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Thread: No Ground?!?

  1. #1
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    No Ground?!?

    Why is there no Ground wire in the pressure switch box of Market Forge M36G Boiler?
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  2. #2
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    I'm not sure why you're looking for a ground there. Your pic is too small too, so I can't make out what your meter is connected to.

    From the service manual's schematic, ground is used -
    • as reference for the water control board's sensing of water level (boiler is grounded),
    • as COMMON for the 24v circuit,
    • for the igniter circuit to spark to for lighting the pilot...and
    • as 1/2 of the flame rectification circuit for proving flame (local sensing IPI).


    Here's the manual:
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  3. #3
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    So you're not seeing continuity between the control box and the pressure switch box? Well, they're both mounted within the cabinet and the boxes should both be bonded to ground in that fashion. As such, there should be no need for a ground wire.
    Are you sure your meter is working and test leads are good?
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    "You never know what others don't know." -

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  4. #4
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    Thread Starter
    Sorry for the small image... here's the original

    I'm looking for a ground wire in there because had there been one I wouldn't have been shocked when using the drain bypass switch. That was before the cover was off. The meter is showing 118.8 volts ac potential between the pressure switch box and the control box. Major hazard and seems like an oversight from the manufacturer.
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  5. #5
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    Thread Starter
    The pressure switch box is not bonded... it would be if they used metal conduit. The pressure switch box is mounted to a brass manifold via the pressure switches themselves which are not metal.
    Last edited by FieldGen3; 08-12-2019 at 01:00 PM.

  6. #6
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    Perhaps "someone" isolated it due to not being able to find the short? Have see this sort of hack before. J-Box should never be hot.

  7. #7
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    Thread Starter
    I'm pretty sure it came this way. I remember when the unit was purchased and as far as I know I'm the only one who's worked on it. To follow up, the short was in the drain valve bypass switch itself. I removed it, (it's normally closed so i put in a jumper,) and ran a ground wire between the two boxes. Parts on order.

  8. #8
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    That short should have tripped a circuit breaker.
    That's quite an oversight on Market Forge's part. I'd call them and let them know.

    Lucky that your getting shocked wasn't under conditions which could have made it worse.
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    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  9. #9
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    Thread Starter
    Yea I’ll call and see what they say. I measured 650 ohms between the switch terminals and the toggle so 0.18 amps of current that I took. It probably wouldn’t have tripped a breaker but given an alternate path it would take the least resistive route. The switch would’ve probably overheated at some point if the current was constantly flowing. I don’t know, just happy to be home.

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