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#26249 - 06/03/03 09:52 PM Two UPS in series?  
drillman  Offline
Member
Joined: Mar 2003
Posts: 97
Somewhere in Texas
Let me explain.

I got a work order stating that a computer that links to the outside that is on a UPS goes down when the power blips.

I did some crawling around, there is a UPS machine rated for 15 amps (big one) with two critical computers on it. One of them went down, they said.

Did more crawling around, found out that there was a real small ups plugged into a power strip in series with the big one that was also plugged into the computer that was going down.

Not knowing what else to do I unplugged the small ups, tossed it aside and plugged it directly into the big one.

Did a smoke test. That means I shut the breaker off feeding the big and only UPS.

Everything worked fine.

I do not know how or why that little one was there, my question is would having two of them in series cause a problem?


Work Gear for Electricians and the Trades

#26250 - 06/03/03 10:06 PM Re: Two UPS in series?  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,826
Brick, NJ USA
Did ya check the "small unit" to see if it functions by itself??? Plug it into a hot receptacle, put a load on it (a lamp is good)and yank the plug. The small unit battery may be shot.
John


John

#26251 - 06/03/03 10:20 PM Re: Two UPS in series?  
Mike_Riverside  Offline
Member
Joined: Aug 2002
Posts: 33
You are not supposed to connect UPS in series... there is more info here http://www.apc.com/support/index.cfm

[This message has been edited by Mike_Riverside (edited 06-03-2003).]


#26252 - 06/04/03 10:59 AM Re: Two UPS in series?  
Ron  Offline
Member
Joined: Mar 2002
Posts: 582
White Plains, NY
Consider the fact that if the small UPS where to fail (and I think that is what happened), it will drop the load whether the utility power is there or not. The small UPS' are not arranged for dual inputs, so a small "in sereis" with the large will negate the benifit of the large, since it has no way of getting power to the computers if the small fails.
There are so arrangements in which series units are helpfull. Those are when the middle UPS has the ability of dual feeds and the large unit would be connected to the bypass of the small unit. So if the small unit where to fail to bypass, the big UPS would carry the load. I don't think this was your situation.


Ron

#26253 - 06/04/03 07:30 PM Re: Two UPS in series?  
jdevlin  Offline
Member
Joined: Aug 2002
Posts: 402
welland ontario canada
It could also be that another device(computer, router, modem) that the computer is connected to is not on a ups.
Also the second UPS would never see a failure if the first UPS was good.

[This message has been edited by jdevlin (edited 06-04-2003).]


#26254 - 06/04/03 09:54 PM Re: Two UPS in series?  
drillman  Offline
Member
Joined: Mar 2003
Posts: 97
Somewhere in Texas
Thanks that link was most helpful. I was not aware how bad it was to plug a surge protector into a UPS.

I have tested and figured out that the small ups which was at the output of the big one, is in fact dead as a doornail.

I belive that this was basicly an accident, as there is lots of power strips with stuff plugged in left and right. The small ups was stashed under the desk next to a router type thing and had a rather thick covering of dust on it.

Now for the really fun part, the big UPS has plugs on the back for the computers. When someone installed it they plugged in a male/male cord and plugged the other one into an outlet. Can you say BACKFEED. The homerun for that outlet was taken off the breaker and wirenuted to the homerun of another outlet across the room, in the panel no less.

It took me 4 hours of head scratching with a circuit tracer to figure this out. Never thought anyone could be so stupid.

The other thing is the subpanel has all the grounds landed on the neutral bar. There is no seperate ground bar.

I am aware that this needs to be fixed and will put in a proposal to do it right. Just got to wait to see if they will pay for it.


#26255 - 06/05/03 04:04 PM Re: Two UPS in series?  
nesparky  Offline
Member
Joined: Jun 2001
Posts: 642
omaha,ne
Drillman
Never under estimate what those with little knowledge will do.
We can make things realitively safe. We cannot make them fool proof, despite all the safety regulations and codes in the world.
Good luck with the job. Hope the price will be right.


ed

#26256 - 06/05/03 06:02 PM Re: Two UPS in series?  
wa2ise  Offline
Member
Joined: Nov 2002
Posts: 782
Oradell NJ USA
Quote
Now for the really fun part, the big UPS has plugs on the back for the computers. When someone installed it they plugged in a male/male cord and plugged the other one into an outlet. Can you say BACKFEED. The homerun for that outlet was taken off the breaker and wirenuted to the homerun of another outlet across the room, in the panel no less.

It took me 4 hours of head scratching with a circuit tracer to figure this out. Never thought anyone could be so stupid.


Sounds like something an "Electrical Engineer" would do. The ones with a BSEE, like myself. [Linked Image] Some manager didn't want to spend money for a second UPS, or an engineer knew that the boss wouldn't approve it so came up with this kludge with materials on hand (male power plugs are pretty common, so are power cords, and the outlets exist and I can get the UPS power to the other site by doing some bad wiring in the panel..."

As mentioned in a previous thread, BSEE people don't have any training in the NEC or any other building codes. The general attitude is that "house wiring" is hundred year old technology, and thus too simple to bother with. Or that that's something that is farmed out to 'lectricians. Well, the above kludge should have been farmed out. [Linked Image]

It would probably be cheaper for the customer to buy a second UPS than to have special wiring done to properly feed the distant site.



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