Clone 320.40 into 330

[tonyi]

IMO, its goofy to think that MC armor won't somehow ding up insulation while AC's could...

I've always put anti-short bushings into MC ends, but I've seen some installations where they weren't used.

[jimwalker]

I would not even think of risking a short over something so easy to use

[charlie]

Gentlemen, if you are using the correct connectors, you do not need the anti-shorts on MC cable any more than you need bushings on the EMT connectors for #12 wire. Workmanship or doing a good job has nothing to do with it. :D

Edited it so my answer made sense.

[ November 10, 2004, 08:21 PM: Message edited by: charlie ]

[tonyi]

I disagree. I've seen the insulation damage.

Many prebushed MC/AC compatible connectors (ex. SpeedLock or Arlington L15A) displace the armor off-center as the saddle clamps down. The section of wire coming through the bushing is fine, but the wire right as it exits the armor gets shoved against the armor's edge. There's nothing you can do to in terms of "workmanship" to avoid this off-centering displacement on the smaller cable sizes like 14-2/12-2. Its somewhat less an issue with 12-3,10-2 or 10-3's as the diameter of the armor is larger and tends to center somewhat better as the saddle clamps down.

IMO, if bushings are somehow deemed REQUIRED for AC, then then they should logically be required for MC since the mechanical aspects of the connectors and armors are virtually identical.

[roger]

Tonyi, make a proposal.

Roger

[tonyi]

Real insightful Roger...

[charlie]

Tonyi, I don't think Roger was making a wise a** comment. If this is really a problem, that is what the proposal process is all about. This intent of this portion of the forum is to look at the language of a proposal and massage it so you will have a solid proposal to send in to the Code Making Panel and it having a chance to get passed.

Personally, I think this is a performance issue with a particular connector that should be brought to the attention of UL. If that is something that is going on with all brands, then I am with you. :D

[rbalex]

Originally posted by tonyi:
Real insightful Roger... tonyi,

Roger's reply is "on point."

Please reread the "Welcome" (http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=21;t=000001) to this forum.

Make a specific "Proposal" that you intend to submit to the NFPA. Then the members of this forum will "critique" it for you. It will give you a "sense of the consensus" and help you make a stronger "formal" Proposal, if you choose to do so.

It is not the purpose of this forum to make the proposals for you.

[tonyi]

How's this then?

Clone 320.40 into 330 replacing all instances of the term "AC" with "MC".

If someone could explain to me how, by whatever mechanism, MC has some sort of immunity to damage from rough armor ends that AC somehow doesn't have, then I'll become a believer that everything is fine the way it is.

[don_resqcapt19]

Tony,
Look at this statement from NEMA (http://www.nema.org/DocUploads//8B117E35-EFF9-4B09-B6E4722E1E6DFEF3/BULL90.pdf).
Don

[tonyi]

I guess I should give up - there's no logic at work here :eek:

If NEMA believes MC is fine without anti-short bushings, why not remove the anti-short language from 320.40 as being unnecessary?

Of course, there's the dreaded 90 degree connectors...that don't have insulated throats and pretty clearly allow the wire to rub against cut ends if someone starts yanking the wires around.

[roger]

Thanks Charlie and Bob. Tonyi, If it makes you feel better, do as Jim does and use the "Anti Short Bushings".

Seeing how NEMA, who sees a lot more installations than you or I do, does not see the need for "Anti Short Bushings" on MC, I would be looking at the individuals installing the MC around you if you are seeing this many problems.

We use T&B TITE-BITE insulated throat MC connectors, and have very few problems with or with out the Red Heads (slang).

BTW, we use alot of Arlington products also, especially in the over 3" category.

Roger

[don_resqcapt19]

Tony,
The designs of the listed MC connectors and AC connectors are not the same. The listed MC connector will prevent conductor damage without the use of anti-short bushings. Note, just because the connector fits on the cable does not mean that it is the correct connector for that cable.
Don

[ November 11, 2004, 01:34 PM: Message edited by: don_resqcapt19 ]

[rbalex]

Originally posted by tonyi:
IMO, its goofy to think that MC armor won't somehow ding up insulation while AC's could...

I've always put anti-short bushings into MC ends, but I've seen some installations where they weren't used. tonyi

CMP7 controls both Articles. I haven't set in on any of their deliberations but I know several members and I don't believe they would consider this an adequate substantiation.

However, your personal experience is still a valid place to begin your substantiation. If you have personally observed problems with conductor failures caused (or permitted) by connectors properly installed and listed for terminating MC cables - then you have a case and a solid proposal. If you simply think it’s a good idea, it probably won’t fly – no matter how reasonable it may be.

One proposal I had accepted a while back resulted in what is now 300.18(B). It was simply based on my personal observation of damaged raceways and there was enough universal experience to validate it.

[tonyi]

Originally posted by don_resqcapt19:
Tony,
The designs of the listed MC connectors and AC connectors are not the same.
Don AMC-50/75, L15A, 8400's, 850's are all listed for both AC and MC. I'm sure I could find a dozens more similarly dual listed if I went looking for parts I don't buy on a regular basis.

[roger]

Tonyi. of the connectors you listed which ones do you find are being used on the problems you frequently encounter?

We literally use 1000's a week at times and have very few problems.

Roger

[tonyi]

Originally posted by roger:
Tonyi. of the connectors you listed which ones do you find are being used on the problems you frequently encounter?

We literally use 1000's a week at times and have very few problems.

Roger Of those thousands, how many do you ever have occasion to take apart and inspect the result?

Have you ever done a post-install disassembly on something that passed inspection and appeared to work?

This is something people doing new installation aren't going to notice or realize is happening.

Any connector that saddles the cable off the connector throat centerline where the spiral armor's thickness is less than the distance from the throat bottom to the connector bottom will tend to drive the wires upward as the saddle clamps down.

Rather than jawing about it ad-nausaeum, why not just construct a couple and look at how the saddles clamp down. Install an AMC-50 on a some 14-2 MC. Look down the throat. The off center displacement of the connector is enough to allow for the cut armor end to rub on the wire insulation as the wires in the box are worked on.

Note: the AMC-50 is even prebushed and still exhibits the kind of issue I'm talking about due to the off-center displacement effect.

An ordinary 8400 with smallish diameter cable (AFC's 14-2 is the smallest I've seen)will exhibit the same offcentering and allowing wires to contact cut ends as they're worked.

[ November 11, 2004, 10:19 PM: Message edited by: tonyi ]

[roger]

Tonyi, you didn't answer the question, specifically. of the connectors you listed which ones do you find are being used on the problems you frequently encounter?

I would stop using these, and as Bob stated earlier, make a proper proposal and if the sustantiaion can show sufficient cause you may get your wish.

We simply don't have the problem you seem to be having.


Roger

[ November 12, 2004, 01:33 AM: Message edited by: roger ]

[iwire]

Originally posted by tonyi:
Originally posted by roger:
Tonyi. of the connectors you listed which ones do you find are being used on the problems you frequently encounter?

We literally use 1000's a week at times and have very few problems.

Roger Of those thousands, how many do you ever have occasion to take apart and inspect the result?

Have you ever done a post-install disassembly on something that passed inspection and appeared to work?

This is something people doing new installation aren't going to notice or realize is happening.

Tony I am sure like myself Roger hears about the job for at least a year after completion.

Seriously, and I am not being a wise guy, submit a proposal. :)

Bob

[elektrafried]

For what it's worth I just finished a rather large commercial building and I did have several shorts where the MC conn was the problem.My opinion it's not the product it's the men putting it in.Every short in the building was MC connector screwed down too tight and/or stripped with something besides MC strippers. (dykes,lineman's pliers,etc.)

[msd]

If someone could explain to me how, by whatever mechanism, MC has some sort of immunity to damage from rough armor ends that AC somehow doesn't have, then I'll become a believer that everything is fine the way it isinside ac cable is twisted/braded paper leaving conductors exposed to contact with the jacket.

inside mc cable the conductors are wrapped in a plastic jacket. sort of a pre-anti-short bushing

when properly installed in a prebushed compatible connector (ex. SpeedLock or Arlington L15A)the "plastic wrapping" acts as the anti-short bushing. the plastic wrapping should extend throught the insulated throat of the connector.

the connectors are ul listed for use without the anti-short bushings.

what i see all too often is mc cable that has been cut in the field with either "wire cutters" or "tin snips" and the plastic jacket cut or folded back before being placed in the connector. RED TAG for that !!!!

use a Roto-Split to cut your mc cable and bring the plastic wrap through the insulated throat of the connector and you have a code compliant and ul listed install.

that being said - i always use anti-short bushings with mc too.

[iwire]

Originally posted by msd:
when properly installed in a prebushed compatible connector (ex. SpeedLock or Arlington L15A)the "plastic wrapping" acts as the anti-short bushing. the plastic wrapping should extend throught the insulated throat of the connectorCan you provide any reference for that?

I have never seen any instructions or codes that require the plastic wrap to extend through the connector.

I do not believe for a moment that the plastic wrap is there to act as an anti short bushing.

NEMAs own statement about terminating MC makes no reference to the plastic wrap.

Originally posted by msd:
what i see all too often is mc cable that has been cut in the field with either "wire cutters" or "tin snips" and the plastic jacket cut or folded back before being placed in the connector. RED TAG for that !!!! Red Tag?

What code section do you cite?

Unless the folded back plastic is interfering with the grounding of the MCs sheath I see no violation.

There are snips on the market specifically for stripping MC.

In my opinion you are trying to enforce your own preferences not actual code requirements.

Bob

[ November 17, 2004, 03:45 AM: Message edited by: iwire ]

[peter d]

Sometimes local codes require the use of "rotosplits" and insulated throat connectors.


(Add) 13.8.10.6.2.3

A cable-cutting tool with controlled depth of cut shall be used in all MC cable installations.

(Add) 13.8.10.6.2.4

UL listed type MC cable connectors with insulated bushings and screw type cable attachments shall be used in all MC cable installations. Connectors shall be steel, not the cast type.

Taken from Rhode Island Fire Safety Code

The above rules apply to fire alarm system wiring only.

[ November 22, 2004, 07:55 PM: Message edited by: peter d ]

[iwire]

Peter I was unaware of that RI FA rule, thanks. :)

I am familiar with the strictly enforced color code and the "no wire nuts" rule. :roll:

It was not until recently that you could get permission to run MC, pipe was preferred.

Bob

[peter d]

Bob,

You're welcome. :)

That was my reaction as well when I did my first fire alarm: :D

It's ok to wire nut 277 volt circuits together, but not 24 volt FA circuits. :confused:

Here are the specifics:

(Add) 13.8.10.6.5

Any fire alarm wiring between the fire alarm control unit and remote terminal cabinets or between remote terminal cabinets may, at the option of the installer, be a multi-conductor cable with each conductor numbered at two-inch (2") intervals. All wiring from a terminal cabinet(s) to an alarm device(s) shall conform to the color code specified before herein. Terminal cabinets with hinged, lockable red covers shall be provided at all junction points. All conductor splices or terminations shall be made on screw-type terminal blocks - wire nuts, butt or crimp type connectors shall not be used. All terminals within a terminal cabinet shall be properly labeled. EXCEPTION: Crimp-type connectors may be used on bonding conductors.

(Add) 13.8.10.6.1

All fire alarm system wiring within a building and between buildings in multiple building clusters shall be installed in metal raceway with steel couplings and box connectors or type MC cable rated as FPLP and 2-hour fire rated for penetrations by UL.

(Add) 13.8.10.6.2.1

All conductors shall be minimum #16 gauge solid copper, type thhn, thwn or tfn. All wiring shall be run continuously from device to device. With the approval of the AHJ, junction points may be made due to construction hardships where a continuous run would be impractical or when one of the exceptions to 72:6.4.2.2.2 applies, provided the requirements of § 13.8.10.6.5.1 are met.


I'm sure you've been to the Providence Place Mall. There's miles of FA MC in there.

Out of curiosity, how do you do FA's in Mass? FWIK, every town seems to have their own code.

Edited to include ammendments, because I just found them.

[ November 23, 2004, 08:14 PM: Message edited by: peter d ]

[jwelectric]

Gentlemen
I had the good fortune of being at the seventy fifth Diamond Jubilee meeting of the IAEI in Orlando Fla. We were at lunch break and at the table beside where we were eating I overheard the discussion about AC and MC Cable and its use. To make this short and sweet they said that the biggest problem with MC Cable was that the installer’s way of cutting the amour. MC comes with a plastic wrap between the amour and the conductors and the use of lineman and diagonal cutters being used to cut the amour was the problem in the abrasion of the conductors.
The one thing to remember when making a proposal for a code change is that personal prefaces are not considered.