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How to wire transfer switch
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30 Amp Generator Transfer Switch Kit Transfer switch
Purpose is to switch power OFF on specific breakers when you connect generator to household breaker panel.

Why you need transfer switch
When power goes out on the grid, any electricity that you generate can go backwards to the power company transformer and be converted to high voltage on the distribution wires. The existance of electricity of these wires is a danger to anyone coming into contact with the line, including linemen trying to do repairs. The situation slows repair and increase cost. As a result, a transfer switch is required to shut off home-generated power from reaching the main breaker panel and then out to the grid wires. Same requirement is true for home-generated solar power: it must be connected to equipment that automatically disconnects grid connection when grid power is OFF.

When you need transfer switch
Whenever you connect generator to any wire that is connected to main breaker panel.
You can run a generator and plug in tools etc without a transfer switch.
Buy
Transfer switch at Amazon

Resources:
Reliance 31406CRK manual/pdf
generator You can run a generator and plug in tools etc without a transfer switch as long as home-generated power is not connected to any household wiring
120 and 240 volt generators are used for homes and construction businesses etc
Check the total wattage output, portability vs need
If you are connecting the power to main breaker panel, you MUST turn off main breaker and disconnect from power company service ... or use a transfer switch.

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Generators at Amazon

Resources
How to wire 240 volt outlets
twist lock plug     
Twist-lock plug will not pull out of receptacle
Twist lock plug for extension cord that plugs into generator
Install 20 or 30 amp as needed.
X Y terminals go to either Hot wire.
W is always Neutral.
G is always ground.
These are standard markings for 240 volt plugs and outlets.
Connect X to one hot busbar inside the transfer switch, connect Y to other hot busbar, ground and Neutral to respective terminals
Buy:
Leviton 2711/ 125-250 volt/ 20-30 amp/ 3 pole
Resources
How to wire subpanel
How to wire 240 volt outlets, plugs, switches
Difference between single-phase and 3-phase
Image below shows main breaker panel without transfer switch
In a time of power outage, it is very important that generators are not sending power to the main panel, because that power will travel backwards out the main breaker and re-energize the distribution lines that enter house.
If the main distribution lines are still energized, that can be dangerous and slow the rate of repairs.
Image below shows Transfer switch installed
When generator is OFF, the transfer switch breaker is pushed one direction. Power leaves from the main breaker panel, travels through the transfer switch breaker, and then goes to 120-240V load.

When generator is ON, the transfer switch breaker is pushed the other direction. Power leaves the main panel breaker and travels to the transfer switch breaker .... but cannot go farther, so the transfer switch effectively turns off any power that could come from breaker, and turns off any chance of generator energizing the breaker panel and power company wires. When generator is ON power from the generator leaves the transfer switch breaker and travels to the load.
Each main panel breaker that is wired into the transfer switch will operate the same.
The transfer switch only designated loads that are connected as illustrated below.
Transfer switch
Image below shows how to toggle water heater from 240 volt to 120 volt
Works any time, not just when the generator is on.
If your transfer switch does not have 30 amp breaker it is a problem UNLESS you change elements to 3500 watt,  in which case water heater will work fine with 20 amp.
The math: Volts x amps = watts.
4500 watt element divided by 240 volt = 18.75 amp
So technically a 20 amp breaker is sufficient for 4500 watt water heater, except when applying the 80% safe maximum used to calculate loads today.
20 amp breaker x 80% = 16 amp maximum ...; which means 20 amp breaker is undersized slightly.

30-amp 3-way switch (SPDT switch) can be added to the circuit so you can toggle 240 volt water heater to 120 volt.
Works for ordinary residential water heater, but not heaters with electronic circuit board, electronic thermostat, This means the diagram will not work for tankless, heat pump, energy smart etc.
Reducing to 120 volt reduces heat time by a factor of 4, so typical tank will heat 4+ gallons per hour at 120 volt ....  gives you some hot water and more generator capacity to run lights, water well pump, grandpa's oxygen machine etc.
Adding a 30 amp SPST switch to either wire going to water heater will let you turn off heater completely.
Caution: You can toggle any time when generator is running as long as generator loads are relatively balanced.
Balanced load: a residential generator produces two out-of-phase 120 volt legs, with 240V potential across both legs. If you draw too much power off one leg, it causes disturbance in the magnetic field around the generator, and alters the waveform of electricity ... which can affect electronic devices inside house, and overheat generator.
All 240 volt loads are automatically balanced because they draw from both legs, but imbalance occurs when pulling power off 1 leg.
If you want to use the 120 volt strategy, set up your balanced generator loads to accommodate the change, usually within a range of 80% watt rating of generator.
Buy SPST:
Cooper 3032 switch at Amazon
Leviton 3032 30 amp switch at Amazon
Leviton 30 amp switch at Amazon
30 amp switches at Amazon

3-way switch wiring

DPDT switch wiring
Image below shows best way to toggle water heater from 240 volt to 120 volt
Works any time, not just when the generator is on.
If your transfer switch does not have 30 amp breakers it is no problem if you're connecting 120 volt, but IS a slight problem for 240 volt  ... UNLESS you change elements to 3500 watt,  in which case water heater will work fine with 20 amp.
The math: Volts x amps = watts.
4500 watt element divided by 240 volt = 18.75 amp
So technically a 20 amp breaker is sufficient for 4500 watt water heater, except when applying the 80% safe maximum used to calculate loads today.

20 amp breaker x 80% = 16 amp maximum ...; which means 20 amp breaker is undersized slightly. 30-amp DPDT 3-way switch with center off solves all the problems with imbalance, toggling between voltages, and turning off heater entirely. Bang done right.
But this design takes more breaker spaces in the transfer switch and requires dedicated 30 amp breaker in the main panel.
Works for ordinary residential water heater, but not heaters with electronic circuit board, electronic thermostat. This means the diagram will not work for tankless, heat pump, energy smart etc.
Buy double-pole double throw 30 amp
2 DPDT switch with center off 
2 DPDT switch with center off

Resources:
30 amp switch controls water heater
How to change 240V water heater to 120V
Figure volts amps watts
How to wire 240 volt outlets
Generators
What is 3-phase
wire transfer switch

30 amp DPDT switch

For certainty, always Test switch terminals using continuity tester before wiring.
24 amp safe maximum
Toggle water heater between 120Volt and 240Volt
30 amp 2 pole DPDT switch with center off
Use diagram that comes with device. Diagram shown might be different from your switch. Check terminals for continuity using multimeter.
120 volt Hot and Neutral connect to A1 A2 in either order, or you can connect to B1 B2. Water heater must be connected to L1 L2
Max 4500 watt non-simultaneous water heater
Use 240Volt when electric prices are lower, and faster recovery is needed. Use 120Volt during peak prices when less hot water is used
Buy
2 DPDT switch with center off
Multimeter

Connect 120Volt wires as Hot and Neutral. Black connects to 120Volt circuit breaker and White connects to neutral busbar.
Connect 240Volt wires as Hot1 and Hot2. Both wires connect to 240Volt breaker.

Double pole double throw 30 amp switch
Buy DPDT 30 amp switch w center off
2 DPDT switch with center off at Amazon
2 DPDT switch with center off at Amazon
Risk to motors and HVAC from generator
Generator can cause low voltage and phase fluctuations.
The problem of low voltage and phase fluctuation (lower voltage on one wire and not the other) do not affect resistance loads like light bubs or electric water heater, except to make them burn at dimmer capacity.
However low voltage and phase fluctuations do affect inductive loads like contactors, relays, motors, pumps, HVAC causing problems such as chatter on contactors and relays, and lower rotation speed on motor, causing higher temperatures, and burning out the motor or shortening motor lifespan.
voltage monitor
Larger image
IMC492 Single-phase Voltage monitor
Household power 120-240 volt is single phase.
Voltage monitor Protect motors and equipment from low voltage.
Adjustable voltage range
Caution: select monitor voltage to match incoming Line voltage
Select amp rating of contactor to match amp rating of Load (motor, pump etc)
Select matching contactor voltage and coil voltage range
Undervoltage on contactor coil will cause chattering and malfunction, Overvoltage on coil will melt coil.

Buy:
Single phase 95-270 volt range
3-phase 80-300 volt range
ICM phase monitor
Siemens monitoring relay

Resources:
Fuseholders
Contactors
Surge protector
Difference between surge and ground
Difference between single phase and 3-phase
IMC492 manual
Siemens .pdf


Locking plugs
Locking plugs/ twist lock
Nema L5 (look at bottom of graphic for Nema category) is same configuration for 20P or 30P/ use for 15, 20 or 30 amp
Nema  L6 is same configuration for 20P or 30 P/ use for 15, 20, 30 amp
Nema  L14, 4-pole is same configuration for 20P or 30P/ use for 20 or 30 amp
125 volt 3-wire has silver, brass and green screws
250 volt 3-wire has brass, brass, and green screws

Buy:
Leviton 2611/ 125 volt/ 15-20-30 amp/ 3-pole
Leviton 2621/ 250 volt/ 20-30 amp/ 3-pole
Leviton 2711/ 125-250 volt/ 20-30 amp/ 3 pole

Resources:
Locking plug Wiring diagrams
Wire 240 Volt outlet Resources
How to wire 240 volt outlets
Cooper 30 Amp switch Water heater can be controlled directly with 30 Amp switch.
Use green color-coded 30 Amp switch and & 10 gauge wire.

Buy 30 amp switches:
30 amp switches
30 amp single pole switch
30 amp double pole switch
30 amp 3-way switch
30 amp switches at Amazon

Resource:
See 30 Amp switch installation
Double pole double throw 30 amp switch Toggle water heater between 120 volts and 240 volts
Use DPDT 30 amp with center off
Ordinary 30 amp 3-way switch will do same job, but without center off
Slower heating during peak electric pricing can save money where hot water is still needed during peak pricing.

Buy double-pole double throw 30 amp
2 DPDT switch with center off at Amazon
2 DPDT switch with center off at Amazon

Resources:
How to convert water heater to 120Volts
See wiring diagram
See off-peak water heater options

Orange 10 gauge 30 amp breaker


Orange/ #10 gauge for for 30 amp circuits including water heater
with ground
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10-2 gauge/ 30 amp
10-3/ 30 amp

NMB is house wiring
UF is underground
Yellow 12 gauge 20 amp breaker


Yellow/ #12 gauge wire for 20 amp
with ground
Buy
12-2 gauge/ 20 amp
12-3/ 20 amp

Rolls of stranded wire

NMB is house wiring
UF is underground
White 14 gauge 15 amp breaker


White/ #14 gauge wire for 15 amp
with ground
Buy
14-2 gauge/ 15 amp
14-3/ 15 amp

NMB is house wiring
UF is underground

Copper ground wire
Use same size as other wire in circuit

Buy
Spools of ground wire

elements
Elements

Contactors/ relays

Z-wave/ wifi
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Troubleshoot electric water heater
Point of use water heaters
Resources:
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Icon gas valve

How to replace water heater element Waste King disposal
How to wire tankless electric


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Titan tankless

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