EXTERNAL TRANSFER RELAYS
It is not acceptable to switch the AC input from one AC source to another while the inverter is
connected. This applies whether the inverter is in battery charging mode or inverter mode. Switching the
AC input from one source to another can result in a loss of synchronization that can cause a severe
overcurrent condition that is far worse than short circuiting the inverter. Two separate AC inputs are
provided to eliminate the need for use of external transfer relays. If a transfer relay is used, it must provide
a center ?OFF? position (?break before make?) that causes a loss of input power to the inverter for a period
of at least 100 milliseconds. This will allow the inverter to disconnect from the original AC input and then
re-synchronize to the new AC source although the same AC input terminal is being used. During the
transition period, the inverter will have to operate the load while it re-synchronizes to the new AC source
(about a thirty-second period at the minimum). Most transfer relays will switch too fast for the inverter to
detect - and will cause the inverter to lose synchronization with the AC source. This is indicated by the
inverter shutting down upon transfer and the red overcurrent LED indicator flashing or turning on.
Manually, hand operated transfer switches may be acceptable since the transfer time can be slow enough
for the inverter to detect. The switch must go through a center ?off? position. They are often used to switch
from one generator to another. Since the inverter has a separate AC input for a utility grid, a transfer
switch is not required to switch from the utility grid to a back-up generator. The inverter will not allow the
generator to be connected to the utility - if both are available, the generator will be disconnected and the
inverter will connect to the utility on AC HOT IN 1.