I retired from a major US appliance manufacturer and some of the design changes required, for the sake of the bottom line, had us all scratching our heads at times.Even though all products in our country are approved by UL or ETL, there still exists "uncharted territory" in which design teams make the call.More and more, the person or persons on the team have cost-cutting responsibilities and get the nod.We engineers get the challenge. There are two requirements I definitely applaud resulting from recent changes to applicable standards:1.) Four-wire systems for 220 VAC inputs and 2.) Element fusing (or circuit breakers) for independent legs of 220 VAC system. Unfortunately, these are fairly recent developments (within the last 10 years) some older appliances will not have these upgrades.
LloydP; Yes. I often hear news stories about the shortage of skilled workers. There is no 'shortage' of skilled workers, just a shortage of skilled workers who are willing to work for the low wages offered.
Not a long unsupported span but rather the element coils are not secured to the insulators. Portion of the element came loose shorting to the housing, in time it overheated causing the high-limit to finally pop but it did not prevent operation of the drier. When the motor was energized, the shorted portion of element was as well so there was no indication of failure until it caused the circuit breaker to open. Checked the amperage finding it pulling 42a on one line and 5a on the other. It's now repaired and modified with a different t-stat that allows for the "off" cycle to be disproportional to the "on" cycle, clothes dry in the same amount of time but the energy consumption is reduced by approximately 30%.
This unit "requires" a 3-pole/4-wire connection, however, it's a waste of time and money jumping through hoops to comply with the NEC and satisfy inspectors because the appliance mfg defeated the entire system by making an internal "common" to "equipment ground" connection. Why are they allowed to get away with this nonsense?
Grounding an appliance is certainly about being responsible for your own safety, and in this area the GFCI circuit breakers are indeed relatively expensive. Those that install in an individual outlet box are less expensive, but you will not find one of them made for the 240 volt electric dryer outlets. In fact, you may not even be able to find a GFCI for 240 volt circuits.
Besides that, in an electricly heated clothes dryer with the three wire plug, some of the components that only require 120 volts are connected between one side and the neutral, which would certainly provide a lot of unneeded tripping of a normal GFCI. A dryer with a 4 wire connection might not have that problem, but there is still the issue of finding a 240 volt, 30 or 50 amp GFCI device.
So being responsible enough to provide an external ground connection to the dryer frame is still the way to provide adequate safety. You can not expect others to always watch out for your safety, sometimes you must do it for yourself.
B'gosh and B'golly I had the exact same experience with Whirlpool heating elements in the 80's. Got sick of changing out the dryer element to the extent that I cobbled a new one out of the old ones so that it had a "proper" ceramic element distance involved. :-)
It's not a question of being responsible for your own safety. The fault described here could have caused a fire, and a GFCI would have prevented it. A GFCI will also trip if a child sticks a wire in a mains socket and provides a path to ground for a lethal voltage. You only need one in the main panel and they are not expensive. They are useful for protecting you from monkeys who can't design a heater element support.
I would lke to reply to some of the comments made concerning my dryer overheating problem.
1. Old_Curmudgeon is correct; I should have mentioned that the monkeys that did this design were at Whirlpool, not Sears/Kenmore.
2. To Evan, and a few others that mentioned it. This was not a lint problem. The vent was always cleaned regularly and was a very short run to the outside. Also, when I took the back off of the heater compartment there was no sign of lint or dirt of any kind, other than what I would call a small amount of dust. We always cleaned the lint filter before running the dryer, and that was one of the first things I checked when the wife explained the problem to me.
3. To Jon Titus, as I said in my original post, all of the control switches, including the over-temperature sensor, were in only one side of the line. That is why half of the heater element was able to continue to be energized. The over-temperature element was actuated properly as was the control thermostat, but only on one side. The Monkey part was that the designers, or maybe the bean counters, decided that one was all that was needed. The only thing that controlled the voltage to both sides of the element was the main control switch, which was fortunate other wise the heater would have been half-on all the time.
The GFCI comment is abit off base, since in a dryer made to run on 140 volts there are several 120 volt items. Thus the GFCI would have had to monitor each side seperately, and would not have detected a draw to the neutral. Besides that, all of the large appliances usually also include a separate frame ground connection, and those that don't instead include a four conductor plug.
So don't go telling us that the only way to be safe is to mandate those GFCI devices in every breaker panel, OK? It is really offensive for municipalities to mandate all sorts of things under the premise that we are too stupid to be responsible for our own safety.
Of course, inadequately supported heating elements is not something new to the Whirlpool company. There was a large dishwasher recall a year or so back because the heater element was not supported adequately in the plastic bottom of the dishwasher.
I used to have a Speed Queen electric dryer, it was about 35 years old when it was pretty much just worn out after serving my parents family and then my family. The heating coil failed three times during its lifespan, all three happened when the coil just broke and opened. The length of each span was around 15 inches but each span was supported by two additional ceramic supports placed at the proper intervals, so it was virtually impossible for the broken wire to touch anything else. An usupported span of 18 inches is wholly unacceptable and is asking for trouble.
The original heating element lasted nearly 25 years before breaking at a weak point in the wire. The following two elements, same gauge and diameter coil, each lasted about 5 years because each one of them had a void in the wire which eventually failed from the thermal cycles. A manufacturing defect. In the larger gauge coils, such as dryer heating elements, a void in the alloy can manage to sneak through during the drawing process which is nearly impossible with finer gauge wire.
Generally, unless the wire breaks during drawing, it remains hidden, in rarer cases, the wire can also break during coil winding if the void is large enough, otherwise the coil makes its way into the finished product and there, waits to eventually fail.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.