Grounding conductor question

Status
Not open for further replies.
Those are not equipment grounding conductor, they could have been cut off or back wrapped on the armor.

Those silver conductors are the bonding strip required in type AC cable.
 
tonype said:
Just for my own education - what is the history/reason why the bare grounding conductor would be connected to the outside of the panel enclosure? Is this done when a panel is replaced, but older wires are still in service?

http://i15.photobucket.com/albums/a352/TonyPE/P1080701.jpg
Click to expand...

That is the old bx and that is not the proper termination for it. It should be wound around the cable. I believe the old bx didn't provide a great ground but with this extra wire it would be fine.
 
ultramegabob said:
I never understood the purpose of the bonding wire in AC cable, what does it do that the flex itself isnt doing?
Click to expand...


Without the strip the armor can turn read hot under fault conditions.

The strip which the NEC requires to be in contact with the armor essentially shorts each wrap to the next reducing the impedance.
 
iwire said:
Without the strip the armor can turn read hot under fault conditions.

The strip which the NEC requires to be in contact with the armor essentially shorts each wrap to the next reducing the impedance.
Click to expand...

I thought the wrap was a single continuous piece that is wound and interlocked.
 
ultramegabob said:
I thought the wrap was a single continuous piece that is wound and interlocked.
Click to expand...

It is, your right.

But I do know that the bonding strip was added when they found that the older AC cable was not handling fault current well enough causing the armor to get hot enough to start fires.

Now how does that little strip really get the job done?


I really do not know the answer to that. :confused:
 
More impressive is the aluminum strip in the new MC AP cable. You just cut it off. Apparently the fit is so precise that is touching the sheathing the entire way. No extra ground is needed.

cableboxes.jpg
 
ultramegabob said:
seems to me that making the armor a little thicker would have done the trick:roll:
Click to expand...

I would have thought so as well but it does apparently work. :confused:

Dennis Alwon said:
More impressive is the aluminum strip in the new MC AP cable. You just cut it off.
Click to expand...

You can do that with standard AC cable as well. The NEC does not require back wrapping it.

That said I am a back wrapper, it helps hold the anti-short bushing in. :smile:
 
The armor of AC cable is spiraled. A 250' coil may have over 1000' of metal in the armor. Fault current is likely to follow the circular wraps of the armor which in turn act like a big coil. Think about a coil and think about the spiraled armor with current flowing on the armor's surface in a circular motion. This would mimic the effects of a coil and have a large impedance, not really what you want when your armor EGC is supposed to be opening an OCP during a fault.

By putting the bonding strip against the armor the current will now travel in a straight line more like a wire EGC and less like a coil. This will drastically reducing the impedance of the armor and safely open the OCPD.
 
Dennis Alwon said:
More impressive is the aluminum strip in the new MC AP cable. You just cut it off. Apparently the fit is so precise that is touching the sheathing the entire way. No extra ground is needed.

cableboxes.jpg
Click to expand...


Why did they choose aluminum for that strip?
 
frizbeedog said:
Why did they choose aluminum for that strip?
Click to expand...

It was originally aluminum that they chose for AC cable. My guess is that AL is lighter and much cheaper than copper.
 
Dennis Alwon said:
More impressive is the aluminum strip in the new MC AP cable. You just cut it off. Apparently the fit is so precise that is touching the sheathing the entire way. No extra ground is needed.
Click to expand...

Some of us here are still going to try to pull an EGC through it.;)
 
Thought I would post the benifits OF MCAP over AC

http://www.edi-nc.com/edi/featured/SouthwireMCAP.asp


As an alternative to conventional AC cable, MCAP cable yields significant benefits. To begin with, it reduces termination steps, compared to AC.

? More conductors than AC
Types AC and AC cables for health care facilities are limited to four current-carrying conductors. MCAP and HCF MCAP cables have no limits on the number of conductors in a cable. That means you may see multiple neutrals and home run cables where MCAP cable is used, even in health care facilities.
? Equipment grounding conductor capacity
The armor of MCAP cable delivers 350 percent more effective ground-fault current path capacity than AC. This is based on the UL maximum permitted armor resistance for MC and AC cables. With the addition of a green insulated grounding conductor, HCF MCAP cable meets NEC 517.13 requirements for health care facilities.

? No bushings, less support than AC
Because MCAPP and HCF MCAP cables are Type MC products, they require no anti-short bushings where the armor has been cut. For more information regarding the use of anti-short bushings, refer to NEMA?s Engineering Bulletin No. 90, ?Use of Anti-Short Bushings for Terminating Type MC Cable? (available at www.NEMA.org). In addition, they require less securing and supporting than Type AC cables. Like
conventional MC, MCAP and HCF MCAP cables need support only every six feet, compared with 4.5 feet for the AC constructions.

First Interlocked Armor Type MC Cable for Health Care Facilities
HCF MCAP cable is the first interlocked armor MC cable that meets NEC 517.13 requirements for redundant equipment grounding conductor paths in health care facilities, and, as noted above, HCF MCAP cable has a 350 percent better ground-fault current path in the armor than the armor of AC cable suitable for use in health care facilities. Figure 5 shows a comparison of HCF MCAP cable with AC cable suitable for use in health care facilities.
Click to expand...
 
Status
Not open for further replies.
Top