Re: Pole Pig Question: (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Thu, 24 May 2007 21:33:39 -0700 (PDT)
From: J. Aaron Holmes <jaholmes@xxxxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Pole Pig Question: (fwd)

I'll take a shot at this ;-)

There are two secondaries on the average U.S.A. pole
pig, each providing 120V.  Whether these windings are
in-phase or out-of-phase with respect to each other
simply depends on how you connect them.  For most
practical purposes, you may regard the two 120V
secondaries just as you would the output from two
*separate* transformers fed from the same source.  In
most applications, these secondaries are connected in
series inside the can for 240V with the connection
being named "neutral" and the unconnected ends of each
secondary being "hots" (contrary to popular belief,
pigs are NOT "center-tapped").  In this configuration,
the two 120V secondaries are connected "in-phase".  If
you swapped the leads on any one secondary, they'd be
"out-of-phase", and the voltage across this series
configuration would be 0V instead of 240V, as the sine
waves would cancel instead of adding together.

To make matters somewhat more confusing, it is
sometimes desirable for a pig to only put out 120V and
not 240V (this is for 208Y three-phase power).  In
those cases, the 120V secondaries are configured in
parallel (in-phase) instead of in series.  So there
are only two leads.  In this configuration, one
connection is called "neutral" and the other "hot". 
There is no second "hot" and the third low-voltage
bushing on the can goes unused.  (You'll often spot
unused low-voltage bushings like this in situations
where three pigs are on the pole together, as this is
a good indication of three-phase service.)  If you
swapped the leads on any one 120V secondary in this
parallel connection, then the 120V secondaries would
be connected in parallel out-of-phase.  Unlike series
out-of-phase, which simply yields 0V, parallel
out-of-phase creates a fireworks show because you're
shorting out the transformer.  Hence, the nameplates
on pole pigs tell you exactly which leads to connect
together for all the various configurations, and the
leads are conspicuously labelled inside the can.

Know your pig!

Cheers,
Aaron, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: List moderator <mod1@xxxxxxxxxx>
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Thu, 24 May 2007 16:14:32 -0500
> From: Jim <branley1@xxxxxxxxxxx>
> To: tesla-request@xxxxxxxxxx, Tesla list
> <tesla@xxxxxxxxxx>
> Subject: Pole Pig Question:
> 
> 
> Hi Folks:
> 
> I have received from you a bucket truck load of
> insightful input on pole 
> pigs that has helped me to better understand them,
> thanks.
> What seems to be evading me is  How can a single
> primary feed create 2 - 
> secondaries that are alternating in current.
> I always assumed that 1 - primary feed equals 1 -
> secondary wave form 
> not 2 - alternating wave forms.
> 
> Your help is greatly appreciated,
> 
> Jim
> 
> 
> 
>