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Basic 240 volt water heater circuit

Dia 1) Typical residential water heater: 240 Volt 4500 watt:
Black and White wires are hot > bare copper is ground
240 volt water heater circuit
Back to connect wires

When using black-and-white wires for 240Volt, add tape to white wire.
This action will tell next electrician that white wire carries power

Breaker box
Dia 2) Typical residential water heater: 240 Volt 3500 watt

240 volt water heater circuit
30 amp 10 gauge wire supports up to 5500 watt non-simultaneous water heater

20 amp 12 gauge wire supports up to 3800 watt non-simultaneous water heater

Read label on side of water heater.

Using 12 gauge wire on 4500 watt water heater can overheat wire and breaker, causing shortened breaker life and possible damage to breaker panel busbar

Using 12 gauge wire on 5500 watt water heater will blow breaker

Figure volts amps watts for water heater
Choose correct wire and breaker size
Water heater is tripping breaker
Dia 3) 3-wire 240 Volt circuit with neutral wire: uncommon
Not typically found in residential water heater circuits
Black and Red wires are hot > bare copper is ground > white is neutral
240 volt water heater circuit 
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Dia 4) 120 Volt water heater circuit: for under counter water heater 
Typical example of under-counter water heater
Black wire is hot > white wire is neutral > bare copper is ground
120 Volt water heater circuit
Water heater will work on any voltage
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Convert water heater to 120 volts

Main breaker
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Ordinary Main panel for home has 120 volt and 240 volt circuits.
This is called single-phase electric power. Phasing is determined by the power company transformers.

- Each 120 volt circuit can include up to 12 outlets, and supply power to lights inside a room.
- Generally each 120 volt circuit sends power to one area of home. This is because the wire leaves breaker box and goes to first junction box inside a room. From the junction box, the wire splits off and goes to each individual box, jumping from box to box until the final box is reached. So each box will have 1 black hot wire, 1 white neutral wire, and 1 ground wire that connect back to main breaker box.
- Some circuit breakers are dedicated to 1 specific appliance. For example the kitchen microwave is usually wired to 1 circuit breaker and no other outlets or lights are connected to that breaker. This is because microwave draws so much amperage. That is called dedicated circuit, and dedicated breaker.

- Each 240 volt circuit is usually dedicated to one appliance. For example electric water heater is connected to 1 240 volt breaker. The electric dryer is connected to another 240 volt breaker. The heat/AC is connected to another 240 volt circuit breaker, and so on.
See inside main breaker box
How to replace circuit breaker
How to install subpanel
Figure volts amps watts for electric water heater
Difference between single-phase and 3-phase
Main breaker box
How to replace circuit breaker

Inside main breaker box are Three busbars.
One busbar is Neutral busbar.
Two busbars are Hot busbars.
Each Hot busbar is 'out of phase' with the other.

All residential circuits require Two wires to complete circuit.
120Volt circuit requires 1 Neutral wire and 1 Hot wire.
Hot wire can come from either Hot busbar.
By Code, these wires are Black-Hot and White-Neutral.
If either wire is interrupted, the circuit turns OFF.
By code the Black Hot wire is switched ON-and-OFF.

240Volt circuit also requires 2 wires to complete circuit.
In the case of 240V, the circuit requires 2 Hot wires.
One Hot wire from each 'out of phase' busbar is required to complete 240Volt circuit.
These wires can be Black and White or Black and Red, and with heavier gauge wires, like 6 gauge and 4 gauge, the wires are Black and Black.
If either wire in 240V circuit is interrupted, the circuit turns OFF.
See 30 amp switch turning off water heater
Bare ground wire connects to Neutral busbar as redundant safety.

Electricity from pole to breaker box

How to install Subpanel
Electricity is a wave that oscillates at 60 cycles per second. This is called 60 Hz.which appears on electric device labels.

120 volt is like pedaling a bike with one leg. 240Volt is like pedaling bike with 2 legs.
Commercial 3-phase is like pedaling a bike with 3 legs.

Household power is called single-phase or split phase.

Electricity from power plant to distribution substation
What is 3-phase electric: power plant to end user
The grid is defined by three parts: transmission, distribution and end user. The following links show how it works
Power plant to end user power pole
Power pole to residential breaker box
Power pole to commercial breaker box

How to wire residential electric
How to wire commercial 3-phase

Why you need ground wire
How to wire 3-phase timer
3-phase water heater
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