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Does the ground have to be on X2?

  1. Jan 20, 2010 #1


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    In this schematic there is two potential transformers on the left and two current transformers on the right.

    The potential transformers on the left are connected together by a wire between X2 of the left transformer and X1 of the right transformer. Then there is a wire that must come from one of these two transformers to the test switch location that also has a ground connected to it.


    My first question on this is, does the wire that connects these two ends of the transformer to the switch have to be connected to X2 in that part or can it be connected to the X2 or X1 of those two directly connected terminals?
    I ask because I notice that the schematic rearranged the way that the current transformers on the right are oriented so that the X2 wires that are going to the switch will also be grounded. Althought they are not connected in series with each other like the left ones are.

    My second question is, are the potential and current coils connected at the tops past the switch so much less resistant than the earth ground that an earth ground can be connected in this way without causing a short? Will only excessive current go to ground? And under what kind of conditions will current decide to go to ground?
    Last edited: Jan 20, 2010
  2. jcsd
  3. Jan 21, 2010 #2


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    I see nothing wrong with the wiring here. Ground is just your reference when taking measurements (I assume the components above your test switch are meters). The voltage transformers are wired so that the connection of X2 and X1 is like a center tap. You are measuring the voltage of each leg to ground; (they are usually wound to provide a nominal operating voltage of 115Vac which represents the lines higher voltage). And the current transformers are wired to measure the current through each leg; (they are usually wound to provide a nominal operating voltage of 115Vac which represents the lines normal current).

    Note that the test switch shorts out the CTs secondary when the switch is open (not taking a reading).
    Last edited: Jan 21, 2010
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