When terminating #14 or #12 stranded copper wire to a device, is it acceptable to merely wrap the strands around the terminal screw? How about the use of Sta-Kons?
We've all back twisted the strands of the wire and wrapped the wire around the terminal screw, and we've all used Sta-Kons, but are these methods really approved? Even though I've used these methods for years, both seem a little hokey to me. Many devices do not have the room for the Sta-Kons, and can break easily when the terminal is tightened, and the back twisting method seems like it could very easily let go.
Some devices seem to be designed for stranded wire. The ones with the internal clamp behind the terminal screws. This seems like the only really good method of terminating stranded wire to a device.
Matt, The UL white book say that "terminals of the wire-binding screw, setscrew, or screw actuated back wired clamping types are suitable for use with both solid and stranded building wires". This is under the "receptacles for attachment plugs" listing. It gives no directions as to how the termination should be made. I prefer to use the back-clamp type of receptacle when using stranded wire, but these are usually somewhat more expensive. Don(resqcapt19)
#3137 - 08/07/0101:54 PMRe: Stranded wire on devices?
So I take that to mean that it is OK to wrap the stranded wire around the terminal screws. With all the other small details required by the NEC, you'd think that this type of termination wouldn't be allowed.
[This message has been edited by Matt M (edited 08-07-2001).]
#3138 - 08/07/0109:03 PMRe: Stranded wire on devices?
I strip an additional small piece of insulation to leave at the end to keep things tidy... then I twist the wire clockwise to tighten the wrap, bend a U while twisting clockwise, place it over the screw while taught, and hold it there until the set-screw grabs it tight.
Works perfectly every time!
Occasionally I'll use these Ideal brand terminals that look like a little blue wire nut with a forked terminal on the end. Much easier to install, and 10 cents cheaper than sta-cons. I always use these for the EGC bond to the ground screw when dealing with stranded wire.
[This message has been edited by sparky66wv (edited 08-07-2001).]
-Virgil Residential/Commercial Inspector 5 Star Inspections Member IAEI
#3139 - 08/07/0109:18 PMRe: Stranded wire on devices?
I do like sparky66wv does. Most of the electricians at the facility leave the insulation on the end of the wire. If I have room I usually use the fork terminal, seems to handle vibrations better when the receptacle is mounted on a punch press or air ram press.
#3140 - 08/10/0111:24 AMRe: Stranded wire on devices?
I've done it like Redsy for years, and it actually does do a good job of keeping the strands from fraying, but none of these methods seem like they are positive. I've always used extra care when pushing the device back into the box so that the wire doesn't slip out.
If you hold the device in one hand, and then wiggle and tug on the wire with the other hand, it won't take long before the stranded wire worms its way out from under the screw. You could tug and wiggle all day on a solid wire under a binding screw or a stranded wire on a device with an internal clamp, and it will not work loose.
1. Twisting the strands: It seems that twisting the strands other than their manufactured lay could be a problem, not so much with the NEC but in industrial manufacturing. I've been told it violates IPC (electronic/electrical quality) and UL but I can't find it.
2. Sta-cons and other crimp lugs: These cannot be used on devices that are not specifically listed for lugs, forked, ring, or single. The white book says that switches can use lugs but that outlets cannot (unless so identified by the manufacturer). Problems that can occur are uneven loading and bending of the screw head (single lugs), spreading of the fork under pressure, and terminal screw must be removed to install a ring.
The "White Book" has a few problems. First off, it's not 'law;' it's just a handy reference.
More important, UL will usually say something has "not been evaluated for ..." This does NOT mean such a use is banned - it's only UL's way of saying 'we don't know.'
Likewise, devices are evaluated for only ONE 'pass through." I've seen receptacles with a wire landed under every screw - another situation 'not evaluated for.'
Devices ARE tested with stranded wire - the 'normal' stranded, that is. If one of UL's drones can make a good connection, there's no reason you and I cannot.
It's true that various crimp connectors will not fit onto receptacle screws without some trimming. That's a problem, from a 'listing' angle. There's also a problem fitting the attached lugs into boxes, without bending the dickens out of them.
All told, the 'wire wrapped around the screw' way of landing the wires is a poor one, and I'd much rather have pressure plates. For that matter, I'd much prefer that solid wire be used.