circuit breakers instead of a transfer switch

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johnjohn

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Has anyone had any experience with installing a board that comes with multiple automatic circuit breakers controlled by computer logic to control the transfer of power from utility to generator instead of using your basic transfer switch?

Does UL have a listing for this type of arrangement? The breakers will at one point be back fed.
 
This is a fairly common arrangement of devices. It is often called an auto throw-over or an automatic transfer scheme.
An yes there can be requirements on their performance.

What is your application?
 
The ones I have installed, the breakers have a mechanical as well as an electrical interlock, the controller opens the utility breaker before closing the generator breaker, so there is no backfeed, but they are closed transition types that both breakers are closed momentarily when both sources are in phase, If this is type your working with.
 
If it is a manufactured assembly, I say it would be. I'm pretty sure those that I've installed were, if not the inspectors would be quick to point it out, and none of them did in Ohio, Kentucky, Indianna, Tennessee, North Carolina, and West Virginia.
 
johnjohn said:
Has anyone had any experience with installing a board that comes with multiple automatic circuit breakers controlled by computer logic to control the transfer of power from utility to generator instead of using your basic transfer switch?

Does UL have a listing for this type of arrangement? The breakers will at one point be back fed.
Click to expand...

There are complete UL listed assemblies and AFAIK feedback or paralleling of feeds is mechanically impossible.

http://www.eaton.com/Electrical/USA/ProductsandServices/ElectricalDistribution/ATS/Breaker/index.htm
 
Is this an ATS that is using breakers instead of contactors, or is a switchboard or switch gear lineup where 'transfer mechanics' have been added to electrically operated power breakers?

ATS's rarely have true paralleling capabilities, while power breaker are routine in paralleling switchgear.
 
Given my understanding of the way the folks at UL think, such a shceme would be required to prevent cross-feeding bot mechanically AND electrically. Simple PLC logic would not be enough; there would have to be a switch physically thrown, as well as a rely interlock. MAYBE the PLC would be allowed to serve in place of the relay.
 
renosteinke said:
Given my understanding of the way the folks at UL think, such a shceme would be required to prevent cross-feeding bot mechanically AND electrically. Simple PLC logic would not be enough; there would have to be a switch physically thrown, as well as a rely interlock. MAYBE the PLC would be allowed to serve in place of the relay.
Click to expand...

The ones I have installed, have a cable mechanical interlock between the breakers. One of the installs, a spring flew out the first time it was used! Could not find where it came from, apparently it was a part left laying around in the switch from the factory, because the switch worked perfectly, and no damage was apparent.
 
There is a separate and very specific UL Standard for "Automatic Transfer Switches", UL-1008, here is the Scope. You would have to buy the full standard documents from UL if you want to know more. Most standby and emergency operations will require having a listed ATS if it is "automatic", but may not if it is "manual". Both terms are in quotes because it isn't exactly black and white.

There are indeed ATS systems made with electrically (motor) operated MCCBs and PCBs, and there are those that are UL-1008 listed. You can also "roll your own" but they would NOT be UL-1008 listed unless you want to go to great expense to do so, typically in the high 5 figure range.

As to whether or not you must have this listing on a piece of equipment or a switchgear arrangement you are using or about to use, that is up to you local AHJ. I for one would just ask first rather than be surprised later.
 
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