Anti-short bushings

[MR. S]

In Art.320 it states type ac cable needs an insulating bushing (red head)when terminating. No where in Art. 330 does it say an insulating bushing is needed for type MC cable, so we are under the assumption type MC cable does not need a red head at the termination (we use them anyway). Someone brought to our attention Art.300.42. We are in dissagreement over this article. Does 300.42 state an anti-short bushing is needed for MC cable?

 

[petersonra]

300.42 says something like "where it is necessary".

if the code doesn't say it is necessary, it ain't.

 

[bphgravity]

Follow the manufacturer's installation instructions...

 

[M. D.]

[FONT=Arial, Helvetica, sans-serif]Anti short bushings are not required for M.C. cable.[/FONT]
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[FONT=Arial, Helvetica, sans-serif]

[FONT=Arial, Helvetica, sans-serif]ROP #7-116 from the May 2001 Report on Proposals (ROP) for the 2002 NEC was a proposal seeking to require anti-short bushings on all MC Cable termination installations. The following is an excerpt from the Panel statement rejecting the proposal:[/FONT]
[FONT=Arial, Helvetica, sans-serif]Anti-short bushings are not required for Type MC cable in accordance with the listing for the product. The termination fittings approved for use with Type MC cables are designed such that the wires will not come in contact with the cut edge of the armor; the throat of the fitting is small enough to prevent contact with the armor. Type MC termination fittings perform the same function for Type MC cable as Type AC terminations plus the anti-short bushing do for Type AC cable.[/FONT]
http://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/Use-of-Anti-Short-Bushings-for-Terminating-Type-MC-Cable~20050630.php

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[celtic]

http://www.nema.org/stds/eng-bulletins/upload/Bulletin-90.pdf

 

[Jim W in Tampa]

Not required but great idea.Any man on my crew either uses them or gets sent to office.Why would you risk a short over something so simpple and cheap ?

 

[dnem]

In Art.320 it states type ac cable needs an insulating bushing (red head)when terminating. No where in Art. 330 does it say an insulating bushing is needed for type MC cable, so we are under the assumption type MC cable does not need a red head at the termination (we use them anyway). Someone brought to our attention Art.300.42. We are in dissagreement over this article. Does 300.42 state an anti-short bushing is needed for MC cable?

If 300.42 existed in a vacuum, then my answer would be yes the antishort is needed so that "Where conductors emerge from a metal sheath and where protection against ..... physical damage is necessary, the insulation of the conductors shall be protected by a cable sheath terminating device".

But 300.42 doesn't exist in a vacuum. . 320.40 states that AC cable needs to have "an insulating bushing or its equivalent protection shall be provided between the conductors and the armor". . But the same committee wrote 320 + 330 and CMP7 chose not to put that wording in 330.

"Does 300.42 state an anti-short bushing is needed for MC cable?"
My interpretation is that CMP7 has determined that "protection against ..... physical damage is necessary" does not apply to MC cable. . I guess they feel that MC has a magically barrier between the jacket and conductor insulation. . All I've ever seen was a thin clear plastic sheet that installors tear off even with the jacket cut edge.

They don't care if the freshly cut jagged metal jacket edge of MC slices into the insulation. . It's not a code or listing requirement.

But don't confuse code requirement with the concept of "needed".
"No where in Art. 330 does it say an insulating bushing is needed for type MC cable"
It doesn't say it's "required". . It says nothing about need. . Of course it's needed ! . Why would you want to compress the freshly cut metal jacket edge into the conductor insulation ? . It's not code required but it absolutely is needed. . Don't operate under the assumption that the NEC is always correct !

Determining whether it's NEC required or just needed isn't important to the electrician but it makes a huge difference when you're an inspector. . It sometimes is what causes you to pass an inspection that is of very poor quality.

David

 

[dnem]

ROP #7-116 from the May 2001 Report on Proposals (ROP) for the 2002 NEC was a proposal seeking to require anti-short bushings on all MC Cable termination installations. The following is an excerpt from the Panel statement rejecting the proposal:
Anti-short bushings are not required for Type MC cable in accordance with the listing for the product. The termination fittings approved for use with Type MC cables are designed such that the wires will not come in contact with the cut edge of the armor; the throat of the fitting is small enough to prevent contact with the armor. Type MC termination fittings perform the same function for Type MC cable as Type AC terminations plus the anti-short bushing do for Type AC cable.
http://www.mikeholt.com/mojonewsarch...e~20050630.php

"The termination fittings approved for use with Type MC cables are designed such that the wires will not come in contact with the cut edge of the armor; the throat of the fitting is small enough to prevent contact with the armor. Type MC termination fittings perform the same function for Type MC cable as Type AC terminations plus the anti-short bushing do for Type AC cable."

File that under the file named "Lie of the Day"

 

[iwire]

Just a reminder.

300.42 only applies to installations over 600 volts.

 

[dcspector]

David I agree,

When I wired we used them with MC. Just because we cared as others do. Just another small touch of prevention. But enforce it......No way.

 

[benaround]

David,

That's quite a bit of drama over a mc fitting!! I'm Old School also and I have

installed red heads thru-out the years,but it's time to let go and use the new

products. As far as I'm concerned the new mc connectors work great without

using a red head. I have had no 'shorts' at all, and hear no complaints from

the shop that others do. I just don't see what all the fuss is about.

 

[peter d]

David,

That's quite a bit of drama over a mc fitting!! I'm Old School also and I have

installed red heads thru-out the years,but it's time to let go and use the new

products. As far as I'm concerned the new mc connectors work great without

using a red head. I have had no 'shorts' at all, and hear no complaints from

the shop that others do. I just don't see what all the fuss is about.

As I've been known to be somewhat outspoken on this topic , I was going to add my 2 cents but you did it for me pretty well. So yeah, what you said.

 

[iwire]

I agree that good MC connectors exist that could be safely used without red heads. OZ-Gedney makes some nice ones.

However there are many more UL listed MC connectors that do absolutely nothing to protect the conductors from the sharp edges of the armor.

Considering that many times I do not get to choose the connector type and usually receive the less expensive junk connectors I will stick to using red heads. :smile:

I think some may want to skip them just 'cause they can and it makes people ask questions.

 

[dnem]

I think some may want to skip them just 'cause they can and it makes people ask questions.

The difference between the people that ask what they can do and those that ask what they should do shows up in the quality of the job.

 

[dnem]

David,
That's quite a bit of drama over a mc fitting!!

Would you call it ?drama? if you agreed ? . I doubt it.

I'm Old School also and I have installed red heads thru-out the years,but it's time to let go and use the new products.

Why would it ever become time to ?let go? of protecting the conductor insulation from the cut metal jacket ? . I?m not seeing a requirement that any new product fit between the jacket and the conductor.

I?ve seen a spec sheet detailing a UL test of an MC connector. . The test speced a torque pressure for the connector screw. . Have you ever seen an electrician install MC connectors with a torque wrench ?

The factory rep tells the CMP, ?Our new MC connector is soooo wonderful that you don?t even need an antishort bushing !? . . And the CMP says, ?WOW !? and falls for the sales pitch.

As far as I'm concerned the new mc connectors work great without using a red head. I have had no 'shorts' at all, and hear no complaints from the shop that others do.

I see jobsites where an MC termination short is found on power-up and the drywall gets cut away for the repair. . Since the short is at the connector and the conductor has a hole blown in it or partially damaged, the run is usually short and the electrician either reruns the run or reroutes the cable on some kind of diagonal. . It?s a rare event but thankfully it?s always happened in a Commercial metal stud building. . Inspectors see a lot of ?rare? events moving around 10 to 20 jobsites per day, plus we talk among ourselves about uncommon things we?ve seen.

When armored cable becomes common place in wood stud homes, I think we?ll see those rare jacket-slices-the-conductor-insulation shorts causing fires [210.12(B)x1]. . Maybe the CMP will take notice.

I just don't see what all the fuss is about.

There?s a lot of ?fuss? involved in a quality installation.

David

 

[M. D.]

David ,I use mc connectors and I too use anti short bushings ,but I do it out of habbit more than anything else ,.. Why?? because I use these(click link) and if your conductor's insulation is able to get damaged using these you've got bigger problems IMO. :smile:

Duplex Snap2It(TM) for MC-AP and Health-Care Facility MC-AP Cables

 

[benaround]

David,

All I can say is the mc connectors in Ohio, or the East Coast for that matter

must be different than the connectors in the S.W. part of the USA, it is

a non-issue here. I'm going to let the rest of this slide.