Electric Cooktop 3-Wire Connection

[jap]

The existing circuit is 2 ungrounded conductors and 1 grounded conductor connected to a 120/240V system panelboard. This is a 120/240v, single phase, 3 wire circuit any way you look at it (2 ungrounded conductors would be a 240v, single phase, 2 wire circuit...1 ungrounded conductor and 1 grounded conductor would be a 120v, single phase, 2 wire circuit.)

Whether or not there is current being carried on the third wire is not one of the conditions set forth in 250.140.

Current being carried on the third wire is not one of the conditions, but, The 1st Condition of 250.140 to be
able to ground the frame to the grounded conductor specifically states the supply circuit is to be 120/240v
Single Phase,(Meaning a Neutral is envolved) it does not however mention 240v Single phase (Meaning a
Neutral is not envolved).

If you were dealing with a 240v Single phase installation, whats the need of even looking at 250.140
for grounding to the grounded conductor?

On another note, to me, by the way exception #3 of 250.140 is worded, if the grounded conductor (Neutral) in the branch circuit was insulated you could use it to ground the range or clothes dryer if all the other
conditions were met regardless of wether it came from the service panel or sub panel.

To me,by the way its worded you could also use the uninsulated conductor to ground the frame if Type
SE cable was used for the circuit to the Range or Dryer coming directly from the Service Panel.

 

[kwired]

When SE was used for a 3 wire feed the neutral could be bare, if I used NM for the circuit the neutral would have to be insulated.

This meant when I would run a 3 wire dryer circuit I would actully have to use a 4 wire NM and leave the bare EGC unused.

Back then it was common to find 3 wire cable with no grounding conductor. Now there is hardly a need for it and you don't find it anymore.