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Joined: Sep 2006
Posts: 155
I've tried to search this here, old 20-30's building, orig wired in old bx (four spirals of steel around rubber, cambric, then cambric jacket, 2 cond no ground cond.)
Previous owner had someone upgrade the receptacles to decora type grounded, but no pigtail to the box. the main service was replaced in the last 20 years. question is are these replaced recep's in violation, or accepted under previous code, can this grade of bx be used for grounding? thanks chris

Joined: Oct 2006
Posts: 65
I doubt that BX is suitable for grounding. I certainly wouldn't trust it.

Use GFCI breakers, and it becomes legal - 406.3(D)(3)

Joined: Apr 2003
Posts: 362
The old BX is most certainly legal as a ground. You do need the tail to the device. and the box must have the right claamps/conns. Bx is no longer available. so m/c will be the choice if you want to stay with armored cable.


Choose your customers, don't let them choose you.
Joined: Oct 2006
Posts: 745
No kidding. I can't imagine a better grounding means than an entirely metal-clad wiring system. Not to mention, hasn't BX started making a comeback due to increased labor savings by eliminating the separate EGC? I think that Southwire is making BX again.

All of that talk about the separate aluminum grounding strip? The same one that was included in BX in the 50's-80's? BX is the bomb.


"But the guy at Home Depot said it would work."
Joined: Sep 2006
Posts: 155
This stuff predates the stuff with the alum bond strip, I know that old bx used to be approved, and that the recent decades stuff was no longer accepted, mainly with this client its the fridge plug, and I prefer not to see the ground lift adapter put in, and the personal or laptop computer, thanks for all the info, chris

Joined: Mar 2005
Posts: 399
Concerning the old steel BX cable. It did not have a bonding strip to bond the steel jacket together. Electrically you would have the conductors inside a coil. Fault current would follow the circular jacket and end up getting red hot while the impedence would not allow it to trip the breaker or blow a fuse.
This problem was the basis of the restriction to six feet for armor flex when used for grounding. The six feet of conductor length would have over 18 feet of return path on the steel jacket.
The Copper conductors are good compared to the resistance of steel.
I would recommend GFI receptacles rather than trusting the BX. For the fridge you may have to just pull a new circuit.

If it was easy, anyone could do it.
Joined: Sep 2006
Posts: 155
I know its been awhile but on the topic of using this wiring in this building, the old heavy wrapped steel. Would it be more dangerous to leave on without gfci circuit protection, I havent opened the main service yet but I expect the 2 pole 40s only have one leg attached, as the units have 120v 3 circuit fuse boxes original. so would a 2pole gfci still provide protection. or do we change to single poles in the main. as the temporary fix. The original intact wiring is done, stacked fuse boxes, shared sub feed pipes with upper units feeders wiring through lower fuse boxes, so replacing fuse boxes would a whole building affair. thanks chris

Joined: Sep 2006
Posts: 155
I opened the main today and found that it is in fact two pole fortys with only the no. 1 pole connected on each breaker, I only had time to look at the three meter can and not the other four meter can, but I assume they hooked up the same way, but hope fully on the other phase, but the white wire from the service head appears to have been losing its outer clear jacket, inside the disco there appears to be some calcification?(white powdery residue) on the lugs of the neutral, I assume from condensation dripping but maybe overheating also has that effect. There is a green AHJ approval sticker on the main disco and seals on the hot sections of the meter cans. Was this a approved way of replacing a old 240 service to 120v apts.? this is in Oakland calif. thanks chris

Joined: Jan 2005
Posts: 5,316
Cat Servant
Well, I guess we're all getting a lesson in 'finishing the inspection' before we start 'groping for a solution.'

The original armored cable (BX) did not have a bonding strip. The jacket alone was considered a perfectly acceptable ground ... until the 60's came around, and some guys wanted to market a new product, one with a ground wire in it (MC). There was an endless debate, with each camp insisting that their product was better. The end result? Two different wiring methods adopted into the NEC - and the little strip added to the AC jacket.

Naturally, the sundry advocates didn't settle for that. As a result, many municipalities went on to ban AC .... while the NEC itself decreed that MC was not acceptble for health care facilities. Go figure.

The six foot limit Alan refers to is for flex and sealtite, where provided for flexibility. It was never applied to either AC or MC.

Getting back on point ....

Using the jacket for the ground path likely would comply with code ... so installing three prong devices is not an issue by itself. You still need to be sure there is a good connection to the box; too often the box isn't quite flush with the wall. GFCI (breakers or devices) might be a good idea, but I don't see the NEC as requiring them.

The clear acket on modern wire (THHN) is there only for ease of pulling. It, by itself, is not sunlight resistant. The underlying insulation is sunlight resistant, so i would not worry about those service conductors.
IF you are referring to a gray colored triplex on the PoCo side of the connections, then I would be concerned. There was a lot of bad wire sold to utilities, which now has it's insulation flaking off. Call them, and they'll replace it.

The calcification you refer to is certainly corrosion. I'd look into the cause. A loose connection will certainly encourage this, as will using a non-approved lug. It can also be caused by outside factors, like salt in the air.

I'd look at the feeder arrangement closer. If the PoCo is delivering 240 volts, there is no good reason to have only 120 at each panel. It is very possible that there was an illegal "service change," with the result that the PoCo upgrade didn't come until some time later - and the other hot wire isn't connected to anything.
(When permits are pulled, there's usually a line crew out there ASAP to upgrade).

Joined: Sep 2006
Posts: 155
The permit search resulted in a service change in 1991, the exterior closet, knife switch disco's w/30amp sockets were converted to splice box's. the orig, bldg disco was upgraded to a fpe 400a disco and two ge three and four meter sockets fed from a gutter. 2 no. 8 wires one phased white was pulled to each pair of apt feeds and the new flexes from the new meters with a no 12 green for the egc all together in the original shared box lugging to the can. Apt feeds go up two 1 inch ridgeds two wires each, for three apts each side, I believe no 12 but could be 10ga. the 8's in the new meter cans only one wire per each 2pole 40amp bkr.
Now the question I have is. Is it ok to leave as is or replace the 40s with a 30 amp single pole gfi or afci breakers at the main, until later on the when I can coordinate refeeding all six apts with new three wires each and new subs, or is it ok to have just 1 wire on a two pole breaker? as the 1991 install, the contractor now has a expired lic. crs

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