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Re: AC Plugs!

Posted: Thu May 31, 2012 6:01 pm
by Robert Reed
"As for the cost difference, its not just the tab but the 6 feet or so of copper conductor in the cord that attaches to it. That's 33% more metal in the cordset, not just the prong."

The prongs use the same amount of wire in ether case. Remember the post only applys to two prong ungrounded plugs probably using zip cord- Not grounding plugs.

"That's similar reasoning to why romex cable with the extra hot conductor (3 cond plus gnd) is so popular. it reduces wiring by half because you can use the neutral and ground for two branch circuits"

Don't know if this type of circuit is valid anywhere any more. I don't think it will work with GFIC. Current residential NEC code requires either GFIC or AFIC (arc fault interrupter breakers). I not sure about AFIC in split circuit operation.

Re: AC Plugs!

Posted: Fri Jun 01, 2012 5:19 pm
by haklesup
I don't think there is any such thing as a 3 prong plug at the end of a 2 conductor wire. It would be unnessary serving no purpose and misleading to the user and potentially hazardous if used on a removable cord set. Polarization takes care of guaranteeing the correct orientation. Reference a power cord venror like and you won't find one. Can you provide any examples?

4 cond romex (NM 12/3) works just fine with GFCI and it is very much compliant with current electrical code. GFCI is required in bathrooms, kitchens and garages and outside branches. AFCI is only required in bedrooms. circuit breakler only is allowed in lighting and livingrooms and hallways but GFCI is allowed. using the wrong type especially AFCI can result in unnessary false trips (these often trip on motorized appliances like vacuum or when plugging things that are turned on or under load). There are other subtleties but its not my intent to requote the whole code.

Re: AC Plugs!

Posted: Fri Jun 01, 2012 9:33 pm
by Robert Reed
AFCI is only required in bedrooms.

The current code now requires arc fault breakers almost every where gfi is not required. Having just completed wiring of my new home and passing final inspection, I am painfully aware this recent change in code.

Three prong plugs without a ground wire? That doesn't make sense. Where did that come from?

Re: AC Plugs!

Posted: Sat Jun 02, 2012 1:25 pm
by haklesup
Recent changes, I suppose, it was a few years since my last house wiring project. AFCI was only a couple years old then and not abundantly available.

A little more clarification A GFCI breaker in the main panel pretty much has to be installed with 12/2 wire since the return has to go all the way back to the breaker but if you are using GFCI recepticles, you can use the 12/3 out to the point of the first GFCI in each branch then you have to maintain a pair of hot and neutral after the first GFCI recepticale. So it depends on where the protection device is installed.

I don't think AFCI recepticales are available and only breakers are possible meaning that you may be restricted in the use of new branches and 12/3 wiring

Re: AC Plugs!

Posted: Sat Jun 09, 2012 11:36 pm
The three prong plug, with a safety ground was introduced for safety as others have said. I can recall some lamps and other devices of the 50s and perhaps earlier that were a real safety hazard with their two prong, un-polarized plugs. In my teenage years I repaired many such devices that scared the heck out of me. Cheap components, like lamp sockets with a cardboard insulator that almost always disintegrated with the heat of the bulb, rubber insulation that dried up and cracked off, etc., etc., etc. It really scared the heck out of me. Also remember that plastic was just being introduced and most items were still made of metal, usually steel. So the outer shell WAS conductive in most cases. Plastic was "cheap" and frankly not anywhere near as good as the plastics we have today. If a plastic item was dropped, it was trash.

The insurance companies probably got tired of paying for burned down houses and accidental deaths. So the three prong grounded plug and cord was born. At least the FUSE would blow. Breakers were also rare. Pennies were more frequently encountered in the service boxes then breakers (under the blown fuse). Don't laugh, I watched my grandfather do this.

Now, manufacturers do count every penny. It is not only the extra metal in a three wire plug and line, but also the extra rubber or other insulation used. Don't laugh, at some times in the past and for some types of wire the insulation costs twice or even four of five times as much as the copper. When you are making 10,000 or 100,000 items, the price of each component is measured in as many decimal places as the above numbers have zeros. So if one supplier can cut a dollar off of a contract for 100,000 plugs or cords, then he gets the contract. The actual saving on each item manufactured is only one thousandth of a penny, but it is in the books and it does count to the bean counters.

So, the new, three prong plug and three conductor cord costs more in metal and in insulation material. We are not talking the thousandths of a penny here, but multiple pennies, perhaps 10 or 20 cents or even more per item. Major, major expense when multiplied by 100,000 or more. We are up to thousands of dollars and that definitely does get attention.

So, how does the poor manufacturer fight these evil cost increases that the regulators have saddled him with? That is how "double insulated" was born. If an item can be designed to have two completely independent insulation barriers to prevent shock and fires, then they, the manufacturers, reasoned and argued that the third wire was not needed. So in many cases the clever designers found ways to provide that double insulation without actually increasing the cost by a lot. Better plastics were developed and plastic outer shells became more common because they were the second layer of insulation.

It is all dollars and cents. It isn't just the few pennies they save on one item, it is the thousands of dollars they save on a factory run of hundreds of thousands of them. And the competitive advantage that a company has when it figures out how to make the same device at a cheaper price. Thanks to this effort, many devices that are basically unchanged in function from those of 50 years ago actually cost fewer of today's inflated dollars than the ones of that era did then. I was looking at prices for blenders a few days ago. I recall prices of $40 or more in the 50s and 60s. It was a luxury. Today $25 ones are common. And probably better made and longer lasting. And they have a double insulated design with a two wire plug and cord.

Re: AC Plugs!

Posted: Thu Jun 14, 2012 5:40 pm
by haklesup
Excellent response. I might point out that this cost reduction engineering has become the hallmark of cheap knockoffs. It's as if a generation or 2 of engineers have been taught to reducte costs at the risk of compromising quality because consumers care more about cost than quality. In the end its our own fault for demanding cheaper prices and putting up with walmart which is a prime driver in cost reduction.

I however have never seen a quantity component cost with more than 4 decimal places. Thats still pretty fine resolution.

Re: AC Plugs!

Posted: Fri Jul 27, 2012 11:55 am
by richfloe
Hacklesup (and others for purposes of edification),

A change in NEC 2011 (Article 210.4) ruins the 3 wire system of two circuits ("multi-wire branch circuit") as it now requires a means to simultaneously disconnect all ungrounded (aka Hot) wires. This either means that the two breakers have to have the handles tied together or you have a double-pole switch that could break both ungrounded lines. Having a two pole breaker (with handles tied) would be a lousy solution because if you overload one circuit, the other circuit gets shut off too.

I'm sure this ruling came about as a result of someone doing something stupid (the usual reason for many laws). If you were to turn off one of the breakers and then opened the grounded (aka Neutral) conductor at a splice point, you are going to get a surprise. I'm also certain that there were times that the two ungrounded lines were Not of opposite polarity and the grounded conductor was overloaded. Even if things were wired up correctly, years later someone else moves things around in the panel and doesn't even realize that he has overloaded the line.

When you are running wiring in conduit or raceway, since you can no longer share the grounded conductor, you will have several white wires. Obviously you don't want to mix them up so they are now selling white wire that has a small colored stripe that you match up with the ungrounded conductor it is associated with.

For those of you unfamiliar with the NEC terminology:
"Ungrounded conductor" is the Hot one that will bite you.
"Grounded conductor" is usually white (could be gray), commonly called the neutral.
"Grounding conductor" is the safety ground (earth) connection, green or bare.
GroundED and GroundING both connect to the same place in the breaker panel; ground. The grounded line is an intentionally 'current-carrying' conductor. The grounding line only carries fault current, and only until the breaker trips.

BTW I'm not an electrician, I just play one at work.