[AT] Why Ground a Generator

[Dave Ernst]

DAVIESW739 at aol.com


----- Original Message ----- 
From: "Mary S Peak" <marypeak at washington.usa.com>
To: "Antique tractor email discussion group" <at at lists.antique-tractor.com>
Sent: Saturday, December 15, 2007 12:08 PM
Subject: Re: [AT] Why Ground a Generator


> As a female here I wouldn't want to sound dumb but when I use the
> generator in my motorhome do I have to go out and put in a ground.
> Mary.
> PS
> Boy I got back from visiting my sister in Coeur d'Alene and found that
> some of you are real nasty to an old lady, some even accued me of not
> being who I am. Well for that part they are correct I am not using my
> real name so as to protect me from cyber attacks.
> 
>  ----- Original Message -----
>  From: "Dudley Rupert"
>  To: "Antique tractor email discussion group"
>  Subject: [AT] Why Ground a Generator
>  Date: Sat, 15 Dec 2007 00:57:08 -0800
> 
> 
>  Maybe we can get a good argument going on generator grounding (but
>  treat
>  this as a wind chill free zone) -
> 
>  Dudley
>  Snohomish, Washington
> 
>  I would think that grounding the frame of a generator that has a drop
>  cord
>  or two plugged into it, as well as grounding one side of its' output,
>  would
>  ensure that IF a short ever developed between either of the output
>  terminals
>  and the frame of the generator then a potential difference
>  would/could not
>  be created between the generator frame and the
>  ground/concrete/grass/etc
>  that it's sitting on. In other words, the innocent bystander would
>  not get
>  shocked if he touched the generator and the chances of arcing between
>  the
>  generator and the ground would be lessened. Note: I wonder, however,
>  how
>  often the generator is ever grounded in this case.
> 
>  BTW - This is the same grounding design as in the old steel power
>  tools that
>  had the 3-prong plug. The third prong, the grounding prong, connected
>  the
>  steel case of the power tool back through the ground wire to the
>  ground bar
>  in the service panel. The neutral wire (white wire) was also
>  connected to
>  the ground bar. The ground bar, of course, is connected to a ground
>  rod and
>  probably the copper/steel water pipes as well. I think good grounding
>  of a
>  generator with drop cords would/should. emulate the typical/good
>  service
>  panel ground design.
>  When it comes to a generator that is connected to the service panel I
>  don't
>  know. I would think, however, that if the generator neutral is
>  connected to
>  the frame of the generator (I have no idea on this ... would like to
>  hear
>  from someone who does) then I think one could argue that the service
>  panel
>  ground would ensure that the frame of the generator is kept at ground
>  potential and thus there would be no need to have a separate
>  generator
>  ground. However, I don't know what having one could hurt. If the
>  generator
>  neutral were not connected to the frame of the generator then it
>  would seem
>  that providing a ground for the generator would give the safety
>  benefits
>  described above.
>  WOILF (Way Out In Left Field) - Another case could be made for good
>  grounding of the power source but I am not sure how really applicable
>  it is
>  to the generator in the home environment (I don't think any at all).
>  But -
>  not that any old iron lover should care - in the avionics world it is
>  big.
>  A typical avionics unit, say a Flight Control Computer (Autopilot),
>  communicates (both inputting and outputting data) with literally
>  dozens of
>  other units. Protocols (i.e., ARINC specs) have been established to
>  govern
>  the precise transmission and reception of this data. For example, say
>  the
>  Flaps Control Unit uses a logic discrete to output to other units if
>  the
>  flaps are properly configured for takeoff. So, let's say the Flaps
>  Control
>  Unit does determine that the state of this discrete is True. In this
>  case
>  the protocol says it should output a DC voltage of 3.5 or less. The
>  protocol also says that any unit inputting this discrete should
>  consider it
>  True if it sees a DC voltage of 4.2 or less; otherwise consider it
>  False.
>  This communication requires not only good grounding of each unit
>  involved
>  but good grounding to a common source; that is, to the frame of the
>  airplane. Otherwise the design used in many units permits the ground
>  to
>  "float" to an undetermined state. Say, for example, the sending unit
>  is not
>  grounded, or not grounded well, to the frame of the airplane but that
>  the
>  receiving units are. Then it is a real possibility that the sending
>  unit
>  could be outputting, for example, say 2 volts with respect to its'
>  ground
>  (to indicate a True) but, if its' ground is at say +5 volts with
>  respect to
>  the frame of the airplane, then the receiving units will see this as
>  a +7
>  volt input and interrupt it as False. OK, way off the subject of
>  generator
>  grounding -
> 
> 
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