Question about Intermatic GM40 - 24 Hour/7-Day Dial Electromechanical Time Switch - NEMA 3

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Replacing an old timer with a new gm40.

I currently have an intermatic timer that is not working properly. I have purchased an intermatic gm 40. I'm trying to figure out which wires go where on the new timer. I have 2 black, 1 white, and a ground. The terminals are labeled differently than the one I'm replacing. It's 120v single load.

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Here is the instructions for your unit:

Intermatic GM40

Go to page #4 for wiring instructions on 120v dual loads.

Hope this helps and please rate this!

Posted on Dec 09, 2008


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Have Grasslin GM Series 30 amp timer. R1 resistor is burned out. Can you give me the ohm value and wattage for R1 on the pc board.

R1 is probably different for different models of the timer.

Normally if R1 is burned... look carefully and other nearby parts have signs of burning also.
R1 is the first place you see the overheat problem,,, and that's true with the older and newer models in the GM and Woods series timers, including defrost series.

Contact and see if they offer a schematic and replacement parts sheet... but I've not seen a parts sheet.

The timer is usually taken out of service and replaced once R1 is burned.
Frequently these timers with burned R1 are sold on ebay after they have been removed from service... simply because the timer looks good or repair seems simple.

Replace timer?


Oct 08, 2014 | Hardware & Accessories

1 Answer

2red wire and one green going to switch, need to hook up timer gm40av which wires go where

GM40AV automatically detects line voltage. So there are NO dip switches. Timer handles 120V thru 277V, including 208V and 240V.
Probably both red wires connect to terminals L1 L2. And this will power the timer clock. Green goes to green ground screw.
Wiring for GE40 and GM40AV is identical, except no dip switches for GM40AV
GM40 series timers are very versatile and can be wired many different ways, including 3-phase applications, multiple loads with different voltages etc. Add comment and describe what you are wiring, and attach photo if needed, and I can go step by step.

Aug 08, 2013 | Hardware & Accessories

1 Answer

After lighting strike my grasslin gm40 only works manually are the relays fried?

1) Something is fried. Probably the electronics if relays turn on-off with override.

2) Try moving dip switches to different voltage, and change wiring and voltage for possible work around.
For example if you are controlling 240Volt, then move dip switches to 120V and run neutral wire to timer and use one 120V hot leg from 240Volt circuit to power clock motor.

3) If timer module is not rotating, then remove module for identifying marks on back. Order new FM1 timer module.

4) There is no reset protocol for this timer, or surge protection. Timer has one year warranty against workmanship defect. There are no replacement circuit boards.

5) Buy cheaper-made GE 15207 timer at Home Depot. Then if timer goes bad, buy another timer and return defect in new box for refund. This gives timer owner unofficial extended warranty.

Feb 12, 2013 | Intermatic GM40 - 24 Hour/7-Day Dial...

1 Answer

How to wire my intermatic GM40 to a two speed pool motor

Copy following link for illustration showing GM40 controlling 2-speed pool pump.
Same wiring applies for 120Volt or 240Volt.
Voltage, Wire colors and wiring illustration appear on pump name plate.
Be sure to set dip switches before applying voltage to timer.
Do not test wires by sparking against terminals. Use a tester.

Jul 14, 2012 | Intermatic Hardware & Accessories

1 Answer

I need to hookup up a Grasslin GM40 timer controlling one load and a 120vac application. Just wondering if someone could verify the hookup terminals as I cannot read the schematic as it is mostly gone. ...

Open following links to identify timer and download manual:

GM40 can be used for 120V or 240V 277V applications for single-phase and some 3-phase applications.
For 120Volt, set all 4 dip switches to ON position BEFORE applying power.
ON position is pushed to left.

120Volt cable from breaker box has black hot and white neutral wire.
Black hot typically connects to terminal L1
White neutral connects to terminal L2/N
This action will power the time clock and relays.

Other terminals on GM40 are the relay terminals, and these terminals are dry.
Dry means they receive no power when wires are connected to L1 and L2/N.

There are two independent relays and each relay has 3 terminals: NC NO and COM.
If you are controlling one 120volt Load, then use one relay.
Run a jumper wire from terminal L1 to COM terminal.
So COM terminal is connected to Hot.

Cable going to 120V Load has black and white wire.
Connect black Load wire to terminal NO (normally open).
Connect white Load wire to L2/N.

Jul 19, 2011 | Intermatic GM40 - 24 Hour/7-Day Dial...

1 Answer

How do I wire a 220 volt two speed swimming pumpmotor using aground fault circut creaker

More information is needed.
Is the circuit breaker 240Volts or 120V?
Is the pump 240V?
What kind of switching timer is connected to pump?
What color are your wires?
Read information below and then add a comment.

Typically, the pump is 240Volts.
Pump is wired to mechanical timer with NO NC contacts for example GM40 series:
The timer sends power to one speed or the other speed but not both speeds at same time.
Timer can be mechanical or digital.
Mechanical timer is used if pump is supposed to be ON at all times.
Digital timer like P1353 is used to control pump more exactly.
See example1 for 240V
Timer is rated or set for 240Volts.

GFCI protected 240Volt line leaves circuit breaker and goes to timer. Then timer and pump are both protected.

Jul 09, 2011 | Electrical Supplies

1 Answer

Lights come on but don't stay on even though the tabs are set for it to stay on say from 4-12 it will go off at 7:30. Someone got thier hands on this before i did---could the tabs have been broken if...

GM40 is commercial-grade electronic time piece with FM1 analog timer dial.
I bought a used GM40 once and the electronics were bad, so if this is a used timer, it might not function as expected.

I don't think the tabs/pins are broken. FM1 timer module is heavy duty.
Turning the dial clockwise does not damage timer. That's how you set current time and test timer.
Rotating dial counterclockwise is not possible without breaking the timer.

FM1 analog timer module can be replaced if timer stopped working.

If certain pins/tabs are broken, you might be able to work around problem by offsetting current time by 6 hours or 12 hours. Or you can move wires from NO to NC terminals and see if the relays are causing a problem.

To set FM1 timer, the pins are pushed outward or inward.
For example to turn on Load for 1 hour, then 4 consecutive pins are moved.
To turn on Load for 3 hours, then 12 consecutive pins are moved.
To test if pins need to be inward or outward, set some pins and then manually rotate timer dial clockwise and watch when the Load turns on-off.

Jun 19, 2011 | Intermatic GM40 - 24 Hour/7-Day Dial...

1 Answer

I have a GM 40 Series Multi Voltage Commercial DPDT time switch .Voltage reading across L1 L2 is 240. Orange and green light are both energized wired NO COM water heater not turn on.

Online manual for GM40:

You own a high-quality time piece.
I have defrost versions of same timer and have tested aspects of the timer, and own few FM1 series clock mechanisms for various projects.

Complete run down for setting GM40:
1) For 240Volt the dip switches are set: Please set dip switches before applying power to timer.

2) Line wires are the Hot wires from breaker box.
Line wires connect to terminals L1 and L2N

3) Load wire are wires that go from the timer to water heater.

4) Jumper wires are short lengths of same gauge wire.

5) There are many ways to wire GM40 timer
Open manual and look at wiring diagram titled: Controlling one 240VAC (Dual Phase) Load

6) A jumper wire is added from terminal L1 to COM
Another jumper wire is added from terminal L2N to COM2

7) Load wires going to water heater are connected to NO and NO2

8) Following image shows typical FM1 timer dial:
As timer dial rotates the pins move small red switch that turns Load on-off.
Move pins in-or-out to control Load.

9) If you are uncertain about your pins, then set 20 consecutive pins one direction and then manually rotate dial and watch green indicator light turn on-off.
Put tester across NO and NO2 terminals and check when 240V turns on.

10) If you have defective timer, contact Intermatic:

11) Add a comment for more free help.
Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.

Feb 27, 2011 | Intermatic 7 Day Electronic Timer Eh10...

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