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See step-by-step how to wire contactor See basic water heater circuit How to install Old Work Box Compare 16 electric and 2 gas  water heater timers Do-it-yourself
water heater timer on wall

How to install water heater timer

Page 1 of 2: Overview /and Gather materials
Skip to Page 2: Connect the wires
install water heater timer

Project overview:

Attic installation shown.
Same plan works for water heater in basement or garage or closet.
Also works for any heavy-amp load such as heater, motor, pump etc single-phase or 3-phase.

See inside box with contactor

See wiring for all switches and timers
Control 2 water heaters with 1 switch
Control water heater with 2 switches
Control 1 water heater with 30Amp switch
See box-type timers
See Intermatic 'box-type timer' installation
See GE 'box-type timer' installation
ST01C timer controls 240Volt water heater
Larger image/ ST01 timer no neutral wire needed
Larger image with timer that has neutral wire

Example using ST01C 7-day timer

ST01C timer does not require neutral
Battery operated
Can control any voltage
Must be fuse-protected
240Volt coil DPDT contactor
Intermatic ST01 timer
See wiring for other switches and timersm

Gather materials for project

materials for water heater timer
Intermatic EI500  Grasslin ET616   

Choose timer or switch

Intermatic ST01 in-wall programmable single-pole or 3-way timer
More Intermatic in-wall timers (suggest Ei500 or Ei600... do not use EJ500)
Intermatic Ei200 single-pole countdown timer
Woods In-wall programmable single-pole timers
GE in-wall programmable single-pole or 3-way timers

More in-wall programmable
Spring wound mechanical timers
More countdown timers
Ordinary 15-20 amp switches
Old work boxe

Buy old work box

Available home center or online

Thomas and Betts old work box at Amazon
Old work boxes at Amazon
See How to install old-work box

Buy contactor with 240V coil

Project calls for 2-pole contactor with 240Volt coil
Available local electric supply or HVAC supply
240Volt coil 2-pole contactor At Amazon
120Volt coil 2-pole contactor At Amazon

Read more about contactors

Metal box

Buy 6x6x4 junction box

carlton 6x6x4 junction boxPlastic box
Available home center/ electric supply house/ or online

Buy: 6x6x4 plastic box:
no pre-drilled holes... must drill holes for romex connections, 1/2" hole for fuseholder, 3/16" holes for bolts to hold contactor, plastic box does not need ground screw connected to box
Cantex 6x6x4 PVC plastic enclosure with cover at Amazon
Thomas and Betts 6x6x4 plastic with cover at Amazon
Bud industries 11x7x5 box without knockouts
Buy: 6x6x4 Metal box: has knock-outs for 1/2 and 3/4" ... must drill 1/2" hole for fuseholder, bolt holes to hold contactor, threaded holes for 10-32 ground screw, metal box must be grounded.
Raco 6x6x4 metal pull box with cover and knock-outs
Raco 6x6x4 metal pull box with cover and knock-outs
RACO outdoor 6x6x4 box with bottom knockouts
Wiegmann 67x6x4 pull box with knockouts on 4 sides
Hoffman 6x6xx4 pull box with knockouts on 4 sides

Buy tapered drill/ step drill bit for drilling various size hole
Step drill bits at Amazon
Neiko tapered drill bit 1/4"-1-3/8" hole
See more about boxes
household wire
120Volt 14-2 wire will have Black-white wires
240Volt, 10-2 wire can have red-black or white-black wires... alsways add piece of black tape to white wire when used for 240Volt power. Adding black tape will signal that wire carries power


See wire color code and amp ratings

buy Lengths of wire

I prefer 14 gauge wire for timer connection for this project because it is easier to connect to fuseholder if fuseholder requires solder connection.
Also 14 gauge is easier to bend, and to easier to attach to small wires on timer

White/ #14 gauge wire for 15 amp
25 foot 14-2 NMB indoor wire with ground
50 foot 14-2 indoor wire with ground
100 foot 14-2 indoor wire with ground
100 foot 14-2 UF outdoor burial with ground
Yellow/ #12 gauge wire for 20 amp
25 foot 12-2 NMB indoor with ground
50 foot 12-2 indoor with ground
100 foor 12-2 UF outdoor burial with ground
#10 wire required for water heater
Orange/ #10 gauge for for 30 amp circuits including water heater
25 foot 10-2 NMB indoor with ground
100 foot 10-2 NMB indoor with ground
50 foot 10-3 indoor with ground
See wire color code and amp ratings
fuseholderBusman fuse holder

Buy fuseholder and 15 amp fuse

Panel mount fuse holders at Amazon
Buy fuseholder at Amazon
Buy fuseholders at Amazon

Ceramic fuses at Amazon

Read about fuseholders
wire nuts     

Wire nuts

Wire nuts at Amazon
Push-in wire connector up to 14-12 gauge

How to install wire nut

Optional Indicator light

240Volt Pilot light at Amazon
120Volt pilot light at Amazon
Indicator lights at Amazon
See illustration of 120Volt & 240v pilot light
cable staples Cable staples plastic at Amazon
Cable staples metal at Amazon
romex connector Romex connectors at local hardware or home store


Terminal kit at Amazon with crimp tool
Electrical terminals at Amazon
Blue 14-16 gauge female terminals 20 pcs at Amazon
Yellow 12-10 gauge female terminal 16 pcs
More about #10 & 14 female terminals

notes 14-16 B002UZXTYC   B002UZUIYQ   B000FPAJXS
12 ga  B00G9VVL0M   B00176877E
12-10   B0071NBGMA   B0071NC78C  B00176877E
8-32 bolts

8-32 x 3/4" bolt w lock nut

Ground screws at local home store or hardware

ground screws

Ground screws at local home store or hardware

Needed when using metal box so ground wire can connect to box
Use 10-32 tap to thread hole
Use regular 10-32 bolt with small washer
100 pack ground screws amazon
tapered drill bit

Optional: Tapered drill bit for plastic or metal box

Buy tapered drill/ step drill bit for any size hole
Step drill bits at Amazon
Neiko tapered drill bit 1/4"-1-3/8 holes

Buy electric wiring Book
Black and Decker Complete guide to wiring
More resources;
See inside main breaker box

You have the materials.

hand Go to Page 2: connect the wires.
main breaker box
Larger image
Gas and electric water heaters Support the economy:
Buy water heaters  from my associate links:

50 gallon Gas water heaters at Amazon
40 gallon gas water heaters at Amazon
50 gallon Electric water heaters at Amazon
40 gallon electric water heaters at Amazon
Hybrid / heat pump/ water heaters at Amazon

How to install gas water heater
Troubleshoot gas water heater
Troubleshoot electric water heater
box timers Compare box timers
programmable timer Compare programmable timers
Countdown timers Compare countdown timers
Compare power packs

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