external bypass for ATS?

[malachi constant]

Is an external bypass for a large ATS something that exists? The client thinks an external bypass is a possibility, like you can get for a UPS. The ATS rep tells me this does not exist for ATS's, but that they can do an internal bypass which basically amounts to a second backup transfer switch.

I'm thinking the rep is on the right track as far as what is appropriate for this installation, but hesitate to tell the client "it doesn't exist" if in fact it does.

 

[GoldDigger]

It is called a manual transfer switch.
It would have to be connected to the output of the ATS as one source and the utility connection as the other source.
It would not be able to pass generator power to the load without it going through the ATS.
The situation seems different with a UPS because both the ATS and the alternate power source are in the same enclosure.

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[qcroanoke]

Is an external bypass for a large ATS something that exists? The client thinks an external bypass is a possibility, like you can get for a UPS. The ATS rep tells me this does not exist for ATS's, but that they can do an internal bypass which basically amounts to a second backup transfer switch.

I'm thinking the rep is on the right track as far as what is appropriate for this installation, but hesitate to tell the client "it doesn't exist" if in fact it does.

A bypass Isolation Switch. here is a link: http://www.russelectric.com/products/bypass-isolation-switches

 

[steve66]

The devil is in the details. You could bypass it with interlocked circuit breakers, just like they do with a UPS.

But every time you bypass it, the generator will start as soon as the ATS doesn't see the power.

Also, you would be bypassing the normal power, but what happens if the normal power goes off while the unit is bypassed? I think only the internal ATS bypass can be bypassed to either utility or generator.

This would also take extra wiring and connections, and in my opinion, lower the reliability of the entire emergency system.

All in All, I'd just say the external bypass isn't a very good idea.

 

[GoldDigger]

The integrated unit linked in post #3, OTOH, makes sense since among other things it allows servicing the removable ATS unit.
The devil is in the details and a simple manual bypass certainly has more disadvantages than advantages if the ATS is reliable in the first place.

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[malachi constant]

Excellent information. Thanks all!!

 

[ATSman]

The subject has been pretty much covered but I would be remiss if I did not mention the company I represent:

http://www.geindustrial.com/cwc/Dispatcher?REQUEST=PRODUCTS&famid=3&catid=6002&id=ZBTSSStran

IMO the top 3 ATS manufacturers: GE-Zenith, Russelectric and ASCO. They all provide reliable Two Source Bypass-Isolation transfer switches up to 4000A rating. With all models, when the ATS is bypassed to utility and isolated for the purpose of PM or repair, the Bypass Switch becomes a manual transfer switch and the load can be transferred to alternate source.

 

[kwired]

Now, can we have a bypass for the bypass?

 

[ATSman]

Now, can we have a bypass for the bypass?

Interesting question and it would solve the following problem we run into all the time when performing PM on Bypass ATS's.
What do you do if, due to lack of maintenance and exercising, the bypass switch does not close into the bypass mode. The work has to be aborted because the load cannot be shut down. Or worse, after the PM is performed, the bypass switch will not open putting the critical load in jeopardy until the problem is corrected. If you think about it, the bypass switch is never shut down when the ATS is serviced, the lube grease in the mechanism dries up with the dirt and you have a real mess. An external bypass system similar to what supplies a UPS would allow for servicing of the bypass switch and the ATS.
But usually it's the bean counters that prevent such a system from ever seeing the light of day.

 

[steve66]

Now, can we have a bypass for the bypass?

If you want that much redundancy, its probably time to add a second, redundant path or feeder for power. It's not unheard of in data centers.

This would probably consist of a second ATS, with a second set of feeders, and breakers to isolate either ATS, and to connect either ATS to the load.