[Boatanchors] Running European 230 VAC on our AC

[Albert LaFrance]

A GFCI works by detecting a difference between the current flowing in the
hot and neutral (grounded) conductors.  In normal operation, the currents
will of course be equal.  But in the case of fault, such as a grounded
person touching the hot conductor, the currents would be unequal because
some of the current from the hot would be returning through the normal path
(the neutral) and some through the "fault" path (the person).  When the
difference exceeds some milliamp threshold, the GFCI trips to open the
circuit.

 

I think the actual sensing mechanism is a current transformer with the hot
and neutral grouped together as the primary, so that the secondary voltage
represents the difference between the current flows.

 

The GFCI actually doesn't monitor the protective (green/bare) ground - it
only "looks" at the hot and neutral.  GFCI receptacles have a ground
contact, but it just "passes through" the ground connection from the branch
circuit wiring, providing an additional layer of safety.   

 

Albert

 

 

From: Mark Richards [mailto:mark.richards at massmicro.com] 
Sent: Friday, October 19, 2012 5:58 PM
To: boatanchors at mailman.qth.net
Cc: albert.lafrance at coldwar-c4i.net
Subject: Re: [Boatanchors] Running European 230 VAC on our AC

 

On 10/19/2012 17:50, Albert LaFrance wrote:

A basic 240 volt circuit is two hots and a (safety) ground.  The hots can be
any color except white (reserved for neutrals) and green (reserved for
ground).  Typically they will be black and red.
 
A 120/240 volt circuit will have two hots, a neutral and a ground.  This
four-wire circuit is required whenever any part of the load requires 120V;
for example a range which puts either 120 or 240 on a heating element
depending on the temperature setting.  This can be confusing because, in the
past, the National Electrical Code allowed one conductor to serve as both
neutral and safety ground in specific cases (ranges  being the one I know
for sure), but  now that's prohibited.  The neutral is considered to be (and
is!) a current-carrying conductor and must be separate from the ground,
which is provided for safety.  The neutral and ground are only
interconnected at the service panel.  I believe the reasoning is that, if
the neutral carries current, it will have a voltage drop, and if the neutral
were tied to an appliance cabinet, there would be a possibly hazardous
voltage difference between that appliance and a nearby grounded object.

Albert,

I love these types of exchanges.. as I always learn something new.  Thanks
for this clear description.

Would you know how neutral is used in a GFCI?

Seems like Neutral would be a good means of detecting protective ground
issues.

/m