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How to wire Tankless electric water heater
Stay safe.
Turn power OFF
FYI; Manufacturer's literature and side-by-side research shows whole-house tankless electric, for average family of 4, costs $100 more per year to operate vs ordinary tank-type heater.
Large research file
General troubleshoot .pdf

I have to read ? 

EcoSmart tankless

EcoSmart manual
Rheem tankless

Rheem tankless
Rheem tankless

Rheem manual
Breaker size chart
Atmor tankless
Atmor tankless

Atmor manual
Stiebel Eltron tankless
Stiebel Eltron
Stiebel Eltron tempra

Steible manual
Eemax tankless
Eemax tankless

Eemax manual
Chronomite tankless
Chronomite tankless

Chronomite manual
iHeat tankless
iHeat tankless
Titan tankless
Titan tankless

Titan manual
Bosch tankless
Bosch tankless

Bosch manual
Step 1: getting started
circuit breakers are warm
Do not install tankless electric if main box is overheated
Test if electric service panel is adequate for tankless:
1) Open following link to Stress-Test main breaker and service panel:  Main breaker stress test
Example: if you have 150 amp service, maximum load is 80% or 120 amps. Exceeding 80% causes main breaker to start getting warm. Over time, the breaker gets weak, and overheats on busbar, damaging panel. 
So if you add small tankless unit requiring 50-60 amp breaker, you might need larger service. Do the stress test.
Example:, if you have 200 amp service, maximum load is 80% or 160 amps.  So if you add whole-house tankless requiring 120-180 amps, you probably need up-size to 250 amp service depending on other household loads such as freezer, pool pump, oven etc.
2) To Figure amps for tankless: Read label on side of tankless for Volts and Watts. Divide watts by volts to get amps.
3) Add amps from tankless to service panel stress-test.

If electric service is too small, then install new service.
Or use ordinary tank-type heater and save your money, and headaches How to increase amount of hot water
Look at rating plate located on side of unit
Read the manual
1) Look at electrical rating plate showing voltage and wattage
or -Look at product spec sheet.

2) Consult Tankless manual if available
Failure to follow steps in manual will void product warranty

3) Warranty Caution:
The warranty covers defects in manufacturer's workmanship, but does not cover DIY installation or electric wiring.

Overview of installation steps
Step 2: If tankless has factory-connected wire
Do not undersizes wire and breaker
How to wire tankless electric
Larger image
Factory-connected wire/ or pigtail attached to tankless
Read rating plate on side of unit for amps and watts.
Connect wire from breaker and factory pigtail inside octagon box using wire connectors
This type of tankless will have 1 heating element.
How to select and install correct wire connector
Select correct wire and breaker size
How to wire 240Volt outlets
Step #3       Look inside tankless unit for wire connections
Single wire cannot be split apart to connect to multiple terminals.
tankless electric
This Example shows tankless supplied by 1 wire

Wires can be black-black, white-black or black-red
Ground wire is required
Tankless MUST be grounded
Color code for wire
Single 240Volt has L1 and L2
L1 L2 means 240 volt with 2 Hot wires
Use 1 circuit breakers

1) Look for single block with L1-L2 terminals where you will install wires under screw plate
-or- look for 2 wires where you will connect with wire connectors
Single wire cannot be split apart to connect to multiple terminals.
2) Look at rating plate on tankless to determine total watts
3) Scroll down to see wiring examples for breaker
How to select and install wire connector

2 wire 240Volt has 2 sets L1 and L2
Single wire cannot be split apart to connect to multiple terminals.
Use 2 circuit breakers
Rheem RTE27: use two 60 amp breakers, and two 6 gauge wires

3 wire 240Volt has 3 sets L1 and L2
Single wire cannot be split apart to connect to multiple terminals.
Separate wire needed for each set L1-L2 terminals
Use 3 circuit breakers
Main breaker warning
Screws on main breaker are HOT at all times
Even when main breaker is OFF, both screws are HOT
Only if meter is PULLED are these screws safe to touch
What size breaker and wire should you use?
240Volt ratings:
7.7 Kw= 7600 watts / 40 amp breaker/ 8 gauge wire
9.6 Kw = 9600 watts/ 50 amp breaker/ 6 gauge wire
11.5 Kw = 11500 watts/ 60 amp breaker/ 6 gauge wire
13.4 Kw = 13400 watts/ 70 amp breaker/ 4 gauge wire
16.3 Kw = 16320 watts/ 85 amp breaker/ 3 gauge wire

This example shows Tankless with terminal connections for 3 wires
Larger image
Example shows 3 wires connected inside tankless
Electricity supplied by 3 separate wires from 3 breakers
Total electric consumption for typical tankless electric is 96 to 120 amps.

Before installing tankless electric, look at main breaker on household service panel.
If main breaker is 150 amps, then it is max-ed out carrying this tankless load.
Breakers are rated safe maximum at 80%
Main breaker 150 amps x 80% = 120amps safe maximum

Tankless electric water heaters consume large amount of electricity
This is because electric elements cannot heat water as fast as natural gas or propane gas.
Tankless electric water heater will cost more to operate than ordinary tank-type electric water heater.
This is because so much energy is wasted trying to heat water as it passes quickly in pipe.

To reduce energy consumption, add a tempering tank to preheat incoming cold water, keep thermostat setting low, reduce consumption, lower water pressure, add low-flow shower heads.
If water moves too slowly through the pipe, tankless may not activate

Step #4       Inside Main Breaker box

Main breaker warning
Screws on main breaker are HOT at all times
Even when main breaker is OFF, both screws are HOT
Only if meter is PULLED are these screws safe to touch
Main breaker box for tankless electric
Larger image
Three 50 amp 240Volt breakers
Use 50 amp breaker with 6 gauge wire
No difference if all breakers on same side of panel, or on different sides.
Requires 250 amp service and 250 amp main breaker.
Wire size chart
Main breaker Stress test

Circuit breakers at Amazon
Shop Amazon - Industrial Electric Products
wire size chart

Buy circuit breakers
Eaton CL series circuit breaker
CH circuit breakers at Amazon
Federal Pacific circuit breaker
QO circuit breakers at Amazon
double-pole breaker
Buy circuit breakers
Choose from 15 to 125 amp
Siemens circuit breaker
GE circuit breakers at Amazon
Double check wire size and distance
100'-150' etc requires larger diameter wire

240 volt/ each breaker
greater than 7.7 Kw= 7600 watts / 40 amp breaker/ 8 gauge wire
greater than 9.6 Kw = 9600 watts/ 50 amp breaker/ 8-6 gauge wire
greater than 11.5 Kw = 11500 watts/ 60 amp breaker/ 6 gauge wire
13 Kw = 13400 watts/ 2 60 amp breakers/ 6 gauge wire
Select correct wire and breaker size
50-60 amp breaker use 6 gauge /
6-2 wire
6-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
40-50 amp breaker use 8 gauge /
6-2 wire
8-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
30 amp breaker use 10 gauge /

10-2 gauge/ 30 amp
10-3/ 30 amp
Southwire electric tools
Install subpanel for Tankless electric
Larger image of 240 Volt subpanel
Image of 120V-240V subpanel
240 Volt Subpanel for Tankless electric
***White Neutral wire is not needed for 240Volt breakers.
Ground wire arriving from main panel can be connected to busbar at top of subpanel, or install a separate ground busbar lower on panel. Keep ground wires away from Hot connections and Hot busbars.
Sometimes it is easier to add ground busbar near bottom of subpanel so ground wires can be kept away from Hot connections.

Illustration shows how to install subpanel for adding more breakers to main panel
With tankless electric, install 150amp breaker/ replace any 2-pole breaker close to top of panel
Use 2/0 wires with 150 amp breaker
2/0 copper wire between main panel and subpanel, up to 100 feet.
Install 3 40-amp breakers in subpanel to supply each of three 240Volt #8 wires going to Tankless.
Read nameplate on Tankless for watt rating.
#8 wire for 240Volt loads up to 7680 watts
Use 50 amp breaker and #6 wire for 240volt loads above 7680 and less than 9600 watts
For example tankless with single wiring terminal, might require 9600 watts or more
How to install subpanel

*Neutral wire is not needed if subpanel is NOT going to have 120volt breakers.

Place subpanel within eyesight of Tankless to avoid disconnect requirement
Disconnect lets electrician cut power to Tankless unit.
Disconnect is for safety. Electrician or homeowner knows for certain when power is OFF.
Never touch leaking water heater or wet water heater unless power is OFF
Never run water pipes directly above tankless where leaking and condensation can drip on water heater.
If tankless flooded, disconnect power and replace water heater

Larger image
Option: Install meter on 120-240V subpanel
***White Neutral wire not needed for 240Volt breakers.
Neutral wire only necessary for 120Volt breakers
Illustration shows Neutral wire in event you want a 120V-240 subpanel
Meter will read all voltage that passes to subpanel

New and used electric meters
Buy subpanel:
Main lugs at Amazon
Siemens 125 amp/ 8 space at Amazon
Siemens 125 amp/ 12 space at Amazon

How to install electric meter on water heater or subpanel
How to get electric service
Step #5      Power cut-off -or- disconnect
30 amp safety cut off


Electrical Code may require disconnect at Tankless unit, if Tankless installation is not within view of  main breaker box
Call local electrician for specific local code

Buy non fused safety switch:
60 amp 2-pole safety switch
Pullout Disconnect at Amazon
Fusable pullout disconnect
2-pole 30 amp non-fusable safety switch/ power cut-off
2-pole 60 amp non-fusable safety switch

Shop Amazon - Industrial Electric Products
Step #6   Protect with surge protector
Intermatic IG1240RC3 Whole house surge protector
Tankless electric water heater is not protected from surge
Appliances, water heaters, timers, circuit breakers are not protected from surge
Most appliances today have electronics. Few of these appliances are protected from surge
Water heaters the plug into outlet are not protected from surge
Homeowner insurance might have appliance exclusion. Read policy
Water heater warranty does not cover surge event.
Protect 120V and 240V circuits with whole house surge protector
How to wire whole house surge protector
Intermatic IG1240RC3 whole house surge protector/ pdf
Other considerations:
Tempering tank Think about freezing temperatures
Locate tankless in naturally warm location
Tank-type heaters are warm full time.
Tankless will only heat with water demand.

Add tempering tank to passively preheat incoming cold water.
Add power to tempering tank in winter.
Some tankless will not activate if incoming temperatures exceed set point.
Reliance water heater
Reliance water heaters

How to wire under counter water heater
Water pressure should not exceed 80 psi
Connect pressure gauge to spigot
For example
200 psi Rain Bird P2A or 100 psi Brady BTG 100
Use pressure reducing valve and expansion tank on incoming cold water lines
Water pressure gauge
Temperature-pressure gauge
Safety Equipment for Professionals
Industrial and scientific Amazon
Clogged water lines/ Low water pressure
Tankless will clog with sediment Tankless cannot be exposed to more than 11 grains hardness in water
Efficiency will decline within months.
Parts such as pressure sensor will fail within 2 years
De-liming will not prevent failure
Warranty does not cover failure due to water problems
Hard water testing kits
Bradford White side-by-side study
Water softener research pdf
Delime tankless
Larger image
Delime tankless yearly

Buy project materials
Tankless flushing kits
Tankless service valves
Submersible pump
Filter washers at Amazon
Washing machine hoses at Amazon

Deliming will not restore full efficiency. Read research
How to delime tankless water heater
Maintain water heater 2012/ pdf
Clean water filter monthly
Warranty does not cover failure due to water problems
Read typical maintenance pdf
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