Re: [Phys-l] home wiring catastrophe

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

Thanks Carl for introducing a real-world physics topic and thanks John
for the excellent analysis.  It would seem that beyond severing the
neutral line, two other things have to be/go wrong for the result to be
such a catastrophe.  One would be the load imbalance described by John
(if you put in a housing division you might want to wire the breaker box
in any home to be the mirror image of each of the boxes in the next door
neighbors' homes!) and the other would be a bad or missing ground
connection at one end or the other (transformer or home).  According to

< http://en.wikibooks.org/wiki/Basic_Electricity >
--------------------------------------------------------------------
  Single phase power is what is commonly available to
  residential and light-commercial consumers in most
  distribution power grids. In North America, the
  single phase that is supplied is developed across a
  transformer coil at the utility pole (for aerial
  drop) or transformer pad (for underground)
  distribution. This single coil is center tapped and
  the tap is grounded ...
-------------------------------------------------------------------

the center tap is grounded--I would guess that it is connected to the
transformer case which is grounded separately from the neutral wire.
The neutral bus in the home is or should be grounded as well.  In my
home the neutral bus is grounded by means of (what I estimate to be) an
8-gauge metal-clad copper wire clamped to the water main a few inches
above where the copper water main disappears into the ground.  If the
grounding is ideal on both ends, and the neutral wire (but not the
ground connection) is cut near the transformer, the earth would play the
role of the neutral wire.  I wonder if the neutral bus was properly
grounded in each of the homes.

Jeff Schnick


> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
> Sent: Thursday, May 17, 2007 9:52 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] home wiring catastrophe
>
> On 05/17/2007 06:35 PM, Carl Mungan wrote:
>
> > While working on one of those cubical boxes that distribute power
> into local houses (for
> > underground wiring, as we have in our subdivision), the power
> company accidentally severed the
> > neutral line. This fried the circuit panels (and possibly the entire