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380-480v ±15%

  1. Aug 23, 2013 #1
    Ok, I'm no electrical engineer. but I am an automation engineer with a cheme background who, by the nature of my job gets stuck tinkering around in PLC cabinets. My company has spent probably well over 200 man hours trying to secure proper documentation to run equipment which states a voltage of 480 on the nomenclature at 492. I have no Idea why we are at 492. The electrician must have done something funny with the ground.

    Anyway. So I have some schematics for one of the power supplies and it gives me an input voltage of "380-480V ±15%". Can someone tell me how this makes ANY statistical sense. How can you have a accepted deviation on top of a range? I've seen this before and wondered about it. But in this case the range is huge. Not to mention I don't know what to take 15% of. The max voltage? Thats 72V. A range of 308 to 552 is just plain stupid.

    Am I wrong? Any insight?
  2. jcsd
  3. Aug 23, 2013 #2


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    Just for an example the voltage range for some universal switching power bricks is 90-230V so a wide range input voltage for electronics is common. It's also possible the power supply has a tapped input transformer that can be set to match the input voltage from 380-480 so the transformer can provide the correct secondary voltage ±15%.

  4. Aug 23, 2013 #3
    I know thi seems wierd, but the 380 and 480 are common voltages in Urope or USA - so it is a Universal PS + a standard tolerance to allow for the voltage variations - esp. in inducstrial environments. Your 308 to 552 range is probably accurate - of cource there may be a tap or switch to match the main supply, but this should be pretty evident. Lastly - doesn't the PS manufacturer respond to the question? -- If not return it.
  5. Aug 23, 2013 #4
    We have been working with the end manufacturer. (Not the one who made the power supply but the one who used the power supply in their product. However I was recently able to obtain the the original drawings for that PS.
    Thanks for your input. I know for a fact that it does have a tapped input transformer and the voltage can be adjusted. So I guess that makes sense. Now I just have to convince everyone else around here :(
  6. Aug 23, 2013 #5

    jim hardy

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    With just the littlest bit of luck the transformer itself will be marked as to nominal voltage for each tap.
    And that might not make it into the user manual .
    Especially if the poor engineer writing the manual at last minute on midnight before ship date had specified tap voltages to be written on the transformer so he never thought to put it in the book too.
  7. Aug 24, 2013 #6


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    I assume it is a three phase transformer. You will need to move three links to select your appropriate input voltage.

    The 15% is to allow for two things. Firstly, a typical 5% variation of line voltage resulting from changing load on the network, and secondly the finite choices of tap voltages available on the transformer.
  8. Aug 24, 2013 #7


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    Right, it is a mathematically cumbersome way of saying either standard will work and then some.

    Also, nominal voltages are just that: nominal. The power company is allowed a certain deviation(can't remember, but maybe 2 or 4%.).
  9. Aug 24, 2013 #8


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    quote="russ_watters"]Also, nominal voltages are just that: nominal. The power company is allowed a certain deviation(can't remember, but maybe 2 or 4%.). [/quote]Throughout the network and the customer's wiring there is a maximum line resistance specification based on a voltage drop of 5%. That effectively sets line voltage variation to +/– 2.5%.
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