Index Home About Blog
From: John De Armond
Subject: Re: Gorilla Solar Question: how to deal with 3-phase feed from pole
Date: Fri, 01 Aug 2008 11:32:51 -0400
Message-ID: <>

You have a "split delta" or "wild leg" or as your utility man called it a
"stinger" feed.  It's not called a "stinger" for nothing.  One side of the
pole transformer delta is center-tapped to feed you 120/240.  The junction of
the other two windings is brought in to provide 240 three phase.  that third
leg is called the "wild leg" because it is about 207 volts to ground!  Not
phase to phase but phase to ground.

If you connect something between the stinger leg and ground, thinking that you
have 120 volts, you'll be vividly and unpleasantly surprised!

The meter can handle any combination of connections so you don't have to worry
about that.

I think I understand why they call it "guerilla" (NOT the ape).  It's because
it looks like the guy is wearing camo.  It's actually where all the blue smoke
leaked out very rapidly and deposited on his face when he made a little bitty

On Fri, 01 Aug 2008 06:31:25 -0500, Jim <> wrote:

>This is a theoretical question, as I am just thinking of going Gorilla
>solar and feeding some juice back into the grid.
>We have a 3-phase input to the meter, as we once had a large 3-phase
>4 ton condenser.  Now everything is running on single phase, just by
>tapping off one or the other of the 3 phases.
>The question is, would it make any difference as far as the meter goes
>and feeding juice back into the grid which phase the 220V would be fed
>back on?  I think the power company man told me that we had 3 phases
>and a "stinger" phase coming into the box (I think that is grounded at
>bottom of box, not sure about that).
>Could you feed the juice back on any of the 3 phases and would it slow
>the meter down, or would I have to get a single phase feed to the
>I wonder if anyone has come across a situation like this before?

From: John De Armond
Subject: Re: Gorilla Solar Question: how to deal with 3-phase feed from pole
Date: Sat, 02 Aug 2008 02:24:08 -0400
Message-ID: <>

On Fri, 01 Aug 2008 21:00:22 -0500, Jim <> wrote:
>  They are not cheap, and require solar voltage inputs
>of 72 Volts to 200 VDC, so you have to put several panels in

I just can't figure any reasonable payback on this kind of system unless the
goodies are bought surplus or given to you.

>I was just wondering about the present meter, but as
>suggested changing back to regular feed might be possible
>if the power company would not charge too much.

To borrow a phrase from my friends at the NRA, "They'll take my 3-phase from
my cold dead hands!"  I'd NEVER give up three phase power once it is
installed.  That is, if you do anything mechanical.  Lots and lots of machine
tools and stuff are available very cheaply because they have three phase
motors.  And though they've narrowed the gap, three phase HVAC is still
cheaper to run and usually cheaper to buy than single phase.

I don't know of any utility around here that has a 3-phase surcharge.  In
fact, 3-phase residential service is becoming more popular as houses turn into
McMansions.  It gets quite uneconomical to run anything over about 7.5 tons on
single phase - if a unit an be found.  The starting inrush of a compressor
that large guarantees dimming lights and stuff.  So 3-phase is becoming
common.  Heck, there's even three phase here in front of my cabin, 25 miles up
a winding mountain road from town.

Of course, you should check your utility's rate card to be sure that you're
not paying a surcharge.  If you aren't then leave well enough alone.  If you
are, maybe you can talk them into dropping it.

Most split-delta services like you have are actually implemented as a
split-open-delta, with one large pole pig to supply the main single phase
loads and only one more, usually significantly smaller pig for the other leg
of the open delta.  The cost to the utility is therefore only marginally
higher than single phase.  In return, they get some benefit (assuming the
3-phase is being used) in the form of better balance on each leg of the
distribution feeder.  Therefore the utility doesn't have any real reason for a


From: John De Armond
Subject: Re: Gorilla Solar Question: how to deal with 3-phase feed from pole
Date: Sun, 03 Aug 2008 18:15:13 -0400
Message-ID: <>

On Sun, 3 Aug 2008 11:44:16 -0700, "Ulysses" <> wrote:

<solar farts deleted>

>Forgive me if this has already been answered, but if you have 3-phase power
>aren't they 120 degrees apart?  I understand how this would work just fine
>for single-phase 120 volts but if you want to use it for 240 volts would it
>work?  Don't they need to be 180 degrees apart (exact opposite phase)?

True.  To understand, draw out a delta connection.  Three coils arranged in
series in a triangle.  Each secondary is a 240 volt winding.

Now pop down a center tap on one of the coils.  Draw three wires coming away
from that one wire, one from the center tap and one from each end.

There is your 120/240 single phase.  Over on the other side of the triangle,
draw a 4th wire.  That is the "stinger" or "wild" leg.  It and the two wires
from the ends of the center-tapped winding form the 240 volt 3 phase supply.

This is called a split-delta because one side of the delta is center-tapped or

Now erase one of the coils.  If the center-tapped coil is on the horizontal
then you'll have one horz coil and one angling off.  You STILL have 4 wires
exiting, three from the horz coil and one from the diagonal coil.  Still
120/240.  Still 240 three phase.

This is called a split open delta.  It can supply less power than a full delta
but with the advantage of only two pigs.

This type of service, open or closed split delta, is used when the majority of
the customer's load is single phase but he needs just a little 3 phase.  A 3
phase HVAC unit, for example.

There is another connection commonly used in industry.  Draw your coils again,
except arrange them in a "star" configuration.  One end of each coil is
attached to all the others.  This is the neutral.  Each coil is good for 120
volts.  Two coils are good for 120*sqrt(3) = 208.  A wire from each of two of
the coils and one from the neutral form the familiar 3 wire service, only this
time it is 120/208 volts.

This is commonly done when the majority of a customer's load is 3 phase but
where some lighting power is needed.   The 208 is a PITA because 240 volt
heating appliances don't work nearly as well.  Motors are usually designed to
run on voltage that low.


Index Home About Blog