timmermeier
Member
- Location
- alton il
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- electrician
Their is a bare wire in ac cable it helps to ground the cable , why and how does it work, why not in mc cable ?????????????????????????????????????
AC armored cable
- Thread starter timmermeier
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winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
In type AC cable, the armor is considered the EGC, much like EMT. The tiny wire is there to jump from one turn of the spiral armor to the next, reducing the impedance of the armor.
In type MC cable, a full size wire EGC is present. The impedance of the armor doesn't need to be reduced.
There is a hybrid cable called MC-AP which uses a full size bare aluminum EGC placed in contact with the armor.
In type MC cable, a full size wire EGC is present. The impedance of the armor doesn't need to be reduced.
There is a hybrid cable called MC-AP which uses a full size bare aluminum EGC placed in contact with the armor.
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- New Jersey
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- Journeyman Electrician (retired)
I agree. You can use it to hold in the anti- short bushing but it's not required. I hate when guys wrap it around the armor.
Seen where it was terminated to the ground bar.I agree. You can use it to hold in the anti- short bushing but it's not required. I hate when guys wrap it around the armor.
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- Journeyman Electrician (retired)
I've seen that too. Harry Homeowner doing his best work.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
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- Electrician
I will confess I did that early on in my career. I was only a couple years in and didn't even know what AC cable was, it's not used in my area. Went down to Maryland to do some stuff for a friend of a friend.... It must be common there cuz Big Orange had it. I was like what the heck is with this little tiny puny EGC???? I didn't know what else to do but carefully terminated under a ground screw
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
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- Electrician
I actually don't understand the NEC's logic here. It seems like any armor or raceway should need to be an acceptable EGC. How is it ok for it to not be an acceptable EGC when it must serve as one for itself?
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- New Jersey
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- Journeyman Electrician (retired)
With regular MC the EGC is the green or bare conductor. The armor just needs to be bonded via the connector because it's metal.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
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- Electrician
Right, but if a fault occurs in the cable, from the ungrounded conductor to the armor, the armor needs to be an effective ground fault current path. Shouldn't it be required to be an acceptable egc? Why is it okay for that type of fault but not other types of faults?
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
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- EC
I guess you could say that because the MC armor is bonded to the green EGC at every box and device, in the very unlikely event that there is a fault only to the armor, the length of armor carrying the current is limited and would have no problem tripping the breaker. This is the same reason we bond metallic water lines, so they don't become energized. Not so they can carry current.
-Hal
-Hal
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
I don't know. Maybe the CMP didn't consider the cable armor 'likely to become energized'
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- New Jersey
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- Journeyman Electrician (retired)
I see your point. I guess that the thinking is that if a screw penetrated the cable it would somehow be close enough to a grounded cable connector which would open the OCPD. Maybe a 250' run of MC with a screw penetration right in the middle would not open the OCPD. Also if the installation involves MC cable often there is other grounded metal (steel beams, metal studs) involved that is in contact with the cable so collectively it seems to work.
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