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Timer caught fire/ Fire inside
timer/ Overheating melts part of timer Causes: Door not closed or missing, wires or timer not secured to structure, wires not clamped to box, wrong wire or breaker, never use extension cord, load and timer rating not matched, stranded wire instead of solid copper, ground wire missing etc |
| 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 |
| 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 |
 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 |
 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 |
 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" and 2" 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 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 |
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1. Keep enclosure door closed All electrical connections must be made inside an electrically rated box, and each box must have a matching cover or door to prevent fire from spreading. High heat will be confined inside the box, and provide fire safety 2. If enclosure door is missing Then find it and put it on, or buy another box. Improvised, or homemade enclosures are not rated for electrical and are against code. Resource: Intermatic boxes and enclosures |
 2. Attach wires and boxes to structure All boxes must be attached to structure ... meaning 2x4 frame etc, and not to bare drywall or siding. Electrical cannot be in located where impact from cars, equipment etc can impact. Electrical must be in dry location, or use waterproof IP65-IP67 enclosures etc. All wires must be firmly attached. Use Wire connectors, or conduit clamps to secure wire to enclosure. Use Wire connectors, or conduit clamps to secure wire to enclosure By code, all wire must be securely attached to enclosure to prevent wire pull-out. Wires or conduit must be secured to structure, so there are no loose wires. Wires inside the enclosure cannot lay over top of wiring connection terminals or top of circuit breaker etc. Join all ground wires together and cover with wire connector. Push ground wires down and away from connection terminals. Resource: Wire clamps | |
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3. Match load rating and timer rating Match timer rating with load For example, the WH40 mechanical timer is rated 240 volts, 40 amp maximum, which is sufficient for 30 amp water heater, but not two heaters. The maximum wire size for timer is 8 gauge, with minimum 14 gauge. 10 gauge wire is correct for 30 amp, and 8 gauge for 40 amp. Note that wires are attached to enclosure using a clamp. The box itself must be firmly attached to structure. Resources Color code for wire and breaker Load ratings for Intermatic timers/ pdf |
 | 4. Match breaker and wire size with load Chart shows wire and breaker chart for single-phase residential or commercial wiring. Controlling the heat caused by amperage is key component of safe wiring. If wire is undersized for the breaker, then wire is in danger of getting hot and catching fire inside wall. Also the wire and breaker must match the load. So if you have the WH40 timer shown above, and are using it for a 240 volt, 30 amp water heater, then the double 30 amp breaker with 10 gauge wire are the correct choice for safe wiring. Resources Color code for wire and breaker Figure volts amp watts for water heater |
  | 5. Ground wire must be connected All electrical installations require grounding. Add 10-32 ground screw if steel enclosure has no ground connection. Plastic boxes, conduit etc do not require grounding, but ground wire must be present and connected to any metal surface in a residential or commercial electrical installation. Avoid cheap Denwillis timers and off-brand timers and contactors etc with pot metal screw connections and perhaps no place for grounding etc. Remember, grounding is essential for GFCI and AFCI operation. Grounding assists circuit breakers and wires from becoming damaged during short circuit. Resource: Why you need ground wire |
 | 6. Never use extension cord for permanent household wiring. Electrical wires are rated 600 volt. Extension cords are rated for 300 volts, lamp cord for 150 volts, and thermostat wire 100 volt, but extension cord and structural wire are never approved by code to replace permanent 600 volt electrical wiring. Extension cords must be plugged in and cannot be hard-wired into a circuit. Cords should be used with original factory installed plug. Resource Extension cord safety |
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7. Use solid copper wire, not stranded Timer fire caused by stranded wire under screw plate. Note also that extension cord was used instead of 600 volt electrical wire. Two violations of safe electric practice. Stranded wire under the COM2 terminal got hot, came loose and caused fire. High amp loads cause heat on wire ... wire expands and contracts as wire gets hot then cools when load is off ... the stranded wire splays apart and gets loose. The loose connection begins to arc, and eventually melt and can cause fire, or damaged screw terminal. Always use correct-sized screwdriver and hand tighten screws very tight against solid copper wire.  Use solid copper 12-2 NM-B or UF or 10-2 NM-B or UF double-sheathed cable is code. Solution for damaged timer Replace timer, or if possible, shift load to single-pole etc. 8. Do NOT solder end of stranded wire to make solid ... amperage will melt solder. Connect stranded wire to short jumper of solid copper wire, and cover the connection with twist on connector. Resources GM40 series, GE 15000 series, Tork series Intermatic defrost timers Resources Match breaker and wire size How to wire 240 volt plugs, outlets, sockets |
Alternatives for stranded 1. Connect stranded wire and solid wire, and put solid under screw terminal 2. Crimp a ferrule onto the wire 3. Crimp a terminal onto the wire  |
9. Avoid stranded wire
Do not use stranded wire under screw plate on timer, contactor, relay, outlet, switch or any electrical device. Do NOT solder end of stranded wire to make solid ... amperage will melt solder. Connect stranded wire to short jumper of solid copper wire and cover with twist on connector Do NOT solder end of stranded wire to make solid ... amperage will melt solder. Connect stranded wire to short jumper of solid copper wire and cover with twist on connector. Resources: Terminals What is amperage Basic house wiring How to troubleshoot household electricity |
10. Avoid cheap timers with pot metal screws Avoid cheap Denwillis timers and off-brand timers and contactors etc with pot metal screw connections and perhaps no place for grounding etc. Image shows screw terminal on Intermatic GM40AV series timers, and T104 timers which are superior quality vs the old GE timer shown above that had fire. These are solid screw terminals made for 40 amp loads Use correct size screwdriver or square driver and tighten very tight against screw  | |
| 11. Causes of timer fire | |
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Both wires MUST be same
gauge Straighten each wire If wire is corroded or overheated, clean the end with sandpaper and wipe with cloth. If wire has been melted, cut back and reattach, or replace wire. Tighten screw very tight against copper wire |
Use wire connector  Use push-on wire connectors |
3
wires/ or different gauge wires Join wires with wire connector or push-on connector Run jumper to screw terminal. Buy: Push on wire connectors at Amazon Red 3P connector (shown) for 10-14 gauge wire Connector assortment Resource: How to select and install wire connector |
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  12 Ga |
10 gauge or 12 gauge? Compare your wire with short pieces of 10 and 12 gauge wire from local box store 10 gauge for 30 amp breaker. 10 gauge wire can have black-white and sometimes black-red 12 gauge for 20 amp breaker 12 gauge will have black and white wires . Resources: Match color code and amp rating for wire Basic house wiring |
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Add black tape when White wire
carries voltage (applies to 208 and 240V
circuits) With 120 and 277 Volt circuits, White wire is Neutral, and Black is Hot With 208 and 240 circuits, both wires are Hot, and both wires carry voltage Black tape on White wire identifies wire is Hot and not Neutral |
| Prevent fire | |
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Arc
fault breaker can prevent fire inside timer caused by a loose wire or
stranded wire Arc fault breaker trips when there is short to ground (same as GFCI) but it also trips when a spark is detected on the line Spark from loose wire will trip breaker... this will signal that wire is loose under the screw plate, or there is a ground fault on the line Only one GFCI-protection device per circuit... so you cannot have GFCI and Arc fault on same circuit... nor can you have 2 GFCIs on same circuit.... they will cause tripping It is OK to have more than one ordinary breaker or fuse per circuit Buy Arc fault breakers at Amazon Resources: How to wire arc fault How to wire GFCI |
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General household check-up Feel if breakers are warm-hot Check outlets, switches and other electrical devices for heat Use nose to smell for burned parts Use ears to hear cracklings Use eyes and look for sparks Resource: How to troubleshoot household electricity |
| Burned R1 Resistor | |
 This timer appears to have damage on 1 component... but actually several components have dark solder connections, showing that several parts overheated Burned resistor on timer R1 resistor burned, R2 resistor burned Replace timer No prevention steps Check that timer is receiving correct voltage and Load does not exceed rating. This is common problem as timer ages Normally if R1 or R2 are burned... look carefully and other nearby parts have signs of burning also. R1-R2 are usually first place you see overheat problem This is true with older and newer models in the GM and Woods and Tork series digital timers, including defrost series Frequently these timers with burned R1 are sold on ebay after they have been removed from service... simply because the timer looks good or repair seems simple. Check if one of the relays is still functional.. sometimes a timer can be used with one relay. Related solutions: Use correct voltage to match timer Do not exceed load rating on timer Use correct wire and breaker Resource: Match breaker and wire size Figure volts amps watts More resources: Compare similar timers Compare all box timers GM series defrost timers |
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Unburned R1 R2 resistors Note there are no high-heat or burn residue at end of each part |
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Unburned R1 R2 resistors Note there is no high-heat or burn residue at end of each part |
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 Relay points Points on timer relay can get burned It is normal for carbon to build up on points, causing loss of electrical contact. Turn power off, and use nail file to clean points There are no replacement relays for these timers... but you can clean points with a nail file... and if relay is bad, frequently one of the two relays will still function, and load can be controlled by turning off 1 hot wire Resources: How to wire GM40 timer Difference between relay and contactor Contactors |
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Burned
part on electric water heater Replace part, cut back burned wire Resource: Electric water heater parts and replacement |
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