31 Jan
2011
31 Jan
'11
1:28 p.m.
On Monday 31 January 2011, Tony Duell wrote:
Sort of. Technically, there was no "ground" wire, and the appliance
chassis (if connected) was connected to the neutral line. This is no
longer allowed. As long as there's no electrical faults, neutral and
ground should be at the same potential (but obviously for safety
reasons, one shouldn't assume this). They're usually bonded together at
the service entrance - wherever the main circuit breaker (which may
actually be up to 6 breakers for separate loads) is.
In any case, that's not allowed in new construction or appliances
anymore, only grandfathered in, in existing situations.
One thing to watch for is that clocks, etc, may well use the mains
freuqency as a timing refernece (electromechanical clocks almost
certainly use xsynchronous motors, electronci ones may well use the
mains as the timing input). US mains is 60Hz, European mains is
50Hz. Such clocks, fed froma step-down transofmrmer, will run slow
in Europe.
-tony
--
Purdue University Research Computing --- http://www.rcac.purdue.edu/
The Computer Refuge --- http://computer-refuge.org
On Sunday,
January 30, 2011, Brian Lanning wrote:
I thought there used to be an (IMHO dangerous) bit in the US
elcectircal regualtiosns which allowed cookers to have a 3 wire
mains cable (the 2 phases and protective gorund., the last being
wired ot the metal frame of the cooker) but they coulsd still have a
110V timer wired from one phase to the _protective ground_ wire. 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.
Some things don't have a separate neutral line, in which case they
don't require 120V power. Taht wouldn't work in Europe (since the 2 sides of
the 230V mains are
not balanced about ground), and anyway AFAIK making the protecive
ground wire carry any current under normal conditions is totally
forbidden.
Right. Like I said, the chassis was bonded to neutral, not neutral
bonded to ground. I guess it's the same situation as an 120V appliance
whose chassis is bonded to the neutral line in a 2-wire, non-grounded
plug.
Though, ground carrying some current isn't all that uncommon. There are
plenty of things that have a non-trivial leakage current (eg, MOV or
other surge protector devices). I've seen some computer equipment with
warnings about having a "high leakage current".
Because of this arrangement, sometimes appliances (I
believe,
maybe I'm wrong) will pull 110 from one of the legs to power
electronics in the appliance.
Yes, some do that. You can always wire in a 240V to 120V step-down
transformer to run the extra bits. It's rarely much power (timers,
clocks, etc), so you probably could get away with a 100W or so
step-down transformer, which should be pretty cheap.