310.4 and switches

[mc5w]

(1)Code Section: 310.4

(2) New text

(3) Proposal:

{Execption #5: Where conductors are paralleled from time to time by relay or switch contacts ( mechanical or solid state ) the conductors shall be permitted to be smaller than 1/0 and to be of different sizes and lengths provided that the smallest conductor is protected against overcurrent as if it were the only conductor.}

(4) Reasoning and substantiation:

A long standing and unwritten exception for paralleling of conductors has been control circuits and 3-way and 4-way switches. Examples are the traveling bus 3-way circuit, override switches, and relay contacts that are connected in the logical OR configuration. Therefore, this exception needs to be formalized.

Deleted Personal Information

[ April 08, 2005, 08:11 AM: Message edited by: rbalex ]

 

[George Stolz]

Re: 310.4 and switches

Michael, your exception is very similar to exception no. 2 of that section. You might be more successful if you revise that exception, rather than attempting a add a new one that says virtually the same thing.

I would delete "from time to time" from the first sentence. It reads clearer without it.

A long standing and unwritten exception for paralleling of conductors has been control circuits and 3-way and 4-way switches.

That's not technically correct, as control circuits are covered under exception 2.

 

[kiloamp7]

Re: 310.4 and switches

310.4 = electrically joined at both ends to form a single conductor.

Isn't the logic OR configuration really "contacts" connected in parallel & not really meeting the intention of what NEC is calling parallel conductors ?
Also what am I missing ? In a standard 3-way and or 4-way ckt. what conductors are in parallel?

 

[mc5w]

Re: 310.4 and switches

Look in Practical Electrical Wiring in the section on wiring detached garages. There you will find a 4-wire ( not counting the EGC ) circuit for 3-way switches that has always on power at both ends and in between and power controlled by both switches at both ends and in between.

 

[mc5w]

Re: 310.4 and switches

310.4 exception #2 really only covers control conductors that are permanently connected in parallel to control voltage drop. There really is no rule covering relays and switches.

There is also another problem that when there are say 14 control relays you need redundant neutral conductors arranged in loops and/or networks for reliability purposes. I have had to do this with 2 punch press controls that had the neutral current for the 1/8 HP oil pump going through all 14 relay and motor controller terminals. This eventually created a mess. I rewired it so that if any coil neutral terminal loosened the other relays would still have a good neutral path. This greatly simplified troubleshooting in that a loose neutral terminal would only impair 1 relay.

What would have been a better solution was to use radial neutral wires to a neutral bus next to the control transformer. You can buy neutral bars from SquareD as separate components.