I have a garage and a house. They are connected by a breezeway. The garage is now considered attached. I want to put a 400 amp panel in the garage. I want to make the 200 amp house panel a sub panel. The garage has no water pipes. The house main panel is bonded to the water pipes. I plan to drive two electrodes at the new 400 amp service in the garage, and pipe a four wire new run to the house panel. Do I have to run a bonding (water pipe) conductor to the house? If so, can I connect the bonding conductor to the isolated ground (bonded and grounded) in the 200 amp sub panel? There is an electrode at the house that is now my sub panel. The neutral and ground will be seperated.
If I must run a (water pipe) bonding wire to the house, can I run it in the conduit with the other four conductors?
Also, Should I size the bonding conductor for 200 amp or 400 amp. I appreciate any comments or suggestions.....John

Why do you want a 400A panel in the garage, and will your local POCO even let you put one that big on your garage?

I see no reason why you need more than the 4 wire feeder. The water pipe is bonded to the ground rods via the EGC in the feeder.

I agree. I did exactly the same install on my house a couple years ago - just with a 200A main and 100A existing in the house. That satisfied the inspector.

That is why I posted the question. I too assumed that the EGC and EMT would allow for a four wire feeder to the 200 amp sub panel. But I am getting conflicting advise on this matter. Several members at the Mike Holt forum have indicated that I need a bonding conductor seperate from the feeder to the sub panel, to go all the way to the house unbroken and connected to the water line at the house. Just as if the new service was at the house. I have also been advised that I can go with a three wire feeder since I am using EMT. I am going to contact the inspector and see what he requires. thanks for your feedback fellow forum members.......John

ps....400 amp service is needed for the new testing facility that will be in the garage.

The way I see it the main panel at the garage will need a GEC going unbroken back to the water meter.

Its going to bubble down to what the inspector wants to see.

What my inspector said was he is no longer considering the water supply as a ground. It simply needs to be bonded along with the gas supply.

That said, I do not have water or gas in the garage area. They are contained to the house where it is served by the existing panel. So that may be a factor.

Like LK said if it's an attached garage.

I suppose it gets down to what 250.64(C) exception means
.

It doesn't say "busbars in the same enclosure"

Unbroken, OR spliced via busbars or exothermic welds. Routing the GEC through the existing panel's busbar is acceptable per 250.64. In this case, the ground between the two panels is an GEC and must be a discrete wire sized IAW 250.66.

That said, the GEC is still required to be as short and straight as possible*, so the AHJ may feel routing through the old panel is unnecessarily circuitous and may require a more direct connection between the new panel and ground. In this case, the connection between the two panels is no longer a GEC, but merely an EGC, and EMT is acceptable if properly bonded.

* 250.4(A)(1) became stricter about this in NEC 2008.

OTOH you could just say that water pipe transitions to plastic right outside the wall (and it might) then you are only doing 250.104 bonding.

Greg, I am asumming that you are correct about the water supply pipe being PVC. I haven't been in the crawl space yet. I gotta go now but I will check out 250.104 as soon as I get back. Depending on the inspector, I will most likely have to run a #2 all the way from the new 400 to the water line under the house and within four foot of where it enters. 150 feet. This is going to be an issue as it cannot be run underground. It has to travel through the garage, the breezeway, the house, then down through the house then over to the water line. I hope the inspector can make life a little easier. The customer said if he has to he will hire a carpenter to detach the garage, even if it is only a few inches. But then I have a common slab to content with. Anyone see an issue with the slab?

Why wold detaching it change things?

yur only hope is the water main is Plastic.

This running of the GEC on jobs like this is a common thing, I can't see why the owner is all bent out of shape.

Detaching the garage would allow for a second service drop, eliminating the long bonding conductor run. Two rods bonded at the new service and your done. Since the structures are connected only one service drop is permitted.

Greg,

Can't JValdes run a 3 wire from the house to the garage, and drive ground rods at the garage and tie the neutrals/grounds together at the garage and make it a sub feeder or sub service? This would also protect an out building if the out building had a metal or gas pipe from the house to the out building. Right?

I don't usually comment on technical things but this one - I gotta say this:

Please don't use a separate grounding connection to the planet(earth) to the sub-panel.

We've run into a couple of cases where this happened and it leads to all kinds of problems. Corrosion of ground connections is one of them, depending on the soil conditions that you might run into. It's a problem that happens almost right away - within a few days sometimes, the connectors tying into the earth (water pipe, ground rod/plate - whatever)grow a lovely white insulating substance on them and the lights and all the household electronics start to go all weirdo on everybody as the EGC's go a bit resistive and start to get significant voltage differences between the EGC and the neutrals in the separate panels.

This is not to mention the possible damage to the metal water pipes that might be tied into the vicinity, which could be a whole other set of problems down the road. (Not for you, mind you, just the poor unlucky turd herder that can't figure out how come the pipes are rotting away so quickly).

We now know it's best to just run good old #6 or #4 copper, in your case, if it's a longer run, right back to the main panelboard and tie it all together neatly in one spot to one connection to good old planet earth.

I do not know how sub panels are wired in Canada, but it sounds like to me the sub panel had the neutral and ground bonded. That is a no no in the US unless the feeder does not include a grounding conductor. Of the sub was not bonded and no grounding conuctor was with the feeder and you had ground fault that was not clearing (long shot).

Re: Canadian sub panels: I think they are the same here as in the U.S.. The neutral must NOT be bonded to the enclosure, unless it is fed by a separate 3-wire sub service which in that case you would have to bond the neutral and drive rods or use a plate.. Personally I agree with Check Pilot 100%.. Separate bonding conductor back to the main, and ONE connection between the earth and your neutrals. Way less headaches and chances of weird things happening.

A.D

Could you run a conduit to the house from the garage and use #2 as the ground. Then continue the #2 to the water pipe. The rods would terminate at the main as well as the sub panel, water pipe. As long as the ground and neutral and ground are separate you are good to go. I think 250.30 allows this. Please correct me if i'm wrong:)

Ob

Obsaleet,
Yes, That is exactly what must be done. It (bond conductor) does not have to be in conduit though. Also, I can pull three wires if I use metal conduit which I will not do. So it's 4 wires and the long bonding conductor run.