On 4/6/2011 19:31 PM, m II wrote:


"daestrom" wrote in message ...
One issue that utilities worry about is the available fault current.
The breaker main in a typical home might be able to safely interrupt as
much as 10 kA. The current of a dead short in your home is a function
of the sources feeding it. If the total is less than 10 kA, the breaker
opens and everyone's safe. If the sources could feed more than 10 kA,
the breaker may fuse/melt and the fault will continue to draw current
and your house burns down.

So when adding new sub-station equipment and generating units, they have
to calculate the available fault currents and make sure it's still under
the breaker/protection equipment capabilities.


All that being said, I can't honestly think a small grid-tie PV
installation would make enough of a difference to be a problem. Worst
case is your neighbor has a fault and the combined current from the
utility and your PV setup exceeds his breaker's interrupting capacity.

But a good EE could sharpen his pencil once and do the calcs and
probably find there is a wide margin between what the pole transformer
can supply to a fault and what your PV system would supply. They're
probably just to worried about their liability to bother.

daestrom
P.S. Maybe if every household in a whole development had such a
microFIT installation? I'd have to see the numbers though to believe it.


-----------------

The fault capacity of a household main breaker or fuses is not an issue,
unless very old technology, like you.
One hundred feet of twisted triplex supply cable limits faults to well
within the fault tolerances.


Got some numbers/calculations to support that? Is that including the
next door neighbors with their PV installation?

daestrom