- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I learn something new every day. Thank you-- I'll still wire it without the EMF's.
Dennis Alwon said:I learn something new every day. Thank you-- I'll still wire it without the EMF's.
"1/0 and larger"?georgestolz said:Al, remember that the travelling bus threeway does constitute a 310.4 violation.
georgestolz said:When the light is extinguished by flipping both threeways to the "common-to-hot" position, then the receptacle in the detached building (I'm thinking of the full schematic, with receptacles included) is supplied by two hot conductors.
They are smaller than 1/0, probably not the same length, and might not even be terminated in the same manner.
al hildenbrand said:Therefore, referencing my circuit sketch above, the parallel conductors aren't covered by 310.4.
The ring circuit is just another form of the unfamiliarity that one finds in the "travelling bus" 3-way setup in my diagram.iwire said:We could start running British ring circuits. :smile:
To that I would add: "only if metal boxes are used and the cables enter the box through separate knockouts and a notch is not cut between the entries (300.20(B)) and the conductors are not grouped to avoid inductive heating (300.20(A))."stickboy1375 said:I was thinking of a violation of 300.20 but only if metal boxes are used and the cables enter the box through separate knockouts.
The continued service of all of the oldest K&T metal boxes on 15 and 20 Amp circuits, to me, is prima facie evidence that, even though the K&T single conductors enter separate holes in ferrous metal, the conductors are "grouped together" "to avoid heating the surrounding metal by induction."300.20 Induced Currents in Metal Enclosures or Metal Raceways
(A) Conductors Grouped Together Where conductors carrying alternating current are installed in metal enclosures or metal raceways, they shall be arranged so as to avoid heating the surrounding metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
Look at 300.20(B). The wires are required to enter through a common hole or have slots cut between the holes. As a practical matter, the heating is not a problem at the current level that would exist in K&T wiring systems. I have been told that the Canadian code does not require slots unless the current is in excess of 200 amps.The continued service of all of the oldest K&T metal boxes on 15 and 20 Amp circuits, to me, is prima facie evidence that, even though the K&T single conductors enter separate holes in ferrous metal, the conductors are "grouped together" "to avoid heating the surrounding metal by induction."
:smile: Interesting.don_resqcapt19 said:I have been told that the Canadian code does not require slots unless the current is in excess of 200 amps.