# concentric ko's and service equipment



## william1978 (Sep 21, 2008)

I Conduit said:


> Does this hold true for residential service equipment like meter sockets, disco's and panelboards as well ?


 Why wouldn't it you wouldn't have over 250v on a dwelling.


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## ralpha494 (Oct 29, 2008)

I would make sure it says so on the unit. I saw a newer Square D disco that said so, but no panelboards or meter sockets. It might also need SUSE (Suitable for use as service equipment) markings. Sounds like a UL question.


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## william1978 (Sep 21, 2008)

What type of conduit are you using?


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## william1978 (Sep 21, 2008)

I would use PVC and you wouldn't have to worry about it.


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## 220/221 (Sep 25, 2007)

> Does this hold true for residential service equipment like meter sockets, disco's and panelboards as well ?


If the unfused service conductors pass thru the nipples, we are required to bond them.


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## william1978 (Sep 21, 2008)

220/221 said:


> If the unfused service conductors pass thru the nipples, we are required to bond them.


 I agree. If your running metal conduit and have unfused wire you will need to bond the conduit.


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## I Conduit (May 4, 2009)

Thanks for all of the answers guys. The bottom line is if you are using metal conduit with unfused service wires it must be bonded to your enclosure. If the meter socket has concentric ko's or not it doesn't matter because the neutral is bonded to it and if you connect to a service disco the neutral will also be bonded there as well. I think I got it now.


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## raider1 (Jan 22, 2007)

Take a look at 250.92(B).

You can't use a standard locknut for bonding on the line side of a service regardless of whether or not a concentric knockout is used.

Chris


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## Adam12 (May 28, 2008)

And you only have to bond one end of the raceway not both.


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## te12co2w (Jun 3, 2007)

Adam12 said:


> And you only have to bond one end of the raceway not both.


 Really? My inspector insists on bonding on both ends. Now I'll have to look it up.


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## manchestersparky (Mar 25, 2007)

Just a side note to the topic:
You can not use reducing washers on fittings that contain service conductors .
So be careful when your taking those concentric / eccentric ko's out.


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## raider1 (Jan 22, 2007)

> You can not use reducing washers on fittings that contain service conductors


You can't?

What code section prohibits using reducing washers on service raceways?

Reducing washers can't be used for bonding on the line side of the service, but there is nothing that I am aware of that would prohibit their use for other than bonding.

Chris


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## manchestersparky (Mar 25, 2007)

Raider-
From the 2008 UL White Book:
Outlet bushings and Fittings ( QCRV)

Grounding
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 Volt and where installed in accordance with ANSI/NFPA 70 " National Electrical Code". Reducing washers are intended for 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 the knockouts being removed.

It's like you said it's all about the bond.

The listing clearly prohibits them on service conductors, so we can fall back on NEC 110.3(B).


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## raider1 (Jan 22, 2007)

> The listing clearly prohibits them on service conductors, so we can fall back on NEC 110.3(B).


The listing prohibits reducing washers from grounding and bonding raceways that contain service conductor. But it does not prohibit reducing washers from being used to secure the raceway to the service equipment provided that other means are made to ground and bond the service raceway in accordance with 250.92(B).

Chris


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## manchestersparky (Mar 25, 2007)

Subject to interpretation. 

This section is the only place reducing washers are discussed. 
It states that they are intended to be used on metallic enclosures only. Enclosures must be 0.053 in in thickness minimum. for Non- service conductors.

Can be read as enclosures that do not have service conductors in them.
Have you ever seen them on plastic boxes? Is this allowed ?

This has been a topic of debates at the IAEI meetings. 

I have an email in to UL on the matter. I am currently waiting on a reply.
If I don't hear from them soon, I will call them directly.


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## raider1 (Jan 22, 2007)

The requirements that you are quoting come under the heading "Grounding". That means that all the requirements you are talking about deal with grounding and bonding using reducing washers, not with the actual mechanical connection of a raceway to a box.

I do not see that section as not permitting the use of metal reducing washers with non-metallic boxes or raceways. 

Chris


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## 220/221 (Sep 25, 2007)

> Really? My inspector insists on bonding on both ends. Now I'll have to look it up.


Are we talking about a rigid nipple here?

Kinda dumb to hit both ends, huh?:jester:


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## Bob Badger (Apr 19, 2009)

raider1 said:


> Take a look at 250.92(B).
> 
> You can't use a standard locknut for bonding on the line side of a service regardless of whether or not a concentric knockout is used.
> 
> Chris


I agree with the head banging dude. :thumbsup:


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## Bob Badger (Apr 19, 2009)

raider1 said:


> The listing prohibits reducing washers from grounding and bonding raceways that contain service conductor. But it does not prohibit reducing washers from being used to secure the raceway to the service equipment provided that other means are made to ground and bond the service raceway in accordance with 250.92(B).
> 
> Chris


Again I agree with the head banger. :thumbsup:


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## Bob Badger (Apr 19, 2009)

manchestersparky said:


> Subject to interpretation.


No, not subject to interpretation, subject to reading it as written. 

The UL white book section entitled "Grounding' is in fact only about grounding.

It has nothing to do with how the reducing washers can be used other than the grounding issue.


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## markore (Dec 7, 2011)

*Yes but grounding is a workmanship issue*

Manchester, thank you for posting this useful section from the white book on use of these washers. It is useful to have a definitive installation note requiring removal of all knockout rings before using these adapters on boxes not listed for continuity of eccentric knockouts.

True this section does appear to only apply to grounding/bonding.

However, many inspectors require all non-recessed metal parts including screws be grounded/bonded.

Thus, if you were to close a large knockout in a plastic box using a metal reducing washer set (always used in pairs with one on the inside and one one the outside) then you may be required to provide a bonding bushing/locknut to ground the metal parts. This is to protect the user or workman against coming into contact with metal parts which are energized, and to protect from the case where energized screws driven into concrete or wood can cause a catalytic reaction over time.

You may find that duplex connectors are helpful when bringing two metal raceways into non-metallic enclosures, as the duplex connector itself provides continuity between the two raceways, locknut(s) and any reducing washers used.


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