Does this Fitting Require a Bushing?

[M. D.]

.... The potential for damage with a cable connector and an EMT connector is identical. If one needs protection they both do.

The potential is not the same ,.. I cannot imagine what would cause those wires to to suddenly become damaged by that cable clamp,. a hundred years from now if Pierre were to take another picture those wires would look the exactly same ,... the wiring methods are completely different.

 

[electricmanscott]

The code needs to be changed to either require a bushing for #4 or larger conductors or require that the sheath be inserted past the inside end of the cable connector. The potential for damage with a cable connector and an EMT connector is identical. If one needs protection they both do.

I disagree. Once those cables are landed on whatever they are connecting to they are not moving. Even when they are not connected you would have to make a real effort to cause any worthwile damage to the conductor.

I'd have to see a "body count" so to speak, before I would see a need for a bushing on a cable.

 

[don_resqcapt19]

The potential is not the same ,.. I cannot imagine what would cause those wires to to suddenly become damaged by that cable clamp,. a hundred years from now if Pierre were to take another picture those wires would look the exactly same ,... the wiring methods are completely different.

The inside edge of the cable connector is almost identical to the inside edge of an EMT connector. The only way the conductors can be damaged by either connector is if they are bent tightly against the edge of the connector when they are installed. Over time the connector may cut into the insulation. I would agree that this is somewhat rare, but the code should be same for both installations as they are exactly the same inside the enclosure.

 

[don_resqcapt19]

I disagree. Once those cables are landed on whatever they are connecting to they are not moving. Even when they are not connected you would have to make a real effort to cause any worthwile damage to the conductor. ...

I would say that the same applies to a raceway installation, but the code requires a bushing for the raceway. If one connector needs a bushing, they both need one.

 

[macmikeman]

My uneducated guess as to why required for raceway and not for cable fittings is because the conductors are pulled into raceway, raising the possibility of damage to the insulation at the time of pull. Remember that raceway systems must be complete before conductors are pulled in and that leads to having the bushing on when the wires are pulled in. Cables on the other hand, can have the connector installed without the locknut before the cable is placed into a box, and then secured with the locknut, and then the sheath removed. Less chance for imagined damage to the cable. I think we all have witnessed conductors get damaged when pulled into raceways at one time or another, even while proper pull methods were used.

 

[electricmanscott]

I would say that the same applies to a raceway installation, but the code requires a bushing for the raceway. If one connector needs a bushing, they both need one.

As pointed out, other than pulling the conductors into a raceway there is really no need for a bushing there either.

 

[M. D.]

The inside edge of the cable connector is almost identical to the inside edge of an EMT connector. The only way the conductors can be damaged by either connector is if they are bent tightly against the edge of the connector when they are installed.....

Cable is not a conductor ,.. if I had to install the conductors into the cable sheath I would agree with you ,..

 

[LJSMITH1]

Cable and Conduit connectors share the same design requirement in UL514B. They both need to have a radius or chamfer on the inside throat edge of the fitting. This is to prevent conductor insulation damage during a pull or installation.

Conductors can be damaged in a cable fitting (that has a sharp inside throat edge) while making up the terminations and manipulating the conductors. Once the conductors are static, there really is no chance for additional conductor damage.

The primary design intent of a bushing is to protect the conductors from abrading on the inside edge of Rigid conduit during a pull. Workmanship standards dictate that after conduit threading, the ID edge should be de-burred properly. However, in practice, this does not always happen. With conductors smaller than 4AWG, there is typically less pressure applied to the ID edge of the conduit - therefore less likelihood of conductor damage. With 4AWG or larger, the typical pulling/abrading forces are much higher and even a gently de-burred edge will seem as sharp as a razor blade to conductor insulation.

Personally, for any conductor larger than 4AWG, I like to see a bushing used - even on a cable fitting (assuming there are at least 2 threads left after the locknut is on). This is mainly due to the inconsistent quality of many cable fittings on the market. On quality cable fittings you would not need one because the ID edge is properly and consistently relieved - you can feel it with your finger. However, on some fittings there is a very sharp edge, which probably does not meet the requirements of UL514B.

 

[don_resqcapt19]

Cable is not a conductor ,.. if I had to install the conductors into the cable sheath I would agree with you ,..

The conductors within the cable can be damaged by the connector when the sheath is not extended into the enclosure. I stand by my statement that if an EMT connector needs a bushing, so does a cable connector.

 

[CFL]

The conductors within the cable can be damaged by the connector when the sheath is not extended into the enclosure. I stand by my statement that if an EMT connector needs a bushing, so does a cable connector.

The funny thing is that the EMT connector does not require a bushing. It's not a raceway, it's a fitting. The other funny thing is you opened my eyes to this on you're earlier post. I've always used bushings and probably always will (local ahj's require it) but I don't think the CMP intended this, especially when using pvc fittings. As far as an SE cable connector requiring a bushing, I disagree, yet I have always been required to use them by local ahj. I don't have an issue with using them and sometimes I use them just cause they're there, but after pulling some 500's through a pullbox using pvc conduit and forgetting the bushings, I definitely want to use the code to my advantage.

 

[don_resqcapt19]

The funny thing is that the EMT connector does not require a bushing. It's not a raceway, it's a fitting. The other funny thing is you opened my eyes to this on you're earlier post. I've always used bushings and probably always will (local ahj's require it) but I don't think the CMP intended this, especially when using pvc fittings. As far as an SE cable connector requiring a bushing, I disagree, yet I have always been required to use them by local ahj. I don't have an issue with using them and sometimes I use them just cause they're there, but after pulling some 500's through a pullbox using pvc conduit and forgetting the bushings, I definitely want to use the code to my advantage.

I don't think that there is any question that 300.4(G) requires a bushing when conductors #4 and larger are used with EMT...unless the EMT connector has an insulated throat.

(G) Insulated Fittings. Where raceways contain 4 AWG or larger insulated circuit conductors and these conductors 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.

It remains my opinion that this section should also apply to cable installations...of course as it is now written it only applies to raceway installations.
As far as using busings with PVC, you have to look to 352.46.