Help settling an argument? Ground bond when replacing two prong w/ three prong in late 1960s residential.

[Mull20014]

I've run into this a few times in residential and am hoping to find a definitive answer to settle an argument (if there is a definitive answer).

I've run into a few houses wired just after 1965 with NM containing the safety ground that was properly bonded to the metal box, however, there were a few years where two-prong plugs were still the standard. When replacing said two-prong plug, is it necessary to connect a separate bonding pigtail from the new outlet (or switch) to the box, or is the metal-to-metal contact between the mounting tabs and the box a sufficient enough bond to satisfy code? It is electrically sufficient, but from everything I've found, there is a bit of a gray area in the code (if I'm not looking at it cross-eyed). And before anyone says it, yes, we know it's good practice to go ahead and bond it with a pigtail for redundancy.

Thanks,
Nick

 

[infinity]

If the EGC is properly grounding the box then a self-grounding receptacle may be used without a bonding jumper. Switches connected to a grounded metal box do not require a bonding jumper or a self-grounding switch.

Welcome to the Forum.

 

[romex jockey]

egc's have evolved , for ex the old 'boston backwrap' ,along with what was maybe a #18 under the metal box clamp and/or rx conn. was a standard for many moons>>>

so the trick is, will it all ring /meg out to the service panel?

~RJ~

 

[Mull20014]

If the EGC is properly grounding the box then a self-grounding receptacle may be used without a bonding jumper. Switches connected to a grounded metal box do not require a bonding jumper or a self-grounding switch.

Welcome to the Forum.

Hi Rob,

Aha! Yes, and therefore falls under 250-146 (A-D).

Thanks and thanks!

Nick

 

[Mull20014]

egc's have evolved , for ex the old 'boston backwrap' ,along with what was maybe a #18 under the metal box clamp and/or rx conn. was a standard for many moons>>>
View attachment 2556722
so the trick is, will it all ring /meg out to the service panel?

~RJ~

Very true!

 

[infinity]

Hi Rob,

Aha! Yes, and therefore falls under 250-146 (A-D).

Thanks and thanks!

Nick

And for grounding switches look at 404.9(B)(1).

 

[drcampbell]

I would dare to say that the pigtail is more than "redundant", even though it might be optional under the Code.
If the receptacle mounting ears land on the plaster(board), or if there's a paper or plastic washer between the receptacle and box, there may not be any metal-to-metal contact. And it there is, it's certainly not a tight connection. Remember that its purpose in life is to carry fault current during a short circuit event.

 

[hbiss]

If the receptacle mounting ears land on the plaster(board), or if there's a paper or plastic washer between the receptacle and box, there may not be any metal-to-metal contact. And it there is, it's certainly not a tight connection. Remember that its purpose in life is to carry fault current during a short circuit event.

You are forgetting about the screws as well as the "self grounding" spring clip that one screw passes through to ensure continuity from the screw to the ears or yoke. Rarely do device ears or yoke sit directly on a metallic box. If the plate is installed properly, it will pull the device outward pulling the yoke tight against the screws also.

Grounding screws are primarily for use when using non-metallic boxes, in those instances where a ground is required or if the device is not self grounding.

-Hal

 

[retirede]

Rarely do device ears or yoke sit directly on a metallic box.

-Hal

Right - around here, those are called “plaster ears”...even though most of them land on sheet rock.

 

[romex jockey]

If it can't handle the AIC back to the OCPD, all bets are off here fellas....~RJ~

 

[drcampbell]

I didn't forget about them.
I just lack confidence in their ability to maintain a low-enough impedance while carrying fault current, I think there are too many variables during installation, and I'm not sure every receptacle even has a self-grounding spring clip.

 

[infinity]

I didn't forget about them.
I just lack confidence in their ability to maintain a low-enough impedance while carrying fault current, I think there are too many variables during installation, and I'm not sure every receptacle even has a self-grounding spring clip.

No they do not. To eliminate the bonding jumper you need to install a receptacle that is listed as self-grounding, those devices will have the clip. Also they have been designed and tested to handle the current generated in a ground fault.

 

[kwired]

I didn't forget about them.
I just lack confidence in their ability to maintain a low-enough impedance while carrying fault current, I think there are too many variables during installation, and I'm not sure every receptacle even has a self-grounding spring clip.

Seems typical the low grade devices don't but spec grade or higher usually does anymore.

 

[jap]

You are forgetting about the screws as well as the "self grounding" spring clip that one screw passes through to ensure continuity from the screw to the ears or yoke. Rarely do device ears or yoke sit directly on a metallic box. If the plate is installed properly, it will pull the device outward pulling the yoke tight against the screws also.

Grounding screws are primarily for use when using non-metallic boxes, in those instances where a ground is required or if the device is not self grounding.

-Hal

Very well put.

Jap>

 

[Ravenvalor]

If it can't handle the AIC back to the OCPD, all bets are off here fellas....~RJ~

I would imagine that if the 6/32 screw were replaced with a longer one or if the original screw was pulled back the spring would lose its tension.

 

[ramsy]

..those (receptacle) devices will have the clip. Also they have been designed and tested to handle the current generated in a ground fault.

Per 404.9(B)(1) are 6-32 screws good enough for switches without a self-bonding clip?

 

[infinity]

Per 404.9(B)(1) are 6-32 screws good enough for switches without a self-bonding clip?

Yes if the metal box is grounded.

 

[hbiss]

I would imagine that if the 6/32 screw were replaced with a longer one or if the original screw was pulled back the spring would lose its tension.

No. It's a spring. You could do that many times and as long as you don't damage the spring clip it will be fine.

Per 404.9(B)(1) are 6-32 screws good enough for switches without a self-bonding clip?

Switches yes. Receptacles no because receptacles rely on that ground for the ground for the device plugged into it.

-Hal

 

[ramsy]

Switches yes. Receptacles no because receptacles rely on that ground for the ground for the device plugged into it.

Thank you,

2015 UL White book also specifies:

Snap switches without a grounding connection are intended for replacement use only in accordance with NEC 404.9, Exception to (B).

I believe snap switches that meet UL Listing requirements for grounding have a bonding screw or self-bonding clip, tested under fault current conditions.

 

[infinity]

Switches yes.

-Hal

I agree, the NEC clearly spells this out in 404.9(B).