3 way switches

[Jpflex]

230608-1434 EDT

I do not understand what most of you have been saying.

Don't use the words hot, neutral, and .EGC.

A 3-way circuit consists of a power source, a wire from the power source to a first switch, next two wires to a second switch, a single wire to the load, and a return wire to the power source.

The important point is that this circuit needs the return path for any conductor to have in close proximity a conductor that carries the same current in return to provide a counteracting magnetic field to the forward current's field.

...

You mean circuits need to be in close proximity for low impedance for EGC and EMT for ground fault return path

 

[Jpflex]

My understanding is that standard screw terminals are listed for both solid and normal stranded wire. (But this is from memory, so take with a grain of salt.)

There is a trick for using stranded wire on screw terminals. After you strip the wire, twist it in the 'backward' direction before forming the hook and placing on the screw. When you tighten the screw it will tend to _tighten_ the twists of the wire and snug the hook into the terminal, rather than loosening the twists and making sort of a bird's nest.

Another trick is to strip the wire in such a way as to leave a bit of insulation right on the tip of the wire, forming a little ring that holds the strands together.

-Jon

Great advice as this has been a problem I encountered with stranded wire

 

[Jpflex]

My understanding is that standard screw terminals are listed for both solid and normal stranded wire. (But this is from memory, so take with a grain of salt.)

There is a trick for using stranded wire on screw terminals. After you strip the wire, twist it in the 'backward' direction before forming the hook and placing on the screw. When you tighten the screw it will tend to _tighten_ the twists of the wire and snug the hook into the terminal, rather than loosening the twists and making sort of a bird's nest.

Another trick is to strip the wire in such a way as to leave a bit of insulation right on the tip of the wire, forming a little ring that holds the strands together.

-Jon

Great advice as this has been a problem I encountered with

Another way to do this is to leave extra length in the bare wire after the point where you start to strip it, then leaving the cut insulation entirely on the extra length of wire, not just a small ring. Once the wire has been wound around and been held by the screw you can cut off the excess wire with the cut off insulation still attached.

I came across a code that wires serving no other purpose must be bonded to box. Therefore if white wire for future neutral ran with other circuits is not connected to anything then wouldn’t current code require it to be bonded to metal box?

I don’t have specific code but I could lol for it

 

[Jpflex]

Look for it but not “lol” phone likes to change typing

 

[Little Bill]

No such rule that I'm aware of.
If the neutral was ran for the rule to have the grounded (neutral) present at the box, it would be a "live" neutral because it has to serve the lighting load. Connecting that to a metal box would put voltage on the metal box and violate having the EGC and neutral bonded past the service. Also, how would you bond to the box if the box was plastic?

 

[Jpflex]

No such rule that I'm aware of.
If the neutral was ran for the rule to have the grounded (neutral) present at the box, it would be a "live" neutral because it has to serve the lighting load. Connecting that to a metal box would put voltage on the metal box and violate having the EGC and neutral bonded past the service. Also, how would you bond to the box if the box was plastic?

This is a metal box with metal EMT, the white wire in second box does not have to be connected to neutral for circuit to work. However code seems to show that all free conductors serving no other purpose must be bonded to box

 

[ActionDave]

..... However code seems to show that all free conductors serving no other purpose must be bonded to box

That makes no sense. There is no code that says that and nothing that would even suggest that in any official publication.

 

[don_resqcapt19]

230608-1434 EDT

I do not understand what most of you have been saying.

Don't use the words hot, neutral, and .EGC.

A 3-way circuit consists of a power source, a wire from the power source to a first switch, next two wires to a second switch, a single wire to the load, and a return wire to the power source.

The important point is that this circuit needs the return path for any conductor to have in close proximity a conductor that carries the same current in return to provide a counteracting magnetic field to the forward current's field.

...

This is a code rule discussion and the only terms that apply are they ones used and defined in the NEC.

 

[Little Bill]

This is a metal box with metal EMT, the white wire in second box does not have to be connected to neutral for circuit to work. However code seems to show that all free conductors serving no other purpose must be bonded to box

You keep saying "code says", please show us the code you are referring to! I'm very sure you won't find such a code.

 

[letgomywago]

This is a code rule discussion and the only terms that apply are they ones used and defined in the NEC.

And you can have spare hots or nuetrals that need capped or equipment grounds that need bonded.

 

[jmellc]

I don’t like using stranded but that’s all we had for ground wire

Also I was not aware devices had to be listed for stranded

Wire insulation is not under screws

Stranded is not supposed to be terminated under screw heads.

 

[letgomywago]

Stranded is not supposed to be terminated under screw heads.

Just going to throw this out there. Where I'm the receptacle and device termination instructions does it say solid only. Often you'll find no distinction so then it comes down to specs or professional opinion.

 

[jmellc]

Just going to throw this out there. Where I'm the receptacle and device termination instructions does it say solid only. Often you'll find no distinction so then it comes down to specs or professional opinion.

I think it’s code, though I can’t quote chapter & verse. I think too, I’ve seen a few pieces of equipment that spec’d solid wire for similar terminals.
Some devices have the clamp on the side that handles stranded. I like them.

 

[letgomywago]

I think it’s code, though I can’t quote chapter & verse. I think too, I’ve seen a few pieces of equipment that spec’d solid wire for similar terminals.
Some devices have the clamp on the side that handles stranded. I like them.

Look for it and look in the instructions for multiple brands and have your mind blown.

 

[jmellc]

Great advice as this has been a problem I encountered with stranded wire

I know a guy who does that sort of OK but I use a solid jumper.

 

[ActionDave]

I think it’s code, ......

Nope. It's in the UL white book and all listed devices are tested to work with solid and stranded.

 

[gar]

230610-2345 EDT

don_resqcapt19:

I am trying to describe the problem from a basic electrical circuit theory perspective. Thus, my choice of words. One needs to understand the basic circuit theory in order to understand how something works.

A single long straight wire with current flow in the wire produces a magnetic field around that wire where the field intensity drops off as K * 1/"radial distance from the wire". Real close to the wire this is somewhat inaccurate because the wire is not of zero diameter.

Take any combination of different wires in a single bundle carrying current in the one direction, and you can consider this as one wire carrying the total current.

Add a second current carrying path with the same current, but the current flows in the opposite direction. Now we have a second magnetic field of the same intensity vs radius. But now the magnetic field is of opposite polarity.

Place these two wires directly adjacent to each other. Now as you radially move away from this wire pair the two magnetic fields come very close to canceling each other.

This is what you need to do to reduce magnetic interference with other systems. What you call the wires, and whether any are earthed or not does not matter. What matters is that the wire pair be in close proximity to each other, and carry equal but opposite currents.

.

 

[winnie]

@gar the issue being discussed here is not current balance in the cables.

Yes, the current balance you describe is important for reducing stray magnetic fields, and is usually required by code.

Current will be balanced in a properly wired switch loop, even without the grounded conductor present.

Code requires the grounded conductor be brought to the switch location for possible future use.

This unnecessary at the present time grounded conductor is the focus of this part of the discussion.

Jon

 

[roger]

Gar, as Jon points out the discussion is about bringing a neutral to the switch location for electronic devices, could be an occupancy sensor or lighted switch. As stated earlier, in the past it was common for an installer to just finish the circuit with the EGC, the code rule is trying to eliminate that from being the case going forward.

 

[Jpflex]

@gar the issue being discussed here is not current balance in the cables.

Yes, the current balance you describe is important for reducing stray magnetic fields, and is usually required by code.

Current will be balanced in a properly wired switch loop, even without the grounded conductor present.

Code requires the grounded conductor be brought to the switch location for possible future use.

This unnecessary at the present time grounded conductor is the focus of this part of the discussion.

Jon

I actually didn’t think about neutral having to be at box for low impedance purpose for metal box and EMT EGC.

Thinking of this now, neutral requirements for it to be in box may not be for this purpose since line goes into switch one direction line side and wraps in opposite direction on load side of switch so perhaps magnetic fields cancel in this manner for low impedance from canceling magnetic fields which would otherwise create induced voltages in EMT or EGC through induction and capacitance