[AT] : Ice Storm

[charlie hill]

Thanks for the explaination Henry.  The reason I raised the question is that 
my original post referred to generator sets that might be mounted on 
trailers or some other way that was not grounded and were not wired into the 
house grid.

Charlie
----- Original Message ----- 
From: "Henry Miller" <hank at millerfarm.com>
To: <at at lists.antique-tractor.com>
Sent: Sunday, December 16, 2007 11:37 PM
Subject: Re: [AT] : Ice Storm


>
> Excellent question Charlie, the short answer is in an ideal world if the 
> GFCI
> is not connected to earth, you can't get a shock and so the GFCI does
> nothing.  Sometimes the world is not ideal, and something gets connected 
> to
> the earth, and then the GFCI protects you.
>
> There are two different things we mean by ground.   One it an actual
> connection to the Earth, and the other is the ground wires run all over 
> your
> house.  I did not specify (and in fact rarely does anyone specify), but 
> the
> two are very different.   We don't think of them as difference because the
> ground wires are normally (but not always!) connected to the earth at some
> point.
>
> Power comes always comes in 2 sides.   We say hot and neutral, but in 
> truth,
> both wires are equally hot - the only difference is one wire is connected 
> to
> the ground wires (which are normally connected to the earth), and the 
> other
> is not.   We call this hot wire neutral, but there is no significant
> difference (note that your house is 220, and there is a difference, but 
> not
> in any way that is important to this discussion so I'm going to ignore 
> that
> case to avoid confusion).
>
> For electric current to flow there must be a connection between the two 
> hot
> wires.   If there is no connection no current flows.   If there is no 
> earth
> connection and you grab a hot wire nothing happens - you don't get a shock
> because there is no way for power to get between you and the other hot 
> wire.
> Connect one wire to a ground rod though, and grab the other and you will 
> get
> a shock because current can flow through you, through the ground, and back 
> to
> the other wire.
>
> If you understood the above you will now be asking "Why do they have 
> ground
> rods if they just make electric shock possible?"    The reason is the real
> world is messier, and an ungrounded system can burn your house down in 
> some
> situations where a ground would not.   If a mouse chews on the wires in 
> your
> walls (which happens all the time), you can have a bare wire providing a 
> poor
> earth connection.   If a second mouse chews the the other wire elsewhere, 
> a
> small amount of current can flow - not enough to blow fuses, but plenty to
> start a fire in the walls.     By adding a ground wire and earth 
> connection
> odds are much better that enough current will flow to blow a fuse long 
> before
> a fire can start if there is a problem.
>
> As you see, the earth/ground system is for fire protection, not human 
> safety.
>
> So if your generator is not earthed, why the GFCI?   The problem is you 
> cannot
> be sure that the entire system isn't earthed.   An internal problem may
> connect one wire to the frame, which touches the earth.   Now you have a
> grounded system.   A GFCI will protect you from trouble now, just like it
> will in hour house.
>
> Note that a GFCI does NOT require a ground/earth connect.  The GFCI just
> measures the current in the two hot wires.   If there is any difference, 
> the
> rest of the current must be getting back some other way - by which it 
> assumes
> the earth via your body, so trips to protect you.   Code allows (as in
> strongly discouraged but sometimes there is no choice) a GFCI protected
> outlet to have a ground terminal that is not connected to anything.
>
> So I say use a GFCI outlet on your portable power generators because they 
> will
> protect you in case something is wrong.    There is a small possibility 
> that
> something could go wrong and cause a fire, but since this is a portable
> power, you should be right there to see problems before they become big.
>
> When connected to your house, use the house's ground/earth system for fire
> safety.
>
>
> On Sunday 16 December 2007 19:57:01 charlie hill wrote:
>> Henry,  I've already admitted that I'm no electrician but I have to
>> question one thing you are saying.  How is a ground fault interupter 
>> going
>> to work if it's not connected to a ground?  If you are using any sort of
>> tool that has a three prong plug and you don't have an earth ground on 
>> the
>> generator YOU are going to become the ground if something goes wrong 
>> inside
>> the tool.
>
>
> _______________________________________________
> AT mailing list
> http://www.antique-tractor.com/mailman/listinfo/at
>
>
> -- 
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.503 / Virus Database: 269.17.4/1187 - Release Date: 
> 12/16/2007 11:36 AM
>
>