Two Buildings, One Generator

Status
Not open for further replies.
N

Npstewart

Senior Member
Working on a project out of the continental US in a US territory. There is an existing building with a 200A SER ATS and a new building being built adjacent to it which will also require a 200A service and will also have a 200A SER ATS. This will most likely end up being a 100 kW diesel generator but im trying to figure out how to feed each individual transfer switch. Would there just be a tap inside the generator itself?? I know this is done all the time for campuses but I havent personally worked on one before. Also, if one building loses power how would the generator know to start?
 
You expect someone to answer in the middle of the night? :roll:I haven?t even had my coffee yet this morning. :happysad:

There are a few items you left out of the description. Most notably, is this an article 700, 701, or 702 system, or a combination of two or more of these? Also, you speak of an existing ATS, but speak of the generator as though it were a future item. What is the present installation, then?

I should think you can double tap the generator breaker, if you get one that is listed for that application. If you select the wire sizes correctly (in keeping with the generator rating and the rating of the generator breaker), you should be able to run a wire between the alternate power supply lugs of the two ATSs. But if there are any emergency (700) or legally required standby (701) loads involved, the game is significantly changed.
 
charlie b said:
You expect someone to answer in the middle of the night? :roll:I haven?t even had my coffee yet this morning. :happysad:

There are a few items you left out of the description. Most notably, is this an article 700, 701, or 702 system, or a combination of two or more of these? Also, you speak of an existing ATS, but speak of the generator as though it were a future item. What is the present installation, then?
Click to expand...

They installed an ATS on the first building knowing that they would be installing a generator one day. Now that the 2nd building is being built they want to proceed with the generator to feed both buildings. This is a optional standby system not powering any emergency loads.

charlie b said:

I should think you can double tap the generator breaker, if you get one that is listed for that application. If you select the wire sizes correctly (in keeping with the generator rating and the rating of the generator breaker), you should be able to run a wire between the alternate power supply lugs of the two ATSs. But if there are any emergency (700) or legally required standby (701) loads involved, the game is significantly changed.
Click to expand...

Thats what I was hoping for. So there will be a tap inside the generator itself which will take care of the power. In order for the generator to know when to start there will need to be some type of control wiring running between the two ATS? Im just worried about the rare occurrence where one building loses utility power and the other doesn't.
 
Just put the two ATS voltage sensing devices in parallel for the start command of DEG. That way either one that loses power will cause it to start.

You did not mention your load served, so don't know if you need to consider load shedding.
 
It is my understanding that there are sensors located within the ATS that can be used to start the diesel. If one building loses power, the generator will start, thus providing power to the alternate source side of both ATSs. The ATS in the building that lost power will transfer. The other ATS, still sensing the availability of normal power, will remain on normal.
 
kingpb said:
You did not mention your load served, so don't know if you need to consider load shedding.
Click to expand...
You also didn't state the voltage level. So we can't check the suitability of a 100 kW generator to serve two 200 amp ATSs.

 
Voltage is 240-1. Load shedding wont be necessary. Since my original post I have finished the load calculations and the load on the buildings is approximately 78 kW (325A @ 240-1). I have since change the generator size to 80 kW. This is basically two small offices so not dealing with any motors or anything.
 
You may want to reconsider keeping it at 100kW. Unless the generator is prime rated, it's only listed to run at 80% of its rating for longer than 3 hours.
 
You might also wish to consider the step-load capabilities of the generator.

You cant expect to drop a load of 78kW onto an 80kVA machine ..... and expect it to keep running!

I fact, you cant ever expect to get 78kW from an 80kVA generator!!!!!

(Most are rated at 0.8pf so for 80kW you need a 100kVA machine...........)
 
Last edited:
Npstewart said:
Working on a project out of the continental US in a US territory. There is an existing building with a 200A SER ATS and a new building being built adjacent to it which will also require a 200A service and will also have a 200A SER ATS. This will most likely end up being a 100 kW diesel generator but im trying to figure out how to feed each individual transfer switch. Would there just be a tap inside the generator itself?? I know this is done all the time for campuses but I havent personally worked on one before. Also, if one building loses power how would the generator know to start?
Click to expand...

It seems that if one bldg lost power both would loose power. Parallel gen feed to each transf switch (inside gen or Jct box outside.) If A and B phase for each bldg is the same you can series the voltage loss sensor circuit, bldg one and two. however if only one bldg goes down the other will transfer to gen power as well.
 
What you need to do, to allow for testing and maintenance as well as power feed loss to one building is to keep the transfer trigger of the two ATS separate but allow either power fail detector to start the generator.
Depending on the design of the generator autostart/stop system this could involve as many as three wires and some timing circuitry.
Talk to the generator manufacturer about how to do the dual start function.

Tapatalk!
 
Daja7 said:
It seems that if one bldg lost power both would loose power. Parallel gen feed to each transf switch (inside gen or Jct box outside.) If A and B phase for each bldg is the same you can series the voltage loss sensor circuit, bldg one and two. however if only one bldg goes down the other will transfer to gen power as well.
Click to expand...

You'd think that if one building lost power, the other would, but that's not always the case. Where I work, two of our theaters share a generator, but have separate transformers, fed from different city substations. We have had several instances where one theater's power goes down (unfortunate squirrel in the substation), but the other stays up. We discovered - the hard way - that there was a control wiring problem when the generator started but the ATS wouldn't transfer in the building that lost power.


SceneryDriver
 
In addition to the OP's original question, it seems that each building has it's own service and this would require switching the neutral. Otherwise you would have a parallel neutral path and also would have the neutral grounded through the other service in violation of 250.24(A)(5).
 
As I understand this service is 240V SINGLE phase. Stick with the 100 KVA generator! A 100 KVA generator is good for 417 A at 240V. Order the generator with two - 200A mains (standard option) - keeps things clean. Problems with one building will not take the generator out.

The comment about switching neutrals was right on.

Just be sure to test everything - real carefully.

RC
 
Ragin Cajun said:
As I understand this service is 240V SINGLE phase. Stick with the 100 KVA generator! A 100 KVA generator is good for 417 A at 240V. Order the generator with two - 200A mains (standard option) - keeps things clean. Problems with one building will not take the generator out.

The comment about switching neutrals was right on.

Just be sure to test everything - real carefully.

RC
Click to expand...

I am with RC on this.
 
To clarify further: switch the neutrals and set up the generator as a separately-derived-source i.e. provide a neutral-to-ground bond at the generator to an approved ground electrode.
 
Status
Not open for further replies.
Top