over 250V

[Ponchik]

First question: Would you consider metallic outlet box or a box an enclosure?

2nd question: Would you require a bonding conductor if the conduit housed circuit or feeder conductors of 480V and 277 to ground originated in a panel and ended on a 4s square box? Or if the feeder conductor originated in the one panel and ended on another panel.

Based on the UL listing, I would not require the conductor type bonding, but I like to know your comments. I got into a debate with an inspector and want to get clarified.

Thanks

From UL 2012
CONCENTRIC OR ECCENTRIC KNOCKOUTSAll boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric (or eccentric) knockouts where used in circuits
above or below 250 V, and may be marked as such.

 

[ActionDave]

First question: Would you consider metallic outlet box or a box an enclosure?

Box

2nd question: Would you require a bonding conductor if the conduit housed circuit or feeder conductors of 480V and 277 to ground originated in a panel and ended on a 4s square box?

No. And I wouldn't put one in. I am of the understanding we are talking about metallic conduit.

Or if the feeder conductor originated in the one panel and ended on another panel......

Panels can be different, but if you are not using concentric KO's then no. It's time to get rid of pre-punched KO's in panels anyway. We all have cordless drills and knock out sets in out trucks.

 

[Ponchik]

Box

No. And I wouldn't put one in. I am of the understanding we are talking about metallic conduit.
Panels can be different, but if you are not using concentric KO's then no. It's time to get rid of pre-punched KO's in panels anyway. We all have cordless drills and knock out sets in out trucks.

Besides service equipment, for panels and switch gears that have eccentric and concentric KO we will need grounding bushing with bonding wire for 480V feeders and circuits. But for 4s and 5s boxes we don't??

 

[ActionDave]

It gets even better. You can knock out all the concentric rings out, stack as many reducing washers as you need for a smaller pipe and your effective fault current path is complete and completely compliant.

 

[Ponchik]

It gets even better. You can knock out all the concentric rings out, stack as many reducing washers as you need for a smaller pipe and your effective fault current path is complete and completely compliant.

I know about the reducing washer.

But my main question still lingers around "Enclosures". The UL white book and the code book talk about "Box/KO and 277/480V" they don't mentioned "Enclosure" specifically. :?

That is why my first questions was about a box an dan enclosure.

 

[iwire]

First question: Would you consider metallic outlet box or a box an enclosure?

It is both.

Enclosures are a general term, metallic outlet box is just a specific form of enclsure.


Like a panel box is an enclsure but it is specifically a cabinet.

 

[ActionDave]

250.97 Bonding for Over 250 Volts
For circuits of over 250 volts to ground, the electrical conti-
nuity of metal raceways and cables with metal sheaths that
contain any conductor other than service conductors shall be
ensured by one or more of the methods specified for services
in 250.92(B), except for (B)(1).
Exception: Where oversized, concentric, or eccentric
knockouts are not encountered, or where a box or enclosure
with concentric or eccentric knockouts is listed to provide a
reliable bonding connection, the following methods shall be
permitted:

blahh, blahh, blahh

Boxes with concentric KO's are listed by UL as fine for bonding over 250V, panels have a label inside them that you have to read and interpret. I don't have the patients for that, I just figure they are not.

 

[iwire]

Most small 'boxes' are listed for grounding over 250, most panel cabinets, disconnects etc are not.


I don't think that wireways or pull boxes are listed for grounding over 250


That said I avoid using concentric KOs, I will make a new hole right beside it if I have to.

 

[ActionDave]

...That said I avoid using concentric KOs, I will make a new hole right beside it if I have to.

I so wish that manufactures would stop making panels with pre-punced KOs.

 

[iwire]

I so wish that manufactures would stop making panels with pre-punced KOs.

Panels are the worst when you need to bring in say a 2" into a field of 1/2" KOs.

I bolt a 4" square blank over the area than drill and punch the 2" in through the blank on the panel.

 

[infinity]

Most small 'boxes' are listed for grounding over 250, most panel cabinets, disconnects etc are not.


I don't think that wireways or pull boxes are listed for grounding over 250


That said I avoid using concentric KOs, I will make a new hole right beside it if I have to.

I agree, only boxes have the listing for over 250 volts. If you had a disconnect switch for example it would not comply with 250.97. From UL:

Other Types of Metallic Enclosures
Cabinets and cutout boxes, in accordance
with NEC Article 312, as well as junction and
pull boxes, in accordance with NEC Article
314, may also employ concentric or eccentric
knockouts, and are evaluated for UL Listing
in accordance with UL 50, the Standard for
Safety for Enclosures for Electrical Equipment
(CYIV and BGUZ).
In contrast with metallic outlet boxes, these
other types of metallic enclosures with
concentric or eccentric knockouts are not
required to be subjected to a short time cur-
rent test. As such, NEC Section 250.97 would
require that bonding jumpers be used unless
all concentric or eccentric knockouts were
removed. For UL Guide Information, please
refer to pages 69 and 84 of the 2008 Edi-
tion of the UL White Book for these product
categories, or view this information online
at www.ul.com/database. Enter “CYIV”
or “BGUZ” into the database field for “UL
Category Code.”

https://www.google.com/url?sa=t&rct...HgCVJO6VQ&sig2=-RgBXrTztuDFABMe6uQpQQ&cad=rja

 

[Ponchik]

I agree, only boxes have the listing for over 250 volts. If you had a disconnect switch for example it would not comply with 250.97. From UL:



https://www.google.com/url?sa=t&rct...HgCVJO6VQ&sig2=-RgBXrTztuDFABMe6uQpQQ&cad=rja

Thanks for your replies.

Infinity that is exactly what I am looking for.

I could not find this in the latest UL white book. But I will keep searching in the book to see if UL may have taken that requirement away.

 

[don_resqcapt19]

It gets even better. You can knock out all the concentric rings out, stack as many reducing washers as you need for a smaller pipe and your effective fault current path is complete and completely compliant.

I am not aware that the listing or testing includes "stacked" reducing washers. As far as I know it only includes a single pair or reducing washers.

 

[iwire]

I am not aware that the listing or testing includes "stacked" reducing washers. As far as I know it only includes a single pair or reducing washers.

Does it even indicate either way?

 

[Ponchik]

Spoke with UL this morning:

1. The eccentric and concentric knockouts on enclosures (panel boards, MCC, pull boxes...) are not tested for 277V-480V. So a bonding jumper is required.
2. For a pull box if splices are not made then a jumper is required between the conduits that house the 277V-480V circuits/feeders.
3. If the enclosure is galvanized (not painted) then only one set of reducing washers are allowed. Reducing washers can NOT be stacked.
4. Only eccentric and concentric knockouts on 4" & 5" square boxes have been tested 277V-480V circuits without a bonding jumper between the conduit.

 

[Carultch]

It gets even better. You can knock out all the concentric rings out, stack as many reducing washers as you need for a smaller pipe and your effective fault current path is complete and completely compliant.

If you have a raceway properly grounded on the other side, do you still need to do anything special if you have ring KOs remaining on the other side (and over 250V to ground)?

In otherwords, I can run a conduit from a no KO metal box to a plastic box with a wire EGC, and I'm fine with using standard locknuts only to establish continuity to the conduit. But is there a difference between no continuity at a plastic box and insufficient continuity at a ring KO remaining in a metal box?

 

[iwire]

If you have a raceway properly grounded on the other side, do you still need to do anything special if you have ring KOs remaining on the other side (and over 250V to ground)?

In otherwords, I can run a conduit from a no KO metal box to a plastic box with a wire EGC, and I'm fine with using standard locknuts only to establish continuity to the conduit. But is there a difference between no continuity at a plastic box and insufficient continuity at a ring KO remaining in a metal box?

In general it is a violation to use a plastic box with metal raceways unless you comply with one of the exceptions.

314.3 Nonmetallic Boxes. Nonmetallic boxes shall be permitted only with open wiring on insulators, concealed knob-and-tube wiring, cabled wiring methods with en-tirely nonmetallic sheaths, flexible cords, and nonmetal-lic raceways.

Exception No. 1: Where internal bonding means are pro-vided between all entries, nonmetallic boxes shall be per-mitted to be used with metal raceways or metal-armored cables.

Exception No. 2: Where integral bonding means with a provision for attaching an equipment bonding jumper inside the box are provided between all threaded entries in nonmetallic boxes listed for the purpose, nonmetallic boxes shall be permitted to be used with metal raceways or metal-armored cables.

 

[Carultch]

In general it is a violation to use a plastic box with metal raceways unless you comply with one of the exceptions.

Exception No. 1: Where internal bonding means are pro-vided between all entries, nonmetallic boxes shall be per-mitted to be used with metal raceways or metal-armored cables.

Exception No. 2: Where integral bonding means with a provision for attaching an equipment bonding jumper inside the box are provided between all threaded entries in nonmetallic boxes listed for the purpose, nonmetallic boxes shall be permitted to be used with metal raceways or metal-armored cables.

In general, most people would comply with these exceptions anyhow, when using non-metallic enclosures and metal raceways. It all goes back to the basic principle of all metal that doesn't intentionally carry current needs to be bonded.

 

[augie47]

Associated question:
If I have a 480v branch circuit run in EMT with an equipment grounding conductor.
The conduit originates at a panel thru an eccentric knockout and terminates at a 4" sq thru an eccentric knockout. The EGC is bonded to the 4" sq box.
Since my box is grounded by the bonding jumper and my box is listed for grounding is the attached conduit considered to be grounded via the box connection or do I still need a bond jumper at the panel.

 

[iwire]

In general, most people would comply with these exceptions anyhow, when using non-metallic enclosures and metal raceways.

Apparently not judging from the questions posted to this forum.