In reply to 03Panther :
Hmmm.... It is true that the ones I've repaired were pretty ancient. It was my side-hustle in college in the 90s, so most of them were 70s and 80s machines.
In reply to 03Panther :
Hmmm.... It is true that the ones I've repaired were pretty ancient. It was my side-hustle in college in the 90s, so most of them were 70s and 80s machines.
Did a little homework...
Apparently it was once common years ago to sell dryers that could be used on either 120 or 240 Volt supply. (Not all houses had 240V). The motor would work either way, but drying time would be 3-4 times longer when connected to a 120V supply.
Additionally, a 120V motor will run on 208V (which is sometimes the source voltage for apartments).
This is why dryers are sold without cords on them. Manufacturers didn't know what voltage they would be run at.
The problem with this is that an open neutral could potentially electrocute a user if they touched the case of the dryer at the same time as another grounded appliance. So now dryers have 240V plus a neutral.
In reply to SV reX :
208VAC is one leg of 3 phase (either Yee or Delta, I forget which) and back in the days when "240VAC" was expressed in 220 (or 230), a motor rated for 220 (or 230) but not rated for "208" would draw more current than rated for, and eventually burn up, if ran on the 208VAC.
Most 220/230/240 only motors today, are rated for 208, even when the label does not specify.
the half dozen to a dozen dryers I have worked on for myself or friends, (repaired in the 80s, average ten year old dryers) were ALL 120 motors ran off one leg. Blower being 120, also. And heating elements ran off both legs (without a neutral) for 240 for the heat
All were in either Hampton, Williamsburg, or Richmond area. Before dryers were required by code to have neutral and ground, for a four pole plug.
In reply to 03Panther :
I'm not disagreeing with you. I'm just saying the only way to get 110/120V is to have a neutral. Since the wiring in those days was usually 10/2 with ground, there was no neutral. They were using the ground as a neutral, and that means that if there was ever an open "neutral" then the case was hot. A user who was touching it and a nearby water pipe or other appliance BECAME the ground.
So now we run 10/3 with ground. 2 hot legs, a neutral, and a ground.
In reply to SV reX :
Hope I didn't sound disagreeable; just adding a bit, for clarification to the folks following along.
In the example of the 10/2 Dryer plugs, they got the 110/115/120 to run the control circuit (analog timer, on/of switch, etc) motor and blower from one leg, and the ground - since ground and neutral are bonded in the panel. Would only (very rarely, but once is too many!) shock someone if something was wrong in the wiring. That's , as you mentioned, is why the NEC ("code") was changed to require the 4th conductor. WAY safer, when something goes wrong in a separate part of the wiring. Again, for folks following along, if they are interested in a bit more complete reason.
On the 208, things get more complicated with three phase, with the change in power factor as the two conductors are only 120 degrees out of phase, as opposed to 180 degrees out as in "standard" house wireing. 3 phase theory can make folks brains explode!
In reply to 03Panther :
Yes, I agree.
But there is nowhere else in a residence that ever allows using the ground and a hot leg to get 120V. The ground is supposed to be a redundancy. If the connection ever got loose, then the circuit would not be complete. And since dryers are typically next to other appliances which are grounded (washers), it's easy to imagine a human becoming the ground.
3 phase doesn't really exist in residences, so the 208V isn't an issue. But the motors can run on it.
In reply to SV reX :
The code has definitely improved since the '80s, and a four plug dryer is infinitely safer.
But the 3 plug was "legal" then! My Dad is no longer living to ask when the required 4 plug became required. By the mid '90s, I would guess.
The 208 discussion started from a mention of apartment complexes; although I'd never heard of that. Modern 240 motors are usually rated for 208 as well, even if not marked on the label. Up into the late '70s some early '80s, they were not. But as you say immaterial to the gen pop.
But, some GRM are as big a pack rats as me, and I've still got a dozen motors laying around that it would matter (hey, I'll either fix em or scrap em ONE day!)
the rv 30 amp cord will have the round plug with the 2 slanted leads and the U shaped ground, as shown in your first pic. . 50 amps will be a 4 conductor. The 30 amp cable can use a 30 amp to std wall socket without any issues, and the rv in question may already have that item on hand. I've never seen a 50 amp rv trailer, but I aint all that up on the new stuff. A 4 slide 5th wheel may come std with 50 amp shore power, maybe. Our 36' diesel pusher is set up for 30 amp shore power.
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