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Switching Relays

Switching Relays. Purpose. To use low voltage to control one or more loads efficiently such as fan relays and pump relays Normally they will energize a fan speed a. High fan speed for AC b. low fan speed for Heat c. also can be used for a heat relay. Make Up.

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Switching Relays

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  1. Switching Relays

  2. Purpose • To use low voltage to control one or more loads efficiently such as fan relays and pump relays • Normally they will energize a fan speed a. High fan speed for AC b. low fan speed for Heat c. also can be used for a heat relay

  3. Make Up • Magnetic coil to operate switching contacts when energized • Contacts are either normally open or normally closed A. The normally open contact will close when the coil is energized B. The normally closed contact will open when the coil is energized

  4. GENERAL PURPOSE RELAY 24-volt coil Normally closed contacts Normally open contacts Relay

  5. RELAY – NORMAL OPERATION 24-volt coil Coil energized Normally closed contacts are now in the open position Current flows through closed contacts Normally open contacts are now in the closed position Relay

  6. RELAY – DEFECTIVE COIL - CONTACTS DO NOT CHANGE POSITION Voltage applied to the coil 24-volt coil Current flows through closed contacts Normally closed contacts remain closed Normally open contacts remain open Relay

  7. MOVABLE CONTACTS AND ARMATURE STATIONARY CONTACTS COIL CONNECTIONS STATIONARY CONTACTS HOLDING COIL

  8. Coil ratings A.The coil voltage rating must be matched to the control voltage 1. Coil voltages are 24 VAC, 120VAC. 240VAC, and 460VAC • Contact ratings A. The contacts are rated for the amperage they are controlling B. Contacts use two types of loads- inductive loads, and resistive loads

  9. C. Inductive loads such as motors draw higher amperage when starting D. Resistance loads such as electric heaters amperage draw is consistent

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