I've always been leery of the type that uses a set screw to bite down on the armor. I saw three different types today at Lowes.
One was a type that uses metal straps held in place with two screws at opposite ends. Another type is a sort of compression fitting. A third has a saddle (a piece of metal inside the connector body) that clamps down on the armor.
Each of these seem like they avoid damaging the armor. I've always been leery of having the set screw pierce or crush the armor, yet I want to have a good reliable ground connection.
Those old set screw connectors are only good for steel type AC. Nowadays you are likely to run into type MC as well as aluminum armored type AC. To save alot of confusion I only buy connectors listed for all three types, check the box. I'm not familiar with the compression type you saw but the other two sound good.
yet I want to have a good reliable ground connection.
Most modern BX has a bare wire runner just inside the armor and outside the paper wrapping covering the white and black wires. As I understand it you're supposed to take this bare wire and bend it over the antishort you just stuck in so it doesn't fall out, and then wrap the bare wire back around the outside of the armor so it lays in the groove between adjacent wraps of the armor. Then fit the connector over that and clamp it so the litle indents in the clamp clamp that bare wire. That you're not supposed to have any of this bare BX wire inside junction boxes, unlike romex. The metal box is then your ground connection.
Some BX has aluminium armor sheathing, and it says not to use set screw connectors with it.
Why is it that there is no problem with this aluminium armor BX cable with copper wire inside, but aluminium romex wiring caused lots of trouble? The ground has to be able to take a fault current.
#34532 - 02/15/0409:57 PMRe: What connector do you prefer for BX cable?
heres my theory regarding the aluminum. The main problem with the aluminum is that a very small amount of corrosion increases the resistence slightly. the actually corrosion doesn't cause that much of a problem. However, the heat causes expansion and contraction of the joint. after a while this loosens the connection. thats when the real problems start. In the case of aluminum BX, since there is not normally current flowing in it, the juntions don't experience the heating and cooling that loosens the connections in the current carrying conductors. therefore, even if there is some corrosion, there is still a sufficient ground to trip a breaker in the even of a ground fault.
It's just like steel conduit. it's used for a ground, but when was the last time you saw a steel conductor? (yes, i know some people on here actually have seen them)
[This message has been edited by cpalm1 (edited 02-16-2004).]
#34534 - 02/16/0408:31 PMRe: What connector do you prefer for BX cable?
The compression connector is a sort of sleeve with a screw on the side. When you tighten the screw the sleeve tightens around the armor.
Yup, I think I know what you are talking about. It's not really a compression connector but just another type of clamp. They have actually been around probably longer than the set screw connector. I kind of like them myself when I can find them. They grab the armor real well.