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Jason
Jason, Service Technician
Category: Electrical
Satisfied Customers: 4251
Experience:  Over 20 years of experience in all types of installations, troubleshooting, and repairs.
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I have an unfinished basement that has outlets installed on

Resolved Question:

I have an unfinished basement that has outlets installed on the walls in metal boxes with metal conduit, and they are severely corroded. Is it acceptable to change them to sealed plastic boxes and run the ground back to the metal box they are all fed from?
Submitted: 5 years ago.
Category: Electrical
Expert:  Jason replied 5 years ago.

Jason :

Hello. Thank you for asking your question on Just Answer...

Jason :

Do the conduits go back to a junction box on the ceiling?

Jason :

Is there "romex" type wire inside the conduit?

Customer:

Yes they are all connected to a junction box

Customer:

no they are all armored cable

Jason :

Is there a ground wire in the armored cable?

Customer:

not that I have seen, I just assumed that the sheathing and the conduit would ground all of it back to the panel

Jason :

It may or may not have a ground wire in it. If it's very old, it's likely 2 wire BX, meaning no ground wire. Rather than running an individual grounding conductor, I would probably refeed the outlets with romex and new boxes. If you can route the new wire down the sides of the studs, you won't need to protect it with any tubing. If you just want to replace the boxes, and have 3 prong outlets... but there's no ground wire in the flex, you could replace the standard outlets with GFI type 3 prong outlets. This is a Code legal option, as long as you mark the outlets "No Equipment Ground". Technically, you didn't have an equipment ground before, if the distance from the outlet to the junction box is more than 6 feet.

Jason :

That answer is based on the assumption that you would replace the metal boxes with plastic boxes.

Customer:

I was planning on removing the whole thing and starting from the junction box replace all of it with pvc conduit and boxes, only because the condition of the existing boxes is so bad. They are all surface mounted on brick foundation, that apparently weeps enough water through it to corrode the metal boxes and the conduit that feeds them.

Jason :

Okay, now I understand your question more thoroughly. You can bond the ground wire that will be in each new conduit to the metal junction box that the new plastic pipes will terminate to. If you have the metal flex all the way back to the panel, then the described bonding will ground the outlets. However, today's Code mandates that any flexible metal conduit over 6 feet long is not considered an effective grounding path. But your installation would likely be grandfathered in.

Customer:

yes the two wires that feed the junction box run in a solid metal conduit that runs all the way to the panel so I assumed that if I ran a ground wire through the new pvc conduit and grounded it to the metal junction box the whole thing should be grounded.

Jason :

It would, but I would take a voltage reading from the hot wire to the ground wire at each outlet, after you get everything connected. I would want to know how effective the coiled metal flex is as a grounding path from the metal box back to the panel.

Jason :

Sorry, by "solid" metal conduit from box to panel, do you mean it's not a flexible BX type conduit from box to panel?

Jason :

Is it 1/2" metal EMT (thinwall) conduit?

Customer:

There isn't metal flex to the panel it is a solid metal conduit, but I see your point. Since none of the outlets even have a ground screw on them and they are only two prong the fact that they work at all must mean they are grounded through the conduit

Customer:

The conduit is thicker than the EMT I looked at

Jason :

Actually, the two prong outlets wouldn't be grounded at all, except at the metal yoke when they are touching the metal boxes. Since you have a solid pipe back to the panel from the metal box, and it only has two wires in it, you could add a ground wire to that pipe if you wanted to. However, you don't have to, as the solid pipe itself is considered an effective grounding path.

Customer:

So I can ground the new outlets through a pvc conduit to the junction box and it would be O.K.?

Jason :

Yes, it would be fine.

Jason :

Sorry I misunderstood your original intent.

Customer:

No problem, I know there is no such thing as and easy electrical question I have just never come across this kind of wiring and wanted to make sure I understood what was going on with it before I made a move on it.

Jason :

I understand. I think you have a good plan, it will be fine as described. I appreciate the opportunity to help.

Customer:

Thank you.

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