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UPS Emergency Power Off (EPO) #98598 01/19/05 04:14 PM
Joined: Jan 2005
Posts: 61
jkochan Offline OP
I had a 1750KW UPS drop off line, taking the critical load with it. It was an emergency power off...Self Initiated...and it's not supposed to do that. Why it did this is the Mfg's problem and that is being dealt with. Here is my issue. There is only one EPO switch for the UPS, which is in a card controlled room in a card controlled hall with access limited to 6 people. When the UPS EPO circuit malfunctioned, it dropped the load on power down instead of going to bypass. I was told by various talking heads that this was "CODE". WHICH CODE? However in the wiring harness there is a cross connect plug that when removed allows the unit to go to by pass instead of just dropping the load. Since the unit has to be UL listed, why would they design this feature into the UPS as an option? I can't find any answers in NAPFA other than they (fire marshals) want the batteries off line on power down in the event of fire. So, I thought I would check with the NEC guru's to see if any one can point me at anything the might be related. Your input would be appreciated.

2017 / 2014 NEC & Related Books and Study Guides
Re: UPS Emergency Power Off (EPO) #98599 01/19/05 04:37 PM

.........."Where a push button is used as a means to disconnect power, pushing the button SHALL disconnect the power."

This article does not limit the disconnecting means to be an EPO. You could group disconnects at the door. I wonder if this would relate to how the attached push button can be wired. Meaning maybe I want the button to put the UPS into bypass from a remote location and will use another means to disconnect the power.

And then 645.11......"Shall comply with 645.10. The disconnecting means SHALL also disconnect the battery from it's load.

( I still have not figured out why the NEC doesn't just finish the matter and replace all "shall's " with must.)

In any case power off is power off and not just bypass. I would not want to be a fire fighter going into that room with anything at all live. Is the EPO tied into the fire suppression and or preaction system as well?

I would not want any "live" equipment if either or both of those systems went into alarm either.

The battery issue has gotten so "HOT" in my area that some jurisdictions are requiring that the batteries be put in a room remote from the computer room.

[This message has been edited by kentvw (edited 01-19-2005).]

[This message has been edited by kentvw (edited 01-19-2005).]

[This message has been edited by kentvw (edited 01-19-2005).]

Re: UPS Emergency Power Off (EPO) #98600 01/19/05 06:43 PM
Joined: Jul 2004
Posts: 9,547
gfretwell Online Content
Kent, "shall" means "must".

As for the EPO you are right, it should drop everything. That is the function.

You are also right about the battery room. Except for the smallest units I have always seen the batteries in a separate room from the electronics (inverters and such) and they were all in a room other than the computer room although the UPS hardware might share a room with the 400hz MG.
A lot of times the UPS was the 400hz source, using another inverter. Liebert made most of the units I saw.
I always heard they didn't want a chance of a hydrogen explosion

Greg Fretwell
Re: UPS Emergency Power Off (EPO) #98601 01/19/05 06:57 PM
Man, I just hate it when work gets in the way of posting here. Rather than edit my original message for a forth time I'll post a new one.

I have been in similar situations more than once. I wonder how you are proving that it was not an issue with the EPO system. I had a situation where this was happening and everyone swore up and down that it was not an employee pushing and quickly resetting the EPO........ I ask that they install a video system. "No can not, employee trust bla bla bla". I had the system set up so it would automatically reset when the mushroom was pulled back out. After about the sixth time management was livid and pulled me into a meeting. I kept pointing at the employees and they kept pointing at my system.

I ended up putting in mechanically held contactors which needed to be repowered to reset the system. Bingo. The only way the system was going down was with the EPO. It happened one more time and they put in the video monitoring system..........Funny thing. It never happened again.

Oh man,,,now I gotta edit again. gfretwell, I well understand that shall means must. I was only making the point that it does indeed mean must.

[This message has been edited by kentvw (edited 01-19-2005).]

Re: UPS Emergency Power Off (EPO) #98602 01/19/05 07:12 PM
Joined: Jan 2003
Posts: 4,391
iwire Offline
You can have a computer room without an power disconnect system.

However that changes all the rules as to wiring methods particularly under the floor.

Article 645 loosens the rules from chapter 3 the price you pay for this loosening of the rules is the EPO system. [Linked Image]

Bob Badger
Construction & Maintenance Electrician
Re: UPS Emergency Power Off (EPO) #98603 01/19/05 09:46 PM
Joined: Jul 2004
Posts: 9,547
gfretwell Online Content
"Article 645 loosens the rules from chapter 3 the price you pay for this loosening of the rules is the EPO system."

Among other things, like separate HVAC systems, fire separation and limited personnel occupancy.

Greg Fretwell
Re: UPS Emergency Power Off (EPO) #98604 01/24/05 04:49 PM
Joined: Jan 2005
Posts: 61
jkochan Offline OP
Thank for the replies. I'm still a little troubled. Assuming there is a fire in the UPS room, and the clean agent FM200 doesn’t handle it, then the pre-action sprinkler system will engage and charge the pipes, then the sprinklers discharge if the links melt in the sprinkler heads. Now… there is no shunt trip to shut down the UPS or disconnect the batteries when this happens, and it’s automatic. So there you are with live voltages both AC and DC all over the place, and water everywhere but no one seems concerned about that. So why is it so important to disconnect the batteries and dump the load when the EPO is pressed? There are still AC voltages present at the busses and at the batteries even if the breakers are open. And you have to be in the UPS room to do this. The UPS feeds five PDU’s all with their own individual EPO for their individual loads and circuits. If the problem is in the branch circuits, the breaker for that branch or the main for that PDU should dump that whole section. It would make more sense to shut down the UPS and go to bypass in the event of a failure like this. Why dump the entire load for a branch fault or in this case a mechanical? (Still undetermined) fault in the UPS itself?


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