"Gary Schafer" wrote in message
...

By not turning off your air conditioner systems before disconnecting
your shore power cable or by only shutting down your main breaker this
is what happens:

The fields in the air conditioner motors suddenly collapse when power
is removed. The collapsing fields will generate a high voltage spike
throughout your boats mains system. Any other equipment that is turned
on at that time will receive those high spikes of voltage. Everything
that is turned on is connected to the air conditioner motors. You can
guess what can happen with voltage spikes fed to some types of
equipment.

A few arguments against this: if you use the switch on the A/C unit itself,
you disconnect the motor coil completely. It is virtually unloaded and will
therefore produce a high inductanc voltage.

However, if other equipment is connected while unplugging the shore power,
much of the spike will be dampened by this other equipment. Furthermore,
equipment that is commercially sold, is required by regulations to be able
to withstand spikes up to a certain level, just to prevent this kind of
potential damage caused by other connected (or suddenly disconnected)
equipment.


If you shut down the AC systems first you avoid any kick back voltage
spikes being fed to other equipment. The fields just collapse and no
voltage spikes go anywhere.

Well, the voltage spike will at least produce an arc across the switch,
which in turn delivers the spike onto your power system.

Meindert