Inverter protection [RE-wrenches]

[Phil Undercuffler]

Some really good points here by William.  Posts like his make lists worth
subscribing to.  Some questions, alternatives and rebuttals, however....

----- Original Message -----
From: William Miller <wrmiller at slonet.org>
To: <RE-wrenches at topica.com>
Sent: Monday, December 11, 2000 5:01 PM
Subject: Re: Inverter protection [RE-wrenches]


> 2. The Trace DC Disconnect enclosures are way too small.  So are most
> electrical enclosures off the shelf.
> Many RE systems require over sizing wire and that means an off-the-shelf
> load center or safety switch would have to be oversized to handle the wire
> as far as lug size and bending radius.

I agree heartily.  It would be interesting to calculate the box volume
required by 4 4/0 conductors used in a single inverter system, not to
mention all the other wires we all too often shove into that little box.

> 3. The DC disconnects have no KOs for an AGC fuse holder.  This is
required
> for monitor systems.  Not a big deal, I just drill for a chassis mount
fuse
> holder.

I often use an inline agc holder (available from Del City) or a 1/4" fuse
block (Grainger 1cz43 or thru Del City as well), the second 300v rated.  Do
you have a source for a UL listed DC rated panel mount fuse holder?  I would
love to mount that accessible without screwdriver

 The TC and PM 60s (from Trace and/or
> Pulse) can be ordered with an integral breaker.  I have seen them wired as
> input and as output breakers, and I have changed them in the field, as
needed.

I used to think this was a great idea, until I had to replace someone else's
TC60 with an internal  breaker wired as the output breaker.  Not much of a
service disconnect in that installation.  Controllers often fail, and if the
client has to shut down all power, lose all inverter (and /or meter)
programming to remove it or risk an impressive fireworks display then we
have not served them well.

> I do also frequently use the add on breakers in the sides of the Trace DC
> disconnect enclosure, but this makes the enclosures even more crowded as
> the breaker can hang over internal equipment.

What I want to see is a stand-alone box made for the Heineman breaker line.
QO breakers do not have a high enough AIC to use in a battery system without
current limiting fuses upstream, which is a limitation often ignored.
Sometimes I will use a 60A class R (oversized relative to breakers and
loads) and a fuseholder, inside a box with labels stating "no user
servicable parts inside" to meet safety and NEC

> 5. The tap connection on the Trace DC disconnect breakers is ludicrous.
It
> is a code violation (and against common sense) to put two leads under one
> lug.  Trace would have you put a lug under the bolt head holding the main
> lug onto the breaker, but this is so difficult to do, especially after
> wiring 2/0 or 4/0 to the main lug.  I have also stripped the threads in
> this lug.  I can't imagine the breaker manufacturer condones this
practice.

I only use the tap connection for powering the meter.  I crimp and solder a
5/16 (?) terminal on #6 or #4 wire, put it under the bolt BEFORE installing
the big breaker, and jump to the closest smaller breaker.  If I have
multiple loads/input breakers, I'll star connect from there.

By the way, has anyone noted that there is a load and a line side to these
breakers?  And an Up and Down side?  Pull out the glasses and squint at the
print.  Which brings to mind, if its an array input, which is the load and
which is the line?  Personally, I always run the battery to the load side.

> I don't particularly mind using a short piece of #6 wire from a battery
> connection to a circuit breaker.  This wiring philosophy is covered under
> the tap rule in the NEC.  I've never seen it directly related in print to
> DC wiring, but the principal is the same:  You can protect a length of
wire
> either at the beginning of the wire or at the end.  If the wire is long,
it
> is safer to protect it at the upstream end.  If the wire is short and well
> protected mechanically, it may be as safe to protect it from over-current
> at the down stream end.
>
> 6.  One place to install over-current protection and switch control is in
> the PV combining box.

I greatly dislike this idea.  Imagine:  if you put the array disconnect at
the array, and turn off the breaker, what have you accomplished? (other than
stopping charging)  Both sides of that breaker are still hot (admittedly,
one side is current limited).  In addition, someone working on the power
system would have to walk out to the array to disable all power sources.  On
the other hand, if the array disconnect was grouped with the power
equipment, especially if it was grouped with the controller disconnect, the
service equipment (controller) could be disconnected from all power sources
with one or two hand motions for easy safe service.

I do not like to plumb to an SW
> inverter via the end panel KOs since this obscures the AC connections as
> well as the relay and temperature sensor connections, however this is done
> in the IPPS.

If I could reach up the Zantrax/Anthrax/Prozac/Trace ladder and make two
changes to their inverters, the first would be to make ALL connections
accessible from the front of the unit:  straight on, no craning necks, no
three-handed needlenose and screwdriver manipulations, no looping the temp
comp from the DC (battery) side around to the AC (who cares what
temperature) side.  The second would be silent sell, but lets not get all
hot and bothered on that again.

> Also, I would not relish handling the weight of an IPPS.

Amen brother.




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