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How to wire Tankless electric water heater
Stay safe.
Turn main breaker OFF
2023
EcoSmart
EcoSmart

Buy:
EcoSmart tankless

Resource
EcoSmart manual
Rheem tankless
(image shows tankless with pigtail attached)
Rheem tankless
Buy:
Rheem tankless

Resource
Rheem manual
Breaker size chart
General troubleshoot .pdf
Atmor tankless
Atmor point of use
Buy:
Atmor tankless

Resource
Atmor manual
Stiebel Eltron tankless
Stiebel Eltron
Buy:
Stiebel Eltron tempera

Resource
Steible manual
Eemax tankless
Eemax/ point of use
Buy:
Eemax tankless

Resource
Eemax manual
Chronomite tankless
Chronomite/ point of use
Buy:
Chronomite tankless

Resource
Chronomite manual

Use only 600 volt wire.
Lamp cord, extension cords are not rated 600 volt.
Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional.

30 amp breaker use 10 gauge /
120-240 volt 30 amp outlet can be installed on 30 amp breaker only/ use 10 gauge wire ... cannot be connected to 15-20-40 amp breaker.

Orange/ #10 gauge wire, with ground ... 30 amp capacity. Safe maximum: 30 x 80% = 24 amps.
Buy:
10-2 gauge/ 30 amp
10-3/ 30 amp
Southwire electric tools
Resource
Safe electric wiring
Yellow 12 gauge 20 amp
120 volt 20 amp outlet can be installed on 20 amp breaker, but not 15 amp breaker/ use 12 ga wire.
... cannot be connected to 30-40 amp breaker. 1

Yellow/ #12 gauge wire, with ground ... 20 amp capacity. Safe maximum 16 amps.
Buy:
12-2 gauge/ 20 amp
12-3/ 20 amp

NMB is house wiring
UF is underground
Rolls of stranded wire
HOOK UP Wires
50-60 amp breaker use 6 gauge /
240 volt 50 outlet can be installed on 50 amp breaker only
6-2 wire
Buy:
6-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
40-50 amp breaker use 8 gauge /
240 volt 40 amp outlet can be installed on 40 or 50 amp breaker only
6-2 wire
Buy:
8-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
Wire size and breaker must match

Use 600 volt copper wire only.
Use solid copper wire for all 14-12-10-8 gauge applications. High amperage loads will heat wire, which can cause stranded wire to expand and contract, and come loose under breaker screw, causing arcs that will melt the breaker and/or cause fire.

Never use extension cord, aluminum wire, undersized wire, damaged wire, or solder .... inside subpanel, or for permanent wiring. Extension cord code
Do not use aluminum wire unless panel is rated for CU-AL. Aluminum wire expands more than copper and will come loose and cause fire.
Never use solder on residential or commercial circuit. Heat from amperage will melt solder, and cause hazard.
Solder is used for low amp application like circuit boards.

240 volt breakers must be double-pole breaker with connected switches, and cannot be 2 separate single-pole breakers, unless the breaker switches are connected together.

GFCI circuit breaker
A GFCI circuit breaker will protect all boxes on circuit.
Circuit must be grounded. Ground wire must be continuous and connected to each piece of equipment.
GFCI breakers have a white wire. This wire must be connected to Neutral busbar inside the breaker panel.
Buy
GFCI circuit breakers
Push down
single-pole breaker    double-pole breaker
1" wide Push down breaker
Plug-in breaker
Buy single-pole:
Choose from 15 to 60 amp
Eaton CL series
Siemens 15-60 amp
Single-pole tandem breaker

2" wide Push down breaker
Plug-in breakers
Buy double-pole:
Choose from 15 to 125 amp
Choose from 15 amp to 200 amp
Eaton CL series circuit breaker
Siemens circuit breaker
Double pole GFCI

Both sides of a 30 amp double breaker are 30 amp, not 15 amp

Step 1: Does main box have enough capacity?
circuit breakers are warm
Breakers should never be hot to touch.
Do not install tankless electric if main box is overheated.

Warm or hot breakers will destroy the service panel (main breaker box)
Test if electric service panel is adequate for tankless:
A) Open following link to do the Stress-Test on main breaker and service panel:  Stress test
Example #1: if you have 150 amp main breaker, the maximum load is 80% or 120 amps for 'continuous operation.' Exceeding 80% on a continual basis will cause main breaker to get warm and then cool and then get warm again ... eventually shorting out and melting the busbar. 

Example #2: if you have 200 amp main breaker (or 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.

B) Each tankless has an amp rating.

C) Add amps from tankless to service panel stress-test.
To Figure amps for tankless: Read label on side of tankless for Volts and Watts. Divide watts by volts to get amps. So if volts are 240V, and watts are 9000, then 9000 divided by 240 = 37.5 amps. A 9000 watt tankless might have two 4500 watt elements, and both elements might or might not activate each time, so actual amp draw off the main breaker can vary depending on incoming water temperature, thermostat setting etc.

D) If electric service is too small for expected load, then install new 'electric service' (breaker box and drop wire from power company). Call power company, or local electrician.
Or if skilled and local codes allow, have the meter pulled and install new panel yourself ... if incoming wires are correct gauge. Wire gauge chart
Or use ordinary tank-type heater and save 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
Look at product spec sheet.
2) Consult Tankless manual if available
Failure to follow installation steps in manual will void product warranty
However, few manuals show how to wire the unit
3) Warranty Caution:
The warranty covers defects in manufacturer's workmanship, but does not cover DIY installation or electric wiring errors.
Resource
Overview of installation steps

Step 2: If tankless has pigtail
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.

Resource
How to select and install correct wire connector
Select correct wire and breaker size
How to wire 240Volt outlets
Step #3  Look inside tankless for connections
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
Resource:
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
Resource
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
 
Example:
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
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

Examplee with 3 wires

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
Example three 50 amp 240Volt breakers
Use 50 amp breaker with 6 gauge wire
No difference if all 3 breakers are on same side of panel, or on different sides. You want to balance the loads on your breaker box ... so each busbar (blue and black in illustration) is delivering same amperage as other .... any 240 volt breaker is automatically balanced because the double breaker draws off both busbars.
Requires 250 amp service and 250 amp main breaker.

Footnote: if double breaker is rated 50 amp, then both wires off the breaker are delivering 50 amp (not 25 amps each wire).
Resource
Wire size chart
Main breaker Stress test

Buy:
Circuit breakers
wire size chart
Double check wire size and distance
100'-150' etc requires larger diameter wire
Some sources say the cut-off is 50' ../ not 100' ... a oversized breaker and wire are OK, and run cooler with more efficiency ... but wire MUST match breaker ... and both breaker and wire be rated for the amp draw from tankless.

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
Resource:
Select correct wire and breaker size
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 not needed for 240Volt

Resource: How to wire subpanel
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
Resources:
How to install subpanel

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

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

Resources:
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

Disconnect

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
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 IG1240RC3Whole house surge protector/ protects every 120-240 volt circuit.
Most appliances, timers, computers etc have electronics today. Few are protected from surge ... unless your 120 volt computer is plugged into Type 3 plug-in surge protector strip ... that jumps the gap to ground wire instead of absorbing or suppressing.
A 240 volt tankless cannot be protected with a Type 3 surge strip like 120 volt loads.
For whole house protection, install Type 1-2 surge protector that absorbs or suppresses surge event. Install either inside the panel in double slot closest to main breaker ... or connect the Type 1-2 to a dedicated double breaker located closest to main breaker. Big screws on main breaker are hot at all times, een when main breaker is off.
240 volt hardwired Type 3 can be installed directly at the tankless unit ... or at 240 volt HVAC etc.
Any circuit can have multiple surge protection. Double, triple protection per circuit is fine. The closer the surge is located to load, the better it protects.
Homeowner insurance might have appliance exclusion. Read policy
Water heater warranty does not cover surge event.
Buy:
Whole house surge protectors
Resources:
How to wire whole house surge protector
Intermatic IG1240RC3 whole house surge protector/ pdf
Other considerations:
Your money
-FYI; Tankless cannot be exposed to hard water. 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
- Tankless heat exchanger is prone to scale build-up, and must be delimed each year. How to delime tankless
-Tankless electric can save money for installations such as small point of use hand washing sink vs pulling hot from tank each time .... or vs cost of installing recirculating system. But a small point of use tank is easier to maintain. How to install point of use
-Ignore the rabid promotion that 'tankless save money while delivering endless hot water' ... promising to suspend laws of physics to supply hot water without using energy. The laws of physics are still in force, despite all beliefs to the contrary, and if incoming water is too cold then tankless cannot keep up, unless you buy a unit rated with enough wattage. Some mauals have a chart that shows the curve based on water temps. See chart
-Very few service resource are available for tankless heaters ... gas or electric. Parts are not generic, and are expensive to purchase. Service folks in your area might not be trainned on your brand heater ... ... tankless are generally the least environmentally friendly heaters, with the offer to 'throw-in-landfill when no longer functioning' recycling and repurposing strategy.
-In all cases, tankless will have more operational issues than ordinary tank-type heater. Ordinary tank type heaters can be maintained to last forever, are not susceptible to surge and can usually be fixed DIY.
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
Buy
Reliance water heaters

Resource:
How to wire under counter water heater
Water pressure should not exceed 80 psi/ 50 psi is best
Connect pressure gauge to outdoor spigot ... check neighbors spigot
Use pressure reducing valve and expansion tank on incoming cold water lines
Buy
Water pressure gauge
Temperature-pressure gauge
Safety Equipment for Professionals
Industrial and scientific Amazon
Resource
Clogged water lines/ Low water pressure
TP valve releasing hot water
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
Buy:
Hard water testing kits
Resources:
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
Washing machine hoses


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

Resource
How to install Tankless recirculation




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