ECN Forum Forums General Topics of the Trade General Discussion Area mc connectors

Where I live the inspector does require antishort bushings he checks for them. I think it is a good practice to use them anyway. I always do.

Welcome to ECN spark1051.



Then the question is there a local amendment that the inspector can cite?

Inspectors can not enforce the use of anti-short bushings with MC cable if there are no local amendments. The NEC does not have an anti short requirement for MC.

If you wanted to press the point you could print out the NEMA bulletin that Roger posted.

For what it's worth I use them too.

I use them on MC cable when I have them handy, but if I don't have one handy, guess what? I won't use one. Sometimes it just takes too much time to hunt around for a little piece of plastic that isn't required anyway.

Peter

if there are no NEC codes for mc cable then what cable do you need to use them on? Also what is the difference between MC and BX? Mc has ground and BX don't thats the only difference right?

You are required to use them on AC cable. See 320.40

Kdrifter, the difference in MC and AC is as follows. (From AFC)

Armored (Type AC) Cable Construction

As described by the National Electrical Code NEC® 2002 Article 320, armored cable Type AC is a “fabricated assembly of insulated conductors in a flexible metallic enclosure.”
Type AC cable is manufactured to UL Standard 4. It consists of 2 to 4 copper conductors in sizes 14 AWG to 1 AWG inside an interlocked metal armor of steel or aluminum construction.
Type AC cable can have no more than four insulated conductors plus a grounding conductor (for a total of 5 conductors only) and cannot be manufactured larger than 1 AWG per UL 4.
A 16 AWG aluminum bonding wire is inside of, and in physical contact with, the metal armor providing a low-impedance fault return path required for the operation of overcurrent protection devices. The bonding wire is unique to AC cable and allows the outer metal armor in conjunction with the bonding wire to be used as an equipment ground. It is important to remember that the bare bond wire is not an equipment grounding conductor. It is the bond wire that, in combination with the interlocked metal armor, provides a low impedance equipment grounding path. Each of the copper conductors is covered with a thermoplastic insulation (THHN with a 90°C rating) and are individually wrapped in a moisture resistant, fire retardant paper.
According to NEC Article 320.40, an insulated (anti-short) bushing is required when installing Type AC cable. It is installed at the time of termination and designed to protect the conductors from damage. AFC provides bushings in bags packaged with the cable.


Metal Clad (Type MC) Cable Construction

As described by NEC Article 330, Metal Clad Type MC cable is a “factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape or a smooth or corrugated metallic sheath.”
Type MC cable is manufactured to UL Standard 1569. MC cables may have 1 or more solid or stranded conductors in sizes 18 AWG and larger. The number of conductors allowed in an MC cable is not restricted by UL. The conductors may be of copper, aluminum or copper-clad aluminum.
The metal armor may be a smooth tube, a corrugated tube, or an interlocked metal armor. AFC Cable Systems manufactures MC cable with interlocked metal armor and copper conductors.
The make-up of AFC’s 600 Volt interlocked armor MC cable consists of:

• Copper circuit and grounding conductors
covered with thermoplastic insulation
• An overall polypropylene cable assembly tape
• An outer galvanized steel or aluminum interlocked armor

Unlike Type AC cable, the armor of interlocked Type MC cable is not an equipment grounding means and Type MC cable requires a bare or green grounding conductor.


Roger



[This message has been edited by Roger (edited 05-01-2005).]

Here in the Phoenix, AZ metropolitan area we use a lot of mc cable. Our company uses the snap-tight mc connectors by Arlington industries exclusively. The labor savings alone make up for the cost. I remember a post a long time ago about this and someone copied 320-40 on it. I don't have the exact code on me but in there it states. "If the mc connector that you are using already has an insulated red throat. that protrudes past the head of the connector and that an inspector can visually see, than you don't need an anti-short". I believe that the type of mc connector that the originator of this topic is using has an insulated red throat.
My theory is why use an anti-short when it really is not doing anything in there. Like the first post states there is no clamp tightening down on the metal jacket. I leave the clear plastic around the conductors, then slide the connector over, snap the mc cable in the connector and then remove the clear plastic. So in essence, the clear plastic can serve as an anti-short.

The purpose of this strip is to short together the turns of the spiral wrap, so fault currents won't turn the armor into an inductor, which can cause major heating and even fire.