power monitoring q

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I got a call yesterday to look at a UPS that was malfunctioning (FWIW it was a Powerware 9170+). Apparently it was cutting out and stopping power from flowing to the connected loads. This was happening even though the utility power was still on. After talking w/ tech support they thought it sounded like a problem with the system being overloaded and it shut itself down to protect itself. His suggestion was to install another power module and sacrifice some battery capacity. That seemed somewhat reasonable but I figured before we go mucking about swapping things in and out we really need to get a handle on what the true draw is. It seems the only accurate way to do this is leave a power monitor on this panel for a week or so. I have never done this before and was looking for some input. The panel is single phase 208 (H-H-N-G). Is this as simple as connecting the leads to the panel lugs and leaving it for a week? When the test is done can I read the results or do I need to bring it back to the place I rented it from and run it through special software? Any thoughts/ input on this would be greatly appreciated.
 

zog

Senior Member
Location
Charlotte, NC
Depends on what you rent, chances are you can have a testing firm do it for you for less than the rental costs and provide a full report.
 

charlie tuna

Senior Member
Location
Florida
there are a few ways to do this. as mentioned, sub contract it out to your competitor. rent a meter and have the rental agent provide you with the information. rent the meter and download it yourself. purchase a data logger.
if your gonna be in the electrical contracting business for any length of time you should really consider owning some type of power monitor. it is a tool that allows you to properly troubleshoot what you and your customer can't see. i bought one and started renting it out to my customers for $35.00 a day plus the time it took to download and formulate the report. i soon had two units, because for some reason i started getting calls for monitoring while the first logger was in use??? it is an investment. but it payed off for me. engineering groups began calling and kept us busy monitoring existing loads prior to expanding electrical systems. i would charge them the time to setup the logger. the daily rental, and then the report time. it worked for me.....
 

brian john

Senior Member
Location
Leesburg, VA
Overloaded UPS should go to bypass.......Till load is within spec then return to service.

Is the site dropping the load?

Is the load close to full load rating?
 

dbuckley

Senior Member
It doesn't actually matter what the power draw is; what matters is what the UPS thinks it is. Check the LCD. One often seen scenario is load imbalance, such as the total load is within the theoretical capability of the UPS, but its misbalanced so one phase is overloaded.

Nevertheless, a UPS should never really just stop supplying power, short of overcurrent devices opening or really catastrophic failure; if it cant take the load it should, as Brian noted, go into bypass. Perhaps it is (being polite) busted?
 
dbuckley said:
Nevertheless, a UPS should never really just stop supplying power, short of overcurrent devices opening or really catastrophic failure; if it cant take the load it should, as Brian noted, go into bypass. Perhaps it is (being polite) busted?

That was my thought too. There is a manual bypass switch located next to the rack, but the whole idea of this thing shutting down when there is a problem seems bizzare to me. In terms of load imbalance that is another reason I want to do a power analysis. When I checked w/ my clamp I was getting about 6.7A on A and 5.8A on B but this was obviously a "point" test. I know they have some refrigeration units on this system and I'm wondering if one one of the condensers is going bad and sending some type of spike on start up (this is a dermatology office and they need the "cryostats" to keep samples or meds or some such thing).

In terms of subbing v. renting v. purchasing I think you guys have convinced me that subbing is the way to seeing as I am having a hard time finding a place to rent one. Charlie, your experience not withstanding, I've never before had this need come up. As a matter of fact I can only remeber one time in my career (ie working for others) that we needed to do this. Just for kicks though, what is the price range on moderatley appointed power monitor? Also what are others experiences with the need to own one?

Thanks
 
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