SideWorker

Then who does the warranty work for a union contractor?

KayJay

Not sure what the hubbub is all about, but those Arlington duplex connectors are listed for NM, MC and BX, at least according to the box I have in front of me. If you use them with BX, you would need the redheads, hence the inspection holes, but not with MC cables. The clamp has nubs that grab and lock the NM sheath or spiral armor of the BX and MC. They also bond and prevent the sheath or armor from slipping in or out after installation. The connector throat is smooth inside to prevent abrasion and contoured to act as a cable end stop and redhead retainer.
I see these duplex connectors used with four NM’s cables stuck in them quite often, even though they are apparently only listed for two cables max of any type.

crazymurph

Then why does a coil of MC come with a bag of red heads?

Protech

Go back to post 14 and read the link

crazymurph

That explains nothing

Celtic

Perhaps because using a red head is considered "good practice" and has been installed "traditionally"...although it's use is not required.

The MFG probably doesn't care one way or the other....the cost just gets moved on down the line.

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steelersman

Umm, I don't think so. The standard single MC connectors (the ones that look just like romex connectors with the 2 screws that clamp down on the MC) don't have a bushing inside of them.

Celtic

I don't know what you mean by "standard".
Standard to you, might be something different to someone else.

Post a link so we are all talking about the exact same item.

Thanks

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steelersman

the kind mentioned here:

only difference i see between an arlington MC connector and an arlington 3/8 romex connector is the bottom that sits inside the panel. the MC connector keeps all the wire in the center and a romex connector doesnt. i never looked up the UL listing of that stuff. i use MC connectors anyway

Celtic

That is why the need for a red head is not required.
The connector holds the conductors away from the sheath.

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steelersman

Oh ok. I never thought about it like that.

LJSMITH1

Red Heads are not typically not required on MC due to the plastic sheathing between the outer sheath and the conductors. In AC cable, there is no plastic sheathing and only paper around the conductor insulation. This is why a red head is typically required to guard against abrasion from the cut edge of the metal sheathing. However, there have been some discussions in requiring these red heads for MC cable for the same reasons as AC cable. I have been told that some jurisdictions require the use of red heads on ANY AC/MC cable.

As for the insulated throats on fittings for MC/AC, again, this is only required in some jurisdictions or when specified by the engineer.

Regarding the difference between a Romex connector and an MC cable connector, the hole is there because UL514B requires a cable stop feature that will prevent the outer sheathing from passing through the fitting. It could be a round hole or a elongated hole. That is the primary reason. The NEMA document talks about centering the conductors, but I am not sure if that is accurate. How do the conductors remain 'centered' in a duplex fitting?...

The sight holes in many AC/AC fittings are there to allow the installer to see where the end of the sheath is prior to tightening the strap. The end of the sheath should be visible in the sight hole.

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Larry

steelersman

Makes perfect sense to me.

Protech

Taken from the PDF:

"The confusion stems from the fact

that some MC cable manufacturers include anti-short bushings with their cable. The inclusion of
anti-short bushings with coils or reels of MC cable is based on historical practice relating to the
requirements of 320.40 of the NEC, which mandates the use of anti-short bushing or its

equivalent protection for Type AC Cable"

Further down:

"Whether or not an insulated throat is part of the listed product, these

listed MC fittings do not require an additional anti-short bushing."

What didn't you understand?

Celtic

So they are required?

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LJSMITH1

Sometimes by the AHJ... They want them on ALL MC/AC cable installs. I think that's the primary reason why some cable Mfr's ship a little bag of them with every roll. It's cheap insurance that there won't be any complaints that they were not installed because there were none on the job site.

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Larry

MDShunk

I would buy that if there wasn't also type MC cable on the market that has no plastic around the conductors. I think it was on the back cover of this month's EC Mag.

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EBFD6

My $0.02, use 'em if you got 'em. I almost always use red heads on MC, they are free and don't take any extra time to install. However, if I don't have one handy I won't make an extra trip to the truck just to get one, just install the connector. I've never lost a wink of sleep worrying about this issue.

DayMan

HCF MC has paper on it.

MDShunk

I was thinking of AFC Cable's MC-Quik, which has no plastic or paper. They also have HCF cable called MC-Stat with no plastic or paper on it.

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