Outdoor lamp supplied through BX

[SpringHill]

I am replacing an outdoor light post at the street with a new lantern mounted on an aluminum post. The new post requires an equipment ground.

The existing circuit runs from the switch through old armored cable (BX) and joins in a junction box under the eaves to new UF, thence underground approximate 20 feet to the lamp post.

Can I assume that the BX (it contains the small ground wire) provides an acceptable ground for this outdoor installation? If not,would a separate ground rod at the junction box properly ground the circuit?

 

[ryan_618]

Re: Outdoor lamp supplied through BX

AC cable (BX) is an equipment ground. It is the contact between the cable armor and the 18 gauge aluminum bonding strip that makes it such. See 250.118

Regarding the ground rod...a gorund rod will NEVER make an installation safe. It can't be used in lieu of an equipment gorunding conductor. See 250.4(A)(5).

 

[mpd]

Re: Outdoor lamp supplied through BX

you had better do a little more investigating to make sure (not assume) that the BX has an effective ground fault path, and like ryan said, never use a ground rod for equipment grounding.

 

[SpringHill]

Re: Outdoor lamp supplied through BX

Thank you for the responses.

It was as I suspected. At this juncture the circuit does not have an effective grounding path.

This 1901 house was upgraded from knob and tube sometime (I surmise in the '40s) to BX. The plumbing has also been upgraded to PEX, thereby losing most of the old bonds. Some Romex was added later and the panel upgraded IAW modern Code. As is too often common, the resulting circuitry is a mishmash of the old 2 wire system and 3 wire.

As an aside, when we excavated the front yard we found that the BX supplying the existing (seemingly abandoned) outdoor lamppost was direct buried for a few feet and transitioned to primary conductors for the remaining distance to the street. The circuit was live to the switch.

It seems there are four options to retain a safe outdoor lamppost: 1) home run a new circuit to the panel, or 2) use the exception allowing "replacement of non-grounding-type receptacles" by grounding the grounding conductor to "any accessible point on the grounding electrode system ...", or 3) installing a GFCI receptacle on the branch extension, or 4) (and perhaps the best solution) replacing the existing branch CB with a GFCI-type circuit breaker.

Comments?