MC/BX/AC, please clarify. Also, what cut and bush do you use?

[fastline]

Firstly, can anyone put any clarity in any difference between MC/BX/AC? The only thing we have ever used is MC, with ground, and indoor only, either in commercial walls or similar.

I don't know if the BX/AC is identical other than conductor types, thickness of jacket, etc? We are looking to use flex in some OH lighting in buildings, and would like to clamp in the top edge of Ibeams so it is well protected.

As well, I will admit that every time I use MC, I cuss like mad because the stupid bushings and connectors do not protect the conductors worth a damn so extreme caution is needed. Does anyone make good and proper MC bushings that actually do something?

I can tell you it got bad enough that on some non-permit work, we resorted to adding sleeves over the conductors we can work with it with more confidence.

 

[infinity]

AC is armored cable made with paper individually wrapping the conductors and a thin aluminum bonding strip which with the armor serves as the EGC. BX is a slang name for AC. Metal Clad or MC cable is different. Regular MC has a green EGC, MC-ap has a #10 aluminum conductor in contact with the armor to create the EGC. MC comes in many different styles, steel, lightweight, aluminum, etc.

 

[ramsy]

AC is armored cable made with paper individually wrapping the conductors and a thin aluminum bonding strip

320.80(A) also limits AC cable to 60°C, except for derating purposes, just like NM, UF, SE, Fire Alarm, & low-voltage structured wiring.

 

[tom baker]

No redhead is needed for MC. Is smart MC or MC-AP available? It has a bonding conductor but no EGC, so makeup at boxes is faster, strap every 6 ft instead of 4 1/2 for AC.

 

[infinity]

Is smart MC available? It has a bonding strip like AC and EGC

Yup, it's called MC-ap, Metal Clad-all purpose.

 

[darekelec]

320.80(A) also limits AC cable to 60°C, except for derating purposes, just like NM, UF, SE, Fire Alarm, & low-voltage structured wiring.

Does it mean I can use max 40 amp breaker using 8awg AC cable but I can use 50 amp breaker if I use thhn in emt?

I thought I can use 75 deg column all day

 

[ramsy]

Does it mean I can use max 40 amp breaker using 8awg AC cable but I can use 50 amp breaker if I use thhn in emt?

I thought I can use 75 deg column all day

See 320.80(A) for AC cable limited to 60C
See 330.80 for MC cable, limited by temperature ratings of terminations and equipment.

 

[darekelec]

I will take that as a Yes

 

[fastline]

See 320.80(A) for AC cable limited to 60C
See 330.80 for MC cable, limited by temperature ratings of terminations and equipment.

I can look in codes, but it won't explain the 'why'.... Is AC cable typically used in residential, thus they want it reg'd down like NM or the limited ampacity of branches? Seems odd.

All in all, trying to examine a cable that is listed to use the armor as ground. I think we typically end up buying what the supply house stocks, and never really ventured out to see what all was possible until a very seasoned sparky dropped off some MC with the 0-10V in it for LED dimming. I had never otherwise see it.

On the smart MC, no, I have never seen a bare Al in the stack, but I am curious how this changes anything? Still another conductor to connect. Or is it just cheaper, using bare Al for one conductor?

 

[tom baker]

On the smart MC, no, I have never seen a bare Al in the stack, but I am curious how this changes anything? Still another conductor to connect. Or is it just cheaper, using bare Al for one conductor?

Smart or AP MC has a bare Al conductor that shorts out the spirals(much like ac) but Al conductor is cut off at the connector

So the smart MC
-No redhead needed
- no egc to terminate
- strap every 6 ft vs 4 1/2
-30% less labor
It’s a newer product, in someways it’s made by southwire vs AC made by AFC. Add an insulated green egc and then it’s good for health care and IG apps

 

[ramsy]

I can look in codes, but it won't explain the 'why'....

See post #2 - maybe a listing limit

Is AC cable typically used in residential

Not to my knowledge

we typically end up buying what the supply house stock..

Roger that, everyone is a supplier now, and also does DIY remodels on the side.

They see you coming, sell old MCCB’s as reconditioned, resell Amazon stock with no NRTL, FCC, or Nameplate, and most contractors love it.

 

[electrofelon]

. BX is a slang name for AC.

This could be a regional thing, but I think of BX as referring to a cable, typically old and existing, that has no wire EGC and no bonding strip. What was it called in the NEC at the time? Maybe it was AC and the bonding strip wasn't required then?

 

[infinity]

This could be a regional thing, but I think of BX as referring to a cable, typically old and existing, that has no wire EGC and no bonding strip. What was it called in the NEC at the time? Maybe it was AC and the bonding strip wasn't required then?

Could be regional but around here BX with or without the bonding strip is called BX. Not many places use AC anymore around here.

 

[electrofelon]

As well, I will admit that every time I use MC, I cuss like mad because the stupid bushings and connectors do not protect the conductors worth a damn so extreme caution is needed. Does anyone make good and proper MC bushings that actually do something?

Could you elaborate more on this? Are you seeing the insulation damaged frequently? Where exactly? What kind of connectors? I typically use arlingtin 38AST's for connectors and I do use red heads. I recommend Klein 1104's for cutting the armor as they do a much nicer job than regular dykes.

 

[garbo]

At a class we were told that AC ( BX ) has a larger ( Heavier guage ) jacket then MC cable. Could never understand how they used a flimsy aluminum wire in direct contact with a steel jacket on AC cable. Was taught to avoid have dissimilar metals in contact with one another. We would double up on the small anti short bushings that came with rolls of armored cable. ( ones that did not do a full wrap around conductors ). In my area for at least the last 40 years AC cable is not allowed in non residential buildings so have to use far superior MC cable. Wish they stopped making AC cable. When I had my natural gas furnace replaced I replaced the old AC cable with MC. Was told the term BX came from :B was the second trial run and X was for experimental. That & $2 will get you a cheap coffee.

 

[infinity]

Homes built around here mid-20th century used BX (Type AC). When NM cable became more popular BX was considered an upgrade to NM cable due to it's steel armor and was used in many higher end homes. Much of it is still in service today. The old versions of AC had rubber insulated conductors and they were subject to failure mostly in ceiling light outlets due to the heat from incandescent lighting. Eventually the rubber conductors were replaced by type TW thermoplastic.

 

[kwired]

At a class we were told that AC ( BX ) has a larger ( Heavier guage ) jacket then MC cable. Could never understand how they used a flimsy aluminum wire in direct contact with a steel jacket on AC cable. Was taught to avoid have dissimilar metals in contact with one another. We would double up on the small anti short bushings that came with rolls of armored cable. ( ones that did not do a full wrap around conductors ). In my area for at least the last 40 years AC cable is not allowed in non residential buildings so have to use far superior MC cable. Wish they stopped making AC cable. When I had my natural gas furnace replaced I replaced the old AC cable with MC. Was told the term BX came from :B was the second trial run and X was for experimental. That & $2 will get you a cheap coffee.

Early versions did not have the bonding wire in them. At some point they figured out this leaves a compromised return path and added the bonding wire. The BX term possibly went away (by manufacturers labeling) but some call any metal sheathed cable BX to this day.

 

[electrofelon]

I Actually hate MC and dont understand why it is so popular. I would love to not have to terminate all these stupid wire EGC's - what a waste of materials and labor. MC-AP does that, just not sure why that stuff is not as universal as MC, seems like a no brainer to me. But the green wire cult is very very strong.

 

[infinity]

MC-AP does that, just not sure why that stuff is not as universal as MC, seems like a no brainer to me. But the green wire cult is very very strong.

You've hit the nail on the head. MC-ap is a good compromise between heavy steel jacketed AC and MC with the green EGC but those who believe in the only good EGC is a wire type are hard to convince otherwise. Given the choice between the three types mentioned I would choose MC-ap every time. Lighter jacket, no EGC's to terminate, easy to strip, etc.

 

[Eddie702]

BX or AC cable (same thing) the older stuff before around 1959 did not have the aluminum strip. Around here some old timers referred to it as "Rat proof Romex" When they switched from 2 wire receptacles to 3 wire receptacles around that time a better ground was required and NM was required to have a ground and AC was required to have the aluminum strip