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UPS splits power?

  1. Aug 8, 2015 #1
    A friend of mine recently asked if I could take a look at his Monster brand power filter that wasn't working and I noticed it splits the power so, what normally would be neutral and hot, legs are split to carry 60VAC each. I think I've seen this on all the UPS's I've measured as well.
    Anybody have some insight on why this split/balanced configuration is used? There must be some advantage?

    Also.....I've come to notice, when this Monster filter and some of the UPS's I've measured in the past seem to keep supplying 60VAC to the legs after the device is off. Measuring between hot and neutral reads 0V but ground to either leg reads 60VAC. Two legs in phase with each other? This seems like a bit of a dangerous setup, any thoughts on why this would be done?
  2. jcsd
  3. Aug 8, 2015 #2


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    Are you talking UPS or power line filter or surge protector? please be specific and post some model numbers or links.
    Last edited: Aug 8, 2015
  4. Aug 9, 2015 #3
    We can stick with UPS's. I only mentioned the Monster "power conditioner" because I had recently fixed it and noticed the same thing. Chances are good the OEM built it that way for marketing as there seems to be some audio voodoo about "balanced power" floating about some audio forums. Chances are better UPS's are designed this way for non voodoo reasons.

    I don't have any specific model numbers. I work in SMT manufacturing and the reflow ovens have UPS's to keep the conveyor running if there is a power problem. The UPS's in this hot environment only last a couple years so, I've replaced dozens of them in my time. I think every UPS I measured over the years had split the legs on the power.
    I might have a working UPS at my shop but I need to measure it and get a model number later in the week if needed.

    I think my biggest concern is that many of the UPS's I've looked at leave 60VAC in phase on the legs when powered off. I often need to be cautious of this when I work on a piece of equipment the uses a UPS, throwing the main breaker isn't always enough!
  5. Aug 9, 2015 #4


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    OK. You are telling me something I don't know anything about.


    It seem like what you are saying is that when the circuit breaker is thrown, you still see 60V on outlet. I'm not sure why that would be.
    Here are some articles --- maybe there is a clue there. http://equitech.com/articles/articles.html
  6. Aug 9, 2015 #5
    Thanks BigGuy. That link should give me a couple days of reading. I did run into that schematic on a few of my searches also.

    "It seem like what you are saying is that when the circuit breaker is thrown, you still see 60V on outlet"
    Now that I read it, I may have misspoke. When I turn the UPS off I still get 60V, I have not tested after I've killed power to the UPS. I just made an assumption and unplug them when needed. I'll take a look at that when I get back to my shop later this week but still wonder why they split the leg in the first place? Maybe your link will reveal more info.
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