some areas of my configuration wouldn't be feasible with the options I could take within the meter pan, meaning I could hit my ground rod right from the meter and I think I've read somewhere that some meter pans come with the mains in it. Again I've been out of circulation for a while, so I'm sorry if this is all old news. I will ask if you are positive about running the GEC from the water pipe all the way back to the main disconnect. I ask because I just checked the layout of our service and the GEC that runs to the water pipe originates in the main load center, which is wired as a sub panel, neutrals and equipment grounds are isolated. The GEC that goes to the ground rod comes out of the main disconnect outside next to the meter. I will agree that the GEC shall be connected to the grounded service conductor at the service as stated in 250.24(a), but this doesn't necessarily mean all GEC must be connected in the same enclosure, my parents house is an example of that. 250.24(d) states "Grounding Electrode Conductor. A GEC shall be used to connect the equipment grounding conductors, the service-equipment enclosures, and, where the system is grounded, the grounded service conductor to the grounding electrode(s)". I appreciate you taking the time to create your post and share your ideas which has caused me to do some research of my own. Thank you, Mark

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

I agree that the GEC's, if more than one, don't have to come from the same enclosure. But I think they must be unspliced from the service neutral. This would prohibit you from using the EGC bus in a subpanel -- that EGC was spliced once at the subpanel. I think 250.24(d) is telling you what purpose the GEC serves and not your limitations on how its installed. 250.24(A)1-5 tells you where it can or can't be. Article 250 can send you dancing all over the place to answer a question...

The first thing to verify is are you bonding your water pipes or are they one of your ground electrodes. If the supply pipe to the house is plastic, then you're just bonding. You can splice a bonding conductor, but not a GEC.

You are also permitted to bond ground electrodes to other electrodes, so you could run a wire from the ground rod to the water pipe. But you'll need to be using 1/0's the whole way in this case and that's hard to do with a rod acorn clamp.

I think no matter how you do things, you end up with a GEC that goes outside and one that goes inside if your water pipe in the dirt is metal. This means you poke a hole in the building to get one of those through to the other side. I chose to use one of my service conduits and passed through the meter can to a PVC conduit to a buried rod. The service conduit was already bonded on both ends, so no extra work there. The GEC didn't terminate in the meter enclosure, so I didn't violate local rules for that. Otherwise, plan for an LB fitting to get through the building for the GEC, preferably PVC.

 

[mark32]

Re: Advice for a typical 400 amp residential service

Thank you suemarkp very much for your informative post, it is appreciated. As you have said, this water pipe may not be a grounding electrode, something that I never before considered and something I'm not sure I can confirm or not. Either way, I now believe this conductor that currently bonds this water pipe, should, as you originally said, originate from the service equipment. I just read 250.104(a) which states: "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." As I see it, the water pipe at my parent's house has been bonded incorrectly, would you agree to that?

 

[jwelectric]

Re: Advice for a typical 400 amp residential service

A true water pipe ground is as rare as dentures for chickens around my neck of the woods for new construction.

When installing a 400 amp service on a dwelling unit the choice of equipment used will mandate the amount of work involved during the installation.

Here is a 400 that I am installing and as you can see all the points of grounding and bonding takes place here. Everything from here on is a lighting and appliance distribution panel (sub panel).

 

[LawnGuyLandSparky]

Re: Advice for a typical 400 amp residential service

Originally posted by jwelectric:
Just like an electrician, standing around doing nothing.

You may not be very fast, but you're sloppy!

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

Originally posted by mark32:
I now believe this conductor that currently bonds this water pipe, should, as you originally said, originate from the service equipment. I just read 250.104(a) which states: "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." As I see it, the water pipe at my parent's house has been bonded incorrectly, would you agree to that?

I'd say it depends on whether you're bonding or grounding because there are subtle differences allowed depending on which one you're doing. If you can't prove the outside pipe is plastic, then I'd assume this is a ground electrode. If that is the case, the wire from the pipe to the service neutral must be unspliced. Your parents connection is spliced in the subpanel. The EGC to the subpanel is probably too small also. The ground electrode conductor must be attached to the pipe within 5' of where the water pipe enters the house.

If you're just bonding and not grounding (outside pipe is plastic which would be common for houses built since the 70's), then you could bond it from a subpanel if the equipment grounds in all the feeder(s) upsteam that get you to the service neutral are sized at least as large as 250.66 requires. This is #4 for a 200A service and 1/0 for a 400A service. This is alowed because you can splice the water pipe bonding wire but not a GEC. It also can connect anywhere to the water pipe -- it doesn't have to be within 5' of where the pipe enters the house.

 

[mark32]

Re: Advice for a typical 400 amp residential service

Okay suemarkp I'm picking up what you're putting down. The contractor obviously viewed and determined this water pipe to be just a bond and not an grounding electrode, it now makes sense to me. Thanks a lot, Mark

 

[jwelectric]

Re: Advice for a typical 400 amp residential service

Hey Mark,
Do you see what happens to electricians when they get old in my post above?

 

[mark32]

Re: Advice for a typical 400 amp residential service

Hey Mike, I see you're always good for a few laughs. You're probably fun to work with. If I ever move back to NC I'm going to come work for you and to make extra cash I'll help you out on the farm you've got there. Have a good weekend, Mark

 

[LarryFine]

Re: Advice for a typical 400 amp residential service

Originally posted by suemarkp:
If you can't prove the outside pipe is plastic, then I'd assume this is a ground electrode.

Around here, the attitude is that, if you can't prove the pipe is metal, it's assumed to be plastic. Two rods, if you please.

 

[macmikeman]

Re: Advice for a typical 400 amp residential service

suemarkp, this post is not meant to bash in any way, it is just meant to bring attention to my own personal interpretation of the code book as it is written. I think you have been doing an excellent job in providing help to the original poster. But.....

Typically, I've seen parallels pulled from the meter base to two (2) 200 amp mcb panelboards in the basement. Why add all that cost, in addition, the outside wall of the residence wont look to pretty. Ever see a 400a meter base, quite hunky.

I do not remember very many basements on houses down in Florida, at least South, or East Coast Florida.

If that is the case, the wire from the pipe to the service neutral must be unspliced.

Please review 250.64(C)(3) Bonding jumper(s) from grounding electrode(s)and grounding electrode conductors shall be permitted to be connected to an aluminum or copper busbar not less than (This is America,I don't do Metric), 1/4" x 2". 250.64 actually has 4 exceptions regarding splices.

The ground electrode conductor must be attached to the pipe within 5' of where the water pipe enters the house.

250.52 (A)(1)"INTERIOR" metal water piping located more than 5 ft from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.

(the italics around interior were added by me for effect. On the exterior you could connect it at 6' or 7' or even 20' away from where it enters the building if you so wish.

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

Originally posted by LarryFine:

Originally posted by suemarkp:
If you can't prove the outside pipe is plastic, then I'd assume this is a ground electrode.

Around here, the attitude is that, if you can't prove the pipe is metal, it's assumed to be plastic. Two rods, if you please.

It doesn't matter if the water pipe is a ground electrode or not -- it needs to be supplemented with something, and two rods are what is normally used. The key to determining if they care about the source pipe material is whether you're connecting the water bonding conductor within 5' of where it enters the house or anyplace on that pipe.

 

[iwire]

Re: Advice for a typical 400 amp residential service

Originally posted by suemarkp:
It doesn't matter if the water pipe is a ground electrode or not -- it needs to be supplemented with something, and two rods are what is normally used.

I don't follow you here.

If you knew the water line was plastic and you had a uffer at the building no rods are required.

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

Originally posted by macmikeman:

suemarkp wrote: If that is the case, the wire from the pipe to the service neutral must be unspliced.

Please review 250.64(C)(3) Bonding jumper(s) from grounding electrode(s)and grounding electrode conductors shall be permitted to be connected to an aluminum or copper busbar not less than (This is America,I don't do Metric), 1/4" x 2". 250.64 actually has 4 exceptions regarding splices.

I always interpreted that to mean bus bars within the service equipment. But I don't see any words actually restricting this to service equipment, so perhaps you're right -- you can splice a GEC in a busbar perhaps even in a subpanel.

 

[suemarkp]

Re: Advice for a typical 400 amp residential service

Originally posted by iwire:
I don't follow you here.

If you knew the water line was plastic and you had a uffer at the building no rods are required.

The answer would be the same if the water pipe was all metal too if you have a Ufer. A metal water pipe electrode has to be supplemented by another electrode whether it be building steel, a ufer, or two rods.

My point was I don't see how declaring the water feed to be plastic reduces the number of other ground electrodes. All I see the water feed meterial affecting is the placmement of the 250.66 sized wire on the pipe -- either within 5' if an electrode, or anywhere if the feed is plastic.

 

[iwire]

Re: Advice for a typical 400 amp residential service

Here is a Handbook picture that shows one way of making GEC taps to separate service disconnect enclosures.

It shows disconnect switches but it could just as well be two 200 amp MCB panels.