220V question

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Chris Lewis wrote:

They need a neutral, but a 3-wire cord doesn't give them one. It dumps the unbalanced return voltage on the ground. A small fixed load, and a very large low-resistance ground. [I didn't design it] Should be OK with copper wires and tight connections; I wouldn't trust it with aluminum wire even with proper terminations. I would use aluminum for a 4-conductor dryer or range circuit.
[now that I shot my mouth off, I gotta go doublecheck whether that grounded wire is technically a ground or a neutral]
My dryer has an old 3-wire outlet; it's connected directly to the service panel with a short length of rigid metal conduit, so even if the grounded wire were to somehow come loose I'd have a good equipment ground through the conduit so I haven't bothered to change it to 4-wires.
Best regards, Bob
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This is really more of a terminology quibble than anything else, for what really matters is what the third wire is being used _for_. The white wire in your house isn't technically a neutral _either_. That's just the term everyone uses. It's official name is "grounded conductor".
It's used as _both_ in the case of a 3-wire stove or dryer. It's being used as frame ground _AND_ neutral return. This starts to become obvious when you start looking into (older) code restrictions where, for example, you (normally) couldn't 3-wire a stove or dryer from a subpanel that has split neutral and ground.

This is slightly better than unconduited 3-wire, in that you have better connections to the ground. However, if the neutral separates in your panel or on the pole, the frame of your stove _still_ goes hot. The problem is that the frame is connected to the device neutral, not how well it's connected to the system ground.
Because the fact of the matter is, if your neutral separates in the panel, AND if you have a neutral-ground interconnect anywhere in your house, _every_ grounded object in your house can potentially go to damn close to line voltage. By NEC rules, ground electrode conductivity is not necessarily high enough even to trip a 15A breaker, let alone the mains.
--
Chris Lewis, Una confibula non set est
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Chris Lewis wrote:

That happens anyway if the service loses its neutral; the bonding screw at the service disconnect panel will energize all the grounds in the house. I think that's why the power company takes it so seriously if you call them and say your service seems to have lost its neutral. (that plus the risk of fire from one leg operating at too high a voltage.)
-Bob
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Minnie Bannister posted for all of us....

How much is YOUR life or anothers worth?
--
Tekkie

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...

interconnect
No, it's not you, but I suspect that was rhetorical, right? Too many people have been taught to look at these things from a voltage standpoint, (e.g. 0Vac = 0Vac = how you get it doesn't matter), instead of correctly considering current flow and direction plus fault control. I'll never forget my first encounter with ground currents: HOW could a wire overheat and melt, when there was 0V measured at BOTH ends of it? I watched 3 wires burst their insulation into flames before I figured it was a problem with me preventing knowing what went wrong! I was an avionics TS at North Island at the time. Of course, if I'd known to use the right meter scale, I'd have seen the voltage diff, but ... .
Regards,
Pop
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4-conductor circuits aren't "240V circuits" per-se. They're 240V/120V circuits. The only place where a homeowner would normally be concerned about four-wire circuits are stoves and dryers which need both 240V and 120V. US code now requires that new stove/dryer installations must be four wire, wheras it used to permit 3 wire. Canadian code hasn't permitted 3 wire stoves/dryers for several decades.
Pure 240V circuits (ie: 240W water heaters) are _still_ 3 wire. They don't need neutrals at all.

Sharing the neutral and ground _can_ be quite dangerous thing, that's why they changed the code and no longer permit it in the last remaining exception I'm aware of in the NEC.
Ie: if you have a neutral separation in the main panel, the frame of your stove _may_ go hot.
--
Chris Lewis, Una confibula non set est
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