Minor item unrelated to the actual element failure problem:
the control circuits on modern ovens are separate from the high voltages and currents. As someone above said, the control circuits cause breakers or relays to trip and channel the higher voltages and currents.
You wouldn't want the 240 volts to be there at the power button when you pressed it, after all.What do they do for European appliances? A lot of stuff nowadays is universal, at least compared to in the past. AC-DC transformers especially, such as phone and laptop chargers, will take 110-240 volt inputs, hence my question earlier about where a DC transformer would be tapped. Is it because our 240 volt appliances are phase-to-phase, whereas European 240 volt is phase-to-ground (would their high-draw appliances then be 480 volt phase-to-phase or something different)?
The element is made of “Calrod” now a generic term but first patented by the Chromalox company. I’ve seen tons of them burn just as the OP described.
Many ovens do not break both lines to the surface elements or the Bake/Broil elements. Or the damaged burner element can weld one set of contacts keeping one line energized even if the switch/thermostat is turned to OFF. So one line can start burning through the sheath to ground and have plenty of resistance in the circuit to prevent the breaker from tripping. About 50% of the time the breaker never trips because the conductor burns up before the resistance drops enough to be sensed as a short. If the NEC drudges get their way we will eventually have Arc Fault/Ground Fault Interrupters on all appliances. And maybe a service disconnect panel in the kitchen. They did manage to get separate neutral and ground in ranges and dryers 50 years after the end of WWII.
I haven’t worked on any electronic ovens with membrane panels but I suspect they are still wired like the old mechanical thermostat units, just using relays for the high amp loads.
No need to let the evaporating element freak you out. Other than ruining your pie or roast, what damage can it do in a nice metal, heat proof box?
Not to speak for igor, but I’m thinking he was meaning the amps. 240 volts, properly protected and grounded and whatnot is going to be just fine behind face of the panel. But you probably still don’t want 20amps running up there. That’s what relays are for. Have whatever power you need to drive the circuit board and switches, the switches can control relays/contractors which handle the amp load of the elements.
240 volts is not that much, not really. The plastic of a knob cover plus the air gap of the shaft plus maybe a plastic insulator is plenty. Unless you are young, you have no doubt used a dial appliance of some sort, where the dial is a timer. Right behind the front cover, about an inch from your hand when you are touching the dial, is full line voltage. (120 or 240). No relays.
20 amps isn’t much, either. It means you need thicker and wider contacts inside there to handle the amps, but it is totally feasible.
I’ve never seen an appliance that used 240V, USA, that kept one wire energized - if you did that, you wouldn’t be able to change the heating element without risking a shock. You would have to turn power off at the breaker to do that. That can’t be legal. Remember, with USA power, any “240V” circuit is between two hot 120V legs. If you disconnect just 1 with the switch, yes, power stops flowing, but you can still be shocked (and killed) if one hand touches the hot terminal and the other hand touches ground.
Yes, true, but since most modern ovens/stoves don’t use knobs and rheostats, but rather digital keypads and circuit boards, relays are, more or less, required. While I’m sure it’s possible to have circuit board logic alone control the full load of a burner, it seems like it would make more sense to me (a non-engineer) to use relays.
Having said that, just taking a quick glance, I’ll admit, I’m surprised that the relays are mounted directly to the circuit board.
I get that it makes repairing it ‘easier’. In that, repair person can show up and replace the entire board to fix just about any problem with little to no troubleshooting. Further more, it wouldn’t surprise me if one board fits many ovens (or can at least be swapped in for testing) so they can just keep them on their truck. But, I hate that it means that a bad relay is going to cost $700 instead of $100.
The fan on my convection oven doesn’t work. It’s probably a bad relay (I’ve never actually poked around to check it out, but I know the fan itself is good and I know the wire is not sending power). The entire board is $300 online. An appliance company would charge Joe Homeowner probably $500 for the part and at least another $100-$200 for labor and drive time. I doubt any appliance company would even think about replacing a component on a circuit board.
If you have the correct tool, you can pull the component. I have done this a few times. The tool you want is a heated bed and a hot air gun. You put the circuit board in the heated bed to warm up the solder, then aim the hot air, set to about 250 C, at the solder balls on the bottom of the relay where the pins come through. Eventually they will melt and then with a bit of talent and a clamp holding the board you can pull it.
Same part might be $5, maybe less if it’s low current like for the fan. $8 shipping from Mouser.
But yes, at $700 it means replace the whole oven unless you have the moderate amount of skill needed to do this.
Note that it might not actually be the relay. You can’t generally trip a mechanical relay with the output from a microcontroller directly. The circuit is probably microcontroller -> FET driver -> FET -> relay. So there are several components between the output from the microcontroller pin and the actual relay, and those can fail as well.
One serious, serious issue is you cannot safely diagnose this unless you are quite skilled. You would need to energize the board with 240 in order to find out what is wrong, and probe the circuit, and that’s too dangerous. You would need to solder wires to each test point and connect your multimeter or oscilloscope, then energize it with your hands kept away from it, then turn off the power before working on it.
As you can see, I guess maybe when I said “moderate skill”, someone who can do all this would cost too much per hour.
You barked up the right tree (nailed it). 240V heating elements typically have a single pole contactor making/breaking the circuit. This is common in electric ovens, baseboard heat, dryers, etc.
What the OP described isn’t rare. Usually people say “It looked like a burning fuse! even after I turned it off!”. Once the calrod finds a path to earth, turning it off just interrupts one leg of the 240V… The other leg is wired directly (always hot) @ 120V, and will continue to “burn” like a fuse.
DO NOT replace your element (or do any other work) unless YOU HAVE UNPLUGGED the stove.
I doubt the manufacturer cares too much about the difficulty or cost of repairing, but they certainly care a lot about the difficulty of manufacturing in the first place. And I have little doubt it’s much cheaper to put all the electronics (including relays) onto one small board, which can be assembled separately and then plunked down into the body of the oven, rather than laboriously attaching lots of electronics all over different places of the oven body.
Some good YouTube videos that mirror my own experience pretty accurately:
Lots of comments on those videos from other folks who had it happen to them as well. I guess maybe this isn’t that uncommon…
Speed of manufacturer is good, but if you watch those lines, they work really, really fast, so having the relays mounted else where, and would add minutes to the production time and maybe a dollar or three in parts.
As for the difficulty or cost of repairing. On the one hand, they may not. On the other hand, some may like to have the reputation of being easy to repair. For example, Chicago Faucets are modular. You can have a 30 year old faucet and put a brand new cartridge into it. You don’t have to spend 2 days hunting down an obscure part and eventually just buying a new faucet when you can’t find it.
Now, the fan on my oven is broken, more or less, right away. Also, it’s a $2000 oven and I can drop a new board in my own. So replacing a $300 board in a $2000 oven doesn’t ‘total’ the oven. But a cheaper oven and/or not being able to do it yourself, and it would really suck to have to replace such a new oven just because of (what’s probably) a bad relay. Have that happen on more than one thing from that brand and you may stop buying stuff from that brand, rightly or wrongly.
OP just put me over the edge after years of idly wondering to buy a fire extinguisher for the kitchen.
I have no idea how How is Stovey Formed. Turn the knob, hear click, burner gas ignites. Now I’m scared of the “click” part.
The OP wasn’t in trouble. He could have just cut the power, opened a window, and left it at any time. The whole reason the oven is in a metal box with glass or rockwool insulation is for this exact reason.
Here is a wiring diagram for a Kenmore electric range. One terminal of the bake and broil elements goes to the oven controller (which is tied to one leg of the 120/240 V - L1). The other terminal of the bake and broil elements is hard-wired to the other 120/240 V leg (L2).
Here is a wiring diagram for another Kenmore range. Same deal.
Here is a wiring diagram for a Maytag range. Same thing.
So is one terminal of the bake and broil elements always hard-wired to 120 VAC? No.
As you can see in this Jenn-Air wiring diagram, one terminal (for bake and broil elements) goes to the oven controller (tied to L1), while the other terminal goes to a Double Line Break (DLB) relay (tied to L2). When the oven is turned off, the oven controller cuts the connection to L1, while the DLB relay cuts the connection to L2. The bake and broil elements are thus completely de-energized when the oven is turned off.
If an oven does not have a DLB relay, then you should unplug the oven or turn off the breaker before messing with the heating elements. If an element does have a DLB relay, then it’s not necessary to do this, though I would do it anyway.
I am curious what percentage of ovens have a DLB relay. Am also wondering if it is still legal to manufacture an oven without one.
I don’t see how it would be, that’s a clear electrocution risk, and many of these ovens are not going to have a disconnect at the oven, you’d have to go to the breaker panel.
This is…shocking information. 
I don’t know if my oven’s manual contains a schematic, but if not I’ll poke around online for one (GE JTP45).
I’d be surprised if it was allowed these days. Even if it is, it seems like a mfr would be crazy to leave either leg hot, knowing that some owner might try to change a broken element without shutting off the circuit breaker.
In the USA, the legal requirements for appliance manufacturers to follow are the listing company requirements. UL being the biggest and most well known. Add in a few Consumer Protection Agency rulings and liability cases lost by manufacturers and there’s your rules. Canada has the CSA and I don’t know what the EU has.
The NFPA and NEC rules cover the installation and wiring TO THE APPLIANCE but not the actual construction of the appliance. Those two agencies are responsible for UL setting a requirement for the separate neutral and ground on ranges and dryers. But it took a long time and they had to fight the Appliance Manufacturers Lobby to get it to happen.
I have worked on plenty of ranges and dryers and almost all of them have one line hot all the time.* The remarkable ones are those that break both lines. The old Frigidaire Custom Deluxe line of ranges had double pole thermostats and surface element switches and they were seriously expensive (for the time) to replace. They had a “Speed Heat” surface element that was rated 1400 Watts at 120 Volts but when you first turned on the switch, it supplied 240 to the element, then dropped it to 120 when the element got to temperature. Even those had the 120 for the element, clock and stove top convenience outlet all dropped through Ground, no Neutral.
All legal.
Clothes Dryers ALL had a 120 Volt drive motor, 120 Volt timer motor, many had 120 Volt tub lights, 120 Volt Low Heat element section, all dropping through ground, no neutral.
All legal.
To my knowledge, the only thing that’s changed is the requirement for Neutral and Ground to be separated.
*The Robert Shaw Infinite switches used by 90% of manufacturers for their surface elements have both poles fed to the switch but only break one line while operating. They do break both lines when OFF.
Very well stated. The only thing I would add: Water heaters and baseboard heat also share the characteristic of one leg always hot @ 120V.
The amazement of some to this fact, and the outright disbelief by others, prompts the reiteration of a good axiom: Warning labels are provided* to prevent amateur electricians from death by imagination. *
I spent an inordinate amount of time investigating the DLB relay and your associated schematic, and found no support to your claim that both legs are isolated, as you claim. Perhaps they are, perhaps they are not… Simply viewing the schematic is ambiguous, and I was unable to locate a logic diagram of the DLB and it’s associated control module to arrive at a conclusion per your claim. If you have a cite, I would appreciate it.
Ambiguous as the conclusion may be, let’s assume you are correct in this instance… Nevertheless, why on Earth would you make the statement below:
Yeah, it’s probably a good idea to power down before working on a circuit,:smack: especially when unsure of what you are doing (like PERHAPS
barehanding a hot, defective heating element). It is amazing how many people feel it unnecessary to observe simple common sense when dealing with electricity, because they consider themselves infallible in their intellect. Do yourself a favor, no matter how smart you think you are, UNPLUG the dammed thing when you work on it.
To the first question, I have no cite other than to offer my opinion that a vast majority do not… Most appliances with 240V heating elements are still manufactured with one leg always hot @ 120V. It is definitely still “legal”.
You need to get over what you think and what you feel is right… And try to understand the why of reality.
