EMT conduit as ground

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  #1  
Old 07-18-05, 01:57 PM
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EMT conduit as ground

I have a situation where EMT conduit runs from a circuit breaker sub-panel to a weathertite box. There is no separate green ground wire running to the box, but the downstream branch is grounded to the green grounding screw in the box. Since the weathertite box is aluminum, I am concerned about the possibility of oxidation where the EMT connector is screwed into the box. Can this be a problem? For that matter, what about the coduit body pull boxes that connect sections of the EMT? They appear to be made of cast aluminum or some other non-magnetic metal. I would suppose since they are designed to be used with metal conduit there should be no problem, but this situation has got me thinking about it. The circuit feeds a jacuzzi so I want to be sure there are no problems with the ground.
 
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Old 07-18-05, 02:23 PM
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EMT can be a suitable ground fault path if the emt is mechanically and electrically continuous to the panel (given the ground in the panel is bonded to the enclosure which it should be). Someone can correct me here, but I do believe it's stated in the NEC that in any raceway a grounding conductor must be pulled. If it were me, i'd leave it alone if it wasn't a jacuzzi, but given that it's a jacuzzi, I'd disconnect everything, tie a string/rope to a wire, pull the string through the pipe, then pull that wire plus a ground back in the pipe.
 
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Old 07-19-05, 01:04 PM
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The jacuzzi needs a seperate insulated green conductor for ground. It also needs a physical disconnect, GFCI protection, and all the surrounding metal must be bonded.

Most jacuzzis are 50A or 60A models which would require #6 copper black/red/white and a #10 green ground in 3/4" conduit or larger.
 
  #4  
Old 07-19-05, 07:23 PM
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Thanks for the advice. I want to do the safe thing here, but I know there can also be problems pulling wire next to existing wire in conduit i.e. mechanical degradation to insulation etc. I have been doing some reading, and in the 18th (2002 NEC) edition of Practical Wiring it states that: "No separate grounding wire is required inside the metal conduit..." In fact, later it says that the preferred ground fault path of the current would be a properly bonded metal conduit, even if there were a separate grounding wire. Of course the question is how sure can I be that the conduit will remain properly bonded--which is why I became concerened with the aluminum box and non-ferrous conduit bodies. I still am interested to know if anyone has any wisdom on that issue, aside from the jacuzzi wiring.

The jacuzzi is small and only requires 40 Amp breakers, so I think #8 copper (which was used) is sufficient. There is also a separate enclosure with a GFCI breaker already in the circuit.

It will be a bit of work (and possibly expense--if I pull all new wire) to run a separate ground wire, so I just want to be sure that there is a realistic improvement of the safety factor, or a specific code requirement that will be fulfilled by doing it.

Thanks again for the input!
 
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Old 07-20-05, 04:16 AM
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Pools and spas have separate rules. They require an insulated ground wire when run outdoors, even if metal conduit is used.
 
  #6  
Old 07-20-05, 07:56 AM
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Originally Posted by Gregor
The jacuzzi is small and only requires 40 Amp breakers, so I think #8 copper (which was used) is sufficient. There is also a separate enclosure with a GFCI breaker already in the circuit.
Sounds like you have met all of the requirements except the ground wire. Just pull it carefully beside the existing wires. Don't yank or use excessive force and use a pulling lubricant. Have another person handy to guide the wire into the conduit as you pull so as to not cause skinning and binding. Lay the new wire out flat and get the twists and kinks out or roll it directly off the spool. With just one wire, you can be pretty gentle.
 
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Old 07-20-05, 10:07 PM
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Alright, thanks, that is what I will do.


Gregor
 
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