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How to wire EH40 water heater timer/ EH10/ WH40/ WH21
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EH40 240Volt timer
30 Amp programmable/ DPST
Minimum 1 minute set times
Up to 6 on-off per week
AA battery for backup and power-outage carryover
1 year limited warranty
Override button located on face of timer.
Temperature range -40F to 104F/ back-up battery will fail when exposed to freezing temperatures
7-3/4" high x 3" deep x 5" wide
Use 10 gauge wire, 30 amp breaker rated for 4500+ watt element

Inductive: 30 Amp, 240 VAC
Resistive: 30 Amp, 240 VAC
Tungsten: 5 Amp, 240 VAC
1 HP, 240 VAC
Reset timer using reset button before programming
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Different arrangement of wires

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EH40 water heater timer
Wiring can vary because both wires are HOT: Jumpers can connect 2-3 -or- 2-5 etc. Different arrangement of wires
Terminals 3-4 and 5-6 are simple on-off relay switches that activate when timer turns on-off.  Terminals 1 and 2 are for powering the timer and relay switches. Relay switch terminals 3-4 and 5-6 are 'dry' and receive no voltage when power is connected to terminals 1 and 2... relay switch terminals are connected to terminals 1 and 2 as illustrated.
Always connect ground wires together on the green ground screw.
If wires are too short, but short length of wire and connect wires using wire connector.
Attach wire or conduit to enclosure using clamp

EH40     240Volt 7-day digital timer
10-2 wire<

EH40 sell sheet
EH40 manual
Figure volts amps watt for water heater
Basic water heater circuit
Color code wire
Compare all box type water heater timers
Compare 16 ways to control water heater

Jumper wire connects two terminals
10 gauge wire, 30 amp breaker
Timer rated 30 amp, 4500+ watt water heater
EH40 does not have a connection terminal for Neutral.

Keep end of wires straight.
Clean wire ends with sandpaper if discolored
Tighten screws very tight
Neutral wire?
Does 240 volt circuit have a Neutral? Generally no, because both wires are Hot. But some 240 volt circuits have 12-3 wire with 2 Hots and a Neutral wire.
If circuit has Neutral, then do not attach to screw terminal. Instead attach both Neutrals together with a wire connector inside the EH40 wiring compartment.
See wiring for main breaker box
Basic water heater circuit
      Attach wire or conduit to enclosure using clamp
Keep enclosure door closed
Keep plastic cover over wiring terminals unless power is OFF
Use correct wire and breaker
10-2 wire
Southwire electrical tools and wire
Electrical testers


 Select wire and breaker size                       
Read about Wire connector
EH40 controls 2 water heaters EH40 controls 2 water heaters/ same schedule
Must use 2 separate 30 amp breakers

EH40     240Volt 7-day digital timer

2 water heaters
Repair EH40?
How to repair EH40 timer
Use 24 hour mechanical  timer
Use ET series timer
eh40 controls 2 water heaters

EH40 controls 2 water heaters/ different schedules
Override button located on face of timer

EH40     240Volt 7-day digital timer

2 water heaters
EH40 controls 120 volt load
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EH40 controls 120 volt load
Use to power power-indicator light, pump, or any 120 volt load with same schedule as water heater


EH40     240Volt 7-day digital timer
Indicator lights
High grade indicator

Water heater recirculation system
EH40 off-peak water heater
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EH40 off-peak water heater
Use off peak strategy in conjunction with timer: Top of tank is heated while lower part  of tank is off. Lets you use timer to produce some hot water during peak prices, without turning water heater completely off.
EH40     240Volt 7-day digital timer

How to wire off-peak water heater
How to wire water heater thermostats

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Fire safety/ Do not use stranded wire under screw plate
Stranded wire can come loose under screw plate, causing connection to heat up, and become fire hazard over time.
Keep enclosure door closed.
Attach stranded wire and solid wire with wire connector, and run solid copper jumper wire to screw terminal
No insulation under screw plate
Use only solid copper wire
Do not put insulation under screw terminal
Take photo of wires before starting
Insdulation under screw plate
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Maximum 2 solid copper wires under screw plate
Max 2 wires under screw plate
Each wire must be same gauge
Attach multiple wires with wire connector, and run jumper to screw terminal
Wire and breaker size charts
EH40 is battery operated timer
Battery compartment located beneath buttons
Size AA battery lasts 2-3 years


How to repair EH40 timer
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WH40 water heater timer
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Optional 240 volt timer: WH40
Timer rated 40 amp.; 240 volt, commercial quality
24 hour mechanical timer
10,000 watt capacity> can control one or two water heaters
WH40 timer is same as T104 and T104-20, except WH40 has external override lever
Up to 12 on-off operations per day
Manual override reverses current program until next tripper returns timer to regular schedule
WH40      208-240-277Volt 10000 watt 40 amp
T104-20 (WH40)     208-240-277V (no external switch)
156T1978 trippers
Replacement trippers
Clock motor WG1573
10-2 wire
Wiring diagrams: How to wire WH40
WH40 manual
WH40 sell sheet
How to operate and set timer
List of replacement parts
WH21 timer
Optional 240 volt timer: WH21
25 amp, 240 volt. up to 5000watt water heater
SPST 240Volt: turns off one hot wire. EH40 turns off both Hot wires
Minimum 1/2 hour on-off times.
On trippers cannot be set closer than 2 hours
25 amp controls 
Red indicator light is ON when Load is ON
WH21      240Volt 23 amp
156EB1945a replacement trippers
WH21 clock motor WG233-18 from Intermatic
10-2 wire
WH21 manual
Wiring and Troubleshoot WH21 timer
Intermatic trippers and parts

Terminals 1 and 2 send power to 120V clock.
Jumper hot wire from terminal 2 to terminal 3.
Neutral wires connect to terminal 1
Ground wires are kept away from other wiring.
Wire connectors used where wire enters metal box.
Tighten screws very tight against copper wire.

120 volt timer: EH 10 timer for 120Volt
30 Amp digital timer
Uses AA battery for backup
Reset protocol for surge recovery
Use whole-house surge protector
1 year limited warranty
Minimum 1 minute set times
Up to 6 on-off per week

EH10     120Volt 7-day digital timer
12-2 wire

Wiring diagrams: How to wire EH10
EH10 manual
EH10 sell sheet

Figure volts amps watts for water heater
color-code household wire Applies to 120 or 240 volt circuits
Inductive loads like motors and pumps might require larger size to meet start amps
Resistive loads like water heater and incandescent light bulbs do not consume more amperage at start up.
Choose correct wire and breaker
Wire connectors
How to twist wire
Wire connectors
Basic house wiring
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