Equipment Grounding with Armoured (BX, AC, MC, etc)

[Ed Battle]

I am re-wiring an older home and desire to install grounded receptacles where there are currently 2-prong receptacles. There was no equipment grounding conductor run to the boxes. I would date most of he wiring pre 1950. There is some type of armored cable used (no NM).

I would like to know if I can use the armor sheath as an equipment ground. I would also like to know if there are approved clamps available to bond a copper wire to this sheath, so that I can bond it properly on both ends.

 

[suemarkp]

Is there a thin metal tape under the armor? If so, it is probably suitable as a grounding conductor. But you'll need enough of the tape available to fold it under the cable connector.

Without the tape, probably not suitable. Would also help to know what this is (is there an "Type AC Cable" imprint somewhere along the armor spirals)?

This wire is old enough you may want to consider replacing it anyways with something modern. Nothing wrong with NM and much faster to work with than AC or MC.

 

[dhalleron]

It's probably AC. I think BX was a brand name for it. We always called it BX.

If it has the metal strip inside to short across all of the spirals in the armor to make the ground path shorter then the armor can be used as ground. Proper connectors are available to ground it to the box and these may already be installed. It would be similar to running conduit and using the conduit as your ground. You then would use a grounding pigtail screwed to the back of the box or self grounding straps on the receptacles.

From my experience most of this stuff had wax impregnated cloth covering the conductors inside. The wax dries out around light fixtures that have had very large wattage bulbs installed. Then the cloth becomes brittle and cracks easily. I have run into some AC cable that was still in good shape. I think I would check out the insulation in various outlets before making a decision to keep or replace this old cable.

In my area, if we extend an old circuit, then we have to arc fault protect it. I don't know for sure but some have told me old cables like that don't always do well on arc fault breakers. Not sure why that would be though.

 

[augie47]

Based on the age, I would say it is BX (AC) cable without the bonding wire. If s,o it can pose a significant hazard. If a fault occurs and the return path is the old armor, it is possible that tat armor jacket will heat. I have seen it so hot it can not be touched.

Replacing it would be advisbel. Maing any connection that would increase the chance of the armor beinga ground path would be ill-advised.