The big issue with 3 wire range and dryer circuits is the rampant mis-understanding about what was allowed, and the variations that were allowed. The requirements were very specific, the 3 wire circuit could be fed with SE (service entrance) cable providing it originates at the service entrance. In this case, using the adapter shown would be no different than an RV outlet connected directly to the main service, as the 3 wire SE is just an extension of the service where the neutral and ground become common.
If the original 3 wire circuit was installed to a sub panel,, a 3 wire cable was allowed as long as the neutral conductor was insulated. This is a little different, since as Mike pointed out, you now have neutral current flowing on grounded parts unless the sub panel is also 3 wire and has no bond to anything grounded, and does not contain any grounding wires to other circuits, but this is rare, most 3 wire sub panels have neutral and ground mixed which in itself presents a hazard.
Then there are the illegal 3 wire hookups that used NM with a bare ground for the neutral/ground.
There is no way the average person is going to know what type he is plugging into therefore I find Mike's advice sound.
I am not a fan of folks using cheater plugs at the RV park or campground to adapt a 12,000-watt RV to a 3,600-watt RV outlet. Or the recharging of EV’s in an RV park unless from a dedicated EV charger. I am not opposed to EVs. I am only opposed to the fact RV park and campground electrical systems were never designed for the electrical loads of using some cheater plugs or EV charging. I think most home owners would want every electrical contact in every electrical outlet in their home attached to a correctly sized wire to the electrical panel. Or at least their home owner’s insurer would. Anything less is setting up an unsuspecting person up for equipment damage, electric shock, or electrocution. If not upgrading a 240V, 3-wire circuit to 4-wires, just do not install a 4-wire outlet on it or use a cheater plug. Just like a bootleg ground connection on a 2-wire, 120V circuit plug. It works until something bad happens.
Thanks so much for all the great information that makes us smarter keeps us safe.
Not to beat a dead horse (no pun intended) but wouldn’t this scenario satisfy the neutral and ground requirements for a dryer to RV adapter where the green ground wire is plugged into the ground of a nearby household outlet ?
AC WORKS RV/EV 14-50R 50-Amp Adapter (3-Prong 30A Dryer Outlet to 50A RV/EV) https://a.co/d/eoRJc3o
That’s not a dedicated neutral connection in the dryer receptacle, and there’s no guarantee that it’s connected to a neutral buss in the panel, since it’s often terminated to the EGC ground bus. Essentially it acts as both a ground (for the dryer chassis) and a neutral (for a limited current 120-volt dryer motor and control electronics). Many users of this adapter will ignore the green ground pigtail or bootleg it to the neutral connection. While there’s circumstances where this can work for a EV charger, there’s too many things that go wrong with it to consider this to be a safe RV adapter. I can’t recommend it for an RV.
There is also the fact that a EGC that is not run closely to the other circuit conductors will experience high impedance during a fault which can be enough to delay the opening of the OCPD (even a delay of less than a second can result in conductor/insulation damage).
The NEC also addresses this: "All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cable bus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B) (1)"
The big issue with 3 wire range and dryer circuits is the rampant mis-understanding about what was allowed, and the variations that were allowed. The requirements were very specific, the 3 wire circuit could be fed with SE (service entrance) cable providing it originates at the service entrance. In this case, using the adapter shown would be no different than an RV outlet connected directly to the main service, as the 3 wire SE is just an extension of the service where the neutral and ground become common.
If the original 3 wire circuit was installed to a sub panel,, a 3 wire cable was allowed as long as the neutral conductor was insulated. This is a little different, since as Mike pointed out, you now have neutral current flowing on grounded parts unless the sub panel is also 3 wire and has no bond to anything grounded, and does not contain any grounding wires to other circuits, but this is rare, most 3 wire sub panels have neutral and ground mixed which in itself presents a hazard.
Then there are the illegal 3 wire hookups that used NM with a bare ground for the neutral/ground.
There is no way the average person is going to know what type he is plugging into therefore I find Mike's advice sound.
I am not a fan of folks using cheater plugs at the RV park or campground to adapt a 12,000-watt RV to a 3,600-watt RV outlet. Or the recharging of EV’s in an RV park unless from a dedicated EV charger. I am not opposed to EVs. I am only opposed to the fact RV park and campground electrical systems were never designed for the electrical loads of using some cheater plugs or EV charging. I think most home owners would want every electrical contact in every electrical outlet in their home attached to a correctly sized wire to the electrical panel. Or at least their home owner’s insurer would. Anything less is setting up an unsuspecting person up for equipment damage, electric shock, or electrocution. If not upgrading a 240V, 3-wire circuit to 4-wires, just do not install a 4-wire outlet on it or use a cheater plug. Just like a bootleg ground connection on a 2-wire, 120V circuit plug. It works until something bad happens.
Mike
Thanks so much for all the great information that makes us smarter keeps us safe.
Not to beat a dead horse (no pun intended) but wouldn’t this scenario satisfy the neutral and ground requirements for a dryer to RV adapter where the green ground wire is plugged into the ground of a nearby household outlet ?
AC WORKS RV/EV 14-50R 50-Amp Adapter (3-Prong 30A Dryer Outlet to 50A RV/EV) https://a.co/d/eoRJc3o
That’s not a dedicated neutral connection in the dryer receptacle, and there’s no guarantee that it’s connected to a neutral buss in the panel, since it’s often terminated to the EGC ground bus. Essentially it acts as both a ground (for the dryer chassis) and a neutral (for a limited current 120-volt dryer motor and control electronics). Many users of this adapter will ignore the green ground pigtail or bootleg it to the neutral connection. While there’s circumstances where this can work for a EV charger, there’s too many things that go wrong with it to consider this to be a safe RV adapter. I can’t recommend it for an RV.
There is also the fact that a EGC that is not run closely to the other circuit conductors will experience high impedance during a fault which can be enough to delay the opening of the OCPD (even a delay of less than a second can result in conductor/insulation damage).
The NEC also addresses this: "All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cable bus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B) (1)"