bx cable for equipment ground

[jmmyers]

Is it "code" to use the metal sheathing on bx, mc or ac type cables as the only means of equipment grounding?

Let me explain. Older homes around here typically use bx style cable between the receptacles with no grounding conductor. Electricians use the metal sheathing on the cable as an equipment ground wire and simply attach a wire from the ground screw on the receptacle to a green ground screw on the back of the metal receptacle box.

Does this comply with the code requirements for equipment grounding? Is this method an acceptable method for equipment grounding when no ground wire exists?

I did a search on the forum without much luck. I believe I remember Mike Holt stating on several occasions this was not an acceptable or code accetptable method for equipment grounding!

Thanks in advance!

Joe Myers

 

[ryan_618]

Re: bx cable for equipment ground

Hello Joe. Take a look at article 250.118(11) and notice that it changed from the 99 NEC. To answer your question, it may have been legal under the 99' an dit may be legal under the 2002, but it is harder to comply with the 2002 provision. Notice in the 2002 that it must be listed FOR grounding.

99 NEC:11. The metallic sheath or the combined metallic sheath and grounding conductors of Type MC cable.

2002 NEC:11. Type MC cable where listed and identified for grounding in accordance with the following:
a: The combined metallic sheath and grounding conductor of interlocked metal tape-type MC cable.
b: The metallic sheath or the combined metallic sheath and grounding conductors of the smooth or corrugated tube type MC cable.

I notice that it seems you are talking about remodels. Are you stating that the electrician is replacing two-wire receptacle outlets with 3-wire receptacles?

[ September 21, 2003, 10:50 PM: Message edited by: ryan_618 ]

 

[charlie]

Re: bx cable for equipment ground

BX is no longer being used. However, type AC cable is still called BX in some places. The old BX cable was simply armored cable but it did not have any grounding capabilities. The new type AC cable is built the same as the old BX with the addition of a small bonding wire that is in intimate contact with the metal armor of the cable. Type AC cable is listed for use as a grounding conductor and it is not required to do anything with the bonding wire (most electricians will bend it back to hold the anti-shorting bushing in place and run it under the clamp but that is not a requirement.)

Ryan has already addressed type MC cable.

 

[ron]

Re: bx cable for equipment ground

We need to clarify what type of cable is installed. AC cable (aka BX cable) in its current form, does not have a grounding conductor, but does have an internal bonding strip. MC cable in its current/normal form, does have a grounding conductor.
Both are acceptable typically for grounding in their current form.
What you describe, and is installed in many older homes, is an old style of AC cable (BX) without a bonding strip. At the time of installation, the circuits in the older home didn't require a grounding conductor. Once grounding became a requirement, AC cable needed to be redesigned to accommodate the reduction of inductive reactance of the spiral armor and increase its effectiveness as an equipment ground. The redesign used the bonding strip instead of a dedicate grounding conductor.
So.... IMHO, the old AC cable (BX) is not an acceptable means of grounding, and all GFCI recepts, and their downstream cousins must be marked "no ground".

 

[russellroberts]

Re: bx cable for equipment ground

I've seen the old bx or ac without the grounding strip in a lot of old homes around here.

I've seen cases of fault current on the armor that would cause the armor to glow a dull red color in a dark attic,but the breaker would not trip.

I'd agree with Ron about it not being suitable for grounding.

Russell

 

[pierre]

Re: bx cable for equipment ground

Ryan, Charlie, and Ron
Your posts are one of the reasons I come here. They are well worded and very informative, thanks.

Pierre

 

[Guest]

Re: bx cable for equipment ground

Originally posted by charlie:
<snip>Type AC cable is listed for use as a grounding conductor and it is not required to do anything with the bonding wire (most electricians will bend it back to hold the anti-shorting bushing in place and run it under the clamp but that is not a requirement.)

Ryan has already addressed type MC cable.

I agree, this thread was really easy to follow because of the clear and cogent answers.

 

[charlie]

Re: bx cable for equipment ground

From the NEC
320.100 Construction. Type AC cable shall have an armor of flexible metal tape and shall have an internal bonding strip of copper or aluminum in intimate contact with the armor for its entire length.

From the NEC Handbook
The armor of Type AC cable is recognized as an equipment grounding conductor by 250.118. The required internal bonding strip can be simply cut off at the termination of the armored cable, or it can be bent back on the armor. It is not necessary to connect it to an equipment grounding terminal. It reduces the inductive reactance of the spiral armor and increases the armor's effectiveness as an equipment ground. Many installers use this strip to help prevent the insulating bushing required by 320.40 (the ?red head?) from falling out during rough wiring.

 

[tonyi]

Re: bx cable for equipment ground

Although the oldest no-bond-wire BX can't be used for EG, and may not trip a breaker even if something faults to it, it undoubtedly WOULD pass enough current to trip an AFCI's 50ma GF protection if those older branches are AFCI protected.

 

[pierre]

Re: bx cable for equipment ground

Actually the GFCI senses between the ungrounded conductor and the grounded conductor, that is why an equipment grounding conductor is not necessary for GFCI installation.
But it is not a bad idea to use GFCI protection on that kind of circuit.

Pierre

 

[tonyi]

Re: bx cable for equipment ground

Of course GF's sense imbalance between L/N. If BX/AC armor is carrying some current, it had to come from somewhere...either a line to armor short, or neutral to armor bootleg ground.

AFCI or even ordinary GFCI protection on these old pre-bond wire BX branches goes a long way towards making them a lot less likely to torch up in the walls.

 

[dana1028]

Re: bx cable for equipment ground

This topic is turning towards recommending GFCIs to protect the circuits; the original querry was about equipment grounding.

GFCIs do not provide a ground and where a ground is called for under the Code (250-114 for refrigerators and a spate of other situations), it is a code violation to install a GFCI in place of the required EGC [i.e. If the Code requires an EGC per Art. 250-114, installing a GFCI does not satisfy this requirement].

 

[tom baker]

Re: bx cable for equipment ground

Dana: A GFCI can be used to replace a non grounded receptacle. A GFCI does provide a ground, however a GFCI does not require an "ground" or equipemtn grounding conductor to operate.
However, installing a GFCI where no equipment ground is present is a trade off in safety, the code makeing panel recognizes this, but it is felt to be safer on a GFCI than on a circuit without an equipment ground.

The provision to replace a non grounded receptacle with a GFCI is in Section 250.130 (C)

 

[Guest]

Re: bx cable for equipment ground

To further clarify the 2-wire GFCI outlet can only be stand-alone-- it cannot have any downstream slaves. You can only have slaves if you have an EGC. You cannot put a GFCI circuit breaker on a 2-wire circuit.

Not to go off topic, but if you cannot put a GFCI breaker on a 2-wire circuit, are you allowed to put an AFCI breaker or AFCI/GFCI breaker on a 2-wire circuit.

../Wayne C.

[ September 23, 2003, 09:32 PM: Message edited by: awwt ]

 

[iwire]

Re: bx cable for equipment ground

Originally posted by awwt:
To further clarify the 2-wire GFCI outlet can only be stand-alone-- it cannot have any downstream slaves. You can only have slaves if you have an EGC. You cannot put a GFCI circuit breaker on a 2-wire circuit.

Wayne you really must get a code book if you are going to make statements like that.

Both of those statements are incorrect.

see 406.3(D)(3)(b) and (c)

[ September 23, 2003, 09:44 PM: Message edited by: iwire ]

 

[Guest]

Re: bx cable for equipment ground

Good catch. I mis-stated it.

Please do a re-write. Thanks! Dinner time.

 

[jmmyers]

Re: bx cable for equipment ground

I am really bewildered why you would place GFCI protection on a circuit that is a safety hazard to begin with.

Grounding has proven safety value in todays installations and to assert that those old installations are safe by simply GFCI protecting them would be mute to say the least. While safer than the were originally, I would hasten to say those circuits were safe.

While there are plenty of them that are still functioning as intended there are many that have become unsafe from loose connectors, frayed wiring insulation, corroded or damaged casings. I believe that using those casings for a ground would be more of a safety issue than just allowing them to exist as originally intended.

If the wiring is in bad condition, I would say it has become a safety hazard and therefore should be removed, disconnected or replaced.

I have had the opportunity to look over the codes which allow the MC and AC style cable casings to be used as a grounding conductor and I thank those of you that posted those references for me. It is apparent that using the casing for the equipment grounding conductor is allowed but that is for the newer style AC style cable with the bonding strip, I have not seen any references about the BX style cable.

Sorry there guys but GFCI and AFCI protection is not going to save the world but is has made it safer.

I would be interested in hearing from those of you that have come across the BX style cable and how you handle it when you come across it in remodel or retrofit work. Are you repairing those circuits? Are you replacing them with newer style AC and MC style cables. Are you completely ripping that stuff out and replacing it? How are you handeling this situation?

Thanks,
Joe Myers

 

[iwire]

Re: bx cable for equipment ground

Originally posted by jmmyers:
Sorry there guys but GFCI and AFCI protection is not going to save the world but is has made it safer.

I do not think anyone here thinks that GFCIs and AFCIs are going to save the world, I think most of us feel one step forward is better then nothing.

As to what to do, replace it with NM in most cases, or if there is a reason with AC or MC.

Something else to think about, if we did not ground anything, we would be safer still.

But now I am into Bennie's domain.

 

[ryan_618]

Re: bx cable for equipment ground

Originally posted by iwire:
Something else to think about, if we did not ground anything, we would be safer still.

But now I am into Bennie's domain.

I think Bennie has changed a lot of people's outlook on grounding (myself included)... a unique indivdual that man is.

Thanks Bennie...

[ September 23, 2003, 10:57 PM: Message edited by: ryan_618 ]

 

[iwire]

Re: bx cable for equipment ground

Yes I will second that, he has made me much more aware of the good and bad of grounding.

Thank you Bennie.

Guys do not think I have stopped grounding things, to go that route would require some major changes, but it is still good to look at things from different directions.