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#200322 - 03/28/11 05:04 PM big generator/transfer switch
Micmann Offline
Member

Registered: 04/22/05
Posts: 20
Hey all.

I have a questions relating to a generator installation. I have a customer with a really rather large house that wants completely automatic standby power. Lights go out, generator fires, can go about using the complete house as if nothing happened. Currently there is an underground service coming from a pad mounted transformer at the property line with a CT meter at the trans. Two 4Ē PVC conduits come into the basement into a trough. In each conduit are 3-600ís alum. I believe itís a 800a 120/240 service. I say ďbelieveĒ because there is no main switch/disconnect stating an amperage size. What happens is, on the trough are three 200 amp 42cir panels and one 200a disconnect feeding a panel elsewhere in the house. One of the conduits coming from under ground has three wires - two hots and a neutral. The second conduit has the same thing naturally. Seems to me it would be parallel, however they never meet in the house. Conduit 1 cables each go to a splice block and feed out of the block with two 3/0 and feed two panels. Conduit two cables each go to a splice block and feed out with two 3/0 and feed the other 200a panel and the 200a disconnect. Is this a correct use of parallel conductors? I assume they leave the same lug at the trans but they never reconnect at the house, they stay split. I always understood they needed to be connected at both ends, but I may learn something here.

That being said I need to get these into an automatic transfer switch. I was planning on making them true parallel and disconnecting them from the splice blocks, feed double barrel lugs on line side of a transfer switch and then feed out with a quad lug on the load side of the transfer switch with 3/0 and hit each panel. The transfer switch is going to be big with 800a feed throughís and probably 400a or 600a emergency feed.

Iíve set a few 600a - 2000a generators and transfer switches over the past few years in commercial, but this residential rework install has be a bit stumped on a few things. So here are the questions.

Is the current parallel setup legal? It will probably disappear so the answer is more for knowledge than the install.

Can I feed a service rated transfer switch and then feed out to the panels and not have a main switch/disconnect? I think I can do this because I donít have more than 6 mains after the transfer switch. One option would be to order a transfer switch with a built in main if need be, but that could take months.

If I come off the load side of the transfer switch with a quad tap to feed panels am I now into the tap rule? Which one 10í or 25í?

I want to feed directly into the transfer switch and directly to the panels from load side. I canít imagine ordering switch gear with a 800a main switch and 4-200a breakers and installing it a basement to make this thing work or is this my only option?

The generator looks like it will be about 15í off the back of the house. (yes, I told them it will be like having a small truck parked next to the house, but itís ok with them. At least until the thing exercises a few times.) Do I need a disconnect at the house for the emergency feed?

Any help to these questions or other issues you see from my description would be very helpful. I have some thoughts to my questions, but need to hear your opinions.

Thanks

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#200331 - 03/28/11 07:05 PM Re: big generator/transfer switch [Re: Micmann]
sparky Offline
Member

Registered: 10/18/00
Posts: 5542
Hi Micmann

i wonder if this is an old 'customer owned' service lateral you've run into

if so, why not get a ruling from the local AHJ?

just a thought, maybe that 'existing' term might work for you to where you end up with 2--400A service rated T-switches w/ the control side in parrallel out to Gennyzilla, and you don't need to pitch for a 800A bid breaker main...?

~S~

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#200378 - 03/29/11 04:59 PM Re: big generator/transfer switch [Re: sparky]
Micmann Offline
Member

Registered: 04/22/05
Posts: 20
The customer owned service lateral thing sounds interesting. However, the house is at most 5 years old, so I donít think it is the case. Iím sure they own it, but donít think itís some funky install with the power company like years ago. Iím planning on asking the AHJ since he probably inspected it when built. Iím just looking for some input to narrow down my questions. I really donít see why I canít take these feeders and make them true parallel and feed a service rated transfer switch and then feed out with quad tap lugs. Or even feed out with parallel 500 copper or 600 alum back in to the trough and then tap up to each main with 3/0. Or is there something in the code that still mandates the main switch. The T switches also sounds interesting if Iím allowed to keep them split.

Also, still wondering if I need a disconnect switch on the house for the emergency feed. I thought this was a recent code change. Generator will have a disconnect built in, but wasnít sure if need one on house also.

Thanks again
Micmann

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#200392 - 03/30/11 06:11 AM Re: big generator/transfer switch [Re: Micmann]
sparky Offline
Member

Registered: 10/18/00
Posts: 5542
Originally Posted By: Micmann
The customer owned service lateral thing sounds interesting. However, the house is at most 5 years old, so I donít think it is the case. Iím sure they own it, but donít think itís some funky install with the power company like years ago. Iím planning on asking the AHJ since he probably inspected it when built. Iím just looking for some input to narrow down my questions. I really donít see why I canít take these feeders and make them true parallel and feed a service rated transfer switch and then feed out with quad tap lugs. Or even feed out with parallel 500 copper or 600 alum back in to the trough and then tap up to each main with 3/0. Or is there something in the code that still mandates the main switch. The T switches also sounds interesting if Iím allowed to keep them split.


i think the rule of 6 in 230 has this covered Micmann, but i'd certainly dig up that ahj and ask here

Quote:
Also, still wondering if I need a disconnect switch on the house for the emergency feed. I thought this was a recent code change. Generator will have a disconnect built in, but wasnít sure if need one on house also.


look up 702.12, it might be what you're after

~S~

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#200410 - 03/31/11 06:30 AM Re: big generator/transfer switch [Re: Micmann]
wire_twister Offline
Member

Registered: 07/25/07
Posts: 265
Loc: Georgia USA
I would not install it without a disconnect for the line side, you will have to clean and service the ATS sooner or later, and do not want to have to get the poco out to shut it down for you. I would look into a sound attenuated housing for the genset, the ones I have been around while running are really quiet, at 15 feet you can have a normal conversation while it is running. I think I would put a disco on the emergency feed from the genset, if for no other reason than to protect some un-knowing soul from an automatic start up of the genset. Just my opinions.
_________________________
Jimmy

Life is tough, Life is tougher when you are stupid

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#200427 - 04/01/11 05:25 AM Re: big generator/transfer switch [Re: wire_twister]
sparky Offline
Member

Registered: 10/18/00
Posts: 5542
well i have to agree twister, besides,anything service rated being introduced usually adds up to $$$'s , along with all the protectants needed to 'code' it right

~S~

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