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S6-Q141.) A transfer switch will:

a.) Not send a start signal to the engine
Automatic transfer switches are designed to start and switch to the generator during outages.
b.) Prevent the generator from shutting down
Engine monitoring equipment controls this function. The engine is self preserving, bypassed.
c.) *Switch to its preferred source position when power is available
Correct. The transfer switch is programmed to return to primary power when that source is
online and stable. It does this by sensing that source.
d.) Transfer to a secondary source even when the secondary is not available
The switch senses if the source is available. If it is not, the switch has no reason to transfer to it.

S6-Q142.) Regarding over-current faults, transfer switches are designed to:

a.) Transfer the fault
This may result in damaging other devices and would not be practical.
b.) Isolate the fault and continue to provide power to the other circuits
This would require multiple circuits with multiple sensors. The function of a transfer switch is to
transfer the load from one source to another.
c.) Repeatedly switch between sources
This would serve no purpose.
d.) *Withstand the fault
Correct. The switch should contain contacts and related equipment of sufficient size to with
stand the fault until the safety devices have cleared that fault.

S6-Q143.) A time delay is used for what purpose in transfer switches?

a.) To allow electric motors to completely wind down before restart to prevent damage
This would not be a concern since motors of this type would be powered by a magnetic motor starter.
Once de-energized, they cannot restart without input. In some cases, motors can be damaged during
transfer by residual voltage, phase shift, and excessive inrush currents. This, however, should not be
protected against by a delay.
b.) *To prevent continuous cycling between sources during brief outages
Correct. Brief outages of up to 5 minutes should be tolerated. Utility circuits sometimes fail
and require a few seconds or minutes to switch to a backup. The generator could see several
start cycles per year if it were allowed to immediately start and transfer each time power was
disrupted.
c.) To allow the generator time to warm-up before applying full load
Engine and power control monitors perform this function. Rather than rely on a timer, sensors
determine when the generator is ready to take the load.
d.) Time delays are not used in transfer switches, this could cause damage to devices that
cannot be without power
All devices must be able to withstand short outages. This would not be a practical method of
operation.

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