power cord -- 3 or 4 wire?

yes, 4 wire is usually for mobile homes.

Not just mobile homes; 4 wire is the new standard for ALL homes as of about 10 years ago. Any new outlets for dryers will be 4 prong outlets.

you have the Hot (+) the common (-) and the ground.  Whats the 4th prong for?

Internet. ;)

I honestly don't know myself, as I'm not an electrician, but any electrician putting in a new 220v outlet for a dryer or range will be installing a 4 prong outlet.

OOH! VOIP!  (crawls in her dryer to make a phone call)

A 4 conductor 240V cord has TWO hot conductors,black and red.The green is for cabinet ground.The new conductor is white,it is known as "neutral".

Less current per hot wire, for less risk of overload/arc?

  No,thats never changed.240V supply is essentially achieved by using two 120v hot conductors (out of phase) with respect to a common ground.The way I understand it the neutral (white) wire is to complete the circuit for the 120v part of the wiring (which runs the light,the timer,the motor.) I'm no electrician either but thats the way it was explained to me when this new code started about 20 years ago.

The fourth wire is a dedicated cabinet ground.

Three wire cords use two 120 volt circuits, that share a third neutral wire.

Which cord you get with your appliance really depends on the "socket" configuration in your laundry room area.

The best approach is to take a digital photograph of your socket or do a pencil and paper "rubbing" of the socket and bring the results to your store to get the correct power cord.

So before the 4 prong it had no ground? YIKES!

It always had a ground.The green wire was and still is the ground.Instead of going through the dryer terminal block it now goes directly to the cabinet.But its still green and its still the ground.

Anytime I've hooked up a dryer cord, the outside terminals and outside wires were the hots. The middle terminal(s) and wire(s) were grounds.

madgolfer said…

Anytime I've hooked up a dryer cord, the outside terminals and outside wires were the hots. The middle terminal(s) and wire(s) were grounds.

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The older 3 prong plugs carried the 2 hots (red and black) and the 3rdp prong was for the white Neutral conductor. Older codes (not every municipality though) allowed a bonding strip to connect the Neutral connection in the dryer to the dryer frame (grounding it). This was not the safest of conditions, and the newer electrical codes specify 4 conductor (actually is 3 current carrying ) conductors plus a ground wire, cable and a matching receptacle for the cord to plug into. I am not sure, but if you are replacing an older dryer with a new one, it may be allowable to keep the original 3 prong plug setup for the new dryer. I believe the code changed in 1996 to require all NEW installations to have a 4 prong plug with the correct receptacle and ussually 3 conductor PLus ground NM B (Romex) cable back to the Electrical breaker panel.

(I borrowed this one from Bob, the master electrician @ allexperts.com - a closed-course professional :-)  )

"Under the new Codes...all dryers (and stoves/ovens) must now be 4 wire....having a seperate neutral and ground wire in NEW construction. In decades past, the neutral was allowed to serve as both - the neutral and ground - typically by means of a solid metal strap or wire strap that bonded that connection to the metal frame of the dryer."

When in doubt, just ask Bob.  ;-)

The clouds have parted.  I can see it all clearly now! (files this new info into the "never going to use" file and carries on.

Either 3 or 4 wired cords will work.

Four wire cords are newer and safer.

But, bottom-line, unless you're will to hire an electrician to modify your laundry room 240 volt outlet, go with what you've GOT.

:)

Oh, just to make things "more interesting", there are two TYPES of 3-wire, 240 volt dryer cord plugs!

there are two TYPES of 3-wire, 240 volt dryer cord plugs!

Hmmm, the right one and the one that looks like a range plug?

Yaa...

The straight pinned plug and the L-shaped pin plug.

:)

Hey!

Don't forget about that funny horizontal pinned Air Conditioner (less amperage) 3 wire plug.

NEMA configurations for plug ends and outlets are designated by amperage/voltage.  The main reason for the difference in the arrangement of the prongs is to prevent the wrong plug from being used on the wrong size circuit, 15A, 20A, 30A, 40A, etc..  Each have a specific style, and SHOULD NOT be purposefully used on a circuit size it is not intended for.

The older style three wire plugs allowed the chassis ground, which is normally bare, to share the neutral (white), or vice versa in some poorly designed cases, in which the bare would be used for the ground/neutral.  This was permitted due to the fact that the ground buss bar is bonded to the neutral in the panel.  The heating element and motor running at 240v is somewhat more efficient, as voltage is inversely proportional to amperage draw.  That is, an appliance that draws 10A at 240V, would draw 20A if it ran at 120V.  Half the voltage, double the amperage.  It's not an exact calculation, but is a solid "rule of thumb".  If the control circuits are to be run at 120V, which is a safer condition, a neutral must be present.

Running an appliance at 240V also helps with durability, as amperage equates to the production of heat energy.  Less amperage draw, less heat.

The problem is, that should this single, shared ground/neutral connection fail, the chassis could become energized (somewhat unlikely, but possible).  Thereby, a potentially lethal situation could occur, as the only path to ground would be via a human being. There actually were some fatal cases involving old panels made by a company called Federal-Pacific.  After many years of use, the breakers would actually fail to trip in the event of an overcurrent, or partial/short circuit condition.  If you still have one with flourescent orange labels on the breakers, I recommend getting a new Square D.

With the four wire type, there are a pair of 120v leads, red and black, a white neutral, and a bare or green wire for the ground.  The green or bare wire is there to provide a short circuit to the chassis a path to ground.  This is the safest possible way to wire a 240v machine, and this being the industry standard is quite overdue.

To upgrade an old 3 wire installation, a new four wire feeder would have to be pulled from the panel, to the laundry.  If perchance it is in conduit for some reason, you would only need to pull a new conductor, space permitting.

In addition, most computers run on 5V DC current these days, so, if you have a machine with alot of bells, whistles, and a motherboard, it would behoove you to run a four wire for equipment protection purposes.