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Old 10-03-2011, 10:09 PM   #1
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New vent hood, no ground in existing wiring?


Hello everyone

I am installing a new wall chimney kitchen vent hood. The wiring for the hood includes ground, but the existing wiring for the old under microwave vent only has 2 wires with no ground. The wires are in the metal armor conduit, and my buddy mentioned that this metal conduit is the ground.

Is this true? If so, what do I do with the green ground wire from the vent? Electrical tape it to the metal conduit?

Thanks for any help you can provide

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Old 10-03-2011, 11:51 PM   #2
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New vent hood, no ground in existing wiring?


The only way that BX or MC outer sheath is a ground, is if it has a grounding strap in it. The little aluminum wire inside is not a ground. You will have to pull new wiring for that range hood, if you want to use it.

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Old 10-03-2011, 11:53 PM   #3
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New vent hood, no ground in existing wiring?


If it’s AC type cable, and has the aluminum strip inside, with proper fittings, it qualifies as the ground (the sheath and bonding wire work together as the ground). Most MC cable doesn’t have a bonding strip (some do now) but will have a green insulated conductor inside.

Good catch Greg.
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Old 10-04-2011, 01:54 PM   #4
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New vent hood, no ground in existing wiring?


Thanks, I will go later to check if it has a grounding strap inside of the outer sheath armor.

If it does, is this ok?: attach a box to the stud. Clamp down the armor outer sheath snugly with the grounding strap bent back on the sheath for a positive ground. Attach and wire up a single outlet 15a GFCI receptacle. Use a short piece of 14g wire from the box ground screw to the receptacle ground screw to ground the receptacle. Attach a plug (including green ground from vent) to the vent wires. Hang up the vent and plug it in.
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Old 10-04-2011, 01:58 PM   #5
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New vent hood, no ground in existing wiring?


Doubt you will find one in it. How old is the home, and were grounded outlets original to the build of the house for the age? If the later is yes, then yes, it should have the strap inside the armor. And installing the hood, they have to be permanent install, which means that you can not use a outlet & plug for it. If it is a microwave unit, with hood fan, most will be hard wired, some will have the vent hood hard wired, and mic with a plug, so you can disco if needed.
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Old 10-04-2011, 02:11 PM   #6
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New vent hood, no ground in existing wiring?


House was built 1964. From what I remember when I briefly looked at it last night, there was brown paper inside of the outer sheath around the wires, I didn't see a grounding strip but again, it was a very brief look. I will look harder when I am working there tonight.

So if it does indeed have the grounding strip, would it ok if I: attach a box to the stud. Clamp down on the metal outer sheath snugly with the grounding strip bent over the outer sheath. use twist nuts to bond the power and neutral wires. Attach the green ground wire from the vent to the ground screw on the box.

Thanks for all the help you are providing
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Old 10-04-2011, 02:15 PM   #7
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New vent hood, no ground in existing wiring?


Quote:
Originally Posted by 6fthook View Post
Thanks, I will go later to check if it has a grounding strap inside of the outer sheath armor.

If it does, is this ok?: attach a box to the stud. Clamp down the armor outer sheath snugly with the grounding strap bent back on the sheath for a positive ground. Attach and wire up a single outlet 15a GFCI receptacle. Use a short piece of 14g wire from the box ground screw to the receptacle ground screw to ground the receptacle. Attach a plug (including green ground from vent) to the vent wires. Hang up the vent and plug it in.
If you install a receptacle to plug the hood into it has to be a dedicated circuit. If you hard wire the hood it can be on another shared circuit. But not a counter top SABC (Small Appliance Branch Circuit).

(Code05, see I remembered)
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Old 10-04-2011, 02:25 PM   #8
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New vent hood, no ground in existing wiring?


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Originally Posted by rjniles View Post
If you install a receptacle to plug the hood into it has to be a dedicated circuit. If you hard wire the hood it can be on another shared circuit. But not a counter top SABC (Small Appliance Branch Circuit).

(Code05, see I remembered)

Sounds good to me!

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