Receptacle grounded via conduit?

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olc

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Hopefully a quick question:
A receptacle installed on a metal box which has conduit (& flex conduit) but no grounding equip conductor. Is it properly grounded (assuming the conduit is bonded back to the ground)?

My first thought is yes - but...

The specific case is an older building that has 2 prong receptacles. Some have already been replaced with 3 prong.
So the question is whether the 2 prongs can just be replaced like the others were? Or if the ones already replaced are wrong.
 
If the box is properly grounded via the metal raceway then a 3 prong self-grounding receptacle can be installed. Flex conduit has limits on where it can be used as the EGC. Look at {250.118}.
 
Thanks
Here's a photo. The box on the other side of the wall has a two prong receptacle.
I haven't looked a 250 yet.receptacle.jpg
 
We can't tell from the picture ---250.118 will have the answer. However this appears to be FMC conduit, not BX, and it would be possible to pull an EGC through it.
 
In addition, FMC is only recognized as an EGC if it meets criteria of 250.118(5)(a)-(e).
 
texie said:
I'm guessing that that flex is to long to be a compliant EGC.
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Or at least not all of it is compliant.

For OP one the main rules with flex is the total length used as an EGC can neve exceed 6 feet. So if incoming supply flex in you case is 6 feet or less then that can be acceptable if no other rules regarding flex are in violation, but you don't start over at the box or a fitting, if you had 5 foot supply flex then only the next 1 foot of flex after that box is allowed to be an EGC.
 
olc said:
The specific case is an older building that has 2 prong receptacles. Some have already been replaced with 3 prong.
So the question is whether the 2 prongs can just be replaced like the others were? Or if the ones already replaced are wrong.
Click to expand...
The history of changes in the NEC for FMC, Flexible Metallic Conduit, is interesting in this "older building" case. For there to be two-prong non-grounding type receptacles present hints that the Code cycle of original construction was under a Code older than the 1962 NEC (the 1962 NEC was the first all-grounding-type receptacles Code.)

As originally assembled, the FMC shown in the photo above (post #3) was approved by the NEC as a grounding means, as an equipment grounding conductor (EGC). The requirement for a wire-type EGC in aggregate lengths over six feet was not introduced for FMC until the Seventies.

Some here have argued that replacing a receptacle alters the entire FMC assembly of that Branch Circuit, taking away its As-Built and Approved FMC-as-EGC pre 1970's NEC status. I am of the opinion that it is a matter for the "older building" local Electrical Authority Having Jurisdiction to settle.

In my work area, the As-Built and Approved FMC-as-EGC status survives a simple receptacle replacement.
 
In addition, if because of grandfathering the FMC counts as an EGC you still have customer preference to consider.

I am guessing that this is an old building with electrical properly installed more than 50 years ago. Upgrades are desired and repairs are required.

If the big barrier to installing a wire EGC is opening walls, pulling a wire EGC in existing FMC might be desirable to the customer even if not strictly required.

Jon
 
LarryFine said:
But, does replacing a non-grounding one with a grounding one qualify as "a simple receptacle replacement"?
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Especially if the wall is not opened and you don't know exactly what wiring method is? You can do fairly simple tests and determine there is continuity through the raceway but you still don't know how well it can handle fault level current, even EMT can have loose set screws or compression nuts.
 
LarryFine said:
But, does replacing a non-grounding one with a grounding one qualify as "a simple receptacle replacement"?
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Wow ! ! Seriously?

OK. My definition of a "simple receptacle replacement" is the removal of the former receptacle device at an existing opening, and the replacement of a new receptacle device in the same opening.

Note that I do not say that the new receptacle device must be identical to the receptacle device. Other than the receptacle device being changed out, the existing as-built-in-the-Fifties Branch Circuit remains un-altered from its original assembly.
 
xformer said:
True - So Bonding receptacle through Metal to metal contact is a no go.
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Agreed. But, as Rob points out in Post #2, a receptacle device that is self-grounding can be used, in lieu of a bonding jumper, to establish the connection to the EGC.
 
So in this particular case one side of the wall has a 3 prong receptacle existing (probably replaced a 2 prong at some time in the past but we don't know that), and a 2 prong on the other side of the wall.
The flex conduit is greater than 6 feet.

Best I can tell:
Technically the 3 prong can be replaced in kind (simple replacement).
On the other hand, replacing the 2 prong with a 3 prong should comply with 250.130(C).

This defies common sense.
What do you think?
 
olc said:
So in this particular case one side of the wall has a 3 prong receptacle existing (probably replaced a 2 prong at some time in the past but we don't know that), and a 2 prong on the other side of the wall.
The flex conduit is greater than 6 feet.

Best I can tell:
Technically the 3 prong can be replaced in kind (simple replacement).
On the other hand, replacing the 2 prong with a 3 prong should comply with 250.130(C).

This defies common sense.
What do you think?
Click to expand...
I think if you know the flex is there you should try to get a compliant EGC there, even if NEC isn't clear about what is required for existing situation.
GFCI may be an acceptable alternative. The problem with flex isn't that it won't carry ground fault current, but it could have enough impedance that overcurrent protection may be less effective and is the main reason for the six foot of flex being max allowed as an EGC path.
 
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