[RE-wrenches] PSX-240 wiring question

[William Miller]

Allan:

 

I would not provide a means to disconnect a neutral.  In 120/240VAC split
phase power systems it is rarely appropriate to disconnect the neutral.

 

I would instead have the generator feed a small subpanel.  In that subpanel
I would have a 2 pole breaker feed the shop tool.  I would have another 2
pole breaker feed the X-240.  You need to make certain the direct hot feed
to the inverter is derived inside of the X-240.

 

I have been at odds with many of the wiring recommendations presented by
Outback.  The diagram you included is drawn poorly, leaving out some
important exterior details, making it easy to wire incorrectly.  The diagram
below (from the July, 2008 manual) is depicted better, but as published, the
wiring is still incorrect.  I have modified the drawing to indicate how it
should be wired.  The problem with the original wiring is that when you open
the breaker, it unloads only one phase of the generator.



One additional enhancement you could provide is you could easily interlock
the breakers in the gen-fed panel so only one breaker can be on at a time.
This is easily done with off-the-shelf interlocks from Square D or GE, or it
is easy to build an interlock from some scrap aluminum angle and a bandsaw.
We build many interlocks in the shop.  Sure, they are not "listed," but they
are a simple mechanical device that one can hold in one's hand, manipulate
and verify intuitively that they work.

 

William

 

PS:  I also disagree with Outback in using black for one phase and red for
the other.  In an Outback AC cabinet it is less important, in my view, to
keep track of which phase is which.  Much more important is to keep track of
input versus output wiring.  I use black for "hot sometimes" and red for
"hot all of the time."  This is not to minimize the importance to wire
correctly according to your stack plan.  The plan I suggested is just easier
for me.  I am interested in any comments on this idea.

 

Wm

 

Miller Solar

V/C 805-438-5600

Note above number is for all voice calls.

Lic 773985

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan
Sindelar
Sent: Saturday, September 07, 2013 11:56 AM
To: RE-wrenches
Subject: [RE-wrenches] PSX-240 wiring question

 

Wrenches,
Here's a small issue on which I need help. It concerns the best functional
way to wire up an Outback PSX-240 balancing autotransformer for a specific
purpose.

I have somehow succeeded in transferring the wiring diagram on page 6 of
Outback's PSX-240 installation manual into this message. This is for a
step-down/generator balancing function. 

The situation: 8kW 240V AC generator serving an older system with a single
Trace SW4024. The 240V from the generator enters the PSX240 as wired
according to the diagram. The primary role of the generator is to provide
occasional backup charging to the batteries through the inverter. The
specific issue is that the client also wants 240V AC from the generator to
be available to a single shop receptacle to run a stationary woodworking
tool. The generator is not large enough to both run the tool and charge at
full (33A @120V AC / 120A @24V DC) AC2 amps in setting, and we don't want to
reduce the charge rate, as it's currently ideal for the new HUP industrial
flooded batteries.

We initially tapped 240V off of the generator feed ahead of the 25A two-pole
breaker in the PSX-240. We instructed the customer to turn off this 25A
breaker when using the power tool (the tool circuit has its own separate
two-pole breaker). What we discovered, which is obvious in hindsight, is
that one of the generator's 120V AC legs continues to feed the inverter AC2
input with the breaker off. This causes the inverter to try to draw too much
current from that AC generator leg only.

My question: could I solve this by simply moving the "120VAC to Neutral"
output feed (now tapped off of L2) shown on the drawing below to the other
side of the 25A circuit breaker; that is, to point 4 in the drawing? It
seems to me that this would work, and would not intrinsically overload
either of the two 25A poles of the breaker. The 120V AC output to the
inverter could in theory draw 50A; 25A from L2 and 25A through the windings
of the transformer. But this solution seems almost too simple. What am I
missing, please?





 

-- 



Allan Sindelar



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