The oldest code book I own is the 1990 NEC here is the wording from the section at the time.
I will do my best to copy it perfectly.
In my opinion it is very clear that they list two allowed wiring methods but either one used must originate from the service panel.
The semi colon IMO splits it into 2 separate parts. Id guess 2 parts exists since the only time the NEC allows for a bare current carrying conductor is SEU cable, however SEU can break neutral to ground isolation in a sub hence for disallowing it. An insulated wouldn't matter in that stance.
OK, can you explain to me why reading that makes sense from an electrical safety standpoint?
The truth is nothing makes sense with the whole article in terms of safety. Using the neutral as a ground is a poor idea no matter its origin. Its the boot leg equivalent of grounding a major split phase appliance. Canada if Im not mistaken never had this problem, they have always required 4 wires.
To which I counter that I do not see any particular reason why running an insulated neutral from a subpanel is any worse than running it from the main.
The additional voltage drop (and hence neutral ground offset) from the feeder wire length may not be any worse than the VD from running the SE all the way back to the main.
Tapatalk!
Id agree with that. If it couldn't reach a local sub panel near by the builder would just run it to the main.
It's such a shame that one needs to be an English major with a law degree to decipher parts of the code.
I agree with you on that
May not ... very likely could be.
I am willing to read it the other way if someone could explain why the concern of a difference of potential is greater when the conductors are buried in a wall or a box .... is greater than where a person actually comes into contact with the items?
It is my belief that goal is to keep the grounded conductor as close to ground potential as possible by mandating it go back to the bonding point.
The code doesn't state anywhere the neutral must be kept as close to ground potential as possible. However, when its also doing duty as a ground, from a safety standpoint it is a better choice.
But, the voltage rise from a sub panel might actually end up being less in most scenarios (most but not all). Think of condo with a second floor subpanel and laundry or a restaurant with a sub-panel in the kitchen and a main else where. Option one is just run the load from the sub panel fed via say a #2 AL for the sub in the condo or a 3/0cu for the restaurant. The sub is 20 feet away. The main is 150ft away. The other option is run 10/3 200 ft to the main. A single #10 carrying 6 amps 180 to 200 feet will have more voltage drop than say #10 only traveling 20 feet then going to a #2AL or 3/0cu. The #2 AL will of course also be carrying imbalance from 120 volt loads, but unless we are talking over 60 amps worth over the typical 10 or 15, the voltage rise will actually be less when compared to ground. In this case relative to the washer. (Think of sub panels being used to limit voltage drop) So in theory if one took a voltage meter to a fully isolated (not in contact with anything grounded) running dryer the frame would read a higher voltage to the washer with the 200ft run back to the main as appose to the dryer being fed via sub panel. This problem could be theoretically verified via voltage drop calculations.
In both cases we are talking only about a few volts potential on the dryer frame at most. The real driver however for the codes reason from 3 wire to 4 wire comes from energized frames stemming from compromised neutral connections. An open connection can easily put 120 volts on the frame of the dryer. Not fun when transferring laundry between a grounded washer with damp hands and the dryer's drum light is making its frame perky
