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Thread: rewire no-neutral devices to avoid ground current?

  1. #1

    rewire no-neutral devices to avoid ground current?

    occupancy sensing switch like MS-OPS2 puts a current on the ground wire. I don't like doing this, since ground wire is not meant to carry current.

    The wiring diagram suggests connecting both the green wire and the metal face plate to the ground wire.

    If neutral wire is available, can I connect the green wire to neutral, and the metal plate to the ground?

    There is no version of this switch that requires neutral wire. There is a more expensive sensor switch that requires neutral wire.

    MS-OPS2 install manual





  2. #2
    Senior Member
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    Nov 2014
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    Did you measure a current level on the ground? Or just assuming because the device needs a ground to work that a current is present?

  3. #3
    Quote Originally Posted by Lukeetal View Post
    Did you measure a current level on the ground? Or just assuming because the device needs a ground to work that a current is present?
    Both.

    I once bought a more expensive dual-sensor lutron occupancy sensor that also did not require ground (MS-A102). I measured it and found current on the ground. I remember the current is much less than what's required to trip a GFCI.

    That is to be expected since the device requires power to work. I eventually returned it and bought a version of that sensor (MS-B102) that required neutral, and therefore did not pass a current into ground wire.

    I want to buy another occupancy sensor switch but the price of the MS-B102 has gone way up. Perhaps I bought it on sale. So I decided the cheaper MS-OPS2 is good enough. But oddly this sensor does not have a version that required neutral, like the MS-A102.

    The instruction of MS-OPS2 said the device would not work if ground is not connected. That also implies a current is flowing into ground; otherwise why would it affect whether it works or not.

  4. #4
    Authorized Lutron Contributor
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    Hello shortcircuit,

    There is a tiny amount of current that runs through the device in the off state. The exact amount is 0.04W/hr. The reason the ground connection is required is that the power supply inside of the sensor needs to see a potential difference via the ground.

    There is absolutely no safety concern with hooking the sensor up with the ground.

  5. #5
    Senior Member
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    Dec 2013
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    How would this get UL approval? Every NEC book and electrician I've met all say the same thing - the grounding conductor should NEVER carry any current and its only purpose is to clear out a ground fault by providing an effecting ground path. This seems to go against all that. Don't get me wrong, it's nice to not need a neutral wire, especially for older homes but some of those older homes also don't have a ground either so it kind of defeats the purpose. Is there a paper on this that proves this is safe for someone upstream who might be working on the circuit in the future? I know Lutron has a great reputation but I'd rather see the study and data than take your word for it.

  6. #6
    Senior Member
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    The MS-OPS6M2U-DV has a neutral connection and retails for $54.

    I'm not sure it is putting much current, if any, on the neutral. It may be using the ground connection as a reference only.

    My guess is that UL has specs about how much current can be put on the ground wire. Lots of devices leak to ground. That is why we complain about microwaves, etc. making noise in AV systems.

    Despite its name, GFCIs don't care about the ground connection. They measure the difference between hot and neutral. If there is an imbalance it trips. GFCI breakers don't even have a ground connection.
    LED, Incorporated
    Raleigh, NC 27614

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