Every once in a while, I drag out my soap box and get long winded. Here we go:
When I first entered the trade in the late 1970s, I was fresh out of high school, in fact I even worked for an EC after school learning my way around. I always had an interest in the trade, so I didn't have a hard time getting my job. I already knew a lot for a kid.
My first days were in northern NJ. My boss seemed to capitalize upon the use of the allowance of the shared neutral and EGC being permissible for these appliances. I knew that it was more of an allowance when using type SEU cable for these applications, however he also allowed us to use 10/2 or 6/2 Romex or even BX (type AC) to accomplish this. We would just run a jumper between the base of the box or receptacle to accomplish what should have been a "neutral". Since he was in cahoots with the local inspectors as they shared "a coffee-dark and a buttered roll" regularly, I suspect that much of the work that we did was wrong. Who was I to question them, right?
To move along, I moved to northern Virginia a few years later and engaged in more new construction. It didn't take long to realize what we had been doing in NJ wasn't permissible down south. The problem is that it became even more confusing for a rookie.
The norm in Virginia was to run 6/3 SEU (AL) for ranges, but that was just fine. It was perfectly acceptable. The problem was with dryer circuits. It was standard to run 8/3 SEU (AL) for dryers.
Again, no big deal, except that the standard practice here was to put the dryer on a 40 amp breaker and place a 50 amp receptacle for it. This meant that there was always the confusion factor as to whether the dryer needed a 30- or 50-amp pigtail. It was a huge PITA for people moving into homes having to deal with the type of receptacle that they had in place. I suspect that since we had so many national builders here, they were trying to up-sell their homes by having a "bigger/better" dryer circuit than their competition. I have no clue as to the real reason.
Over time, the local norm has converted to the 3P4W 30 amp circuit for dryers. I am sure that this had a lot to do with NEC 1993.
Now that I've told you how to build the watch after you asked me to tell you the time of day:
I have come to expect that an electric range goes on a 50 amp circuit and a dryer is on a 30 amp one. That's the way I always thought that it should be. I live in a fairly-newly constructed home now where the range is once again on an unconventional circuit. It is wired with 8/3 Romex and on a 40 amp breaker. Full-sized range, no compact model by any stretch of the imagination.
I've also seen 40 amp circuits for ranges as being the "semi-norm" in North Carolina forever.
I know that local trends seem to last forever, but am I wrong for questioning these practices? I know that what went on 35 years ago would be best just brushed under the rug, but why does such inconsistency still consist with these circuits? They seem to be a no brainer to me.
Well, for starters, I've never seen a range that was left on -- continuously -- for three hours.
So, to my mind it's an intermittent load.
With a 40A breaker, it would seem that the worst that could happen would be a popped breaker.
Electric ovens are very intermittent -- unless it's the owner's habit to leave the door down. Normally they come to full cooking temperature in less that 30 minutes. From that point onward, the system cycles on and off to hold the temperature within standards. If this control function fails -- the baking will be lousy.
You're right, Tesla. I guess that my post was more of a rant about inconsistencies in this area more than anything. Something so seemingly simple appears to be so complicated in this region. It stemmed from a disagreement that I had with a friendly competitor on this subject yesterday.
I doubt there is inconsistency in the code, only how some people read it. In the pre96 code the conductor in question was clearly identified as a neutral that was also being used as a ground and neutral conductors must be insulated with white or natural gray color insulation. This made the point somewhat moot since finding a cable with 3 insulated conductors and no ground was hard to do after the 60s so they usually brought a grounding conductor to the box anyway. (10/3-wg) Best practice was seen to be, to ground the box and bring the white wire out to the receptacle. They still ended up using the 3 prong receptacle so they regrounded the neutral via the bonding strap. To be strictly legal, you had to cut off the ground in the cable.
A bit of history here: the oldest electric ranges tended to have embedded clocks -- typically with timers.
These used synchronous motors, gears, and such -- a design which can still be found at the lowest end of the clock world.
These were 120VAC devices that returned a feeble current. Later, they came with integral back-lit faces and tiny lamps.
So, you can see that at the start, the neutral/ return load was considered utterly trivial -- and not any kind of safety issue -- hence the Code treatment and three wire solution.
The same occurred with electric ovens, too.
Combined ranges and ovens lifted the peak demand to 50A 240VAC.
But then a strange thing happened. Manufacturers started putting integral 120VAC receptacles into ranges. This was so that cooks could use all of the new after-market appliances -- particularly the ones with fine temperature control.
(Like electric frying pans; which could be tuned up and down the temperature range with a dial embedded within the handle assembly.)
The Code committee woke up: return currents were now getting huge. It was too late to ban integral receptacles -- besides, the NEC doesn't operate that way.
It became clear that an isolated neutral return had to be mandated. Because these appliances have such long lives -- and the house wiring even longer -- it is taking decades to re-wire America.
As long as the return current was a joke, the three wire scheme worked fine. Main conductor faults would trip the breaker. The old clock designs didn't have a conductive path in normal operation. (plastic knobs and such)
Now that we have both embedded receptacles AND/OR digital electronics (with an associated switching power supply) it just won't do. Now an open return would expose the public to even lethal amperages.
(BTW, those embedded receptacles preceded GFCI technology. They were 'big' during the fifties and sixties - particularly where the Poco had really low rates.)
I think that 120V range receptacles ended in the 1970's, I have not seen them on any newer ranges in years, my 1965 Frigidaire Flair range had one w/ a 15A Edison fuse to protect it, it was donated to the Local Habitat for Humanity ReStore & sold within an hour of me dropping it off. If you do not know what one looks like, watch old episodes of "Bewitched" all chrome & glass 'cause GM had product placement.
Without a GFCI being installed I doubt UL or other NRTL would list the appliance w/ a receptacle on the range these days.....