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Thread: E682 Power supplies jumpering V- to GND

  1. #1
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    Aug 2011
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    Default E682 Power supplies jumpering V- to GND

    Whats everyones thoughts on binding the two together. In the E682 manual it says too. I've never heard of doing it this way. I do know its best if using multiple power supplies to bind all the v- together. But is this safe?

    Thanks,
    Brandon

  2. #2
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    Default Re: E682 Power supplies jumpering V- to GND

    Although not everyone agrees, I believe that best practice is to connect the negative power supply to earth ground unless there is a specific reason not to. This provides protection against a fault condition in the power supply. Without this connection, an accidental short circuit (or partial short circuit, up to several thousand ohms) in the power supply between the AC hot wire and the power supply + or - would not trip the circuit breaker or GFI. The danger here is that this type of fault could go undetected for a long time. The attached equipment, this case pixels and pixel controller, could all have an unsafe potential relative to earth ground and present a shock hazard that wouldn't be discovered until someone got shocked.

    This type of fault, while not common, could result from moisture in the power supply or a component failure, or a wiring error. By having (-) tied to earth ground (NOT NEUTRAL!!), a fault of this type would not be able to elevate the voltage present on the attached equipment to an unsafe level.


    Think of it this way: Without the safety jumper in place, you could short the power supply's line terminal (L) to the power supply's (-) terminal and absolutely nothing would happen. Everything would continue to operate, but if you measured the voltage from the pixel ground lead to earth ground, or from metal parts on the pixel controller to earth ground, you would measure 120 volts of AC, an obviously unsafe condition. If the safety jumper is in place a short from (L) to (-) would immediately trip the AC breaker.
    Sandevices E682/6804

  3. #3
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    Aug 2011
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    Default Re: E682 Power supplies jumpering V- to GND

    Thanks Jim, for the explanation!!

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