31 Jan
2011
31 Jan
'11
11:15 a.m.
On 31 Jan 2011 at 12:05, Simon Fryer wrote:
It's been 240/120 V in the USA for years. The voltmeter on the
outlet next to my system here says that the line voltage at this
outlet is 122 volts.
Consider the light inside an electric kitchen oven. It's always a
120V item, even though the oven elements themselves run from 240V.
Strictly speaking, a US "crowfoot" outlet used for appliances is not
a grounded one--there should be no continuity between the third
(neutral) leg and the chassis of the appliance. It's a
"grandfathered" situation--a current-carrying supply line should not
also serve the purpose of protection.
Some local codes require that a separate grounding wire be installed
for safety. There are applications where a 3+ground outlet is
required by code, mostly in outdoor applications, such as RV hookups
and generators.
On 31/01/2011, Brian Lanning <brianlanning at
gmail.com> wrote:
In the US, two
separate 110 legs are delivered to the house. When
we need 220, the magic of constructive interference is applied, and
we get 220. The 220 is delivered to the appliance as two separate
110 wires, a neutral wire, and sometimes a separate ground wire for
safety.
This doesn't look quite right to me, but it is probably close enough
for most applications. In Europe, a typical property is supplied with a
single 230V RMS AC
single phase and neutral supply. If you pay enough money and/or are
small industrial etc, you can get a three phase and neutral supply.
Each phase is 230V RMS AC phase to neutral, 400V RMS AC phase to
phase.
In the USA, some locales do not allow 3-phase service to be installed
on a residential property. For 3-phase shop equiment, a rotary
converter (really a 3-phase motor with a large capacitor hooked
between two legs) is often used for the home shop owner who wants to
run his South Bend lathe with a 5HP 3-phase motor.
I'm out in the country, so my service is still single-phase with a
buried 6600V supply drop going to a pad-mounted transformer in my
front yard. I'm sure I could get 3-phase service, but it'd cost a
fortune to install, what with the trenching and all. I was surprised
to see the size of the wire going to my transformer. It must be
something like 3/0 AWG copper--it's heavy. I was told that the same
wire was used for the buried "loop" servicing the neighborhood as
well as all the drops. Seems like a waste of money to me.
If you want to run heavy appliances however, keep in mind the line
frequency issues. While there are lots of appliances that will
accept 50 or 60 Hz line current, it's not universally true.
--Chuck