> Can someone explain the different combinations for wiring 220v plugs? I
> used a 50A dryer receptacle for my welder and changed the cord on the
> welder. The old welder cord used the two hot legs and the green (ground)
> wire.
This is acceptable if the green wire only grounds the chassis of the welder,
and is not used to power anything (like a fan or lamp).
> The dryer cord uses the two hot legs and the white wire. The guy at
> the hardware store said the white and green are interchangeable in this
> case
Assuming your dryer has a 110v light and/or motor, this is an obsolete, not
recommended configuration. The white and green are NOT interchangeable, if
you use only one, use the white (neutral). The best thing would be to put
in a new 4-wire cord, and connect the green directly to the cabinet.
> I notice some 220v circuits use tow hot and white,
This is that obsolete configuration, with no safety ground. White is the
neutral/return for 110v loads.
> some use two hot and green,
This is fine, if there is no load connected to the green. The 220v load is
connected across the two hot wires, the green is a safety ground.
> and some use all 4.
... both neutral and safety ground.
> I also am trying to wire up my
> spa to an
> old outside box that was used for A/C. It is a 50A circuit, but has only
> the two hot wires and green (bare) wire. The spa wants 4 wires, two hot,
> white and green. Do I need to run another white wire from the
> panel to this
> box, and can I run it by itself without any conduit or sheathing?
You need the additional wire, I'm pretty sure it has to be sheathed in some
fashion.
> The spa also needs a GFI breaker. I'm confused.
A 'safety ground' is just what it says, it's to help prevent electrocution
if something goes wrong by providing a return path to ground for any fault
currents. A GFI will monitor the fault current, and shut off the supply if
the fault current exceeds a very small threshold. The safety ground should
not normally have current flowing in it.
OTOH, the neutral/white wire is to carry the return current for any
unbalanced load.
Generally the neutral and safety ground are tied together at the power
entrance, but this is the only place where they should be tied together.
Any exposed conductive part (like the box on your welder and dryer, or the
water in your spa) should be tied to the safety ground, and not to neutral.
This way, if the neutral should open, you still won't be exposed to line
voltage.
I'm not sure when the requirement for safety grounds came into existence,
but I believe it was around 1960. My folks got a new refrigerator in 1955
that didn't have a safety ground, and I remember it was possible to get a
respectable shock by having one hand on the sink when opening the
refrigerator ... you learned not to do it twice !
Randall
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