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Old 08-20-2010, 05:21 PM   #1
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Advice needed for adding grounded outlets in old home


I have a 1930 home with old BX 2-wire and metal boxes and 2 prong outlets. As I have been updating the house (kitchen, basement), I have rewired with 3 wire Romex and AC. I don't intend to rewire the entire house but want to replace the old 2 prong outlets with grounded outlets in the remaining rooms.

My question is: Can I simply install a 3 prong outlet into the existing metal box (w/BX wiring) and ground the outlet to the box and assume the BX sheath acts as the ground path? My house does have a grounding rod from the service panel.

Thanks.

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Old 08-20-2010, 05:37 PM   #2
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Advice needed for adding grounded outlets in old home


Your ground rod outside has nothing to do with your ability to ground your receptacles. A ground rod is for high voltage events like lightning.

Your old cable pre-dates the time when a bond strip was added to BX that allowed it to be used as a grounding means.

You can install GFI protection and then install the three prong receptacles. You would need to add the stickers that state "No Grounding Means".

A side note, these will not allow surge protection to work properly.

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Old 08-20-2010, 07:22 PM   #3
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Advice needed for adding grounded outlets in old home


Thanks for the advice.

Do you recommend I use a GFCI breaker or an GFCI outlet (assuming I can determine the first outlet on the branch)?

Regarding the ground. Not to argue the point, but I rechecked my service panel. From what I can see, there is no ground path attaching to a water pipe from the panel (seems it has been disconnected at some point). There is, however, a ground wire going to the exterior of the house that is attached to a buried grounding rod. I do not have a lighting grouding system on the house. Is this against code and something that needs to be corrected?
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Old 08-20-2010, 07:55 PM   #4
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Advice needed for adding grounded outlets in old home


Older boxes were smaller and the insulation was thicker. It may also be brittle. If your panel would accept a GFI breaker that is the way I would go. It will cost more, but can save you on frustration when trying to find the first in the string or fitting a GFI device into the small box.

If your water line is metallic and in contact with the earth for at least 10' it would be your primary grounding electrode. The rod would be a supplementary electrode. Both of these should be bonded together, possibly in your panel.

This is different than a lightning arrestor system.
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Old 08-21-2010, 11:52 AM   #5
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Advice needed for adding grounded outlets in old home


Add a ground wire (#6 copper for 100 amp or smaller service, #4 copper for larger service). Connect it to the water pipe within 5' of entering the house and before the meter, and the other end to the panel ground (or clamped to the existing ground wire to the ground rod.) (Assuming a metal water pipe)

Add a jumper of the same size around the water meter. Add a jumper of the same kind around the water heater (from cold inlet to hot outlet).

If you don['t have a gas appliance that uses electricity from a properly grounded circuit, add a jumper from the gas entering pipe to the ground wire attached to the ground rod or attached to the water pipe.

Electronic equipment such as stereos, TV's and computers can be grounded by daisy chaining a #14 copper wire from one piece to the next with the far end of the wire connected to a known ground (not the center screw of the cover plate of an ungrounded receptacle).

The BX sheath is not a sufficient ground for the wiring up in the house.
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Last edited by AllanJ; 08-21-2010 at 11:59 AM.
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Old 08-26-2010, 08:12 PM   #6
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Advice needed for adding grounded outlets in old home


Thanks for the responses. This is very helpful. I will fix the ground missing ground to the water pipe.

So if BX is not a suitable ground path, I need help with my current electric project. I have added an exterior security light and tapped into an outlet box in my second floor closet for power. Currently, it works as expected but with the BX as grounds. I want to do the job properly, so based on your feedback I will remove the ground to the BX.

Before I grounded to the BX, when I tested the outlets downstream on the circuit I got an "Hot/Ground Reverse" reading.

I am attaching a diagram of how it is currently wired. What is your recommendation for doing the job properly, but minimizing rewiring the entire circuit (if it all possible)?

Much thanks.

Oh, Outlet #3 is also grounded to the metal box.
Attached Thumbnails
Advice needed for adding grounded outlets in old home-wiring-diagram.jpg  

Last edited by Cool user name; 08-26-2010 at 08:18 PM. Reason: missing info
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Old 08-26-2010, 08:32 PM   #7
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Advice needed for adding grounded outlets in old home


A ground wire (#14 for 15 amp circuits, #12 for 20 amp circuits) may be run, daisy chaining from one outlet box to another, more or less following the route of the existing power cable. If exposed in the room, it can go up and around doorways. The far end is brought into the breaker panel (main or sub) that the circuit cable enters and connected to the ground bus bar (or terminal strip).

If you are cutting open the wall to string a separate ground wire inside and hidden, you might as well replace the power cable with one that has a built in ground wire.
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Old 08-26-2010, 09:11 PM   #8
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Advice needed for adding grounded outlets in old home


I see in your drawing that the white goes to the larger slot on the receptacles which is correct, however, you show it on the wrong side of the receptacle.
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Old 08-26-2010, 10:35 PM   #9
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Advice needed for adding grounded outlets in old home


you're right, I didn't pay attention to that level of detai. Diagram was meant to show the wiring configuration.
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Old 08-26-2010, 10:57 PM   #10
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Advice needed for adding grounded outlets in old home


Thanks Allan, but I perfer not to break that much plaster to rewire the entire circuit just to add this exterior light. Service panel is in the basement, light is on exterior wall (same as service panel, but on second floor and the circuit I tied into makes many stops along the way. I'm beginning to think it would be better/easier just to run a new line to the light from the service panel.

Never heard of running a ground wire on the outside of an interior wall. Not something I would do due to looks, etc.
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Old 08-30-2010, 11:15 AM   #11
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Advice needed for adding grounded outlets in old home


Thought I might get some more detailed feedback.

Other than the semantics on the outlet diagram, is this wiring configuration correct? How can I address the "Hot/Grnd reversed" error on the downstream outlets if I don't use the BX cable as the ground path?
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Old 08-30-2010, 11:52 AM   #12
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Advice needed for adding grounded outlets in old home


Quote:
Originally Posted by Cool user name View Post
Never heard of running a ground wire on the outside of an interior wall. Not something I would do due to looks, etc.
You have a surprising amount of room where your carpet meets the wall, under the trim. You can also go under the carpet straight across a doorway. When you come to the outlet, you drill a hole in the wall under the trim then fish it up to the box.
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Old 08-30-2010, 11:53 AM   #13
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Advice needed for adding grounded outlets in old home


If you know the hot and neutral are not reversed (neutral goes to the larger slot in the receptacle) then if the tester says reversed, don't worry abou it.

YOu do not have to explicitly remove the BX cable cover from any possible grounding path, the only significance is that the BX cover does not make a good and sufficient ground connection (bonding).

Sometimes a ground wire can be run on the exterior mostly hidden where two clapboards meet, with less unattractiveness and less busting up of plaster. It doesn't have to stop at each receptacle, the only disadvantage is that the skipped receptacles remain ungrounded.
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Old 08-30-2010, 07:10 PM   #14
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Advice needed for adding grounded outlets in old home


Thanks for all the feedback, everyone. It is beginning to sink in. I have decided to go with a GFCI breaker on that circuit, leave the grounded outlet/box on the outlet that the light is tapped into, unground and use "no ground" stickers on the second & third outlets.

My thought process is this: Minimize plaster work by not grounding all the outlets on that branch. And since the exterior light has the most potential risk of shorting (due water entry, wear) I will ground the outlet that it is tied into.

Comments welcome if I am off-reservation!

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