Noor, they were probably trying to save money on the switch. Not taking into account the failure mode you ran into, they figured that the 110 volts on the element were not as problem. Not very smart, and how did they pass UL testing?
It's been a while since I've done an oven, but a double line break was not required in the US, however was required in Canada. We used to have two seperate to handle the destination and save money when it was domestic.
A single line switch would not normally be a problem when the mains supply is 230V, at least not in the UK or in the country where I live. But in many EU countries they use the Schuko type plug, which is reversible, meaning you get the live mains on the right hand pin on Mondays, Thursdays, and Saturdays, and on the left pin any other day of the week you plug it in.
Most heating elements in an oven in the US are 220V, which means both hot sides are connected (110V each, opposite phase). If only one side is switched, the element is still live because it is connected to the other hot line. I'm surprised this design passed UL.
The correct way to switch power, at least by JIC standards for industrial equipment, is to break all the non-neutral lines. I think that is also required by the NEC. So a control switch in one side of the 240 volt lines is a poor excuse for a control method in the US. In the UK the power is a basic 230 volts with one side as neutral, which is usually also grounded. So in those systems only breaking the "hot" side would be quite adequate, and would not constitute any hazard in a polarized-connector installation. But with the basic voltage being 230 instead of 120, I am far more likely to disconnect the power before opening anything. But that is a separate issue.
Usually, appliances have a diagram/schematic on the back or on the inside of a panel. So, if you think flying sparks are fun then check out the electric dryer for a shocking good time.
I have worked on a few and was stunned. They use 220Vac as well. But, the motor is not 220V,...it is 110V! So, on three wires, where do they get the tap for 110V? GROUND!!! Thats right. They use the ground wire; the same one that is connected to the chassis. Turns out this is not true in all cases. Some dryers have the option for 4-wire plugs (which provides the neutral). But even they have the option to be wired for 3-wire plugs. My research showed that mobile homes requires 4-wire but a regular house does not.
Safety seems to be suffering in the name of profit; or is simply being ignored.
I addressed this topic in another similar blog last week, but will repeat it for information purposes.
You ARE correct about the 3-wire & 4-wire services to electric ranges & clothes dryers. Up until recently, the NEC allowed the connection of either an electric range OR a clothes dryer with 3-wire in the application of SINGLE FAMILY DWELLINGS only!
In the case of the clothes dryer either 10/2 ROMEX or BX w/GND were allowed, the GND conductor ALSO serving as the "neutral" for the power to controls, solenoids, motors. The NEMA codes for these devices is 10-30 (R) & (P), where the (R) & (P) stands for Receptacle & Plug, respectively.
And, it is true that in MOBILE HOME installations, the feeds MUST have been w/ 10-3 /w GND cable. The NEMA dodes for these devices is 14-30 (R) & (P).
The latest NEC code however has changed the requirement so that the frame of the appliance is connected to the GROUNDING conductor (bare, green or yellow/green), and the two lines & neutral (white) are connected to the terminal block provided on the rear of the appliance.
This change also affects single unit electric cook ranges, except the NEMA designations are 10-50 (R) & (P) for the old-style connections and,
14-50 (R) & (P) for the new code revision requirement.
One final note: Since both electric ranges AND clothers dryers are considered "permanent" appliances from the code's perspective, it is now & has always been that the feed cable may be directly connected to the appliance. However, some installers prefer the added convenience of using a cordset w/ a permanently installed receptacle device, either surface mounted OR recessed in an appropriate device box.
It seems that some of us have made assumptions that may be flawed. First, not all appliances have a wiring diagram included, but I sure do appreciate this when a manufacturer is nice enough to include one. It's not required! Second, we should not assume that the author is located in the US! This person has an Arabic (assumption) last name! Third, UL listing is not required everywhere, so there is no reason to assume that the oven passed UL testing! Last, we don't know where the manufacturer is located, so we should not assume that it should behave like most US manufacturers!
tekochip, that company's policy is an invitation to an unwinnable lawsuit. At least, that's the argument posed by most companies selling industrial safety components. The plaintiff's argument would question why a less safe product was sold in one country and a more-safe product in another.
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