Old BX without ground and New BX with Ground

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  #1  
Old 12-26-12, 01:21 PM
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Old BX without ground and New BX with Ground

My 1920s house is wired completely with BX cable. Non of the cable has a bare grounding wire, and so I'm told that the cable itself acts as the ground.

I'm changing out the light fixture in my bathroom with a new one that has a receptacle on it, and I want the light switch to operate this fixture. I went to Home Depot and explained this to the guy in the electrical area. I explained that the current BX cable in the circuit has no ground wire, and I need additional BX cable to wire up my new fixture to a light switch. He handed me a 25 ft. coil and I went on my merry way.

At home, I began opening up my new cable and I see that the cable the HD guy gave contains a grounding wire. Is this okay to use if the rest of the older cable in the circuit doesn't have one? do I simply connect the ground wire to the grounding screw in the light switch on one end and the other to the grounding screw in the fixture?

re-wiring the entire circuit is out of the question because the current circuit goes all over the place. The power comes into the bathroom from the ceiling to power the bathroom light, then an additional cable is fed off of the light and goes back through the ceiling to the upstairs again.

hope this is a good enough explaination. thanks in advance.

-Ben
 
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  #2  
Old 12-26-12, 01:26 PM
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If the cable is not grounded there will be no ground even if the new cable contains a ground. The grounding starts at the panel. You cannot just start in the middle of a circuit.

You fixture may require 90 degree C rated insulation for the wiring that you certainly do not have.
 
  #3  
Old 12-26-12, 01:30 PM
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Was I told correctly that the metal armor around the old BX Cable acts as the ground for the circuit?
 
  #4  
Old 12-26-12, 01:41 PM
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A bathroom receptacle should be on a separate 20 amp dedicated circuit. It would be best to abandon the old circuit and run a new one from the breaker box.
Reasons:
Wire not rated for 60
Best to have a bath room circuit on a dedicated 20 amp circuit because of loads like a hair dryer.
Many consider old BX ground unreliable.
Your local authority may not consider the existing circuit grounded and an ungrounded circuit can't be extended.

If NM-b is permitted where you live it would make running a new cable easier. Often running a new cable isn't as hard as a first timer thinks. Gives us the details of why you think it would be hard and maybe we can tell you a better way.

I'm changing out the light fixture in my bathroom with a new one that has a receptacle on it,

Read more: http://www.doityourself.com/forum/el...#ixzz2GBx121Wf
This could be a "can of worms". The receptacle should by code be GFCI protected but it is best not to have the light GFCI protected because if the GFCI trips you will be left in the dark. You would have to find a way to separate the light from the receptacle in the light and find a way to provide GFCI protection or find a way to GFCI protect both the light and receptacle. Since this isn't a dedicated circuit though and other loads might be best without GFCI protection a breaker might not be good. Other solutions like adding a GFCI receptacle first might not be permuted because of current code. Are you beginning to see why running a new cable is best? If you did I would suggest a light fixture without a receptacle.


Edit: Question posted while I was writing:
Was I told correctly that the metal armor around the old BX Cable acts as the ground for the circuit
Old BX no because there is no bonding wire and the metal sheaths ability to carry current can deteriorate over time.
 
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Old 12-26-12, 01:48 PM
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The older cable would only qualify as a grounding means if it contained a bond strip. Early AC cable did not have a bond strip and cannot be considered grounded.
 
  #6  
Old 12-26-12, 01:54 PM
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Here it goes.....

My 100 amp service is completely tapped out. there is no room to start a new dedicated circuit. In additon, there are about 5 breakers inside the box running two circuits. I have already purchased new breakers rated for two circuits to replace the breakers that just have two hot wires connected to it.

I plan, in a couple years, to upgrade my service to 200 amps and re-wire the whole house and get rid of all that old BX cableing. I'm not in a position to take care of that right now.

I knocked out the walls in my bathroom because the entire thing was tiled in an ugly hot pink color. when the old wall was taken down, I noticed the wiring in the light fixture was in horrible condition. it was frayed and the insulation around the end was cracking off. I tore off some of the cable armor to expose new wire, and in doing so, the cable running to the lightswitch became too short(hence my trip to the home depot to get new BX cable).

You fixture may require 90 degree C rated insulation for the wiring that you certainly do not have.
how do you know what temperature your wiring is rated for?

am I basically screwed because I opened my walls and discovered old wiring that shouldn't be in place anymore? How would I get this re-wired without having to tear down walls throughout my house? this would be an expensive, messy nightmare since all the walls are plaster.
 
  #7  
Old 12-26-12, 03:37 PM
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Type NM cable has a -B to designate 90 degree insulation. Other types like AC cable will have a label on the insulation like THHN that can be checked against the tables in the NEC.

The NEC does not require the older wiring to be removed. It does limit what can be done when the wiring is ungrounded.

You may need to run the new wiring into accessible junction boxes where you can new wiring at a time when the house is rewired.
 
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Old 12-26-12, 04:26 PM
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If the house is one story with either an unfinished basement or attic it is fairly easy to fish new wires assuming there aren't fire stops. Old cables are abandoned in place by disconnecting on both ends, cutting as short as possible, and shoving back into the walls. If two stories or fire stops it may be necessary to cut a few two inch holes to facilitate fishing wires.

Adding a subpanel to the existing panel isn't that hard or expensive if you do it yourself.

There is really no good way to do what you want to do without running new cable. Best you can do with what you have is look for a fixture rated 60C that does not have a receptacle. Some fluorescent and LED lights may be rated 60 any incandescent with a cover won't be. You may be able to mount a switch to the new fixture* to avoid running a non code compliant run to a switch.

*Mounting a switch though would probably violate the UL listing.
 
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Old 12-26-12, 06:21 PM
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I'm changing out the light fixture in my bathroom with a new one that has a receptacle on it, and I want the light switch to operate this fixture.
I'm not sure a receptacle on a bathroom light fixture is even allowed by code any more. At least, I know they aren't allowed in my area. GFCI protecting that receptacle would also be a problem if your AHJ will allow it.
 
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Old 12-26-12, 07:41 PM
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I'm not sure a receptacle on a bathroom light fixture is even allowed by code any more.
It may have changed in 2011, but I only have the 2008 book at my desk. Just for FYI.

210.11(C)(3) Bathroom Branch Circuits (exception) (2008)
Where the 20 amp circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with 210.23(A)(1) and (A)(2).

210.23 (A)(1) and (2) basically says that the equipment cant be more that 50% of the amp rating if fixed and not more than 80% if cord connected.
 
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