Step Down Transformer Grounding Question

Discussion in 'The Projects Forum' started by Jace, Jun 13, 2008.

  1. Jace

    Thread Starter New Member

    Jun 13, 2008
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    I have a step down transformer that will take 220VAC to 110VAC to use with electronics from the US. I do have 110VAC coming out of the secondary side. A surge protector is following but when I put an outlet tester it indicates 'open ground'. I measured from the hot to ground and got 78VAC and from the neutral to ground and got 30VAC. Is this normal and safe to plug in electronics into the power strip? Do I have to attach the neutral from the transformer secondary to the chassis ground?
     
  2. Jace

    Thread Starter New Member

    Jun 13, 2008
    3
    0
    I'm using a voltage regulator to use a 110 VAC line in, step it up to 220 VAC, have it go through a line filter and circuit breaker, then to test a step down transformer back to 110 VAC. I do get 220 VAC going into the transformer and 110 VAC out of the transformer but an outlet indicator shows me 'open ground'. I measured the voltage at 'hot' line to ground and am getting 95 VAC and from the 'neutral' to ground I'm getting 120 VAC.

    Is it correct to get 120 VAC on the input of the neutral line? I measured the voltage when connecting 110 VAC at the input and I get 0 V at the neutral line and 110 VAC on the 'hot' line.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You should at least put your country in your profile so that we might get an idea of what the electrical standards are which apply to your situation.

    In the USA, for residential electric service, each dwelling is connected to the power company via a step-down transformer which has three outputs:
    1: L1
    2: Neutral (actually, a center tap between L1 and L2)
    3: L2
    Between L1 and Neutral, or L2 and Neutral a nominal 120VAC RMS is measured.
    Between L1 and L2 measures 240VAC RMS. L1 and L2 are 180° out of phase with each other.

    At the main breaker panel, Neutral is connected to earth ground via a large gauge wire. The earth ground is usually provided by at least one 8' long copper-clad stake pounded into the ground. This is for safety; as otherwise the secondary of the transformer could "float" to several thousand volts, leading to a very unsafe condition.

    The main breaker panel is the ONLY place that earth ground is connected to Neutral.

    Old-style 120v outlets have just two sockets that accept a two-pronged plug with flat blades that are parallel to each other. One blade is wider than the other so that it will only fit one way. The wide blade is the neutral connection. Newer style outlets that began to be used in the 1960's have three sockets; a round socket was added to accept a ground connection.

    The ground is connected to the chassis of the appliance to protect the operator, and the neutral and "hot" are used to power it. Bathroom, kitchen and outdoor outlets are protected from ground faults by "GFCI" breakers. If the current supplied by the hot doesn't match the current returning by the neutral within a few mA or there is more than a few mA current in the ground wire of the circuit, the GFCI breaker trips.

    If your power plug from your mains is polarized (to make it impossible to connect backwards) you could jumper your transformer's primary-side neutral line to the secondary winding which is connected to the wider flat socket in the power strip. If your mains power plug is not polarized, do not do this.
     
    Last edited: Jun 13, 2008
  4. Jace

    Thread Starter New Member

    Jun 13, 2008
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    I'm actually using a Voltage Regulator to step up the 110VAC to 220VAC and measured 95VAC from line to ground and 120VAC from neutral to ground directly out of the Voltage Regulator. Is this normal or should there be no volts coming out of the neutral line as the 110VAC line does? Is the Voltage Regulator the cause for the open ground issue?
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Your hot lead should read 110Vac to ground. Your neutral lead should read nearly zero Vac to ground. Is your secondary isolated or grounded?

    By the way, a "voltage regulator" won't do what you are claiming. Can you find the proper term for your device in any of the literature accompanying it?
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    And on an unrelated note... please refrain from posting multiple versions of the same question. It just makes extra work for the moderating team.
     
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