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Troubleshoot household electricity: general reference for homeowner & electrician

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How to troubleshoot loose wire, ground fault, or short
How to wire devices, and how electric devices work/pdf
main breaker box
Larger image

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.

- 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
How to reset circuit breaker

How to reset circuit breaker

Circuit breaker can look ok, but still be tripped.
Push circuit breaker all the way OFF, and then all the way back ON.

Household NM-B Wires are color-coded so inspectors/ electricians can easily identify which wire is used during construction
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.
wire size chart
Rating for short lengths household NM-B and DU-F
Larger image with wire types, temperature, long length
Maximum wattage for household NM-B and DU-F wires
Wire diameter, weight, resistance

How to figure correct size wire and breaker

Use chart on left to select wire and breaker

Look at watt rating of appliance, or motor or tool
Volts x amps = watts
Watts divided by volts = amps
Volts squared divided by watts = ohms

Color code for wire

Simple safety test for household electrical system

Easiest way to see if there are electrical problems is the heat test
All appliances, computers, TVs, AC etc put off heat. But breakers, extension cords, wires, outlets, switches and timers should not be warm.
electrical safety

All electrical boxes, including outlets and switches must have cover plate

To stop sparks and overheating from causing fire
Outlet is warm

Outlets and switches should never be warm or hot

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.
How to wire switches
circuit breakers are warm

Circuit breakers should not be warm or Hot

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
Read main breaker stress test
Read circuit breaker is getting warm/hot
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
Vacuum cleaner cord gets hot

Cords should not be warm/ if they are used full-time

If you are using extension cord as full time source of electricity to pump or fan, the cord should not be warm or hot
If toaster oven cord gets warm, then that is normal
If you operate the appliance full time, then upgrade to larger cord or professional appliance

Vacuum cleaner cord gets hot/ Extension 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.
Warm is not good, but 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

Buy 12 gauge heavy-duty extension cords:
12 gauge extension cords
Dimmer getting hot
Typical 600 watt rotary dimmer
Cover plate must be installed for safety

Dimmers are usually warm when ON/  but Never Hot

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.
Cover plate must be installed for safety

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.

Buy from my affiliate links:
Dimmers at Amazon
1000 watt dimmer
Example 1000 watt dimmer

Transformers are usually warm

Every home has transformers
Transformers should not be hot to touch
Cell phone, computer, alarm system, doorbell etc each have transformers
Transformers are usually warm.
Ordinary household transformer should not be warmer than big screen TV.

Power supply to convert 120 to 240 etc
Doorbell Transformer
24 volt Transformer for security systems etc

Troubleshoot Malibu power pack
Equipment transformers are inside every appliance

12 volt/ 24 volt Doorbell transformer
Add octagon box with twisted wire
Intermatic EI500   Westek TE06WHB   Intermatic EJ351

Timers should NOT get hot to touch

Timer is getting hot

Replace timer. See bottom of this page for links to timers and manuals.
Use product manual to check load rating for timer. Check watt and amp rating 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 or hot, and burn out.
How to wire timers
flickering lights

Flickering lights

1) Check circuit breaker before sparking causes damage in breaker box. Check breaker and listen for fizzing or crackling sound. Check if the breaker screw is tight against wire. Flickering lights are usually a loose light bulb or loose wire at a plug, but it pays to check breaker first to avoid busbar damage.
2) Replace light bulb and see if problem is solved.
3) Next suspects include loose quick connection on back of outlet or switch, and-or loose neutral wires that are bunched together and covered with wire connector. Inspect all wall boxes first. Then inspect ceiling boxes. See if all boxes in the circuit are affected or just a few boxes.
Maximum number of boxes for 1 circuit is 12. A circuit consists of all boxes connected to 1 circuit breaker.
For example 12-2 wg cable connects to circuit breaker.  The cable leaves breaker box and goes to first junction box inside a room. From the junction box, the cable splits off and goes to each individual box, jumping from box to box until the final box is reached. So each box will have more than 1 12-2 cable, except the last box that will have a single 12-2 cable. All the 12-2 cables are connected together back to circuit breaker. Each box in the circuit will have 1 black hot wire, 1 white neutral wire, and 1 ground wire that connect back to main breaker box.
Start by opening each box
Always put cover back on breaker box to prevent sparks from leaving breaker panel.

Sparking wires

Sparks from a loose connection usually will not damage other wires, unless the short circuit has been going on for a while... but usually a short circuit will trip breaker or the arcing will completely short out and no more electricity will flow.
Always use NEW wire connectors
Use silicone to seal outdoor wire connectors
Do not use undersized wire
Do not use stranded wire under screw places on timers, switches, outlets etc
Make sure everything is properly grounded
Overheated wire can catch wire and melt other wires.

Match wire and breaker size
How to install wire connector

Melted wire

Replace wire
Test circuit
Look for other affected wires and bad circuits
Check wire and breaker size
Make sure everything is properly grounded

How to test wires
Burned thermostat

Burned switch / burned electrical part

Turn power off
Check condition of wires
Cut back damaged wire
Test wires with multimeter
Check that device has same electrical rating as wire and breaker
Replace part
Make sure everything is properly grounded

Match wire and breaker size
replace circuit breaker

Circuit breaker is tripping

Use wire size and maximum load calculations above to see if breaker is over-amped.
Move load to different same-size breaker.
If same breaker continues tripping, then replace breaker.
If different breaker trips on same load, then look for shorted wire.

Circuit breaker is warm
Use wire size and maximum load calculations above to see if breaker is over-amped.
Move load to different same-size breaker.
If same breaker continues getting warm, then replace breaker.
If different breaker gets warm on same load, then look for over-mapped circuit.
How to replace circuit breaker
Water heater is blowing breaker

Power safety:

Never stand in water or wet surface when around electricity
Never stand on bare soil
Stand on dry boards
Do not touch or lean into anything made of metal
Use non-contact voltage tester to make sure power is OFF before making repairs

Never assume power is OFF

Use non-contact voltage tester on timer, on wire, on outlet to see if power is present.
Press button on tester, if single beep then no power is present. If continuous beep then power is present.
Never stand on bare ground, always stand on dry boards, do not hold or touch anything metal when working on timer or water heater that has power, tape tester leads to wood sticks, never touch wet water heater, or flooded water heater, or timer that had a short or fire without turning power OFF.

Multimeters at Amazon
Simple multimeter/ Test continuity or voltage
Buy non-contact voltage tester at Amazon
Electric testers at Amazon

Shop Amazon - Industrial and scientific
Shop Amazon - Industrial Electric Products

Intermatic terminal wires

Prevent fire inside timer and electrical boxes

Use only copper wire
Match timer rating with Load rating
Never mix stranded and solid copper wire under same screw plate.
Never mix 2 different gauge wires under same screw plate.
Make sure only copper is under screw plate, and that no insulation is under screw plate.
Always keep timer door closed
Intermatic DTMV2 defrost timer
Keep timer door closed 
Intermatic IG1240RC3

Whole house surge protector/ protect appliances, wiring, timers, water heaters etc

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

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

Main breaker is getting warm

Main breaker is tripping

Calculate PEAK amp draw.

Add up PEAK 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.
Home may only reach PEAK once per week or once per month. Try to estimate actual peak usage that would be likely to occur.
125 amp Main breaker
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.
If PEAK usage exceeds safe maximum for breaker, then breaker is getting warm, and is more likely to get hot and fail.

Main breaker is getting warm/ Hot

If Main breaker is getting Hot

If stress test shows that main breaker is within safe maximum, then replace main breaker.
If stress test shows main is above safe maximum, then upgrade service panel to higher amp load center
How to replace circuit breaker

Circuit breaker is getting warm/ Hot

If circuit breaker is getting warm or Hot

Move wire to another same-size breaker. Check if same-size breaker is also getting warm or hot.
If same size also gets warm, then circuit is over amped. Call electrician. Identify all items using that breaker. Move appliances to different circuit.
If same size does not get warm, then replace circuit breaker that is getting warm.
How to replace circuit breaker
water heater circuit breaker

4500 watt and 5500 watt water heaters should connect to 30 amp breaker and 10 gauge wire.

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.
240Volt 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 is rated too small for most water heaters. Over time the breaker is getting warm, and is more likely to get hot and fail.

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.
Safe maximum for 10 gauge wire at 240volts is 5670 watts See chart
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

Calculate safe maximum for water heater circuit

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.
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.
Figure volts amps watts for water heater
How electric water heater works
How to wire thermostats

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

- 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.

Connecting wires with screws

Examples: Outlet, switch, circuit breaker, timer, water heater thermostats.

No insulation is under screw plate.
Tighten screws very tight against copper wire.
Always use copper wire/ never aluminum wire.

Don't put two different gauge wires under same screw plate.
Don't put solid wire and stranded wire under same screw plate.
in line fuse
Larger image

Use in-line fuse when connecting 2 different gauge wires

Connect 12 gauge wire to 10 gauge wire.
Illustration shows smaller 12 gauge wire connected to larger 10 gauge wire.

10 gauge wire is protected by 30 amp breaker
The amp draw on 30 amp breaker is too large for 12 gauge wire.
12 gauge wire should have 20 amp breaker.

Use busman fuseholder with 20 amp fuse.
Fuse will protect entire length of 12 gauge wire.
Connect fuse to Hot wire.
Not necessary to put fuse on Neutral

If the 12 gauge wire was wired for 240V, then fuse is necessary for both hot wires.
Always make connections inside a box with cover
Panel mount fuse holders at Amazon
Buy fuseholder at Amazon
Buy fuseholders at Amazon

Fuse blocks at Amazon
30 amp fuseholder at Amazon
20 amp fuseholder at Amazon
Electrical terminals
Solder guns
See fuseholder

Some fuseholders accept terminal connections, some have solder-only connections. Fuse block has screw terminals.
Read circuit analyzer

Test outlet with circuit analyzer

This is first line troubleshoot when...
> When gas water heater or gas appliance plugs into outlet, the polarity and ground must be correct.
> When electrical devices, and appliances do not last very long, check outlet for polarity and ground issues.
> When household timers go bad quickly, or more than one timer has failed, test outlet with analyzer.

Circuit analyzer
Analyzer will not detect all electrical problems
Analyzer will detect basic polarity and grounding issues.

For example, gas water heaters that plug into outlet require correct polarity and grounding.
Postage equipment and many basic office tools and computers also require correct polarity and grounding
Circuit analyzers at Amazon
Outlet polarity

Household outlet polarity

Wires should always connect to correct blade.
The wide blade is Neutral. Narrow blade is Hot.
Many appliances and TVs have polarized plug. This is so Hot and Neutral can work correctly with electronics inside the device. If outlet is wired incorrectly, then appliances and timers, etc don't work as expected.
How to wire 240Volt outlets
How to wire 3-phase outlets
Wire connectors
wire nut safety

Never assume electricity is OFF

Turn power OFF
Always stand on dry boards.
Do not stand on soil or metal ladder
Electricians use fiberglass ladder
Do not touch or lean into anything made of metal
Never stand on wet soil when working with outdoor lights, plugs, cords.
Use GFCI-protected circuits for bathroom and outdoor circuits.
How to wire GFCI
Wire connectors
GFCI vs Surge protector
Electricity leaves power plant What is 3-phase electric: power plant to end user


Test for breaks in wire/ Test for voltage
Most appliance require 80% rated voltage to function correctly
Multimeters at Amazon
Electric testers at Amazon 
How to test and replace element
How to test thermocouple
Element tests for 120 volts
How to test wire
Safety when testing wires:
Never touch wet or previously flooded appliance.
Never stand on wet surface when working on electric.
Never stand on bare soil, put down dry boards.
Tape tester leads to wood sticks to keep hands away from power.
Use non-contact voltage tester before touching wires.
Never touch or lean into any made of metal.
Remove metal objects from pockets.
Do not use oxygen or fuel accelerants in same room as electrical repairs

Basic house wiring

Non-contact voltage tester

Test for power without touching connectors
NEVER assume power is OFF

Non-contact voltage tester Amazon
Electric testers at Amazon
How to test electric power is off

How to install terminals


Terminal kit
Blue for 16-14 wire
Yellow for 12-10 wire
Read about terminals
wire connector assortment

Twist-on wire connector assortments

Do not reuse old connectors 

Connector assortment at Amazon
Connector assortment at Amazon

How to select and install twist-on wire connectors
Weatherproof wire connector

Weatherproof wire connector

Connector cavity is full of silicone
Built-in cover keeps silicone in place
Protect from water, dust etc
Buy from my affiliate links
Weatherproof size 14 to 6 Amazon
Weatherproof size 22 to 8 Amazon

How to select and install twist-on wire connectors
Wire connector wrench

Wrench to apply wire connectors

Tighten connector 

Wire connector blaster
Twist connector wrenches at Amazon

How to twist wire
How to select and install twist-on wire connectors
Push on wire connectors

Push-on wire connectors in place of twist-on connectors

Push on wire connectors Amazon
Red 3P connector for 10-14 gauge wire
Lever connectors for stranded wire at Amazon
add solder to stranded wire

Turn stranded wire into solid wire

Add solder to 1" length of tightly twisted stranded wire to make into solid wire
Heat wire. Touch solder to wire. Let cool. File away over-solder.
soldering guns

Timer caught fire

linesman pliers
Buy tools:
Wire strippers at Amazon
Linesman pliers
Utility knife at Amazon
End cutting nippers at Amazon

Fire inside timer caused by stranded wire
Keep enclosure door closed at all times

Fire caused by stranded wire

Do not use stranded wire under screw plate

Applies to timers, switches, outlets, pumps etc.
Small devices, with small loads, such as lamp socket, stranded wire is fine
Add solder to 1" length of tightly twisted stranded wire to make into solid wire
Heat wire. Touch solder to wire. Let cool. File away over-solder.
soldering guns

Timer caught fire
Gas and electric water heaters Support the economy:
Buy water heaters  from my associate links:

50 gallon Gas water heaters at Amazon
40 gallon gas water heaters at Amazon
50 gallon Electric water heaters at Amazon
40 gallon electric water heaters at Amazon
Hybrid / heat pump/ water heaters at Amazon

How to install gas water heater
Troubleshoot gas water heater
Troubleshoot electric water heater
Intermatic control centers Intermatic control centers:
+ manuals and parts

Including Z-wave
box timers Compare box timers

Control with Z-wave
programmable timer Compare programmable timers

Control water heater with programmable wall timer
Countdown timers Compare countdown timers

Control water heater with countdown timer
Compare power packs

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