Middleby Marshall PS555, PS570, PS360, PS220 PS200 electric early with mercury contactors and fuses

SECTION 3 - SERVICING COMPONENTS

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.

Figure 76

PS200 electric (early) with mercury

contactors and fuses

Mercury contactor

Terminal

block

Fuseblock with 50A fuses

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

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 77

PS200 electric (current) with solid state

relays and circuit breaker blocks

Circuit breaker block with 50A breakers

Solid state

relay

140