bushing requirements?

[justin]

recently i have been asked when are we required to use bushings at our conduit terminaions? I have always used bushings on any conduit 1" or larger but i am second guessing myself that there might be a code reference to requirements based on the wire size only. i don't hve the nec available to me right now so if anyone could help me out that would be great, thanks justin

 

[joec]

Re: bushing requirements?

ere's a start...


300.4

F) Insulated Fittings. Where raceways containing ungrounded conductors 4 AWG or larger enter a cabinet, box enclosure, or raceway, the conductors shall be protected by a substantial fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by substantial insulating material that is securely fastened in place.
Exception: Where threaded hubs or bosses that are an integral part of a cabinet, box enclosure, or raceway provide a smoothly rounded or flared entry for conductors.
Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.

 

[bphgravity]

Re: bushing requirements?

I feel it is always best to use insulated bushings on any type of metallic conduit or tubing regardless of the conductor or raceway size. In some cases, the fitting used for non-metallic conduits and tubing meets the requirement in 300.4 without the need of an additional bushing.

 

[hurk27]

Re: bushing requirements?

The only raceway I know of that " enters a cabinet, box enclosure, or raceway," would have threads on the end of it? For all others the raceway is connected to the cabinet, box enclosure, or raceway by a fitting which is not required to have a bushing if it provide's a smoothly rounded or flared entry for conductors.
I was tagged for this a month ago and after showing the inspector the responses he agreed.

The key word here is Enter's

 

[websparky]

Re: bushing requirements?

Hi Wayne,

I believe this is one of the examples of poor sentence structure where the subject of the code article is mis-read.

Where raceways containing ungrounded conductors 4 AWG or larger...

and

Where raceways containing ungrounded conductors 4 AWG or larger enter a cabinet, box enclosure, or raceway

Raceways don't enter raceways!

The proper sentence structure is definatly missing!
This would be better;

Where raceways, containing ungrounded conductors 4 AWG or larger enter a cabinet, a box enclosure, or a raceway, the conductors shall be protected by a substantial fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by substantial insulating material that is securely fastened in place.

[ November 29, 2004, 10:23 PM: Message edited by: websparky ]

 

[hurk27]

Re: bushing requirements?

Raceways don't enter raceways!

They don't? Ever run a conduit to a trough or wireway?

 

[hurk27]

Re: bushing requirements?

Here is how it was explained to me. A conduit is not a fitting or is a fitting a conduit.

Here is a thread I started on this:
300.4(F)

 

[websparky]

Re: bushing requirements?

For all others the raceway is connected to the cabinet, box enclosure, or raceway by a fitting which is not required to have a bushing if it provide's a smoothly rounded or flared entry for conductors.

You changed your mind Wayne?

They don't? Ever run a conduit to a trough or wireway?

[ November 29, 2004, 10:59 PM: Message edited by: websparky ]

 

[websparky]

Re: bushing requirements?

Here is the image from the handbook:

Plus the subject of the article is:

300.4 Protection Against Physical Damage.
Where subject to physical damage, conductors shall be adequately protected.

AND

Exception: Where threaded hubs or bosses that are an integral part of a cabinet, box enclosure, or raceway provide a smoothly rounded or flared entry for conductors.

When read in context, it doesn't say the raceway enters anything!

 

[hurk27]

Re: bushing requirements?

Dave look at your example it shows a threaded race way that "Enters the box" and it even states "note the double locknuts" would you use double locknuts on a fitting?

You changed your mind Wayne?

I'm not sure why you asked this question? I don't think I change my mind ( I don't think they make my model anymore)
I still stand by that the intent of this code is to require bushings on a race way that enters the box. which would only be threaded type race ways.

 

[benaround]

Re: bushing requirements?

Notice the last words on the example "metal conduit fittings " such as an EMT connector that does not have an insulated throat. Just trying to help.

 

[websparky]

Re: bushing requirements?

Gee Wayne!

OK, here is the evidence for 300.4:
The very first thing it says is this below.
(1. Where subject to physical damage, conductors shall be adequately protected.
Then it goes on to say this:
(2. (A) Cables and Raceways....
(3. (B)(1) Nonmetallic-Sheathed Cable.
(4. (2) Nonmetallic-Sheathed Cable
(5. (C) Cables Through Spaces....
(6. (D) Cables and Raceways....
(7. (E) Cables and Raceways...
(8. (F) Insulated Fittings.

And then the handbook has this commentary:

Heavy conductors and cables tend to stress the conductor insulation at terminating points. Providing insulated bushing or smooth rounded entries at raceway and cable terminations reduces the risk of insulation failure at conductor insulation ?stress? points. The temperature ratings of insulating bushing must coordinate with the insulation of the conductor to ensure the protection remains intact over the life cycle of the insulated conductor.
Where 4 AWG or larger ungrounded conductors enter a cabinet, box enclosure, meter socket, or raceway, the conductors must be protected by a substantial fitting that provides a smoothly rounded insulating surface to protect the conductors from abrasion during and after installation. Because this requirement is located in 300.4(F), it applies generally to all wiring methods and all enclosures. See also 342.46, 344.46, and 352.46 for information relating to bushings.

Even benaround agrees and has pointed out another piece of evidence!

Come on Wayne!

 

[hurk27]

Re: bushing requirements?

Providing insulated bushing or smooth rounded entries at raceway and cable terminations reduces the risk of insulation failure

Again the example from the hand book again has the word "OR"
"smooth rounded entries"
Do not most conduit fittings provide this?
The ones I use do. and even the cable fittings I use do.

Fitting . An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.

Raceway . An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.

Now that we know the difference between a fitting and a raceway.
If we look at each raceway requirement for bushings we see a pattern that is the same in each.

IMC/RMC

342.46/344.46 Bushings. Where a conduit enters a box, fitting, or other enclosure, a bushing shall be provided to protect the wire from abrasion unless the design of the box, fitting , or enclosure is such as to afford equivalent protection.

Why is this not in 358 for EMT ? Or in 314 for fittings.

In each of the requirements for a bushing it also states we can use a fitting that provides the equivalent protection.

But I do have to back up on one thing I did notice and maybe this is what you were trying to say.
While doing some searches on fittings I noticed that some of the manufactures had both insulated throat EMT fittings and non-insulated throat fittings. which I thought was odd. But then when looking in 342.46/344.46 Bushing requirements I saw the FPN at the bottom:

FPN: See 300.4(F) for the protection of conductors sizes 4 AWG and larger at bushings .

And that got me to thinking that maybe a fitting with an insulated throat is what would be required when we install conductors over 4 awg.?

Also I'm trying to find the listing requirment on UL for this. or what UL 514B requirments say.

 

[hurk27]

Re: bushing requirements?

Oh by the way Dave I like a good arguement it is the best way I found to learn somthing new. I just wish more would join in here for more point's