Posted by Josepi on June 20, 2010, 4:06 am
Thanx for the info.
You say they use neutrals. Are any of the conductors grounded at any place?
BTW: It always bugged me that N.America used a black wire as the live
conductor. Meanwhile every electronic wiring scheme always used black as the
grounded, neutral or negative voltage. TV and Radio, control circuits,
electronics, etc.. In a DC circuit it represented the negative or return of
the battery as black.
England does use neutrals.
The active used to be red (Brown now?) and the neutral black (Blue now?) and
the earth green (yellow and green now?)
England does not have 120 volts as a standard voltage.
The English system is 3 phase and single phase. Now it was 415 volts for 3
phase and 240 volts for single phase but I think that has been reduced to
230 volts to comply with European standards, not sure how much the 3 phase
voltage has been reduced.
In UK they have a ring main that is used for domestic plugs (13 amp) where
the cable starts at the 30 amp fuse and returns to the same fuse allowing
the current to flow both ways through the cable. The actual appliance plug
has a smaller fuse inside of it to protect the appliance.
Posted by Ralph Mowery on June 20, 2010, 3:09 pm
It does bug me too about the black wires and I live in the US and work on
both electrical and electronic circuits.
The standard house feed in the US is a center tapped transformer. It is 240
volts across both hot wires and the neutral is the center tap of the
transformer. It is grounded. That means in a properly wired circuit you
will never be more than 120 volts above the ground.
I don't know if or when the over seas color coding changed but we got in
some 480 volt equipment that are in big cabinets that are around 6 feet
tall. On the outside there is a disconnect switch. When the power is on
the switch is pointed to the red color and when the power is off the switch
is pointed to the green color. We think it is to indicate that red means it
is not safe to enter as the power is on and green means that the power is
off and it is safe to enter the cabinet. This is exectally opposit from
anything I have seen in over 30 years. It was always green --power on and
red -- power off.
Posted by Jim Wilkins on June 20, 2010, 4:34 pm
You want us to follow standards?
Of course we have standards.
We have LOTS of standards.
Recently I've seen more IEC color coding in new US practice.
Posted by daestrom on June 20, 2010, 5:10 pm
Ralph Mowery wrote:
First commercial control room I was in used red to indicate breakers
closed, and green for open, so that seems the most natural to me. But
over the years I have found some plants have the colors reversed (green
is 'running' and red is 'stopped'). It can be pretty confusing. Funny
thing is, off/open/stopped light seems to always be on the left whether
it's red or green.
Posted by hubops on June 21, 2010, 1:55 am
.... now - let's work fluid valves into the mix ..
where open valve permits flow - open switch or breaker stops flow.
Normally open switches/breakers get a special indicator arrow
on a drawing ; normally closed for valves ... I think.
.. it's all so confusing. :-)