Automatic Transfer Switch in Series

mbrooke

Senior Member
How would you set the timing on two ATS switches in series? Or the start wiring? Start both units, delay transfer by 4 seconds and then shut down one unit?

Also, would you change this design or keep as is? Only certain loads need redundant generation.


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hillbilly1

Senior Member
That’s a heck of a lot of transferswitches! Looks like you have three redundant generators feeding that one distribution panel. Can’t really make out the name when I blow it up, but appears that there is no utility feed at all on that section. One of the generators would have to be running all the time. Since you have three separate generators, you would have three separate start controls, they would not parallel. The primary generator would have the shortest time delay, Depending on how fast the backup two need to come on line, the start times can be staggered, or the same. The transfer time would need to be staggered though. That depends on total allowable down time.
 

mbrooke

Senior Member
Two redundant generators, the 3rd is a plug box for a mobile unit. No utility feed on the emergency section of the switch gear.

Thats what I'm thinking start both and stagger the transfer time.
 

hillbilly1

Senior Member
Two redundant generators, the 3rd is a plug box for a mobile unit. No utility feed on the emergency section of the switch gear.

Thats what I'm thinking start both and stagger the transfer time.
How are you sensing utility loss to start the first generator, and subsequent generator(s)? You will not be able to use the transfer switches unless the first generator is a prime mover. You will need some sort of signal to start the process. I’m assuming the emergency loads are only energized during a power outage?
 

hillbilly1

Senior Member
Looked at your one line again, and I see what’s being done. The start control would require paralleling or series the other three transferswitches start contacts to control a three pole contactor. Series if using a N/C contactor, parallel if using N/O. (Assuming the portable has remote start function)
 

hillbilly1

Senior Member
Looked at your one line again, and I see what’s being done. The start control would require paralleling or series the other three transferswitches start contacts to control a three pole contactor. Series if using a N/C contactor, parallel if using N/O. (Assuming the portable has remote start function)
 

mbrooke

Senior Member
How are you sensing utility loss to start the first generator, and subsequent generator(s)? You will not be able to use the transfer switches unless the first generator is a prime mover. You will need some sort of signal to start the process. I’m assuming the emergency loads are only energized during a power outage?

The first ATS down stream calls for an engine start.
 

mbrooke

Senior Member
Sorry, looks like four ATS on load side, hard to see on iPhone!

3 ATS in series. The first one calls for engine start, the second one upstream is for a mobile genset (normally disabled) and the first one upstream selects between either permanently mounted generator.
 

hillbilly1

Senior Member
The first ATS down stream calls for an engine start.
On the load side of the emergency gear? Can’t be on the line side of the emergency gear, or the generator would never shut off. All of the load side ATS’s can
3 ATS in series. The first one calls for engine start, the second one upstream is for a mobile genset (normally disabled) and the first one upstream selects between either permanently mounted generator.
not those, but the load side transferswitches. They will have to control the generator start. The generator will never shut down if you control it from those. All those switches will do is decide on the available source to use. Voltage sense will be dead on both inputs, which will make the switch call for the second source, this starting the generator. Those start contacts should not be connected.
 

ron

Senior Member
The 3 ATSs on the left side are standard utility / Gen ATSs. When any of the three of them they lose power, they will signal the Gen / Gen ATS (on the far right side) to start the primary generator (you will need to bring external control power to that style ATS since they are normally de-energized) and the Gen/Gen ATS would be satisfied and then satisfy the Utility/Gen ATSs, if after a timeout (in the gen/Gen ATS) if the primary generator doesn't start, the alternate generator starts and the Gen/Gen ATS would be satisfied and then satisfy the Utility/Gen ATSs, if after a timeout (in the 2nd Gen/Gen ATS from the right) if the primary generator and secondary generator doesn't start, then the portable generator would be signaled if there was an auto-start capability present and the 2nd Gen/Gen ATS from the right would be satisfied and then satisfy the Utility/Gen ATSs.
 

mbrooke

Senior Member
The 3 ATSs on the left side are standard utility / Gen ATSs. When any of the three of them they lose power, they will signal the Gen / Gen ATS (on the far right side) to start the primary generator (you will need to bring external control power to that style ATS since they are normally de-energized) and the Gen/Gen ATS would be satisfied and then satisfy the Utility/Gen ATSs, if after a timeout (in the gen/Gen ATS) if the primary generator doesn't start, the alternate generator starts and the Gen/Gen ATS would be satisfied and then satisfy the Utility/Gen ATSs, if after a timeout (in the 2nd Gen/Gen ATS from the right) if the primary generator and secondary generator doesn't start, then the portable generator would be signaled if there was an auto-start capability present and the 2nd Gen/Gen ATS from the right would be satisfied and then satisfy the Utility/Gen ATSs.

Thanks

Would you change this design or keep as is?
 

ron

Senior Member
Would you change this design or keep as is?
The oneline is too blurry to see how the N-G bonding is happening, but if it is occurring at the utility and gens, and no neutrals are brought downstream to any ATS's, and the normally de-energized equipment is in a temperature controlled environment so it doesn't corrode due to condensation, then it seems like a reliable system. Signage would make it easier for the operations staff, but it should get the job done
 

mbrooke

Senior Member
The oneline is too blurry to see how the N-G bonding is happening, but if it is occurring at the utility and gens, and no neutrals are brought downstream to any ATS's, and the normally de-energized equipment is in a temperature controlled environment so it doesn't corrode due to condensation, then it seems like a reliable system. Signage would make it easier for the operations staff, but it should get the job done

Which leads me to ask, how would you ground / bond all this? 3 or 4 pole ATS?
 

ron

Senior Member
Which leads me to ask, how would you ground / bond all this? 3 or 4 pole ATS?
If at all possible, if it were a 480V system, I would leave the neutrals at their source, bond the N-G at each source so it were solidly grounded, and use 3 pole ATSs, then add transformers as needed downstream to derive 480/277V or step down to 120/208V.
 

mbrooke

Senior Member
If at all possible, if it were a 480V system, I would leave the neutrals at their source, bond the N-G at each source so it were solidly grounded, and use 3 pole ATSs, then add transformers as needed downstream to derive 480/277V or step down to 120/208V.
I just want to say that I saw this reply but ran out of time to comment.

Yes- that is what I would do as well. I personally do like 4 wire systems.
 
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