Lennox Signature XP21 Series Installation And Service Procedure page 46

FAN MOTOR SURGE PROTECTION
(XP21−XXX−230−01 only)
Surge Protector (metal oxide varistor) − A component de-
signed to protect electrical devices from voltage spikes that
are 3−to−4 times the normal circuit voltage (See figure 26 for
illustration of component).
How it works: It is essentially a batch of metallic−oxide
grains separated by insulating layers. Repeated voltage
surges break down the insulating layers, lowering the over-
all resistance and eventually causing the device to draw too
much current and trip whatever over−current protection is
inherent in the system.
Surge Protector Check: They are supposed to be located
beyond the line fuse (though possibly not always). In this
case, where the line fuse blows or circuit breaker trips but
there is no visible damage to the surge protector, the sim-
plest test may be to just temporarily remove the surge
protector and see if the problem goes away.
See figure 1 for location of the surge protection device in
the unit control box area.
XP21
Figure 26. Fan Motor Surge Protection Device
(XP21−XXX−230−01 only)
FAN MOTOR SURGE PROTECTION
(XP21−XXX−230−02 and later)
Starting with the reference build above, the fan motor surge
protection is in built into the fan motor itself.
Page 46