wiring outlets


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Old 03-03-03, 01:38 PM
T
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wiring outlets

I am replacing old outlets (2 prong) with new grounded ones. My question is do I need to add a ground wire from each outlet to the box or is the system already grounded. The old wiring is encased in metal. (bx)
 
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Old 03-03-03, 02:40 PM
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Metal clad cable can be considered a ground in many jurisdictions under certain circumstances. The majority of time it is required the cable must be in a metal box and not be terminated in any box in the circuit that is not metal. The cable must be attached to the box with an approved connector specified for the type of cable. The cable must be metal clad or metal conduit all the way through the circuit which means if someone started the circuit from the panel using old Romex then it could not be a means of ground. You would have to check and see if it meets these conditions. If it is then inserting a ground wire from the box to the receptacle is considered adequate.
If the circuit does not meet these points then there is an option to replace two prong receptacles with two prong outlets, or installing GFCI receptacles and marking them.
 
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Old 03-03-03, 03:08 PM
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Is it BX or is it type AC cable?

A lot depends on whether that is type AC cable or it is really the old "BX". Type AC cable has a metal bonding strip inside the armor to make it electrically continuous so that the armor can serve as an Equipment Grounding Conductor (EGC). The armor of the old BX cable has no bonding strip so it acts as a kind of choke to the flow of fault current that will delay the operation of the Over Current Protective Device (OCPD). That delay is often long enough for an arcing fault to do considerable damage and generate enough heat to kindle a fire.

So if the cable really is BX you should do one of the things allowed in 250.130 (C)
(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
(4) For grounded systems, the grounded service conductor within the service equipment enclosure

Alternatively you could use one of the techniques permitted by 406.3 (D) (3)
(3) Nongrounding-Type Receptacles. Where grounding means does not exist in the receptacle enclosure, the installation shall comply with (a), (b), or (c).

(a) A nongrounding-type receptacle(s) shall be permitted to be replaced with another nongrounding-type receptacle(s).
(b) A nongrounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked “No Equipment Ground.” An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.
(c) A nongrounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked “GFCI Protected” and “No Equipment Ground.” An equipment grounding conductor shall not be connected between the grounding-type receptacles.

Although BX will not carry fault current reliably it is likely to carry enough fault current to trip a GFCI. That will take care of the human safety aspect of the installation. It will not provide a low impedance pathway to earth ground to facilitate the operation of surge protection devices.
--
Tom
 
 

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