One generator feeding two automatic transfer switches

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Oh, I see what you were responding to. Maybe the communication wire didn't need to be paralleled since the (let's call it) master ATS would be doing all the communicating.

My expertise is limited because I don't know if that communication wire is a 2 way wire. I suppose it isn't.
Hopefully it will work out... My only concern is some weakness that only crops up under certain scenarios.
 

kwired

Electron manager
Location
NE Nebraska
So it works. I sent the 240 volt to the generator. I paralleled the communication and 12v to each ATS. Inspector was fine with it. The only problem will be if only one unit goes out. But the only reason that would happen is non-payment. It's a 2-family, owner lives in one and rents out the other. So I made sure it was the owner's ATS that controlled the generator.

So if the owner doesn't pay the bill, they can run their generator. If the tenant doesn't pay their bill, they'll be without electricity.
How you get back at the tenant if they don't pay their electric bill and think they will just run off generator? If natural gas powered generator hook it up to tenant's natural gas service - will probably cost them more to burn that gas, especially during low demand periods, and on top of they likey have less overall capacity than if they were running on electric supply to begin with.
 

jaylectricity

Senior Member
Location
Massachusetts
*after much time has passed*

I haven't heard of any issues for this install, but I also don't know if they've lost power since this install. So basically no new info.

But now I'm looking at a building that's four condos. We want to put a single generator, probably a 22K or the like...but have transfer switches for each unit. Unlike the initial subject of this thread, there is no one unit that owns the whole building. As I type this I realize I don't know if each unit pays for their own natural gas. That's a question I'll have to ask the contractor.

Electrically I know how it can be done. I just don't know how to look up and buy the parts.

My idea is a relay that has four separate pairs of terminals. Each transfer switch sends 240 to the generator. So a relay that needs all four 240v feeds to send the 240v to the generator. Then from the generator, a relay that takes in the control signal from the generator and only sends it to the transfer switch that is not sending 240v to the generator.

It's unlikely I'm going to do this job, but I want to learn about how to construct a cabinet with the necessary relays to do this.
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
Electrically I know how it can be done
neat challenge, Off the hip without really thinking about it, I may consider a concept of 4-240v 100A relays (NC) with 4 independent coil references, 1 from every dwelling panel, providing the utility power voltage for each tenants transfer switch as a normal condition. then with any power loss of (all 4 units) the signal to the generator would say power it up, while sending back generated power to 4 similar (NO) relays sharing a common coil reference engaging the 4 relays simultaneously, from there feeding each transfer switch. I may be off somewhere but I think that's something I'd consider.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
*after much time has passed*

But now I'm looking at a building that's four condos. We want to put a single generator, probably a 22K or the like...but have transfer switches for each unit. Unlike the initial subject of this thread, there is no one unit that owns the whole building. As I type this I realize I don't know if each unit pays for their own natural gas. That's a question I'll have to ask the contractor.

Electrically I know how it can be done. I just don't know how to look up and buy the parts.

My idea is a relay that has four separate pairs of terminals. Each transfer switch sends 240 to the generator. So a relay that needs all four 240v feeds to send the 240v to the generator. Then from the generator, a relay that takes in the control signal from the generator and only sends it to the transfer switch that is not sending 240v to the generator.

It's unlikely I'm going to do this job, but I want to learn about how to construct a cabinet with the necessary relays to do this.
there is no one unit that owns the whole building. Usually in such situations there would be common spaces that would require a fifth metering that would be to the building owner or split equally between tenants.
and only sends it to the transfer switch that is not sending 240v to the generator. That would likely not be needed as I don't see a scenario where one unit would be without utility power and not the others other than meter pulled for nonpayment or moving out, or repair service, if the later you wouldn't want the gen to start anyway.
put a single generator, probably a 22K or the like. In this case as well as the first case, but even more critical on second case, load shedding devices would almost certainly be needed to be installed to prevent overloading the gen. Sure it has a circuit protection that would trip, but why create a nuisance trip for everyone else due to one tenants wanting everything on at once. Also, what is the primary feed to the condo building? Minimally I would think 400A, even if that, it would mean 100A distributed to each tenant. Thus a 22kw or even the new 24kw would not be able to handle the entire load for building without some form of load shedding.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
The only way I see to do it, is use a reputable generator like Kohler, unlike Generac, it does not require a utility feed to sense utility loss and control the transferswitch. The transferswitches will be totally independent, and only require two control wires to the generator. The problem that lies therein, is charging the battery, and block heater, if needed. If you are in a warm climate where the block heater is not necessary, a good quality solar panel will keep the battery charged, along with powering the generator controls. If you need the block heater though, a fifth meter, or if available, two circuits from a house panel will be required. You will not need the relays, because each transferswitch has a dry start contact that all will be paralleled back to the generator.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Also you will need three pole switches, as you would be paralleling the neutrals of all four units through the generator if only using a two pole switch.
 

jaylectricity

Senior Member
Location
Massachusetts
there is no one unit that owns the whole building. Usually in such situations there would be common spaces that would require a fifth metering that would be to the building owner or split equally between tenants.
and only sends it to the transfer switch that is not sending 240v to the generator. That would likely not be needed as I don't see a scenario where one unit would be without utility power and not the others other than meter pulled for nonpayment or moving out, or repair service, if the later you wouldn't want the gen to start anyway.
put a single generator, probably a 22K or the like. In this case as well as the first case, but even more critical on second case, load shedding devices would almost certainly be needed to be installed to prevent overloading the gen. Sure it has a circuit protection that would trip, but why create a nuisance trip for everyone else due to one tenants wanting everything on at once. Also, what is the primary feed to the condo building? Minimally I would think 400A, even if that, it would mean 100A distributed to each tenant. Thus a 22kw or even the new 24kw would not be able to handle the entire load for building without some form of load shedding.
There is a common meter, but I'm still not sure what that powers. I don't even see outside lighting.

I especially appreciate your comment about one condo wanting to run everything while the other three "hunker" down during the storm.

That's a large part of why I don't think we should do this job.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
There is a common meter, but I'm still not sure what that powers. I don't even see outside lighting.

I especially appreciate your comment about one condo wanting to run everything while the other three "hunker" down during the storm.

That's a large part of why I don't think we should do this job.
That why I said "load shedding devices" would probably be necessary, PSP products makes a good one, or you can use the Generac SMM product. This allows the use of a smaller generator on an ATS than would otherwise be required for whole house load. You would just have to use most likely more than one for each unit to bring load into specs. They are also available to be a complete shut down of load or selective "if there is enough available power it allows it to be powered, if not it sheds the load.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
*after much time has passed*

I haven't heard of any issues for this install, but I also don't know if they've lost power since this install. So basically no new info.

But now I'm looking at a building that's four condos. We want to put a single generator, probably a 22K or the like...but have transfer switches for each unit. Unlike the initial subject of this thread, there is no one unit that owns the whole building. As I type this I realize I don't know if each unit pays for their own natural gas. That's a question I'll have to ask the contractor.

Electrically I know how it can be done. I just don't know how to look up and buy the parts.

My idea is a relay that has four separate pairs of terminals. Each transfer switch sends 240 to the generator. So a relay that needs all four 240v feeds to send the 240v to the generator. Then from the generator, a relay that takes in the control signal from the generator and only sends it to the transfer switch that is not sending 240v to the generator.

It's unlikely I'm going to do this job, but I want to learn about how to construct a cabinet with the necessary relays to do this.

Any issue that could show up would if one of the ATS had power cut to it while the other didn't, or there was a blip during re-transfer, or something in that effect.

Now if any issue would pop up from the above I have no idea for certain.

Did you contact Genec**p I mean Generac?
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
The only way I see to do it, is use a reputable generator like Kohler, unlike Generac, it does not require a utility feed to sense utility loss and control the transferswitch. The transferswitches will be totally independent, and only require two control wires to the generator. The problem that lies therein, is charging the battery, and block heater, if needed. If you are in a warm climate where the block heater is not necessary, a good quality solar panel will keep the battery charged, along with powering the generator controls. If you need the block heater though, a fifth meter, or if available, two circuits from a house panel will be required. You will not need the relays, because each transferswitch has a dry start contact that all will be paralleled back to the generator.

I've heard of people say that running that gen for an hour every week keeps the bat charged and prevents it from exploding unlike trickle chargers... But that might not work out in resi.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
There is a common meter, but I'm still not sure what that powers. I don't even see outside lighting.

I especially appreciate your comment about one condo wanting to run everything while the other three "hunker" down during the storm.

That's a large part of why I don't think we should do this job.
I know this probably isn't reasonable to even ask, but is there anyway that
Could be done, 12 volt dc time clock set to exercise once a week for an hour.
True, bit I think running the gen an hour (vs 10 mins) a week would cause a rise in the natural has bill.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
I know this probably isn't reasonable to even ask, but is there anyway that


True, bit I think running the gen an hour (vs 10 mins) a week would cause a rise in the natural has bill.
Adding a fifth meter would probably cost just as much though, due to minimum billing charges, so probably a wash on costs.
 
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