BX with aluminum EGC

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  #1  
Old 10-23-04, 03:02 PM
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BX with aluminum EGC

Menard's had a what I thought was a great deal on 12-2 BX, $23 for 100 ft. But when I got home I discovered it had a bare aluminum EGC. The insulated conductors are solid copper. Are there any special precautions I must take when installing this?
 
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Old 10-23-04, 03:31 PM
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You purchased what is called AC Cable (armored cable). It has generally 2 insulated conductors and one bare shorting strip. For this product, the bare shorting strip is for use by the metal cable to act as an EGC (ground). There is no separate copper ground like MC cable (metal clad cable).
It should have come with red insulating bushings for use at the end of the cable to help reduce abrasion of the insulated conductors on the metal jacket.
 
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Old 10-23-04, 06:19 PM
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Thanks for the reply. I did not think to compare the MC and AC, the AC was cheaper and from the outside looked exactly the same. I forgot to mention the included bushings, thanks for explaining their purpose.
 
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Old 10-23-04, 07:52 PM
hex2k1
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HandyRon,

i read an article in the fall edition of the nec digest that specifically talked about the shorting conductor in AC cable and it said that it is a common mis conception that the shorting strip is a egc.the armor is the only egc and the shorting strip was only that a shorting strip to reduce the XL and should not be connected to metal enclosures or used as a egc due to its small cross-sectional area. i have been under the impression that it was the egc for many years until i read this for myself.
 
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Old 10-24-04, 05:19 AM
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hex2k1,
I agree. The armor is the EGC. If you want an actual conductor for grounding, you need "hospital grade" AC Cable (which has an extra conductor), or MC Cable.
 
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Old 10-24-04, 07:11 AM
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I am still a little confused. Is the shorting conductor connected to the green screw of a switch or outlet or is there a different method to grounding using AC cable? Does this cable even provide adequate grounding when used properly? Thanks again.
 
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Old 10-24-04, 07:45 AM
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Both AC and MC are only suitable for use in metallic wiring systems. If you use AC cable, you must also use _metal_ outlet boxes and fittings; you must not use AC cable with plastic boxes.

When you use AC cable with proper fittings on metal boxes, the combination of the metallic armor and the bonding strip will form your equipment ground conductor. This armor/EGC is connected to the metal box by the use of the proper fittings. Then you attach a ground wire to the _box_ to make the ground connection on the ground terminal on the receptacle. If you use 'self grounding' receptacles, then you don't even need this wire; a little clip on the edge of the receptacle yoke makes the ground connection.

When using AC cable, you have to be careful to make sure that all of your cable clamps are properly rated for AC cable. In addition, you have to make certain that you have good metal to metal contact at all of the ground clamps. In particular, when going into your main panel (which is usually painted), you _must_ be sure to remove the paint around the knock out hole, so that it doesn't insulate your ground connection.

The little shorting conductor in the AC cable is part of the EGC formed by the armor. You don't what to cut it off or isolate it. You want to make sure that it is connected to the armor. A common technique is to use the shorting strip to hold the red bushing in the end of the cable, with the shorting strip twisted back along the outside of the cable and under the clamp.

If you use MC cable that has both armor and an insulated EGC, then you have to make sure that both the armor and the EGC are properly bonded to the box. Basically _all_ possible ground conductors must be bonded together in each junction box, with the exception if identified 'isolated ground' conductors.

-Jon
 
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Old 10-24-04, 05:30 PM
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Thanks for the info. I bought all metal boxes, but they don't have grounding screws, nor are the outlets self-grounding, so I am going to exchange the AC for MC.
 
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Old 10-25-04, 07:50 AM
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You can buy the threaded green ground screws separately, or by the grounding clip that slides on the edge of the metallic box.
 
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