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How many amps of electricity does home use |
| 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 |
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 |
White
14 gauge 15 amp 120 volt 15 amp outlet, AFCI, GFCI, timer, switch etc can be installed on 15 or 20 amp breaker. Never connect 15 gauge wire to 20-30-40 amp breaker.  White/ #14 gauge wire, with ground ... 15 amp capacity. Safe maximum 12 amps. Buy: 14-2 gauge/ 15 amp 14-3/ 15 amp NMB is house wiring UF is underground |
| 50-60
amp breaker use 6 gauge / 240 volt 50 outlet can be installed on 50 amp breaker only  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  Buy: 8-2 wire Southwire electric tools NMB is house wiring UF is underground |
  Copper ground wire. Every device, load, metal enclosure etc must be grounded. Ground wire must be continuous throughout installation, never switched on-off, never used as a Neutral wire. Generally ... use same size as other wire in circuit Buy: 12 gauge copper ground wire Ground wire Green ground wire Ground pigtails Ground rods/ ground clamps at Amazon |
 Non metallic flexible cables must carry ground wire, but do not have hazard of short circuit causing injury from shock. Armored steel cable can be used as a grounded connection, and will protect wires from damage. Metal can be energized from an insulation failure. All conduit ...metal, plastic ... flexible and rigid ... must be attached to structure, and attached to enclosures, boxes. Movement, damage and deterioration are major cause of electrical failure. Buy: Non-metallic flexible conduit Power whip Armored cable Southwire armored cable cutter Pull boxes |
 Electrical tools must be insulated. Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off. Buy: Electrician tools kits KLEIN TOOLS Tools kits IRWIN tools KNIPEX Telephone cable knife Low Voltage Mounting Bracket for Telephone |
 600 volt 12 ga Stranded wire ot THHN wire is good for conduit with multiple wires ... but stranded cannot be installed under screw terminals on outlets, switches, timers etc without risk ... of heat causing splayed strands ....that come loose ... and begin to arc. Connect stranded to short piece of solid copper wire, and attach solid to screw terminal. Do not solder residential or commercial wiring. Project wire, extension cords, thermostat, bell and automotive wire are not rated for residential or commercial wiring. Only wire maked 600 volt can be used for permanent household wiring. Buy: Southwire 600 volt stranded wire Rolls of stranded wire HOOK UP Wires |
 Protect wiring from damage Use nipper instead of pliers or screwdriver for removing staples (and nails). Do not damage cable or wires inside cable. -Code says: Cable SHALL BE secured without damage to the outer covering. NEC sec. 336-15 Buy End cutting nippers at Amazon |
  Electrically insulated tools When removing insulation from wire, do NOT score or put cuts on surface of copper wire. Doing so increases resistance and heat on wire and creates possible weak point. Buy tools: KLEIN TOOLS Wire strippers at Amazon Electric Wire Stripping Machine Linesman pliers Utility knife at Amazon |
 Multimeters Voltage is tested across two separate wires. Ohms or resistance is tested across both ends of same wire. Amperage is tested along one or two points on same wire. Buy: Analog multimeter Multimeters at Amazon Klein multimeter Electric testers at Amazon Clampmeter for testing amp flow on line |
 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. White wire on circuit breaker must be connected to Neutral busbar inside the breaker panel. Buy GFCI circuit breakers |
Push down 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 Tandem breakers |
Push down 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 |
 Typical
home has 150-250 amp main breaker which means 150-250 amp serviceThe main breaker is maximum number of amps that can be used before breaker trips off. Actual home usage is usually not as high as the main breaker. Typical usage might be 70-100 amps when everything is turned on. Note that many high-amperage loads like swimming pool heater or air conditioner do not run continuously and will ON and OFF throughout the day. This results in a rise and fall of actual amperage usage. |
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| What are amps: Amps are the current of electrons that flow along electric wire when a load is turned on. No amperage flows unless load is turned on. Electricity is made up of volts and amps. Volts x Amps = Watts is basic formula. Watts are the overall power requirement for operation of a Load (light, fan, motor, toaster etc). Volts are the force that pushes the current of electrons (amperage) along the conductor (wire). Electric reliability is the standard that ensures voltage remains generally unchanged throughout the day ... while amperage (flow of electrons) rises and falls as Loads turn ON and OFF ... with more amperage flowing along wire when loads are turned ON. If voltage on the grid drops below nominal, then loads will draw more amps to meet the amount of watts (power) shown on product label. Every load has a watt rating or amount of power that the load consumes when turned ON. So if volts drop, then the load will make up difference by drawing more amps, and more electrons will start flowing along the wire. Wires are rated by amperage, and are usually not oversized. Why? Larger wire carries more amperage but larger wire costs more. So home builders and product engineers typically use wire that is not oversized because the expectation is grid voltage will remain stable. If voltage drops and loads start drawing more amps, then too many electrons are moving through the matrix (atomic structure) of the conductor (wire), causing more resistance from wire which causes heat which overheats design parameters of wires, motors. Exceeding amp rating of a wire causes a fire hazard that will trip breakers, and generally waste energy. Lower voltage also means your 115 volt
refrigerator and 240 volt AC cannot run without damaging the motor. Why? Two reasons. 1) More heat on wires will exceed design parameters of motor, damaging start capacitor and melting wire insulation. 2) Lower volts reduces the magnetic field needed to spin rotor. Motor slows down and overheats. Heat
is the enemy of all thing electric. Heat is caused when amps are
flowing along wire. Heat is also caused by direct exposure to sun, high
ambient air temperature etc. Sources of external heat can add to the
heat that is generated by amp flow, and causedamage. | |
Calculate household amp usage Add up wattage of all loads that are turned
on and divide by voltage to
estimate household consumption.For example 240 volt, 50 amp
air conditioner is probably using 40+ amps.
240 volt, 4500 watt water heater divided by 240 volts is 18.75 amps 500 watt TV divided by 120 volts is 4.16 amps. 10 incandescent 100 watt light bulbs is 1000 watts divided by 120 volts is 8.3 amps 7.2 amp refrigerator is using 7.2 amps when running Add up total amperage being used at that moment is 78.4 amps However air conditioner is not running all the time, and refrigerator is not running all the time, and water heater is not running all the time. So turn off the TV and half your lights and amp draw can be lowered to 4.3 amps. This illustrates that the amp draw of ordinary home will have up-and-downs throughout day. An energy meter can measure individual appliances, and track them over a period of a day, week etc. Buy 120 volt: Energy meters Buy 240 volt: Bomain power meter 240 volt pass through Kwh meter Resource Add meter to 240 volt water heater Other
issues can affect amp usage:
Wires that are too small for load will run hot or warm and consume extra amperage. For example using 12 gauge wire for 4500 watt, 18.75 amp water heater exceeds the safe maximum amp draw for a 20 amp breaker. 20 amp breaker x 80% = 16 amp safe maximum. Using 30 amp breaker and 10 gauge wire with safe maximum 24 amps ensures wire and breaker are running cool and efficient. Another example is a shop or building located far from breaker box. Long runs of wire over 100-150 feet require next size larger wire and breaker, otherwise the wire gets warm or hot because the long wire offers too much resistance to the flow of electrons. When resistance goes up, it causes heat ... which means more amps are being consumed ...which increases power (watts) usage. The correct wire and breaker sizae mean maximum efficiency and low loss of power ... which meas less amperage is being used. |
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| Use the meter to check actual
usage over a period of 1 day Usage varies per day, but most accurate measure is the electric meter. The power company installs a meter that records Kwh or kilo watt hours ... which is 1000 watt hours. Watts are power, and volts x amps = power  Check
the meter in morning to get reading, then check again following
morning.Experiment by turning off different appliances to see if consumption can be lowered for a day. Since the meter records Kilo watt hours ... which is 1000 watt hours ... you can divide total kilowatts by 1000, then divide by 240 volt to get total number of amps used per day. Buy 120 volt: Energy meters Computer energy meter Buy 240 volt: Bomain power meter 240 volt pass through Kwh meter Resources Add meter to 240 volt water heater Water heater is causing high electric bill |
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 1
MW (megawatt) can supply power to 400-600 homes. Or 200 homes on hot
summer day.Electric service is the installation from power company transformer to the household breaker box. The service includes the amount of power available to home. So one home can have 200 amp service with 200 amp main breaker while second home has 400 amp service. In both cases, the power company transformer and drop wire will be rated to meet the 200 or 400 amp draw of the main breaker (as the grid is designed in 2021). Remember, just because the main breaker is rated 200 amps, it does NOT mean that 200 amps are flowing through the breaker. The flow of amperage only occurs when a load (fan, light, motor etc) is turned on. Because the power company line is 7200 volts, while household voltage is 240 volts (a ratio of 30:1), then the amp draw from power line is much less. For example the 200 amp home will draw maximum 6.6 amps from 7200 volt power line. Read more The 400 amp home will draw maximum 13.3 amps from the 7200 volt power line. Since neither home is drawing maximum amps, then typical amp draw from the power line will probably rise and fall from 5.1 amps to 2.5 amps to .25 amps throughout each day. Divide your total amp usage by 30 to get estimation of amp draw from power line. Residential service in US is typically 120-240 volt single phase that requires 2 wires to complete each circuit: 2 Hot wires for 240 volt, and Hot-Neutral for 120 volt. Main breaker amp rating is the maximum amount of amperage (electrons) that can pass through the main breaker before heat on wire causes breaker to trip. Resources: See inside main breaker box Difference between single-phase and 3-phase |
|
 If main breaker is tripping
frequently,
then home might be using too
much amperage ... or main breaker might be loose on the busbar, or
going bad, or one of the wires could be loose. Another cause can be
short circuit inside the breaker box. These are not DIY repair. The
meter must be pulled before main breaker is safe to work on. Put hand on main breaker and feel if breaker is warm or hot ...a warm or hot breaker is either bad or loose or home is drawing more amps than the breaker rating. A loose breaker will burn out the panel. A bad breaker can be replaced if still available. Loose wire will burn out breaker. If home is using too many amps, then a larger service might be required ... this usually requires a new wire from transformer and new breaker panel. If the home has several large loads turned on at same time, such as air conditioner, pool heater, tankless electric water heater etc, then the amp draw can max out the main breaker, causing it to trip. |
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 Use correct size wire and breaker to eliminate heat and energy waste, and avoid possible fire hazard. |
Volts
and amps Voltage is the force that pushes electrons through the matrix (atomic structure) of a conductor (wire). Amperage is the number of electrons flowing through the wire. Voltage does not change much. It remains fairly constant 120 or 240 no matter how many amps are flowing on the wire. Amperage or flow of electrons rises and falls as usage varies, with more electrons flowing when a load (light, fan, TV etc) is turned on.. Wires and breakers are rated 600 volt by NEC code (this excludes extension cords, thermostat wire etc). Breaker and wire have an amp rating or maximum number of electrons that can safely flow through the breaker and onto the wire. The limit is reached when electrons (amps) exceed the amp rating of the wire. This causes heat on the wire that will trip the breaker. The heat comes from resistance when the voltage is trying to push too many electrons (amps) through the conductor matrix. A larger wire would solve the problem, but the breaker and wire must have matching amp ratings. If the wire is undersized for the breaker, then the breaker can allow too many electrons (amps) for the size of the wire. If the breaker has a higher rating than the wire, the overheated wire does not trip the breaker. This results in hot wires inside the wall and risk of fire. |
 Larger imageOrdinary 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. - Each 120 volt circuit can include up to 12 boxes, switches, lights, outlets - 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 |
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| Main
breaker wires are
HOT at all times Do not remove metal cover over breakers, or the wires and connections will be HOT Main breaker wires are HOT even when main breaker is OFF. Be careful when checking if main breaker feels warm to touch Resource: Do stress test if main breaker feels warm |
| Figure the amp consumption for
120 volt vs 240 volt? Let's say, your house uses 1350 Kwh of electricity per month. Volts x amps = watts. Divide 1,350,000 watt hours by 240 volts = 5625 amp hours Except house also uses 120 volts. Divided 1,350,000 watt hours by 120 volts = 10,833 amp hours. The two numbers are not the same, so this method is not accurate, and 'amp hours' is not a useful way to measure power. Both volts and amps are needed to calculate total watt (power) consumption. Volts x Amps = Watts (power) For best accuracy at amp usage for entire home, add up all usage at your home using the rating plate for each item. For example, 100 watt incandescent bulb runs on 120 volt. This information is printed on end of each bulb. 100 watts divided by 120 volt = .83 amps Electric water heater has a label that shows 240 volt 4500 watts. 4500 watt divided by 240 volts = 18.75 amps. The two calculations show that electric water heaters, and 240 volt appliances in general, consume much more electricity than light bulb, because they do more work. |
| Examples: Basic formula: Volts x
Amps = Watts Volts x amps = watts ... this is same formula as E (volts) x I (amps) = P (power or watts) Each electrical device has a label that gives at least two of the three factors needed for the formula. Example: Microwave oven label shows 120 volts 1500 watts Apply basic formula to 120 volt and 1500 watts: 1500 watts divided by 120 volts = 12.5 amps. This means a microwave oven will consume 12.5 amps when it is running. If microwave is NOT running, it consumes a small fraction of electricity to operate the digital display. Example: 240 volt 4500 watt water heater. Using basic formula: 4500 watts divided by 240 volt = 18.75 amps. How much wattage can 20 amp breaker supply? If you have 20 amp 240 volt breaker: 20 amp x 240 volt = 4800 watts If you have 20 amp 120 volt breaker: 20 amp x 120 volt = 2400 watt Caution must be used for safety. To calculate the safe maximum for a breaker, you must multiply result by 80%. Exceeding 80% on a circuit breaker is not necessarily dangerous, but it can lead to problems over time because an over clocked breaker will get warm. Whenever a wire, switch, outlet, extension cord or breaker is getting warm, it is causing energy loss, and eventually connection points can begin to deteriorate and loosen. This causes heat and sparking, leading to potential fire. For example a circuit breaker that is getting warm or hot will eventually loosen on the busbar. The resulting fire is contained inside the breaker box enclosure, but the breaker and busbar are damaged. A damaged busbar mean a slot inside the breaker panel is lost to further use. Calculate safe maximum for circuit breaker: If you have 20 amp 240 volt breaker: 20 amp x 240 volts= 4800 watts x .80 = 3800 watt. 3800 watt is too small for 240 volt 4500 watt electric water heater, so you would use a 30 amp breaker. If you have 20 amp 120 volt breaker: 20 amp x 120 volt = 2400 watt x .80 = 1920 watts 1920 watts is fine for 120 volt 1500 watt microwave What if you have 120 volt 20 amp breaker that supplies electricity to 1500 watt microwave and 12 amp refrigerator?? Often, appliances with motors show amperage. Inductive loads, like motors draw high amps during start-up, and then run with lower amps. Household circuit breakers are slow acting, meaning the amp draw on a breaker can exceed rating for a short time before breaker trips. The start-up for a household motor is very brief and rarely does a breaker trip, but sometimes lights may dim momentarily when large loads like HVAC turn on. Use the basic formula to figure watts for 12 amp refrigerator. 120 volts x 12 amps = 1440 watts. Add watts from both refrigerator and microwave: 1440 + 1500 watts = 2940 watts. This exceeds the capacity of 20 amp breaker. Solutions: Code today requires a dedicated circuit breaker for microwave. Dedicated circuit means that only the microwave is on that one circuit. If you have too many watts on a circuit breaker, then add another circuit. Short term strategy: Unplug refrigerator when microwave is being used. What size circuit breaker for 1 horsepower motor Usually the wire and breaker size for motors is determined by using a chart: See chart: HP, breaker and wire chart Resources Electrical formulas Basic household wiring Figure volts amps watts for water heater Not enough space in breaker box Match wire and breaker size |
 Larger image |
Match
wire size and breaker amp rating If your home was wired by professional electrician who pulled permits, then circuit breaker and wire size will match. If manufactured home or travel trailer has not been altered by homeowner then breaker and wire size will match. Circuit breaker and wire size must match Chart on right shows that 30 amp breaker matches 10 gauge copper wire. Do not use aluminum wire. Copper wire is safe. Aluminum wire expands when electricity travels through wire. Expansion causes loose connections and fire hazard. If breaker is oversized for wire, then breaker can let too much electricity travel through the wire. Wire can overheat and cause fire. If you suspect wiring is not correct, call electrician. Absolute electrocution danger when removing cover off main panel. More information below. Main breaker terminals are still Hot when main breaker is turned off. Resources: Maximum wattage for household NM-B and DU-F wires Wire diameter, weight, resistance |
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Check
if breakers are warm Put hand on each circuit breaker. Including main breaker. No shock hazard touching circuit breakers when box cover is in place. Always stand on totally dry surface when touching anything electrical. For example stand on dry boards. Breakers should not be warm. Warm circuit breaker indicates problem Make sure cover is put over main breaker box and that box door is kept closed to protect against spark and fire  What does warm circuit breaker mean? It means breaker is Overheating 1) Breaker is going bad 2) Breaker is not big enough to handle Load, so amp draw is larger than breaker. 3) Breaker has been getting warm over time and is loose on the busbar. 4) There are loose wires causing arcs and heating |
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Vacuum
cleaner cord gets hot Put hand on extension cords, and household wires. Feel for warmth. If cord or wire is warm, then that indicates appliance or tool is exceeding safe-maximum. It shows the cord is too small for amp-rating of tool. Or the wire is undersized for load. Use larger size extension cord. For example, upgrade from 14 gauge to 12 gauge or upgrade more to 10 gauge. Cords frequently get warm, and that is not good. Warm indicates high load. Hot is dangerous. Cords and wires should never get HOT. If cord is hot, unplug immediately. Vacuum cleaner cords frequently get hot. This is because manufacturers are under-sizing the cord for the amp-draw of the appliance motor. Over time, the warm cord means motor is starving for electricity. Motor runs under-speed. This causes motor to get warm. Motor begins to weaken. Motor finally gets hot and begins to short. Cord get hot. Vacuum cleaner needs to be replaced. Foreign manufacturer makes more money selling cheap products, while corporate owners complain about government codes and regulation. Then your house burns down and insurance company says you need to sue appliance manufacturer. Win-win for all except you. Space heater cords frequently get warm This means the cord is too small for amp-draw of space heater. Space heaters should never be operated for long hours, and should always be unplugged when not in use Space heaters come with 14 gauge wire, but safe-maximum rule says 14 gauge wire is rated for 1440 watts. 14 gauge wire is OK for space heater, but load is slightly above safe-maximum so wire can feel warm. Always unplug appliances that are not being used |
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Outlet
is warm/ Switch is warm Use hand to check if outlets and switches are warm. If switches and/or outlets are warm, then call electrician. Turn off power. Remove cover and inspect for loose wires. Replace switch or outlet. Monitor if new switch/outlet gets warm. Aluminum wiring is absolute fire hazard If wires are aluminum, then this is absolute fire hazard. Professional electrician must be called to solve problem. Aluminum wire must be replaced with copper. Special outlets-switches required for aluminum wire. Special connections required for aluminum wire. All electrical boxes, including outlets and switches must have cover plate to keep sparks and overheating from causing fire. |
 
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Wall
timer is getting warm. Replace timer. See bottom of this for links to timers and manuals. Use product manual to check load rating for timer. Check watt and amp draw of Load. For example, if timer is rated for 500 watts incandescent light bulbs, but timer is connected to 600 watt TV or 1Hp pool pump, then timer will get warm and burn out. |
 Typical 600 watt rotary dimmer Cover plate must be installed for safety |
Dimmer
is getting hot Change light bulbs to lower wattage. Replace dimmer with new dimmer. Turn off power. Pull dimmer out and look at watt rating printed on side of dimmer. Add up total watts of all light bubs controlled by dimmer. Compare dimmer rating with actual watt rating. For example if dimmer is rated for 600 watts, then four 150 watt light bulbs will cause dimmer to get warm. Change to four 100 watt light bulbs, or buy dimmer rated for 1000 watts. Some dimmers have aluminum fins that work as heat sinks. Aluminum dissipates heat very fast. The aluminum fins can be warm, and that is normal. Aluminum fins should not be hot. |
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Main breaker stress test Using 80% rule: Safe maximum for 125Amp main breaker is 100 Amps Safe maximum for 60 Amp main breaker is 48 amps |
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Main breaker is getting warm Main breaker is tripping |
Calculate
PEAK amp draw. Add up total amp usage using example below. Formula: Volts x amps = watts. or Watts divided by volts = amps. If appliances are gas, then they do not count. Look at labels on each item for watt rating. Add up peak usage for 120Volt. Each electric appliance has rating label. For example: microwave 1500 watts + big screen TV 500 watts + computer 300 watts + refrigerator 700 watts + lights 240 watts + dishwasher 800 watts + 1 Hp hot tub pump 750 watts + washing machine 350 watts etc = 5320 watts divided by 120 volts = 44 amps. Add up peak usage of 240Volt. For example water heater 4500 watts + heat/ac 5000 watts + clothes dryer 1800 watts + 1 Hp water well pump 750 watts + top and bottom ovens 7500 watts etc = 19550 divided by 240 volts = 81 amps. Total PEAK amp draw = 81 + 44 = 125 amps. |
 Main breaker |
PEAK
amp draw is STRESS test for main breaker Example calculation above shows peak 125 amps. If main breaker is 125 amps, then main breaker is too small to handle 125 amp PEAK load. Each time PEAK amps are used, the main breaker gets warm. Sooner or later, the main breaker has gotten warm too many times, and it stops functioning. This may take years before main stops functioning. Electricians use 80% safe maximum rule when calculating capacity of electrical devices such as circuit breaker. 80% rule also applies to switches, outlets, dimmers, timers, etc. If main breaker is rated 125 amps, then electricians multiply 125 x 80% to find maximum safe load for that breaker. 125 amps x .8 safe maximum = 100 amps So safe maximum for 125Amp main breaker is 100 Amps. |
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Calculate
safe maximum for water heater circuit If residential water heater is connected to 20 amp breaker and 12 gauge wire, then the same overheating problem occurs over time. Circuit breaker will not last as long, and damage can occur to busbar. See basic water heater circuit 20 amp breaker is subject to 80% safe-maximum rule. 20 amp circuit breaker x .8 = 16 amps. So safe maximum for 20 amp breaker is 16 amps. As shown above, 4500 watt water heater draws 18.75 amps. And 5500 watt water heater draws 22.91 amps. So 20 amp breaker with 12 gauge wire are rated too small for most water heaters. Over time the breaker can wear out sooner due to overheating. Recommended that all water heaters be connected to 30 amp breaker and 10 gauge wire. Safe maximum for 30 amp breaker x .8 = 24 amps. 30 amp breaker and 10 gauge wire run cooler, with less heat loss and more efficiency. Circuit breaker and main box last longer with less chance for heat damage. Figure Volts Amps Watts for water heater |
| Volts x Amps = Watts Watts divided by Volts = Amps Most residential water heaters are non-simultaneous. This means both elements are not ON at same time. How electric water heater works How to wire thermostats Calculate safe maximum for timers/ electrical circuits Read label on side of water heater for element wattage. Element wattage is tank wattage. For example: If water heater has 5500 watt elements: 5500 watts divided by 240Volts = 22.91 amps 4500 watt water heater divided by 240Volts = 18.75 amps. Electricians use 80% rule for safe maximum. WH21 is rated for 25 amps x .8 = 20 amps. Calculation shows that WH21 is ok for 4500 watt water heater, but beyond safe-maximum for 5500 watt water heater. Exceeding safe maximum means WH21 will run hot and not last as long. If electrical device is run at-or-near maximum amp rating, the device will not last as long because of heat. Same as running a car at full throttle. Car will not last as long. In contrast, 40-amp WH40 and T104 timers are better long term investment for water heater timer. WH40 and T104 are rated for 40 amps, with safe maximum of 32 amps, so they withstand more amperage without heat loss, and will last longer. How to wire WH40 How to wire T104 Intermatic T174 timer is identical to T104, except T174 has day-skipper feature |
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| circuit analyzer surge protection Example Peak usage is 125 amps. 80% rule |
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| - Some gas water heaters plug into 120Volt outlet that should also be on a dedicated breaker. This is to prevent electrical interference from affecting gas control valve. This type of installation should also include surge protector to prevent surge from knocking out gas control valve electronics. | |
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Resource: Compare box timers DPDT timers Intermatic Control water heater w/ Z-wave |
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