Old 2 conductor wiring

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infinity

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Because the metallic sheathing quaulifies as the ground?

Yes. The bonding wire within the cable requirement was added in the early 1950's. Prior to that the jacket was still permitted to be used for grounding purposes.
 

PetrosA

Senior Member
As mentioned, I would opt for the two prong outlets on a GFI breaker or recept. At least the HO will know there's no ground. It's also important to tell them not to use computers or UPS backups in those outlets. I've seen issues with both from lack of ground, most often sudden shutdowns.
 

al hildenbrand

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Location
Minnesota
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Electrical Contractor, Electrical Consultant, Electrical Engineer
Does it?

Does anyone know for sure that the sheathing was listed for use at the time of installation, installed properly and has not been compromised in any fashion since the time of installation?

Now any metallic flexible cable must have a 'drain wire' for it to qualify as a grounding method.
BX has a long history of being an acceptable ground. It was written that way in the Code. That link is to only two citations.

You are right to recognize that the drain wire improved the characteristics of BX needed for a good EGC in modern wiring systems, but it took over half a century for the way we commonly use electricity to evolve, before the change happened.

Pre-1957 BX, as originally installed and inspected, was a grounding means.
 

glene77is

Senior Member
Location
Memphis, TN
If it's an old house with Knob & Tube wiring, the Neutral wires and the Hot wires may not have a one to one relationship. So a GFCI breaker may not be a happy puppy.

Speedskater,

A note on the K&T wiring.

I have seen old houses where the K&T had such great leakage (stray currents) that the GFCI breakers would trip. The use of GFCI recepticals was OK.
 

Speedskater

Senior Member
Location
Cleveland, Ohio
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retired broadcast, audio and industrial R&D engineering
Speedskater,
A note on the K&T wiring.
I have seen old houses where the K&T had such great leakage (stray currents) that the GFCI breakers would trip. The use of GFCI recepticals was OK.

I though that it was more often.
That they would borrow a neutral wire from one circuit for part of another circuit. They would connect to whatever neutral wire was handy.
 

glene77is

Senior Member
Location
Memphis, TN
I though that it was more often.
That they would borrow a neutral wire from one circuit for part of another circuit. They would connect to whatever neutral wire was handy.

Speed,
That is a good observation.
The code, and the costs were different then.

I have enjoyed working with the old K&T,
but not with the 40's romex with the multi-paper wrapping and the carbon-black rubber insulation that falls off in your hands. I always bring a can of liquid-rubber-insulation to help hold the old insulation on as required.

I have enjoyed working with the old K&T,
but I have had trouble making sense
of some of the spaced out wiring in K&T.
For all the hidden wires, where the hot and neutral are separated, down walls, and back up, it is cost effective to just replace the contracted areas with new Romex, and flip the K&T up into a JB in the attic, and then cap-off the K&T.

:)
 

glene77is

Senior Member
Location
Memphis, TN
That is sad.

DC,
Sad indeed!
No appreciation for burning down their own house.

I had one client who went back after the rough-in inspection,
changed/altered/added to 'my inspected' wiring,
and then put up the sheet-rock for the final.
When he moved in I found this out
because things started shorting and sparking!

:)
 
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K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Not necessarily. Surge protection limits voltage between any two conductors, and doesn't 'send the surge into the ground.'

Most surge protectors clamp surge voltage from H-N, H-G, and N-G. The hot-to-ground clamping works even with no EGC.


I should have said 'some' or 'many'.

Indeed, the newer, better strips will actually have 4 MOV's. The three you mentioned plus one in series. Older, cheaper ones did rely on a good grounding conductor. Most I see are the older cheaper kind.

I don't agree that the H-G clamping can occur with no grounding conductor. More likely what is happening is a common mode fault being dampened by a normal mode shunt using the neutral as a path to ground which should still suppress at least one surge. MOV's will fuse open, are usually one time use devices, and offer no protection after the initial surge if that surge is of any size at all. The MOV in series will act like a fuse and open the circuit to ensure no further surges will get to the load. No orderly shut down, though.

Some of these strips pose more danger than protection. They like to catch fire. The newer ones are not as prone and I haven't heard of one catching fire recently.

Some of the really good units use reactance to introduce impedance into the line. The coils don't fuse open (generally), offer continuous protection and need no grounding conductor to function.

For some fun, buy a couple used strips from yard sales. Dissect them. Then ask yourself how a circuit board the size of a postage stamp with MOV's you could hide under a dime are going to function under a high voltage surge or a hit by lightning.
 
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