Generac 24kw w/400 ATS backing 400 amp service feeeding 2/200 amp panels

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Jpiusnorm

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Service splits at meter into 2/200 amp panels - comes out of a wiretex meter base that has a fifth aux contact/lug - right next to the meter base customer set a 24kw generac generator -
2 / 200 amp ATS or 1 / 400 amp ATS size needed on the ATS switch - customer wants whole house backed up - assuming I come straight out of auxiliary contact with 600 kcmil into ATS along with control wires from generator - generator has a 100 amp disconnect inside generator unit do I need to upsize that or is that sufficient to handle the whole load?
 
Upsizing the generator breaker will not increase available power on the genset. It came with that size because that’s what it can handle.

You will either need a much larger genset or load shedding will be needed.
 
Welcome to the forum.

D is correct. Upsizing the breaker will not increase the generator's capacity any more than doing so on a service would be an upgrade. It was selected protect the generator as it was designed and built.

The generator won't run "everything" anyway, as it's only the equivalent of a 100a service. I strongly suggest making two lists with the customer and rewiring the must-haves all into one panel on one ATS.

I usually try to make three lists: Must-haves, definitely-nots, and maybes in case there is some room left.
 
Depending on the loads, it might be far easier and simpler to shed high amp loads with a couple (few) SMMs, instead of doing a “critical circuit” panel.

For example, if there’s a hot tub and a separate pool house, two SMMs take care of that, and the rest of the wiring is straightforward
 
702.4(B)(2) prohibits the use of automatic transfer switches unless the generator can supply the total load as determined by the Article 220 calculations, or unless automatic load management is installed.
 
I appreciate the advice. I'm leaning towards the instal of the 100 amp sub panel with all of the critical loads. Can I control the sub panel through the existing service wire with an SMM or in a different way that I'm not familiar with, so that I can get away from pulling a new line to the meter base? And if so how could I tie that into the ATS? I'm assuming I would run one or both of the existing lines into the ATS so that it would kill all the existing power before starting the generator? Or do I have to run a new service line to the ATS and if that's the case how do I stop the other two feeders from possible power shortage? The meter is a long distance and would be a very difficult run to the panel if I were to trench a new line in.
 
Jpiusnorm said:
I appreciate the advice. I'm leaning towards the instal of the 100 amp sub panel with all of the critical loads. Can I control the sub panel through the existing service wire with an SMM or in a different way that I'm not familiar with, so that I can get away from pulling a new line to the meter base? And if so how could I tie that into the ATS? I'm assuming I would run one or both of the existing lines into the ATS so that it would kill all the existing power before starting the generator? Or do I have to run a new service line to the ATS and if that's the case how do I stop the other two feeders from possible power shortage? The meter is a long distance and would be a very difficult run to the panel if I were to trench a new line in.
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Why don’t you draw out what you have, and I’ll see if I can help you with it.

Generator installations can get complicated, even for my electrical inspector.

Have you done any of these before?

The SMM is a controller in line with a high amp load to shed the load when there is insufficient power available for the generator. It can’t and doesn’t replace feeder conductors.
 
I’m having trouble understanding what you’re describing, but supposing you don’t have an existing 100A sub panel, you’ll come off the main with a feeder, run it to a 100A panel, bring the loads that you want to run into that sub panel from wherever they are, and install the ATS somewhere in that sub panel feeder.
 
Another thing to consider, is if the meter has a fifth jaw, that usually means it’s being fed from a three phase source, although the meter is single phase. So your voltage will be 120/208, not 120/240. I’ve only done that once with a 120/240 volt single phase generator, and it appeared to work fine. But I don’t know if the newer controllers may see it as an undervoltage.
 
Jpiusnorm said:
Service splits at meter into 2/200 amp panels - comes out of a wiretex meter base that has a fifth aux contact/lug - right next to the meter base customer set a 24kw generac generator -
2 / 200 amp ATS or 1 / 400 amp ATS size needed on the ATS switch - customer wants whole house backed up - assuming I come straight out of auxiliary contact with 600 kcmil into ATS along
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I dont get the what and why of this auxiliary contact in the meter base and why feed a ATS with it?
 
tortuga said:
I dont get the what and why of this auxiliary contact in the meter base and why feed a ATS with it?
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I think what the op has is a five jaw meter base that is used when the poco is tapping off a three phase transformer, but only providing single phase at that point. A regular single phase meter base and meter will not meter correctly. @Hv&Lv may chime in on the reason.
 
My suggestion is to connect one output of the meter into a 200a ATS then to one 200a panel, and the other output directly to the other 200a panel.

As long as the loads that can automatically start or re-start are within the generator's capacity, you shouldn't need any additional load-shedding.
 
Jpiusnorm said:
I appreciate the advice. I'm leaning towards the instal of the 100 amp sub panel with all of the critical loads.
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LarryFine said:
My suggestion is to connect one output of the meter into a 200a ATS then to one 200a panel, and the other output directly to the other 200a panel.

As long as the loads that can automatically start or re-start are within the generator's capacity, you shouldn't need any additional load-shedding.
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I agree with Larry. Most of the time it makes more sense to just pull a few big loads off into a non generator panel and have everything else on a generator as opposed to a critical loads panel. One house I did had a 600A service that consisted of 3 200 sets and panels. It was a larger fancy house, but really not much load. I ended up just capping off one 200A set (because it was dumb and pointless, place would have been fine with a 200 amp service), reworked the one from the ATS to feed the three 200 panels, and moved a few big loads into a new panel (all it was was heat pump, range, dryer IIRC). I can't tell you how many generators I see that will never see more than like 5 or 10 amps on them.
 
electrofelon said:
I agree with Larry. Most of the time it makes more sense to just pull a few big loads off into a non generator panel and have everything else on a generator as opposed to a critical loads panel. One house I did had a 600A service that consisted of 3 200 sets and panels. It was a larger fancy house, but really not much load. I ended up just capping off one 200A set (because it was dumb and pointless, place would have been fine with a 200 amp service), reworked the one from the ATS to feed the three 200 panels, and moved a few big loads into a new panel (all it was was heat pump, range, dryer IIRC). I can't tell you how many generators I see that will never see more than like 5 or 10 amps on them.
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I've done that sort of thing also. One or more 200 amp breakers ends up not connected to anything. They spec'ed a 400 amp service and then built an all-gas house.
 
Birken Vogt said:
I've done that sort of thing also. One or more 200 amp breakers ends up not connected to anything. They spec'ed a 400 amp service and then built an all-gas house.
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Yeah I guess if you're building a big fancy house, doesn't matter if it doesn't have many big electric loads, got to put in a big fancy electrical service to match everything else!
 
Back a couple of years, when 400A (320A) meter bases were almost impossible to get, I went with a 200A on a 5200 sq ft house. House was ready for service so I had to settle for a 200A. Largest load was a heat pump for the upstairs and a double oven. Also had an electric dryer. Downstairs HVAC was gas, along with the cooktop. It's been fine for 2 years.

Right next door, was the customer's sister. She had a 400A service with almost the same loads as her brother. I doubt either house pulls much over 100A, if even that. My customer wanted a 400A because his sister had one!
 
Little Bill said:
. I doubt either house pulls much over 100A, if even that. My customer wanted a 400A because his sister had one!
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Ive never gotten demand data for a residence, but have for commercial buildings many times. I am always so surprised at how low it is that at first I used to always think I must be reading it wrong, gave the utility the wrong address, or they gave me the wrong meter's data!
 
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