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#68553 08/10/06 07:32 PM
Joined: Dec 2004
Posts: 1,064
One of my customers bought a natural gas 45Kw generator for his house and wants me to install it.

400A(320) Underground service
twin 2" pvc from the meter can, to (2) 200a panels in basement.
Generator pad @20' from house.

My thoughts are this:

with a gas shut off, I shouldn't need a disconnect for the generator at the house.

I can install a 3R 400A transfer switch next to the meter, install 2 nipples from the meter can to the ats, one for the POCO feed, and one for the service conductors, so I don't have to move the PVC's from the meter can to the ats.
(forgot, I'll install the PVC's from generator to the ats)

Is this do-able, I've been going from 702, to 230, and over to 445 and got myself totally confused.

I'd figure someone here can smack me in the right direction..


(editted in PVC to generator)

[This message has been edited by Dnkldorf (edited 08-10-2006).]

#68554 08/12/06 06:28 AM
Joined: Jan 2003
Posts: 4,391
If you go the route you describe this transfer switch will have to be service rated.

230.82 prevents a transfer switch on the supply side of the service disconnect.

That being the case the transfer switch must serve as the service disconnect as well.

Now that the transfer switch is the service disconnect all bonding and grounding must be moved to the transfer switch or before.

The existing service panels must be reconfigured to 'sub-panels' with the neutrals isolated from the grounds.

Bob Badger
Construction & Maintenance Electrician
#68555 08/12/06 10:59 PM
Joined: Oct 2005
Posts: 100
JJM Offline
I'm having a little trouble understanding the hook-up from the meter pan to the ATS from the description, and it doesn't sound kosher. Maybe I'm understanding it wrong. Sounds like the POCO feeders will be going into the ATS then feeding the meter?

In my opinon, it should go like this:

- POCO feed to METER
- ATS to 200A PANEL(S).

I'm assuming you'll be energizing BOTH 200A PANELS with the genset?

I also would put a SERVICE DISCONNECT between the genset and ATS. That's pretty much standard.

If the ATS isn't service entrance rated, like IWire mentioned, those 200A PANELS become subs, and the grounding bonding happens in the SERVICE DISCONNECT; you can use a 400A service main breaker for that, rather than a pull disco (probably cheaper).

You might also want to consider locating the ATS INSIDE the building. Even though the switch is 3R, a lot of expensive boards and relays are in there, which don't always do well with the extremes outdoors.

Does your local code or poco require switched neutrals?

Electric aside, do they have the gas service for this monster? This thing is likely gonna burn something of the order of 550,000-600,000 BTU/hr, so if the gas service is also 20 ft from the genset like the electric service, better make sure its getting fed by at least a 1 1/4" pipe.

That was just the VOLUME, you also need to consider gas PRESSURE? Most gensets require elevated gas pressure (typicaly 11" WC), well above the normal 4-6" WC supplied by the utility regulator. Often what needs to be done is a seperate regulator is needed just for the genset. The meter and pipe must also be able to accomodate the genset and other gas appliances.


#68556 08/14/06 06:02 AM
Joined: Dec 2004
Posts: 1,064
Bob, the service rated is what I was wondering about.

I was pondering changing the meter can, to a service rated one, or mounting a fused disconnect, then the ATS.

The dilema is, the panels are currently 60' away from the meter. The PVC runs around the perimeter of the foundation, and under cobblestone walkways. The basement is finished, so this makes installing the ATS by the panels, almost impossible.

If I install (2) 200a ATS, do I have to somehow interlock them together?

The gas line Joe, is not my problem. That's on his end to have installed. No to the question of POCO going to the ATS, and then the meter. It would stay the meter, then to the ATS, then to the panels.

#68557 08/15/06 02:16 PM
Joined: Oct 2005
Posts: 100
JJM Offline
I don't think the dual ATS configuration will fly. If you have 400A service, you need a 400A ATS.

Even if there are no code prohibitions against a dual ATS setup, an AHJ would likely look at such configuration with great contempt. If this is to be a separately derived system, such a set-up could not work since I don't know of any way a dual ATS setup could be interlocked.

Why can't you can't simply stick a 400A main between the meter pan and the ATS, if a service entrance rated ATS is not an option for some reason? Fused disco will be fine, but probably a lot more expensive and bulkier than a 400A main breaker. It's always a good idea to have a disconnect on the service side of the ATS anyway, in case the ATS needs to be opened for service. You'll likely be the one working on it anyway. Let's say a board or relay goes bad, servicing the switch now requires pulling the meter... cutting locks, seals, notifiying POCO, and so forth... who needs that? This is another reason why a disco should be on the genny side too, so that the ATS can't be re-engergized should the genset start-up.

As an added bonus to all this, anytime you have to work on the two 200A panels, they can be TOTALLY dead - no fear at all working on them. I've gotten zapped a few times by live lugs on typical services.


#68558 08/15/06 03:12 PM
Joined: Dec 2004
Posts: 1,064
Joe, I hadn't thought of the 400a breaker alone.

I'm looking at the cost of a 400a SR ATS, vs the cost of a meter can with a breaker, and a 400a NSR ATS.

One quote for the SR, was $6800.

Tough to swallow when the gen was only $14K.

Any other options?

#68559 08/15/06 05:12 PM
Joined: Oct 2005
Posts: 100
JJM Offline
$6,800 for a SE ATS... is this ASCO you're looking at? I don't blame you for considering other options!

Are we talking about single phase, 120/240V here? And what kind of genset are we talking about?

If the genset utilizes a simple two-wire start, you can get the GE ZTX40MX60 400A ATS in 3R for probably just under $2,000. It's a good switch in my opinion; Onan labeled switches are made by GE (just slightly different firmware on the board). It's not SE rated, but you can get a GE Q-Line 400A breaker (TJD422Y400) for around $600 from your supply house, plus the 3R enclosure. You'll probably get done with everything for just under $3,000.

I know GE also makes a 400A fused disco for around $600, had one spec'd out on another job, but it's not 3R, and you mentioned you can't go indoors.

If the genset is a Generac and depending on the engine size, you've probably got it made. The RTS appears to fit the bill quite perfectly. The RTS series is service entrance rated, and the 400A RTS-E400 can probably be had for around $1,900. It also seems to have a smaller footprint than the GE box (much slimmer).


[This message has been edited by JJM (edited 08-15-2006).]

#68560 08/15/06 05:17 PM
Joined: Dec 2004
Posts: 1,064
Joe, genset is onan.
RS45000, price 13,999.
Single phase 240/120.

Onan 400a ATS SER $6800.

I am also exploring the idea of someone elses ATS running the genset, like you stated.

#68561 08/16/06 09:58 PM
Joined: Oct 2005
Posts: 100
JJM Offline
Onan RS4500... NICE GENSET! Great price on it too. And good news, you can use any ATS that supports two-wire start, so the GE ZTX40MX60 400A ATS will work no problem. The #3 terminal gets grounded (on the DC side) to terminal #1. These two terminals connect to the two start terminals on the ATS.

The only real difference between the GE and Onan version is the Onan switch has slightly different firmware (the genset transfers over with a shorter delay) and includes a built-in battery charger. It should be noted, however, that the GE version of the switch has the studs already in place on the lower LH portion of the enclosure to accept the charger, and push on terminals above the lugs to power it. Seems kind of cheezy to to have thin little wires connected right above the big current carrying cables, but that's the way the Onan version comes from the factory.

If you need OEM type the battery charger specs, let me know.

Looks like you just saved your customer lots of money.


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