> As we have heard, if one, by mistake, applies grid power to a running
> generator,through a mistaken connection, it leads to destruction of
> the generator end due to the generator being out of phase.
> While every effort should be made to avoid committing such a mistake,
> I would like to know if a properly sized fuse box would prevent this
> sort of damage to the generator in case if such a connection occurs.
-------------------------
HRC (High Rupture Capacity) fuses are the best fuses, while rewirable fuses
are way down the list on protection.
Even so I would not like to see my genny subjected to mains voltage while
running out of phase with the best possible fuse protection.
For instance a 50 amp HRC fuse would let around 500 amps though blowing at
1/10 of a second. That could cause a lot of damage, it could blow at 700
amps at one tenth of that time.
It could hold at 250 amps for a second.
Those times do not seem long, but are you willing to risk your genny, I am
not. A lot of damage can be done in a short time.
-----------------
BTW my 415 volt 3 phase 52 amp per phase emergency genny IS HRC fuse
protected.
I have a circuit breaker rated at 50 amps for overload protection and 60 amp
HRC fuses for short circuit protection.
It starts a motor with a 90 amp start up current without problems, although
the house lights do 'blink' when it starts.
The circuit breaker is a motor start curve one so it does not trip when
motor starts. It has never blown a fuse or tripped the breaker.
Of course there is a proper 63 amp transfer switch fitted between the mains
and the genny.
-----------------
FYI
Fuse chart
http://books.google.com.au/books?id=V1pepm-1m-cC&pg=PA314&lpg=PA314&dq=HRC+fuse+chart&source=bl&ots=Ez8FcEHsSS&sig=9hpmBhAqN_OkwzZ6NAf3FoiA7nQ&hl=en&ei=KRoQS9TnD5TbnAf4xaTZAw&sa=X&oi=book_result&ct=result&resnum=1&ved AgQ6AEwADgo#v=onepage&q=HRC%20fuse%20chart&f=false
Page 314 for chart
On Thu, 26 Nov 2009 22:21:18 -0600, Ignoramus17202
>As we have heard, if one, by mistake, applies grid power to a running
>generator,through a mistaken connection, it leads to destruction of
>the generator end due to the generator being out of phase.
With small portable generators, generally no damage is done. The
incoming AC overwhelms the generated AC, degausses the stator and the
generator ceases to generate. The stator will draw more than maximum
rating from the line and therefore will trip the circuit breaker in
short order. To return such a generator to service, it is generally
necessary to flash the field.
This is the voice of experience. I own one generator that a customer
gave me after "burning it out" by connecting it to line power. All I
had to do is flash the field to "un-burn" it. I have "repaired"
several other customers' generators that suffered the same treatment.
In no case was any damage done.
John
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> generator,through a mistaken connection, it leads to destruction of
> the generator end due to the generator being out of phase.
> While every effort should be made to avoid committing such a mistake,
> I would like to know if a properly sized fuse box would prevent this
> sort of damage to the generator in case if such a connection occurs.