10

Turned on our 2 year old stove (Whirlpool Gold) and heard fizzing noises, then smelled electrical burning. Went downstairs and shut off the breaker (40 amp). That was the only way to get it to stop "fizzing". (6 gauge wire by the way). The range is 240 volt electric 3 wire hooked up to a 40 amp breaker (6 gauge wire). When I took the back panel off the stove I saw exactly where the problem occurred. The black wire was burned, the terminal block was melted, and the inside of the back metal panel that I removed was pitch black in the spot that was facing that area before removal. I removed the stove top and inspected all wires and other electronic components. No problems at all.

So my questions are:

  • Why did the black wire only, at the terminator block, start burning?
  • Why did the breaker not pop off?
  • Is it safe to just replace the terminator block or is this an indicator of a much larger problem?
  • Is 6 gauge the correct gauge for a 40 amp breaker?
Improve this question
1
  • 4
    240VAC can arc through a loose connection but not pull enough amperage to trip the breaker. Arc plumes are dangerous. I watched a burner fail once. It burned through the muffin tin (still have it less one muffin pocket) sitting on top it and scorched the ceiling. There was no way to react quick enough and the 50A fuses never even warmed up. Basically it burnt 2.5" of the element and extinguished because of the gap. Do not allow any Nichrome element to remain in service if it develops a glowing spot. The arc is a high temperature plasma and will cut through any metal.
    – Fiasco Labs
    Commented Jan 28, 2014 at 7:22

1 Answer 1

Reset to default
15

This is a fairly "common" issue, that typically occurs due to high resistance at the terminal. The high resistance can be caused by corrosion, or a loose connection. The high resistance causes heating, which causes higher resistance, which leads to more heating. Eventually the insulation on the wire starts to melt, and/or burn. Usually the heat will transfer through the terminal block, and into the smaller wiring in the stove. When the heat becomes too much, the smaller appliance wiring will fail and open the circuit.

In most cases this is not a super dangerous event, as the wiring is contained within the stove. However, there is a chance that this can lead to a fire in the house, especially if the cover is not properly installed.

Causes

Corrosion

Corrosion is more commonly a problem if the wiring is aluminium, though can still be a problem with copper wiring. Because stoves/cooktops/ranges draw large amounts of current, there is typically some heating of the wiring during operation. The constant heating and cooling cycles of the wiring can lead to corrosion, and/or hardening of the wiring over time. This corrosion and/or hardening increases the resistance of the wiring, which cause the heating to be worse.

Solution

Occasional inspection of the terminal block and wiring, can prevent the corrosion/hardening from getting too bad. If you notice any discoloration or corrosion, have the cord replaced. There are also conductive pastes available, that can be applied to the wiring and terminals to help prevent corrosion. While this should always be used with aluminium wiring, it may also be applied to copper wiring.

Loose Connections

This can be caused initially by not tightening the terminals to the proper torque (usually specified by the manufacturer), or over time by heating/cooling cycles. Loose or bad connections can cause arcing and/or higher resistance. As discussed before, high resistance leads to heat.

Solution

Make sure all terminals are tightened to the manufacturers specifications. It's also a good idea to tighten the terminals after a few hours of operation. As stated before, occasional inspection can also prevent this situation.

Why didn't the breaker trip?

The heating was localized to the stove\cooktop\range, so the thermal protection in the breaker would not trip. Since stoves\cooktops\ranges draw large amounts of current during normal operation, the current during the event likely didn't go high enough to cause heating in the breaker to trigger the thermal protection. It could also be that the breaker is faulty, so it should be inspected.

Is the stove scrap?

The stove may be salvageable, though you'll want to thoroughly inspect all the wiring to insure it is not damaged. Replace any damaged wiring with equivalent parts (cooking appliances use high heat resistant wiring).

If the stove is still under warranty, you'll want to contact the manufacturer to discuss your options.

Improve this answer
5
  • 2
    +1 for a great explanation. It would be a good idea to contact the manufacturer even if the unit is not under warranty to make sure that repairs (if possible) are done thoroughly. There could be hidden damage difficult for even a skilled DIYer to identify.
    – bib
    Commented Jan 28, 2014 at 13:12
  • Damn tester, I've been away for awhile. where do you find time for such a great answer!!! CUDUs.
    – shirlock homes
    Commented Jan 28, 2014 at 21:19
  • 1
    Actually since the connection has a high resistance, the current going through the house wiring will actually go down. So unless the breaker is an arc-fault type, it wouldn't have tripped anyway. At least not until the situation got so bad the loose wire shorted to something else.
    – Brad Gilbert
    Commented Jan 30, 2014 at 5:10
  • 2
    @BradGilbert which is why arc-fault breakers are now being required for certain circuits. Arc-fault breakers look for the ragged RF generated by the arc and trip. This is because the temperatures in an arc are so much higher than you generate from a simple short-overheat by so many orders of magnitude that you can reliably ignite magnesium. A fully developed arc flash can create 35k°F/19k°C temperatures.
    – Fiasco Labs
    Commented Jan 31, 2014 at 18:49
  • and there is no increase in current as the result of a bad connection serving a load. this just happens more on higher current loads like a range.
    – Skaperen
    Commented Mar 5, 2015 at 11:46

Not the answer you're looking for? Browse other questions tagged or ask your own question.