Middleby Marshall PS224 PS310, PS570 Electrical leads disconnected, B. PS310/360-series ovens

SECTION 3 - SERVICING COMPONENTS

B. PS310/360-series ovens

1.Description of heating system

All PS310/360-series electric ovens use an on-off sys- tem for heater activation. When the oven demands heat, the temperature controller activates mercury 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. Because 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 PS310/360-series electric oven uses an on-off system for heater activation, the temperature controller MUST be set to the on-off operating mode. Refer to Temperature Controller on Page 30.

Each bank of heaters (3 total) uses one mercury contactor and three fuses. 30A fuses were used through 1/91. Heat inside the machinery compartment can de-rate these fuses, causing the fuse to blow pre- maturely. To correct this situation, 40A fuses were used 2/91 and later.

NOTE: All control wire used on this oven is AWM rated at 221°F/105°C. DO NOT replace with lower rated wire.

2. Part number reference

Part No. Description

27374-0001 Heating element, 208V

27374-0002 Heating element, 240V

27374-0003 Heating element, 380V

28041-0016 Mercury contactor, 3 pole, 30A

27170-0251 Contactor tube replacement kit

27170-0250 Coil replacement kit

28154-0002 Fuse, 30A, class M (early)

28150-0134 Fuse, 40A, class T (current)

27021-0016 Fuse block, 40A (used when upgrading from 30A to 40A fuse - qty. 3 reqd.)

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.

Figure 80	Figure 81
Removing the element bank mounting bolts	Electrical leads disconnected

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