Power outages are occurring more frequently now than ever, especially during intense summer storms, ice storms, and extreme cold. And that’s without counting the times the power fails due to breakdowns and equipment upgrades.
When power outages or surges happen, home damage also follows, either instantly apparent or temporarily hidden. Sometimes electronics break right away, other times the deterioration builds up within appliances during each occurrence and eventually causes a breakdown.
The cost of repairs and replacements usually falls entirely on the homeowner—most power companies deny responsibility. But when they restore power after an outage, it often requires several tries, each time causing spikes or surges along the lines and hitting the appliances connected to them.
These increases of up to 35% in voltage on a power line can last between three nanoseconds and several minutes. When the voltage increase lasts less than three nanoseconds, it's referred to as a power spike and usually delivers a much higher voltage boost. But in both spikes and surges, the power increases above what the appliances are designed to handle, resulting in damage.
Kitchen Appliances and Power Surges
Some kitchen appliances, even when not turned on, have a clock or a pilot light running, which means they're drawing a small amount of power constantly. In a modern oven, these background efficiency functions can be quite elaborate, and a blown board can easily cost $200 to $350 to replace (not including labor).
Now there are multiple ways to get around most problems, it’s only a matter of looking for and finding possibilities. In a case such as this, keeping the power off the PC board until a few minutes after the power to the house is fully restored, when all the voltage spikes are over, would positively work.
Of course, a 220 volts surge protector on the house’s electric panel also sounds good, but the device is designed to react to the surge, meaning it responds after the fact. Doing this with a delayed relay ensures that the voltage is returned to normal before the appliance powers back on.
Also, when considering that the coil activating the relay is a mechanical device (basically a wire), it is much more resilient than semiconductors to power surges, and less apt to breaking down or burning out. The following shows how to accomplish this for a built-in oven.
The Wiring Procedure
Safety Note: Always turn off your circuit breaker when working with electronics.
Remove the Door - Take off the door, along with the trimmings around it that hide the fastening screws.
Remove the Fastening Screws - Remove all screws holding the oven in place.
Reposition the Oven - Place a support in front of the oven to protect your floor, then pull the stove about 1/4 of the way out of its usual spot, or as far as the wire will permit.
Remove the Covers - Take off the top and back covers, exposing the wiring and control board. The board is right behind the control panel in the front of the oven.
Figure 2 shows that all the wiring to the board are plug-ins. There is one lone black wire plugged into P5 that runs all the way to the back and is connected to a large terminal block with three posts (Fig. 3). A black, red, and white wire are connected to it coming from the junction box on the wall.
After disconnecting the black wire leading to the control board from the terminal block (thus isolating the wire), connect one lead of a multimeter to it while connecting the second lead to the other end of the same wire which plugs into P5 of the control board. With the multimeter set on continuity, identify that this is the correct wire by looking for a no resistance (zero Ohm) reading.
From the terminal post where the black wire was just removed, a heat resistant wire will be added and fed to the 120 VAC coil of a delayed relay, and to a NO (normally opened) contactor of that relay through a wire jumper. The other side of the coil will have to be wired up to the neutral (white) terminal post of the terminal block.
The black wire initially disconnected from the terminal post can then be spliced and connected to the other side of the contactor on the relay and complete the circuit. If the delayed relay is set for five minutes when the power feeds the coil, there will be a five minutes delay before the contactor closes the circuit activating the control board, well after the voltage was restored and stabilized.
Parts List - Description and Specs
The temperature outside the oven box will run at least at 100-150° Celcius, so three Ultra Flexible High-Temperature wires (rated at least at 200° Celcius) should be used to connect to the relay. Due to the heat generated by the oven, the relay should be located in an adjacent cabinet where there is no risk of it getting eventually damaged from exposure to excessive heat.
All you need are 20-25 Ft of ultra-flexible high-temperature wire (if the relay is located within the distance of connections in the oven while the appliance is pulled out from the wall), a relay adjustable to approximately five minutes, with a 120 VAC coil, and one contactor normally opened and timed to close after a specified delay, and also rated at 10 amps, or at the PC Board’s power rating specification if available. Clean up the system with a covered plastic junction box.
Closing Things Up
With all the wiring running from the relay’s junction box and properly connected inside the oven, the junction box should be fastened to the back of its cabinet. The relay can then be plugged in place and the cover put back on. If the relay sits too high, a normal depth box can still be used with an opening the same size as the relay cut out of the cover for the relay to pass through it. Because of all the sharp edges around the oven box, make sure there's no risk for the wires to get cut.
With all the covers back on, before sliding the oven back in, the breaker can be temporarily turned back on to do a test run. The time delay can then be adjusted. After everything is satisfactory, turn the breaker off again and return the oven place, replacing all the screws to reattach the door and any trimmings.
The breaker can finally be turned back on, and the oven should operate as always, except of course for a slight delay after the power is restored.