Grounded Armored Cable?

Discussion in 'Electrical Forum discussion & Blog' started by onestepahead, Jun 8, 2010.

  1. onestepahead

    onestepahead New Member

    Jun 8, 2010
    My house is over 70 years old. Wired with armored (BX) cable - cloth wrapped hot & neutral inside. No ground wire.

    I've been gradually replacing ancient receptacles with 3-prong ones. I've been pigtailing the ground screw to the metal outlet boxes. I've been testing each box with with a voltage tester (one of those little ones that's just a small light), and I've since acquired one with a digital readout for the last few. Indeed, I'm seeing the same voltage (~124v) from hot to neutral as hot to ground - indicating (i think) that the boxes, via the armored cable, are grounded.
    However, I've recently read some postings claiming that armored cable doesn't provide true ground - that there is so much conductive material joined by the boxes and all of the cable sheathing that current will flow into it, but that there still may be a more direct path to ground in the event of a short circuit.

    so, is that true?

    I have no way to measure the current, only the voltage. Do I have a grounded system?
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Jun 16, 2007
    Licensed Electrical Contractor
    NY State, USA
    This is very true.

    The problem is not that of finding a different path, it's one that a fault will follow the spiral of the sheathing and not run along it in a linear path. This creates very high resistance and can cause the sheathing to be a heating element instead of a fault current conductor.

    Modern AC cable (~1960's on) has a thin bonding strip that "joins" all the spiral coils and lats fault current flow directly down the cable.
  3. Sponsor

    Sponsor Paid Advertisement

  4. Ford2001

    Ford2001 New Member

    Sep 11, 2009
    property care taker
    Manchester, Vermont
    Speedy Petey answer was very good. I would just add, If the amored cable is not a good grounding conductor, install GFCI duplex receptacles. This is an opinion on mine. Replacing the old BX cable is better, if you have the funds to do this.??
Similar Threads: Grounded Armored
Forum Title Date
Electrical Forum discussion & Blog Wiremold on ungrounded circuit Jun 10, 2021
Electrical Forum discussion & Blog Residential Electric Panel Grounded at Meter Not at Panel? Mar 31, 2021
Electrical Forum discussion & Blog Extending a grounded circuit Feb 4, 2019
Electrical Forum discussion & Blog Can shorted out or grounded wires cause super high electric bills? Oct 16, 2017
Electrical Forum discussion & Blog Ungrounded light fixture Jan 17, 2016

Share This Page