Garage door grounded?

Discussion in 'Electrical Forum discussion & Blog' started by DIYer101, Sep 2, 2015.

  1. DIYer101

    DIYer101 Member

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    Colorado
    I've got a 70 year old house with an old garage (not sure how old the garage is). The wiring is the black fabric kind. Somehow my outlet tester says the circuit is "kind of" grounded - how is that possible?

    DETAILS:
    Somebody installed a 3-prong receptacle for the garage door opener, so I stuck the outlet tester in there. It showed the 2 amber lights for "Correct." I was surprised and looked closer, but there's no ground wire anywhere... With the garage door opener unplugged, the tester shows "open ground."

    It turns out that when the garage door opener is plugged in, the receptacle seems to be grounded - but only slightly. This is the first time I used the outlet tester... Took it inside the house (which is properly wired) to test and noticed that in the garage, the second amber light is dim. But in the house, both amber lights are bright.

    Are garage door openers grounded, or is something else going on?

    Thank you.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    It is tough to say, but if there are only two wires, it's not really grounded. When you plug in the opener, you're probably reading a ground via the neutral way back to the panel, and since those wires have some resistance because of the connections and length, it doesn't show up as a great one. In reality, that extra resistance is enough to negate the function of the 3-wire safety ground on the thing. If you want it safer, replace the receptacle with a GFCI receptacle. Those ARE legal to install on a 2-wire circuit IF you use one of the supplied labels and put it on indicating that there is no ground, GFCI protected.
     
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  4. Stuff

    Stuff Well-Known Member

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    Could be a bad or mis-wired garage door opener. The motor or something else may have the neutral shorted to ground. How old is it?
     
  5. cacher_chick

    cacher_chick Test, Don't Guess!

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    Receptacles in a garage are required to be GFCI protected, so if it's not, it would be a good idea anyway.
     
  6. Reach4

    Reach4 Well-Known Member

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    Yours is to an extent. Do not worry about it.
     
  7. DIYer101

    DIYer101 Member

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    Thanks all. No idea how old the opener is but here's a photo (below). On closer inspection there are some cracked wires in there (peeking through the slats on the white/light part)... So I wonder if there is a short.

    I will change it to a GFCI receptacle with sticker.

    The whole point of wanting power out there was to supply a little 12v transformer for some low-voltage lights. Is it a horrible idea to run maybe 10 amps (at 12 volts) off of this wiring once I put in the GFCI receptacles?

    Thanks again, I really appreciate it.
    IMG_1722[1].JPG IMG_1724[1].JPG
     
  8. ActionDave

    ActionDave Electrician

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    Sounds like it might be old BX wiring which had a metal sheath. Might be rusted up or a bad connection along the circuit.
     
  9. Reach4

    Reach4 Well-Known Member

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    No. No problem getting some power from the outlet box.

    What I see is that you have a metal track. You have metal straps. They connect to the wood which may have some moisture, so will be slightly conductive. The frame of the opener connects to the track and straps. It is not a short. That would be normal. The frame also connects to the round ground connector on the plug by design. So if the tester does not draw much current when lighting that LED, you could get a little glow. Really. No problem.
     
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If those lights are drawing 10A and you open the door, you'll probably trip the circuit breaker. A 1/2HP motor draws about 400W, and then add the lights in the thing, and the starting surge, and it's probably too much. For safety reasons, you should replace that receptacle with a GFCI AND use the load output of it to feed the new circuit you want unless you're going to run a whole new circuit. THen, I'd run a 12/3 for a shared 20A pair of circuits. This would allow you to use two of the leads for hot from a two-pole CB and share the neutral for two circuits which would have plenty of power for all you want. You could also do it with 14/3, and use a 15A dual-pole CB.

    Old wiring that has cracking insulation is a good thing to replace before you have too many other problems. It will be worse if you start to play with it to make changes...then, you'll probably not have a choice.

    In the house I grew up in, most of it was wired with BX (metal sheath) with two wires (hot/neutral). They expected the steel in the sheath to provide ground, but over the years, especially in the bathroom and in the plaster walls, there was enough corrosion where there was no semblance of a ground connection any more. I ended up replacing all of the aging receptacles with a combination of new, 3-prong ones fed with GFCI devices. Not as good as rewiring the whole place, but it is much safer, was much faster, and less expensive than a total rewire.
     
  11. Reach4

    Reach4 Well-Known Member

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    10 amps at 12 volts will draw less than 2 amps at 12o volts (even allowing for transformer inefficiency).
     
  12. hj

    hj Moderator & Master Plumber Staff Member

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    The ground terminal is connected to the opener's chassis, which is connected to the trackl, opening mechanism, and side rails, plus the metal door if you have one. ALl of that metal could produce a false ground indication.
     
  13. DIYer101

    DIYer101 Member

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    Thanks again all - I really appreciate it.

    I'll update the receptacles and keep a wiring upgrade in the back of my mind. I'm trying to figure out if there's a way to get good "new" wire from the house into the garage (they're only "attached" at the corners) but I'll probably have a pro take handle that if I'm going through walls and running wire outdoors.
     
  14. WorthFlorida

    WorthFlorida The wife is still training me.

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    FYI...The Garage Door Opener (GDO) is a Chamberlain and the small wires you took a picture of is the low voltage for GDO wall switch and the safety sensors. Low voltage for landscape lights is no different than the 24 v AC used for door bells and your furnace thermostat. The only place that low voltage is of concern is in certain areas (usually commercial buildings) is any exposed low voltage must be teflon coated for fire rating. Big cities like Chicago require it to minimize toxic gassing & fuel in an event of a fire.

    The black fabric wire is probable ROMEX brand of wire and in it it might have printing on it (NM) for non metallic. Before PVC insulated cable and wire was common (sometime during the 1960's) fabric was the norm and millions of old homes have this wire and most do not have a ground. You didn't say if the garage is attached to the home or not but if it is and have easy access to the fuse or circuit breaker panel run a new line to the garage with a ground. A 70 year old home you may have the screw in type fuse panel. If it has circuit breakers then it probably was upgraded at one time. If you're not comfortable with this then it might be worth while to have an electrician do this little upgrade. Have him added outlet on the ceiling joist and latter on you can add shop lights with a plug to add lighting to the garage. Landscape lighting is not very bright at all.

    [​IMG]
     
  15. DIYer101

    DIYer101 Member

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    Thanks WorthFlorida, the garage is "kind of" attached (the house and garage overlap by about 4 feet on the corners). Fortunately there's an unused outlet in the house nearby, and that outlet is its own circuit (it's labeled Freezer at the breaker box but there's no freezer there anymore, and that breaker doesn't control anything else in the house as far as I can tell). That wiring has been updated, so I might run that into the garage to make things more modern.

    The low voltage I was talking about was outdoor lighting that I am powering from a (indoor rated) transformer in the garage. For now I've replaced the garage receptacles with GFCI receptacles, but I'd like to get modern wiring in there just because.
     
  16. WorthFlorida

    WorthFlorida The wife is still training me.

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    I do not have my volt meter at home to check this out on my Craftsman GDO (Chamberlain) but I think you are getting the so call false ground from the GDO itself as you noticed with your tester with the GDO plugged in. The purpose of the third wire ground it to assure that should a short occur and/or the neutral wire (wht) was opened that the chassis of the appliance is never hot (line voltage). That is you have a motor and the neutral side of the motor is probably connected to the chassis. Without an earth ground (green wire) the chassis of the GDO would have high voltage on because there is no returned path to ground. You get up on a aluminum ladder and touch the GDO to find out what's wrong and you'll get zapped if one part of your body has a path to ground and your hand is on the chassis. There were many electrocutions because of this. When double insulated motors became mandatory and third wire grounds, the occurrence is now rare.
    To check this out unplug the GDO AC plug and put an ohm meter on the third wire ground and the wide blade of the plug itself. If you get a a reading of zero ohms then then the two grounds are connected inside the unit. If the plug does not have a wide blade then reference this picture.
    [​IMG]
     
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