grounding of old 2 wire sytems

[Riograndeelectric]

I work in Denver and run across many homes that were wired with either the balck grc conduit and cloth conductors or the old 2 wire armored cable with cloth conductors. I have done many a servcie call in these houses where the 2 wire recpticel was replaced with a 3 wire device. I do not belive that either of these sytems are listed as a grounding means. I had a home owner tell me that an electrican told him to just replace all the 2 wire devices with 3 wire devices and that the conduit and or armor would carry the ground. I would hate to see what would happen if there where a serious fult. what is everbodys thought on this?

 

[busman]

Re: grounding of old 2 wire sytems

I've only been in the trade 10 years, but as far as I know both RMC and the sheath of AC cable have always been recognized for EGC. I didn't think the old black rigid conduit was galvanized however.

Anyone with more experience or older code books want to chime in?

Mark

 

[infinity]

Re: grounding of old 2 wire sytems

I would agree with Mark that the old black pipe would qualify as the EGC. Anyone who has working in an old building in NYC will tell you that there are millions and millions of feet of this stuff using the conduit as the EGC.

One thing that you would need to remember is that the receptacles would need to be replaced with the self-grounding type or installed with a bonding jumper to the box.

 

[DaveTap]

Re: grounding of old 2 wire sytems

Being from the Chicago area we see this a lot. The old rigid conduit works fine as a ground when installed properly but there can be problems where they connect to boxes. In the old days they used a lead or "pot" metal bushing inside the box and electrical nut outside. The bushings generally corrode, crack or strip out breaking contact with the side of the box and sometimes allowing the conduit to fall out altogether since they were rarely supported by more than nails. We solve it by replacing the bushing with an electrical nut and plastic bushing, or grounding bushing if required.
For the old BX any run over 6' has to be replaced during a remodel, but sometimes the old wrap wasn't very tight and sometimes we're able to replace the cloth covered wires with thhn and a ground using the BX sheath as flexible metal conduit. (I know technically it's not allowed but I have yet to find an inspector who complains when we're trying to preserve an old plaster ceiling or wall)
All things considered I wish current practices held up as well as these old methods. I commonly am replacing 100+ year old hardware and wiring that is still working and safe... can't say that about most 20 year old romex

[ January 04, 2006, 10:24 AM: Message edited by: DaveTap ]

 

[GUNNING]

Re: grounding of old 2 wire sytems

I agree about the old stuff, it was tuff. Bond it to the box and forget it or use gfci's. I've had homeowners complain about gfci's and where is the little light on the tester. Got a speal down about how its in the definition ... Still like the old stuff though. heavy steel, nickle coated copper, natural stuff that didn't make your hair and teeth fall out after sitting in the ground for a few years.

 

[flick]

Re: grounding of old 2 wire sytems

If the AC doesn't have the bonding strip, then it's the older style and cannot be used for an EGC.

flick