[Boatanchors] Storm Damage to Electronics

[Gary Schafer]

Agreed, typical 240 volt residential power is not two phase. It is single
phase no matter if 120 or 240 volts is being used. It is still called single
phase. Never heard of "flat two phase".

The problem that the original poster observed has nothing to do with
"ground". The ground system is only there for safety purposes. It never
carries current (unless there is a fault).

Yes neutral is connected to ground at the pole transformer. Also the neutral
lead of the two wire 2400 or 7200 etc. feeding the single phase pole
transformer is also connected to the same ground as the 240 volt neutral is
connected to, along with the transformer can. They are all grounded.

On a typical 120-0-120 volt household power feed the neutral may or may not
be carrying current depending on how well balanced the load is on each side
of the 120 circuits. If the load is equal on each side then neutral current
will be zero. This is however rare. If using all 240 volt loads then there
also would be no neutral current.

Older 240 volt appliances like dryers and electric stoves used to only have
3 wires going to them. Two wires for 240 volts and a safety ground wire that
also served as a neutral for any 120 volt circuits in the appliance such as
timer motors and lights. The only place where the ground conductor was
allowed to carry current. It also had to be a dedicated circuit back to the
main breaker panel. Nothing else connected to that line.
Under the new electrical codes, of some 10 or more years ago, those same
appliances now require 4 wires. Two hots, safety ground and neutral for the
120 volt circuits. No current is to flow on the ground lead.

As to two phase power, it is my understanding that in a few places in New
York there still exist some real two phase power distribution systems. These
are not 240 volt systems with neutral 180 degrees apart from neutral on each
side. These are true two phase with 90 degree phase differences. Old and
rare.

73
Gary  K4FMX


> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of rbethman
> Sent: Saturday, November 05, 2011 11:14 AM
> To: Boatanchors List Serve
> Subject: Re: [Boatanchors] Storm Damage to Electronics
> 
> 
> 
> The 240V is NOT a two phase!
> 
> The rest of your comment is correct.
> 
> This can also stem from a very poor ground.  Look at the distribution
> system.  In a heavily populated area.  You'll see three pole mounted
> transformers.  EACH is ONE of the three phase distribution.  For that
> matter, a less densely populated area will have a single pole mounted
> transformer every pole.  Look carefully, and you'll see that each one is
> fed from a different phase.
> 
> This is to keep the entire Three Phase system fairly balanced.
> 
> Each single phase transformer transforms ONE phase down from the
> 4160/2400VAC, (Note the sqrt of three figured in.) down to a SINGLE
> phase 240VAC with a center tap of the winding that becomes the neutral.
> 
> Yes, when the neutral is broken, things get wild.  This also occurs when
> the ground is broken.  The poles in areas of VERY good soil conductivity
> can run ground by pole butt grounding.  However, places like coral
> islands with changing tides, REQUIRE a continuous ground from pole to
> pole.
> 
> Otherwise, the same effect is seen when the tide changes.
> 
> Been there, done that.  Eniwetok Atoll 1977.  The engineers designed the
> system solely on butt grounds.  Bad news!  We spent one day stringing a
> fourth overhead ground over a 40 acre rock of coral.
> 
> The issue went away.  The neutrals were ALWAYS connected.
> 
> The neutral on a single phase transformer is NOT connected to ground.
> The transformer "can" is grounded.  That way if the insulation and oil
> breakdown, the fused disconnect on the pole blows, NOT a surge to the
> residence.
> 
> Bob - N0DGN
> 
> On 11/4/2011 7:22 PM, J. Forster wrote:
> > When the neutral failed, the sides of the flat two-phase were
> unbalanced.
> >
> > Instead of it being 120-0-120; the voltages were divided unequally,
> such
> > as 210-0-30.
> >
> > The line-to-line stayed the same, but the line-to-neutral went way up
> on
> > one side, way down on the other.
> >
> > The overvoltage blew stuff.
> >
> > -John
> >
> > ===================
> >
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