Bonding Bushing for A/C Disconnect

[George Stolz]

If I have an A/C disconnect for a 480v air conditioner, do I need a bonding bushing on the EMT serving it when entering through a concentric knockout?

 

[DARUSA]

Yes unless you are using the maximum size of your concentric knockout.
For exemple if you concentric knockout are 1/2" - 3/4" hole and you have a 1/2" emt pipe you have to install it but if you have a 3/4 pipe no bonding bushing are required.

 

[roger]

Yes unless you are using the maximum size of your concentric knockout.

I agree, see 250.97 and it's exceptions but, per UL you could also remove all the concentric rings and just use reducing washers and eliminate the need for a bushing.

Roger

 

[George Stolz]

What is a typical A/C disconnect called by the UL? The closest thing I can find in the white book is "cutout box." Is that right?

 

[roger]

What is a typical A/C disconnect called by the UL? The closest thing I can find in the white book is "cutout box." Is that right?

George, they would be under "Switches" but that was not what I was refering to, my comment was refering to UL's testing of reducing washers.

OUTLET BUSHINGS and FITTINGS

Metal reducing washers are considered suitable for grounding for use in
circuits over and under 250 V and where installed in accordance with
ANSI/NFPA 70, ??National Electrical Code.?? Reducing washers are intended
for use with metal enclosures having a minimum thickness of 0.053 in. for
non-service conductors only. Reducing washers may be installed in enclosures
provided with concentric or eccentric knockouts, only after all of the
concentric and eccentric rings have been removed. However, those enclosures
containing concentric and eccentric knockouts that have been Listed
for bonding purposes may be used with reducing washers without all​

knockouts being removed.

Roger

 

[Cow]

I usually leave the rest of the concentrics in place and install the reducing washers over them. I do the same with flex connectors into concentrics too, the flex connectors always seem to pull out over time and hang by the wires...

 

[George Stolz]

George, they would be under "Switches" but that was not what I was refering to, my comment was refering to UL's testing of reducing washers.

Yeah, I know.

"Switches" leaves a lot of wiggle room. I'm digging and not finding it, I'll dig a little harder in the morning.

 

[iwire]

Switches, enclosed (wiax)

 

[George Stolz]

Bob and Roger, thanks.

So for this...

It's an enclosed switch (wiax).

For this...

It's a pullout switch, detachable type (WGEU).

And to go a step further, a panelboard inside a cabinet also has no mention that concentrics are listed for grounding.

So, at the end of the day, is it safe to assume that only outlet boxes (QCIT) concentrics are listed for grounding?

My memory stinks lately, and I had it pretty much locked in my head that all listed metal boxes' concentrics didn't need a bonding bushing (or a reducing washer ) and I'm trying to burn the correct info into my head for future reference.

 

[Dennis Alwon]

250.97 takes us to 250.92(B) except B(1). The highlighted section is brand new to 2011.

(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).

Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(3) Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
(4) Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers

 

[chris kennedy]

Are you saying the RW part applies to non service enclosures?

 

[George Stolz]

Dennis, I didn't notice that, and you just sent me on an interesting little trek following that requirement's change around. It looks as though the CMP allowed a change based on the argument "electrician's know it's no good" and then the White Book followed suit to meet the change in the NEC. (QCRV)

Backing up, though: The reason we are allowed to skip bonding bushings in an eccentric in listed metallic outlet boxes is because 250.97 Exception, condition (3), allows the installation. The directive to head over to 250.92 is stopped when you utilize the exception, agreed?

 

[Dennis Alwon]

George I read 250.97 except 3 as referring to fittings other than reducing washers. I think 250.92(B) comes into play. Good question though..

I am thinking there are fittings (connectors) that have a shoulder that somehow touches the box and does not rely on the rings.

 

[George Stolz]

George I read 250.97 except 3 as referring to fittings other than reducing washers.

In the event that you are using the concentric, you wouldn't be using a reducing washer.

I am thinking there are fittings (connectors) that have a shoulder that somehow touches the box and does not rely on the rings.

I don't see any evidence of that in the previously linked to pages, or DWTT.

I should note that the main reason I'm throwing these links up is for practice, and to be double-checked. I'm trying to get more comfortable with the White Book.

 

[roger]

250.97 takes us to 250.92(B) except B(1). The highlighted section is brand new to 2011.

But George's question is not pertaining to bonding services. Service bonding has it's own set of rules.

Roger

 

[Dennis Alwon]

But George's question is not pertaining to bonding services. Service bonding has it's own set of rules.

Roger

No but 250.97 sends us to 250.92. .97 says we must use one of the methods specified for services in 250.92. I don't believe it is saying if it is a service use 250.92 but rather you use the same rules. Maybe I am wrong.

 

[George Stolz]

No but 250.97 sends us to 250.92. .97 says we must use one of the methods specified for services in 250.92. I don't believe it is saying if it is a service use 250.92 but rather you use the same rules. Maybe I am wrong.

No, you're right - but as soon as you make use of the exception, then you don't have to make that jump anymore.

I.E. The rule = go to 250.92. Exception = Use this equipment instead.

 

[roger]

No but 250.97 sends us to 250.92. .97 says we must use one of the methods specified for services in 250.92. I don't believe it is saying if it is a service use 250.92 but rather you use the same rules. Maybe I am wrong.

Oooops, I was reading right past your reference to 250.97 and was stuck on 250.92.

Roger

 

[Dennis Alwon]

Oooops, I was reading right past your reference to 250.97 and was stuck on 250.92.

Roger

I will try and forgive you. Now back to George. So how does exception 3 permit reducing washers? They are not really anything like the examples they give.

 

[Mgraw]

How about 250.97 EX. 4

From UL
GROUNDING
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, "National Electrical Code." Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. for non-service conductors only. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been Listed for bonding purposes may be used with reducing washers without all knockouts being removed.