Timers - Further Reading


Timers controlling pool equipment are necessary to manage energy usage and control that equipment operates in the correct sequence. Typically pump, cleaners, SWGs, heaters, and lights may be controlled by internal timers or external timers. Pool Automation Controllers can provide the timing and control of most pool equipment. Where equipment does not have an internal timer, or connected to automation, then an external timer is used.

Intermatic Timers

Intermatic[1] external timers are often used in pools and spas.

Intermatic T100 Series Timers

The Intermatic T100 Series of timers are mechanical with a 24 hour yellow dial that uses moveable trippers to set multiple ON and OFF times.

Key differences in the T100 Series models are:

  • Clock motor voltage
  • Switch type
    • Single Pole single Throw - SPST
    • Double Pole Single Throw - DPST
    • One Normally Open, One normally Closed Contacts - NONC
  • Enclosure type
    • Outdoor Type 3R Metal (R)
    • Outdoor Type 3R Plastic (P)

Popular Intermatic models are:

  • T101 - SPST with 120V clock motor
  • T103 - DPDT with 120V clock motor
  • T104 - DPDT with 240V clock motor
  • T106 - NONC with 240V clock motor

SPST timer can switch a single 120V hot line DPDT timer can switch two independent 120V hot line or the two hot lines for a single 240V device.

T100 models with a M suffix are mechanism only and can used to replace the timer in an existing enclosure.

The T100 series timers have a manual level below the clock dial that can be moved left or right to turn the power ON or OFF. Moving the lever will not effect the next operation of the trippers.

Heater Control

The T101 or 104 timers can have an optional 156T4042A Heater Control Switch Kit[2] that will open the fireman's switch on the heater 20 minutes before the timer, usually controlling the filter pump, will shut off. The heater control will prevent the heater from operating EXCEPT when the Time Switch contacts are closed (automatically or manually).

Models that have the 24-Hour Mechanical Time Switch in Enclosure with Pool Heater Protection are:

  • T101P201 - 120V SPST plastic enclosure with Pool Heater Protection
  • T101R201 - 120V SPST metal enclosure with Pool Heater Protection
  • T104P201 - 240V DPST plastic enclosure with Pool Heater Protection
  • T104R201 - 240V DPST metal enclosure with Pool Heater Protection

The 156T4042A Heater Control Switch Kit can be added to any existing T101 or T104 timer.

Mechanical Timers with Power Centers

Intermatic has a line of power centers that have one or two timers in an enclosure to meet different needs. One of the more interesting combinations is the T10604R | 30 A Power Center with T106M & T104M Mechanisms[3] that can be used to control two speed pumps.

T100 Series Tripper Pins

There are two different tripper pins for ON and OFF on the 24 hour timer wheel. You position the appropriate timer pin, ON or OFF, at the time you desire. Tighten the screw down tight so that the tripper does not slide on the wheel.

Replacement tripper pins can be purchased at Home Depot, Amazon and other online stores. Make sure you get the tripper pins for the Series timer mechanism you have. The tripper shapes are different for various series timers.

Intermatic 156T1978A Time Switch Trippers is for the T1000 Series.[4] This Intermatic Order Form lists tripper for other series timers.


The T100 series timer mechanisms are not designed to be repaired. When the motor stops turning, the gears wear out, or the tripper pin mechanism wears out the unit should be replaced.

Timer Skipping Times

When the timer dial moves past a tripper pin and does not turn the load ON or OFF as set by the tripper it usually means the mechanism has worn out and needs replacement. Sometimes you can bend the dial to get it to make contact with the tripper for a while but the problem will likely reoccur in a while.

The timer motor turning the dial hots the tripper pin with enough force to move the mechanical level on or off. Over time the constant contact wears the mechanism until it no longer can push the lever and skips by it.

Dial Not Turning

Check that the two white power wires are connected to the 120V or 240 terminals. Conform that you have the correct voltage for the timer motor.

If you have power to the timer motor and it is not turning it is likely burnt out and the timer mechanism should be replaced.