Middleby Marshall PS200 series - Manual (Page 141)

140
SECTION 3 - SERVICING COMPONENTS
3. Supply
Ovens have a 208V, 220-240V, 380V, 416V or 480VAC
electrical supply. The control current of the oven oper-
ates at 110V, single phase. If the oven was specified
for a 3 wire system, it was supplied with an optional
control transformer to step the 3 phase current down
for the control circuit. If the oven was specified for a 4
wire system, the 4th (neutral) wire is utilized to split 2
of the 3 incoming 3 phase legs and obtain a separate
110V circuit. Most export ovens are supplied with a
stepdown transformer for the 110V control voltage.
Figure 76
PS200 electric (early) with mercury
contactors and fuses
Figure 77
PS200 electric (current) with solid state
relays and circuit breaker blocks
Mercury
contactor
Fuseblock
with 50A
fuses
Terminal
block
Solid state
relay
Circuit breaker
block with 50A
breakers
2. Part number reference
Part No. Description
27375-0001 Heating element, 208V
27375-0002 Heating element, 240V
27375-0003 Heating element, 380V
28041-0015 Mercury contactor, 3 pole, 50A
42810-0091
Contactor tube replacement kit (inc.
qty. 1 retainer clip P/N 27170-0248)
42810-0090 Coil replacement kit (inc. qty. 3 re-
tainer clip P/N 27170-0248)
28150-0130 Fuse, 50A, class T
31463 Relay, solid state, 75A
35018 Circuit breaker block, 50A, 3 pole
XI. ELECTRIC OVEN HEATING SYSTEM
A. PS200-series ovens
1. Description of heating system
All PS200-series electric ovens use an on-off system
for heater activation. When the oven demands heat,
the temperature controller activates contactors that in
turn activate the heaters at 100% power. The contactors
open when the temperature rises to 2 degrees above
the set point, and close when the oven’s temperature
falls 2 degrees Fahrenheit below the set point. Be-
cause of residual heat within the oven, however, the
temperature swing after preheating is about 5 degrees
Fahrenheit above and below the set point.
IMPORTANT: Because the PS200-series elec-
tric oven uses an on-off system for heater acti-
vation, the temperature controller MUST be
set to the on-off operating mode. Refer to Tem-
perature Controller on Page 30.
Early PS200-series ovens used mercury contactors.
208-380V ovens used two 3-pole contactors. 416-480V
ovens used a single 3-pole contactor. Six 50A fuses
(one per element) protect the heating circuit. See Fig-
ure 76.
Current PS200-series ovens replace the mercury
contactors with solid state relays mounted on heat
sinks. Six relays are used on 208-380V ovens. 416-
480V ovens use three relays. Ovens that use the solid
state relays also use 50A circuit breaker blocks in place
of the fuses. See Figure 77.
NOTE: All control wire used on these ovens is
rated at 221°F/105°C. DO NOT replace with lower
rated wire.