# UPS and bypass switch



## brucelaird (Mar 20, 2008)

I am being put in the awkward situation of reviewing prints that have been made up by a non engineering person for a job I am coordinating. We are installing a 3 pole 480V 175 amp breaker in an existing 1800amp emergency panel and feeding (through a wall) into another room where we have a disconnect. Out of the disconnect to feed 150KVA 480/208V transformer then to an 80KVA UPS and on to the MDP. When I saw the prints after the last revision a bypass switch (in what looks like a separate enclosure) has been added. 
My question is this: does this set up sound right? Originally designed by a master electrician, the set up didn't include the disconnect or the bypass. I had them add the disconnect for what I think is an obvious reason(175 amp breaker not in site), but don't know about the bypass switch. I guess I figured that the UPS has that internally. As an electrician myself I'm too used to working off engineered prints and not asking questions (you know how it goes). Any help out there? Thanks! Bruce


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## nap (Dec 26, 2007)

I am guessing the bypass switch is used to route the power to the UPS around the UPS and to the MDP. Correct?

Sounds like it would be used when servicing (including R and R) the UPS. If that power would need to be maintianed (since it is from an E panel, I would think it would), there would need to be a method to remove the UPS from circuit, totally, should it require it, without disconnecting the emergency circuit, at least to no more than a very limited time.


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## brucelaird (Mar 20, 2008)

*Response*

Thanks for your response. I agree that it seems a logical approach since the equipment that this transformer and UPS service needs to be powered under all situations. I guess my impression is that the UPS kicks in to supply power during an outage for those few moments when the generator is coming online, giving computers attached a constant supply. But when servicing the UPS unit there has to be a way of isolating it, hence the bypass switch?


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## nap (Dec 26, 2007)

One thing you did not mention and that is something you said in this last post; can you actually and totally isolate the UPS?

Without your drawings, I am only guessing as to exactly how things are interconnected and if not done properly, you may not be able to isolate the UPS with a single switch.


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## brucelaird (Mar 20, 2008)

*Totally Isolate UPS?*

Nap, 
Apparently, as I just found out, both units (UPS and Bypass) have been in service until very recently. They are made by the same company (Leibert/Emerson) and so I figure what came out can go in. 
Thanks, ;
Bruce


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## ghostwriter (Nov 1, 2007)

Where in the NEC does it require a disconnect for the primary side of the transformer? 

Joe


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## randomkiller (Sep 28, 2007)

ghostwriter said:


> Where in the NEC does it require a disconnect for the primary side of the transformer?
> 
> Joe


 
No where that I have ever seen requires a seperate means of disconnect, the breaker should be good enough.


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## brucelaird (Mar 20, 2008)

*Disconnect needed*

I was reffering to the fact that the only disconnecting means for this system on the line side is the breaker that is out of sight (in the next room over) and in a different classified area. If you were working on the transformer and needed it safe I was considering it important to have a disconnect in the same room as the transformer.


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## randomkiller (Sep 28, 2007)

brucelaird said:


> I was reffering to the fact that the only disconnecting means for this system on the line side is the breaker that is out of sight (in the next room over) and in a different classified area. If you were working on the transformer and needed it safe I was considering it important to have a disconnect in the same room as the transformer.


 
It's nice to have but it isn't code required.


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## ohmontherange (May 7, 2008)

A maintenace bypass panel (MBP) provides the means to bypass and isolate the UPS from between line and load typically without service interruption.

Once the UPS is placed into static bypass, the bypass switch can be engaged which routes the load out of the MBP. Then the AC disconnect switch can be opened which removes power from the UPS. Don't forget to open the DC breaker from the battery string to the UPS inverter.

The purpose of a maintenance bypass panel is to be able to remove the UPS for maintenance, repairs, etc without dumping the critical load. 

_*Without dumping...*_ Hmmm 

The reason for static bypass... When the UPS is in static bypass it is not conditioning the power ie; no phase shift, in which the current flows through the bypass windings of the transformer in the UPS. The bypass switches are typically _*make before break contacts*_ ( however many poles ) which means you want both current and voltage to be in phase when you make that switch of faith, especially when you got a couple mil of servers and other data geek things hanging off of it.

hang tough...

*Assumption is the mother of all #@&* ups*


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