My home orginally had some 2 prong receptacles, and BX cable running throughout. I replaced the 2 prong receptacles with 3-prong receptacles on the assumption that they will be self-grounding (through the metal BX cover). Ground testing confirmed this.
Am I OK?
No you are not OK…if you are truly talking about BX cable which was made by GE. It is not intended for use as a EGC .
And since we are talking about a house that DID only have (2) prong plugs in it I would venture to say you ARE talking about BX and again it was not intended for this purpose.
Sure it will read Cont. through it and make a tester show it is grounded but it is not a low impedance path nor does it have a reliable spiral connection without the bonding strip…as it has a tendency to NOT be really consistent in it’s connection points.
I have been into basements ( I explain this story at my seminars ) about a basement that had this and the COIL of the BX through the rafters had gotten to the point it burnt into the holes and was one step from burning the house down…
Note: The bondings strip is NOT the EGC in AC cable…just want to make sure you are clear on that…once it leaves the cable it serves no purpose.
Ian,
In my opinion you are better off going and buying some GFCI receptacles and replace the FIRST one in each circuit and label the others as required and then you can leave them (3) prong plugs.
Another solution is simply to buy GFCI breakers IF you have breakers and do it that way…but probably cheaper with the price of GFCI receptacles today to just replace the first one in each circuit and protect yourself that way.
Some may say…well Paul a little protection on that spiral BX is better than none…NOT if it wont clear the fault or the resistance is so high it heats up or you get objectionable current on it with high resistance and becomes a potential problem down the road.
I have had local electricians use that exact fix in my area after calling out 2 prongers…seems to be the consensus.
Which fix tony…the BX as a EGC or the GFCI replacement option?
Sorry…your fix of course 
I have no idea what I am talking about, but to stimulate debate:
Concerning the replacement of 2-prong with 3-prong receptacles see the following link. Has NEC code references too (Note the table has 2002 NEC references, but the discussion below that table has 1999 NEC references). And it talks about upgrading a 2-prong outlet with the old style AC cable (BX trademark from GE, which does not have the currently required bonding wire/strip per 2002 NEC 320.100). 2002 NEC 250.146(B) does permit “self grounding” outlets without the wire … I know it’s not considered good practice by most sparkies … but you are looking from an HI point of view here.
http://www.codecheck.com/250_50_commentary.html
Now, you’re going to hit me.
Ian,
Again I don’t believe Code Check was written by Electricians…to be honest with you. I can only give you my opinion on what I know and BX casing is not a good choice for a EGC in my view.
Now Code check can say what it wants but where is their reference, just saying BX is ok does not make it OK. Personally I question many things I see sometimes written by Non-Electricians.
Would never hit ya fella…you may get an electrician or two to agree with you or even say…its the lessor of two evils as well…but I don’t like the practice…every wonder WHY AC cable today as the bonding strip within it???
I would venture to say the BX you are speaking of does not have a internal bonding strip…without it you have a higher inductive reactance in the spiral outer case.
AC cable in itself meets the EGC requirement IF the strip is inside the cable as 250.118 allows AC cable IF done in that manner as a EGC.
Paul you need to come back out to Seattle for another road show. I missed the last one. Plus we can go egg Stephen Stanczyk’s house while your out here, LOL.
If that dosnt get you back out here,… I dont know what will,… Mexican food? =)
Peter…I would LOVE to…not sure if it will happen but would LOVE it
Ian, don’t guess. Verify you have BX(which I hate how it’s an over used term), or actually AC.
If you can’t tell the diff, you shouldn’t be working with electricity, for your and your’s safety.
tom
lol…no the RiskWithoutReward policy is probably what will not get me back out their…lol
BUT I loved that Mexican Place right beside the hotel…was AWESOME…simply Awesome except Stephen promised BURGERS on the next trip…someday…
I agree Tom, real BX might be a collector’s item. It has become a generic term for anything with spiral armor. BTW if you tested this with your SureTest I would be a lot more confident that it had a <1ohm grounding path which is the standard. The 3 neon tester … not so much.
Paul,
What would cause the spiral cable to heat to the point of scorching?
Anatol
ANATOL,
Could be current running on the spiral case due to a improper Neutral to Case connection, could be a fault running on the case that simply will not clear a fault. The metal material used in the making of BX (tradename for GE product) was simply not made for the use.
I don’t even like the suggestion that it be used for an effective fault path with regards to BX cable of that time or period.
Last night I did check the wire. It appears to not be BX but old AC (rubber and cloth coated hot and neutral wires). Where the wire has been joined to some of the (terminal/junction) boxes a strip of what looks like flat aluminium bonding wire has been wound back along the outside of the cable. So, although there are only two insulated wires in the cable there does appear to be a seperate strip running throughout it. Does this make any difference? I cannot use this ground wire to ground the receptacles on the ground screw because it does not enter most of the wall boxes (it does on one and I have attached this to the ground screw)?
Yes, It makes a HUGE difference as that strip you are refering to is NOT a EGC…it simply ensures the BOND of the spiral flex cable which in turn is the actual EGC. ( prefer to call it yet again Equipment Bonding Conductor…hope the NEC catches on to that thinking…sigh…
)
I would venture to say if you have AC Cable with a bonding strip inside which SHOULD not terminate into the enclosure…it is useless once it leaves the cable itself unless some old electricians use it to hold in the red hat bushing.
So it makes a HUGE differences and an example of knowing the terminology of BX as a Trade name for a GE product versus an actual cable design.
If your AC Cable DOES have an internal bonding strip then the CABLE itself by NEC definition is designed to be an effective Ground Fault Path and fine, The bonding strip turned back and around the cable it fine…again it in itself is nothing more than a ensured bonding strip.
Thanks. Who would believe a tiny strip would make so much difference. I am still surprised that my old AC has this (rubber and cloth insulation). Genuine BX must be really ancient. Point noted that the strip should not be used by itself as a ground to the receptacle.
Me.
Me Too…