Grounding two (mains and generator) power feeds

I'm posting this here instead of sci.engr.electrical.compliance because I'm looking more for technical answers, rather than code/legal answers.
This pertains to the US power system, either split single phase or wye three phase.
The mains power comes into the building at one point where a panel that splits that power into N different subfeeds. There is a main breaker and branch breakers for each subfeed. The generator power comes into the building at a different point where it has its own panel that splits that power into M (where M <= N) different subfeeds. There is a main breaker and branch breakers for each subfeed. Each of the subfeeds goes to a different area of the building where a transfer switch is located specific to that area of the build (except for areas fed by mains power only). Each area then has its own breaker panel to branch out to individual circuits.
The big question is how to properly ground this. Normally the panel at the service entrance would be grounded. But in this case, there are two service entrances at different locations.
Should both entrances be grounded? Should the grounds wires be run to a common (set of) ground electrode(s) or should the be separate?
Should the neutral be bonded to ground at both entrances or just one?
I'm assuming the neutrals would all be connected together via each of the area transfer switches.
It would seem to me there are a lot of opportunities for ground loops and other strange current paths. Keep in mind that some areas may be switched to generator while others are switched to mains (for example to wait until mains is considered stable before switching back). Also, some areas may be wired as single phase under a three phase setup. And just to make things even more complicated, consider the possibility that the one source might be single phase and the other source three phase, with most loads being single phase and roughly balanced.
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I know this will go on for weeks but the short answer is you only want one main bonding jumper in the system. If you do bond the neutral at the genset and at the service the transfer equipment will have to switch the neutral too.
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| I know this will go on for weeks but the short answer is you only want one main | bonding jumper in the system. If you do bond the neutral at the genset and at | the service the transfer equipment will have to switch the neutral too.
I was afraid of something like that. What I would expect is to ground the genset (outside), but bring in only the hots and neutral (not the ground wire ... e.g. just like the power company does with grounding the transformer and feeding hots and neutral). But having separate points of entrance complicates this. If mains and gen power can be brought in at the same point, then that one point can be the master bonding point for all ground electrodes, all neutrals, and all grounding wires.
The reason for asking this is to figure out how much of a hassle it would be if there were separate entrance points. I was guessing, and you are confirming, that it would be a lot. I'll try to design things around having a common entrance, even if it means the power company might be required to run its service drop around back to the garage, where the generator actually is, rather than the front of the house, which they tend to prefer.
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Just don't bond the neutral in the generator. If you buy one of the homeowner <portable> types the neutral is usually not bonded anyway. Then your main bonding jumper will still be the "master grounding point". You will be running a 4 wire feeder to the genset, just like you would to a sub panel. If you feel you want a ground rod out there it will only connect to the green wire ground. YMMV on the 'legal" need depending on the details of the generator installation.
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| Just don't bond the neutral in the generator. If you buy one of the homeowner | <portable> types the neutral is usually not bonded anyway. Then your main | bonding jumper will still be the "master grounding point". You will be running | a 4 wire feeder to the genset, just like you would to a sub panel. If you feel | you want a ground rod out there it will only connect to the green wire ground. | YMMV on the 'legal" need depending on the details of the generator | installation.
It will be a larger one, and probably three phase even though I don't need three phase (I'll just try to evenly split my loads three ways). I'm already going to be dividing the house power into some subpanels. I'll just try to make the division reasonably balanced.
And that's not my only option. I'm just weighing the options now, and getting valuable input on those weights.
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main
at
Right on
With remote transfer switches you will need to carry a code gauge ground through out the system. You will also have to ground the generator and the electrical service to the same point. That could be some really big conductor a long way. If you have 3 pole transfer switches make sure that the neutral for the generator and the service are at equal potential. Good idea even if you have 4 pole switches.
Take the maroon that designed this out to the wood shed. Won't help your situation but it will make you feel better. Good luck
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| |> I know this will go on for weeks but the short answer is you only want one | main |> bonding jumper in the system. If you do bond the neutral at the genset and | at |> the service the transfer equipment will have to switch the neutral too. | | Right on | | With remote transfer switches you will need to carry a code gauge ground | through out the system. You will also have to ground the generator and the | electrical service to the same point. That could be some really big | conductor a long way. If you have 3 pole transfer switches make sure that | the neutral for the generator and the service are at equal potential. Good | idea even if you have 4 pole switches. | | Take the maroon that designed this out to the wood shed. Won't help your | situation but it will make you feel better. Good luck
Nothing is designed, yet. I'm just looking at options ... and what ones I should disregard (though I'm more wanting to get "why to disregard it" than "I would disregard it").
Maybe a better option is to bring the utility power in at the garage where the generator is, and bond everything together there. Then run things to the house (underground). Either that will be separate runs for generator and utility (switched at the house), or separate runs for switched and utility (for separate circuits at the house). Can that be done with one grounding wire (grounded again at the house) and one neutral (not bonded to ground at the house) even though there are a variety of different hot wires?
The catch will be how readily the utility will go along with putting the service in at the garage (which will be further back from the house) and not at the house. They tend to like putting service entrances at the front (for things like making it easier to access their meter, presumably).
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Snipped

the
that
Good
front
OR you could put the generator in the garage or behind it and locate the service and transfer switch at the service location on the house. Just run a feeder to the transfer switch from the gen set. Check with you serving utility, here, Phoenix area the utilities will NOT put a service on a remote building. Unless the remote building has the load for another meter. A friend has a 3 phase 240 v on his shop and a single phase 240v on the house. He had to show something like 100kw of machines, easy for him to do. Pick up a copy of the Soars book on Grounding. Explains a lot of this in simpler verbiage. Even has pictures. Just a WAG, trying to help not hinder. Sorry about the wood shed quip, it WAS meant in a humorous way
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| OR you could put the generator in the garage or behind it and locate the | service and transfer switch at the service location on the house. Just run a | feeder to the transfer switch from the gen set. Check with you serving | utility, here, Phoenix area the utilities will NOT put a service on a remote
How do they define what "remote" means? I consider all the buildings to be peers. For all the builings being powered by one service drop, why would they care which? Are they merely wanting to drop power into the closest building?
OK, so how then is the garage powered? I've already found that some jurisdictions do not allow "double feeding" (e.g. two ways between the same two buildings).
Here's a thought. I build the garage first. It will have a small living area in the upstairs part of it. I then have power brought out to it first and put in the generator. Then the main house is built, and power is "extended" to it. Then, if necessary, the existing service is upgraded to the capacity needed (I doubt I would need over 225 amps).
There will be a total of 4 buildings.
| building. Unless the remote building has the load for another meter. A
What do you (or they) mean by "has the load for another meter"?
| friend has a 3 phase 240 v on his shop and a single phase 240v on the house. | He had to show something like 100kw of machines, easy for him to do. Pick | up a copy of the Soars book on Grounding. Explains a lot of this in simpler | verbiage. Even has pictures.
Utilities have varied basis for requirements for three phase. Some just plain say no, period. Others say you can have it if you ask for it and the lines are already there. Some require specific size motors. Some require a minimum demand. And some even require you to take three phase over certain demand levels (167 kVA on the last one I saw). All charge extra, but some charge a lot extra (even if they didn't have to extend primaries).
I considered three phase a while back, but ultimately decided it would be a big hassle, particularly running 240 volt stuff on 208 volts. So I don't want it. But with a 12-lead three phase generator, I can get a pair of 120 volt outputs on each phase angle, so I can just use it as single phase. But utility power doesn't come that way, requiring transformers to derive a 240/120 system.
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wrote:

run a

remote
They make the rules, they are the utility...

first
Might work. 225 puts you to a 400 amp service... This is a red flag around here. Yes I have installed 400, 600, and 800 amp services on residences in the past. Most were single phase. A few were 3 phase 208v my choice because of the equipment we were installing. Heck one house had 40 tons of a/c on the gargage. You would not want to get into a hot car would you?

His out building was a shop he has 20-30 pieces of wood working equipment. Smallest has a 3 hp motor.
You really need to contact your serving utility and see what their requirements are. What I am telling you may be a mute point with your utility.

house.
Pick
simpler
the
certain
a
phase.
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| wrote: |> |> | OR you could put the generator in the garage or behind it and locate the |> | service and transfer switch at the service location on the house. Just | run a |> | feeder to the transfer switch from the gen set. Check with you serving |> | utility, here, Phoenix area the utilities will NOT put a service on a | remote |> |> How do they define what "remote" means? I consider all the buildings to |> be peers. For all the builings being powered by one service drop, why |> would they care which? Are they merely wanting to drop power into the |> closest building? | | They make the rules, they are the utility...
But what is the definition?
How would they (or the AHJ doing an inspection) define what appear to be separate buildings, but can be reached by undeground hallways?
|> OK, so how then is the garage powered? I've already found that some |> jurisdictions do not allow "double feeding" (e.g. two ways between the |> same two buildings). |> |> Here's a thought. I build the garage first. It will have a small living |> area in the upstairs part of it. I then have power brought out to it | first |> and put in the generator. Then the main house is built, and power is |> "extended" to it. Then, if necessary, the existing service is upgraded |> to the capacity needed (I doubt I would need over 225 amps). |> |> There will be a total of 4 buildings. | | Might work. 225 puts you to a 400 amp service... This is a red flag around | here. Yes I have installed 400, 600, and 800 amp services on residences in | the past. Most were single phase. A few were 3 phase 208v my choice because | of the equipment we were installing. Heck one house had 40 tons of a/c on | the gargage. You would not want to get into a hot car would you?
What makes it a red flag? Asking for 225 amps (as opposed to 200 amps)? What is it a flag for? Does it indicate someone doing something funny?
How easy was it to get higher amperage service for a residence from the power company?
How easy was it to get three phase for a residence from the power company? Did they want proof of need? How much more did they charge?
Did the homes where you installed 208Y/120 have any 240 volt appliances?
40 tons of A/C? Sounds like an ice factory. A car in an uncooled garage does not get as hot as a car out in a parking space, depending on windows in the garage, blacktop on the parking lot, whether it is Texas, etc. But 40 tons for a garage? What's it holding? An antique car collection?
|> | building. Unless the remote building has the load for another meter. A |> |> What do you (or they) mean by "has the load for another meter"? | | His out building was a shop he has 20-30 pieces of wood working equipment. | Smallest has a 3 hp motor.
My grandfather had a small wood working shop and 3 phase power to it. But I don't think he had anything over 3 HP. He had maybe 6 major machines in about 10 foot by 20 foot space.
| You really need to contact your serving utility and see what their | requirements are. | What I am telling you may be a mute point with your utility.
I won't know what utility will be involved until after I find the land I will be building on, and that probably won't happen for a few more years. But by then I hope to have the choice of house design complete. Right now I have 5 different designs, only one of which looks like a "normal" house.
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Utilities "are" the AHJ up in NESCland. From the "service point", back to the electrical generation plant, is controlled by the utility and they don't operate under the same rules as we do. The electrical inspector may not like something he sees but this will probably end up in the public utilities commission before they do something about it. Utilities do conform to the NESC but that is a more basic code than the NEC and it does not micromanage their installations. As for what types of service they might choose to allow, that is their call with your only recourse being the public utilities commission if you don't like it. Generally, if you can get it past the local engineering office and sales at the electric company, you can have it tho.
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On 22 Jun 2004 04:49:42 GMT, snipped-for-privacy@ipal.net wrote:

Why not get a single phase generator?
Is the generator for backup or some other use?
What are you planning that needs 225a?
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| Why not get a single phase generator?
Suggest a model.
| Is the generator for backup or some other use?
Basically for backup. I might end up locating where power is unreliable. Where I live right now, it seems the POCO has no such thing as tree crews. No granted, tree overgrowth is significant here (many places have primary lines entirely under solid canopy growth). One out of two rain storms will knock out power in ways I suspect is just broken off segment of a tree branch dropping onto the lines and forcing a recloser lockout if it doesn't get it cleared off.
| What are you planning that needs 225a?
The ability to continue with the cooking for a family gathering even if the power goes out. Actually, it's more a case of designing the house so that the design itself does not prevent that capability. So as I do the design, I "drop in" that capability to see how it plays out. I may never actually get a generator that big. But I want to have the option to do so without having to rip out the entire electrical system and rebuild things in some ugly way to work around limitations in the designs. For example, if all I ever wanted to do was run a 5000 watt generator to keep the refrigerator going, I could just stick an inlet on the back porch and set up a small transfer panel and put the refrigerator outlet on that. But doing so with a 60000 watt generator is not so simple. 60000 watts is a big generator you don't just lug up the steps. And running it for a few days requires a lot of fuel. This isn't the kind of thing you want to wait until the power actually goes out to decide how you want to do it. For example I need to decide between diesel and LP gas. The former stores badly, but then, it is likely to get used fairly soon if I stay around here. LP stores better, but requires better planning, like where to put the tank for refill access. A transfer switch for this would basically need to be switching the whole service. And I do not want to have a transfer switch be the main disconnect, so that means a separate main disconnect ahead of the transfer switch (one each for both mains and generator).
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On 23 Jun 2004 18:10:41 GMT, snipped-for-privacy@ipal.net wrote:

See below

Keeping full (NO cutbacks) function in an all electric mansion during a utility failure is a BIG luxury.
My situation is somewhat similar to what you are seeking.
I have a 400amp service that has two 200a main breakers in the meter pedestal, these feed two 200amp transfer switches, which each feed two 200amp 40 space panels.
I can hook up either one or two generators to the transfer switches.
I have successfully used a portable 5kw generator during a winter power outage and Friday I am picking up a Generac 15kw natural gas unit from Home Depot to provide permanent automatic back-up.
I have electric cooking with natural gas for clothes drying and space and water heating . I anticipate that when using the 15kw I will only be able to run one central air conditioner at time and will have to shut down the Jacuzzi and generally be frugal with power. For the 30 hours per year that I experience outages this seems more than adequate.
If there is a long term outage ???, I could bring in a portable generator to supplement or one or two portable generators to replace the 15kw.
If you want massive functionality during an outage you could get a pair of : http://www.guardiangenerators.com/support/guardian_45kW.asp?NavID=1 and connect one to each transfer switch.
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| If you want massive functionality during an outage you could get a | pair of :| http://www.guardiangenerators.com/support/guardian_45kW.asp?NavID=1 | and connect one to each transfer switch.
They don't indicating the winding configuration on that. But I did find another generator of the same size from Kohler, and it does use a double delta type configuration, which is what I want to avoid.
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On 25 Jun 2004 19:35:09 GMT, snipped-for-privacy@ipal.net wrote:

It is a true single phase generator.
All the tech info is in the PDF specification sheet. The link is at the bottom of the main page.
Kohler also offers a true single phase unit in 45kw (model 4Q10) http://www.kohlerpowersystems.com/pdf/G4075.PDF
Why do you want to avoid the Zig-Zag (double delta) configuration?
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| On 25 Jun 2004 19:35:09 GMT, snipped-for-privacy@ipal.net wrote: |
wrote: |> |>| If you want massive functionality during an outage you could get a |>| pair of :| http://www.guardiangenerators.com/support/guardian_45kW.asp?NavID=1 |>| and connect one to each transfer switch. |> |>They don't indicating the winding configuration on that. But I did find |>another generator of the same size from Kohler, and it does use a double |>delta type configuration, which is what I want to avoid. | | It is a true single phase generator. | | All the tech info is in the PDF specification sheet. The link is at | the bottom of the main page. | | | Kohler also offers a true single phase unit in 45kw (model 4Q10) | http://www.kohlerpowersystems.com/pdf/G4075.PDF | | | Why do you want to avoid the Zig-Zag (double delta) configuration?
The power factor applied to the 2 other phases is 0.5 in that case. You only get 2/3 of real power capacity.
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On 5 Jul 2004 14:16:02 GMT snipped-for-privacy@ipal.net wrote:
wrote: | | On 25 Jun 2004 19:35:09 GMT, snipped-for-privacy@ipal.net wrote: | |
wrote: | |> | |>| If you want massive functionality during an outage you could get a | |>| pair of :| http://www.guardiangenerators.com/support/guardian_45kW.asp?NavID=1 | |>| and connect one to each transfer switch. | |> | |>They don't indicating the winding configuration on that. But I did find | |>another generator of the same size from Kohler, and it does use a double | |>delta type configuration, which is what I want to avoid. | | | | It is a true single phase generator. | | | | All the tech info is in the PDF specification sheet. The link is at | | the bottom of the main page. | | | | | | Kohler also offers a true single phase unit in 45kw (model 4Q10) | | http://www.kohlerpowersystems.com/pdf/G4075.PDF | | | | | | Why do you want to avoid the Zig-Zag (double delta) configuration? | | The power factor applied to the 2 other phases is 0.5 in that case. | You only get 2/3 of real power capacity.
Plus, I may be having some occaisional use for three phase power. Given the cost of getting three phase from the utility would be high, and possibly very high, a generator would be a convenient way to get it when the usage is only occaisional.
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On 5 Jul 2004 15:58:04 GMT, snipped-for-privacy@ipal.net put forth the notion that...

Why not use a rotary converter?
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