AC / BX cable construction

[Grouch1980]

Does anyone have pictures of how the bonding strip wire is connected / welded to the armor of an AC / BX cable, on the inside? This strip wire, together with the armor, serves as the EGC... but I would like to see how they are connected if possible.

 

[LarryFine]

Just physical contact, nothing more.

 

[Grouch1980]

Just physical contact, nothing more.

It's not welded together on the inside?

 

[LarryFine]

It's not welded together on the inside?

Negative. If it was, you'd have to break it when you strip it.

Besides, how would you be able to weld inside the sheath?

 

[hbiss]

It's not welded together on the inside?

No, you would see that when you cut and pull the armor off. The strip stays with the conductors.

-Hal

 

[Grouch1980]

Thank you gents.

 

[infinity]

Basically it just shunts each part of the wound circular jacket in a straight line. It doesn't even need to be continuous to perform its function. If the bonding strip were broken inside the cable it would still work. That's one of the reasons why you can just cut it off at the terminations and not connect it to anything.

 

[Grouch1980]

If the bonding strip is broken somewhere along the middle of the run, wouldn't that compromise the EGC as a whole though? if the strip breaks, now you're only depending on the sheath in the area that the strip broke.

 

[infinity]

If the bonding strip is broken somewhere along the middle of the run, wouldn't that compromise the EGC as a whole though? if the strip breaks, now you're only depending on the sheath in the area that the strip broke.

The bonding strip is just shorting across each of the wound interlocking metal armor. It is not carrying all of the fault current. It just keeps the armor from becoming an inductor when a high current is applied so if the bonding strip is broken at some point the current will follow along the armor to other other side of the break.

 

[Grouch1980]

It is not carrying all of the fault current. It just keeps the armor from becoming an inductor when a high current is applied

Nice.

 

[Grouch1980]

The bonding strip is just shorting across each of the wound interlocking metal armor. It is not carrying all of the fault current. It just keeps the armor from becoming an inductor when a high current is applied so if the bonding strip is broken at some point the current will follow along the armor to other other side of the break.

What happens in MC cable? I'm assuming most of the ground fault current will flow in the green insulated grounding wire. When some of the ground fault current flows through the armor, wouldn't you still get the inductor effect across the armor?

 

[infinity]

What happens in MC cable? I'm assuming most of the ground fault current will flow in the green insulated grounding wire. When some of the ground fault current flows through the armor, wouldn't you still get the inductor effect across the armor?

A majority of the current should flow on the green conductor. With MC-ap there is a bare solid #10 aluminum conductor used to short the wound jacket similar to the bonding strip in AC.

 

[kwired]

The bonding strip is just shorting across each of the wound interlocking metal armor. It is not carrying all of the fault current. It just keeps the armor from becoming an inductor when a high current is applied so if the bonding strip is broken at some point the current will follow along the armor to other other side of the break.

Does it become an inductor though? Particularly if it is aluminum armor?

If anything consider the length of the spiraled armor if you straightened it out and what it's resistance would be over that length, the bonding strip shorts across the turns making the path less resistance, if it should miss contact with one here and there it still is pretty effective across the entire length of the run.

Solid sheath instead of spiral sheath wouldn't need the bonding strip

 

[hbiss]

Does it become an inductor though? Particularly if it is aluminum armor?

I don't think we should be thinking of the armor as inductive at all, it's minimally so. It's the resistance of the armor, particularly when the contact between wraps becomes compromised due to corrosion and oxidation over time. That's the reason for the shorting strip under the armor with AC cable. The #10 bare conductor under the armor with MCAP cable is the EGC and any contribution to the conductivity of the armor is secondary.

And I'll say it again, the armor of all MC cable is NOT meant to be or be part of the EGC. It only needs to be bonded to the EGC for safety purposes. So, whether it's inductive or resistive is irrelevant.

-Hal

 

[kwired]

I don't think we should be thinking of the armor as inductive at all, it's minimally so. It's the resistance of the armor, particularly when the contact between wraps becomes compromised due to corrosion and oxidation over time. That's the reason for the shorting strip under the armor with AC cable. The #10 bare conductor under the armor with MCAP cable is the EGC and any contribution to the conductivity of the armor is secondary.

And I'll say it again, the armor of all MC cable is NOT meant to be or be part of the EGC. It only needs to be bonded to the EGC for safety purposes. So, whether it's inductive or resistive is irrelevant.

-Hal

That was mostly my thoughts. If no ferrous material is involved inductance is going to be pretty negligible here I would think.