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  #1   IP: 147.126.101.136
Old February 14th, 2003, 12:40 PM
Anonymous Anonymous is offline
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Default solid vs stranded wire - also grounding conductor connection

As always, thanks for your forum. Here are a few items I have not seen addressed as I look through the archives, nor in books I've picked up.

Are there restrictions on using solid vs stranded wire (or both together) for branch circuit wiring (12 or 14 ga 20 or 15A circuits)?

Particularly,

Is it ok to mix solid and stranded wire in "wire nut" connections? The boxes connectors come in usually state the acceptable gauges and numbers of conductors but have nothing about solid/stranded.

Is it ok to put a stranded wire on a screw terminal (e.g. on a receptacle) which would normally take solid wire, if the stranded wire is first tinned? The alternative would be to put a solid pigtail on the stranded wire (with a wire-nut) and connect the solid to the screw.

Are there some types of terminals which should not have stranded wire attached - in my service panel is a neutral bus bar where the neutral wire is inserted through a hole and compressed with a screw. It looks like a stranded wire could fan out and not stay tight in place under the screw - is this a concern? Service panel mfrs web info did not address this.

Regarding the use of separate grounding conductors (green or bare), I assume that a receptacle, fixture, etc. should always be grounded to a box with some kind of pigtail (so grounding continuity does not depend on the mounting screws). But if wiring to the box is run in metal raceway (EMT or flexible "fixture whip"), is that sufficient to complete the ground to the box (in dry or possibly damp locations, not wet)? Do I ever need to run a separate green grounding conductor through the entire raceway from the service panel or other ground point? Would this be recommendable under some conditions?

Finally, when connecting a green or bare grounding conductor to a box by means of a green tapped screw, should this connection be made with a crimp lug or something which would prevent the wire from moving out from under the screw head? This could happen easier with stranded wire. Unlike most screw terminals on receptacles, busbars, etc, there is nothing inside a typical junction box to corral the wire into place under a ground screw.

These questions are partly motivated by my trying to upgrade and standardize wiring in my old house where original wiring seems ok but I have found numerous loose/uncertain "repaired" connections which seem likely to promote arc faults.

thanks again,
kginsbu
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  #2   IP: 148.78.243.121
Old February 14th, 2003, 02:32 PM
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Wgoodrich Wgoodrich is offline
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Default

Is it ok to mix solid and stranded wire in "wire nut" connections? The boxes connectors come in usually state the acceptable gauges and numbers of conductors but have nothing about solid/stranded.

REPLY;
Solid and stranded is allowed to be mixed in a wire nut. However if you checked UL listing instructions you should find instructions that the stranded wires should lead the solid wires about a 1/4" to ensure the stranded wires make good connections. No tinning or twisting of wires or other preparation is required when installing a wire nut.


Is it ok to put a stranded wire on a screw terminal (e.g. on a receptacle) which would normally take solid wire, if the stranded wire is first tinned? The alternative would be to put a solid pigtail on the stranded wire (with a wire-nut) and connect the solid to the screw.

REPLY;
The NEC requires whether tinned or not to have a UL listed terminal connected to the stranded wire such as a forked spade or a looped spade terminal then connect that terminal to the screw or post.



Are there some types of terminals which should not have stranded wire attached - in my service panel is a neutral bus bar where the neutral wire is inserted through a hole and compressed with a screw. It looks like a stranded wire could fan out and not stay tight in place under the screw - is this a concern? Service panel mfrs web info did not address this.

REPLY;
The holes of a set screw connection such as found on breakers and neutral bars are expecting and is allowed to connect stranded wires without any tinning or twisting or any other concern. These compression connections are listed for both solid or stranded with no other concerns.

Regarding the use of separate grounding conductors (green or bare), I assume that a receptacle, fixture, etc. should always be grounded to a box with some kind of pigtail (so grounding continuity does not depend on the mounting screws). But if wiring to the box is run in metal raceway (EMT or flexible "fixture whip"), is that sufficient to complete the ground to the box (in dry or possibly damp locations, not wet)? Do I ever need to run a separate green grounding conductor through the entire raceway from the service panel or other ground point? Would this be recommendable under some conditions?


REPLY;

All noncurrent carrying metallic parts must be with grounding connections. If you have a grounding conductor in a metal box you may pigtail a grounding wire to the metal box then to the light fixture by way of the metal box, or you may connect two pigtails from that grounding conductor one pigtail grounding the metal box and the second grounding pigtail grounding the light etc. without using the metal box as the grounding path.

When working with a metallic conduit system and that system is complete without breaks then that metallic conduit [not flex or sealtite] may be used as an equipment grounding conductor.

If the box is metal yes that box must be with an approved grounding connection [metal conduit or equipment grounding conductor or both]. If the box is plastic then no grounding of plastic boxes is required it is not a conductor of electricity.

Yes a metal box if with properly connected grounding may be used as a grounding path to provide grounding to a light fixture etc.



Finally, when connecting a green or bare grounding conductor to a box by means of a green tapped screw, should this connection be made with a crimp lug or something which would prevent the wire from moving out from under the screw head? This could happen easier with stranded wire. Unlike most screw terminals on receptacles, busbars, etc, there is nothing inside a typical junction box to corral the wire into place under a ground screw.

REPLY;
A solid wire may wrap around the screw in the direction that the screw tightens. A stranded wire requires a terminal to be installed on that stranded wire in order to connect the terminal to the screw. A stranded wire is not allowed to direct connect to a screw per NEC rules.


These questions are partly motivated by my trying to upgrade and standardize wiring in my old house where original wiring seems ok but I have found numerous loose/uncertain "repaired" connections which seem likely to promote arc faults.

REPLY;
It is better ensure safety than be sorry. Good Luck with your project.

Wg
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