220 volt 3-wire vs. 4-wire

[M.Burns]

I have a 220-volt electric dryer with 3-prong plug going into a 3-prong receptaclet (2 blades on a 'V', and third L-shaped prong). Do newer electric dryers have a 4-wire plug with a ground? Would I have to replace the 20-year-old 3-prong receptacle? Just technically speaking, could the ground prong on the male plug be cut off to fit the old outlet (similar to what people of done for years on

110-volt stuff). Or is the wiring for 4-wire 220 volt completely different because of 2 hot wires, neutral, ground, etc.?

[RBM]

The NEC allows you to use an existing three wire electric dryer feed and receptacle. Typically, dryers don't come with cord sets, so you specify the one you need for your outlet. Any new installations require a four wire feeder and receptacle. If, you do have a four wire feeder, it would be sensible to install a four wire outlet on it, then get the appropriate cord set with the new dryer

[S. Barker]

Dryers don't come with cords. Just use your old cord on the new dryer and go. You'll have to be sure the grounding jumper is in place on the new dryer like it is on your old one.

s

[EXT]

Canadians reading this should note differences that in Canada, dryers and non-built in stoves have all come with 4 prong cords for the past 35 years. Code requires receptacles that are fed by what is labeled a "3 wire plus ground" cable. It is not Code compliant to connect the neutral and ground together in the appliance.

[hallerb]

dryer and

I will add that i think 3 wire is a bad idea, with a bad day it could be a real hazard....

buy a new dryer? then get a new cord and updated outlet

[Beachcomber]

Problem is - Many older houses are not wired for the updated outlet. If you don't have the proper wiring at the outlet (2 hots - Neutral

-Ground), you are not allowed to install the 4 wire code-compliant outlet (vs. the old 3 wire outlet). Hence the grandfather clause...

For many older houses - installing new dryer wiring would be difficult (expensive) and involve pulling new wires and possibly ripping up walls.

The NEC allowed the 3 wire exception to save on copper during WWII. Then, one or two people got electrocuted by their dryers and they decided to go back to 4 wire some years ago.

Apparently Canada never did this. Anyone know for sure?

[hallerb]

for safety its likely worth the effort.

just look at all the other updates required today, GFCI, arc fault, getting rid of K&T to obtain insurance, replacing fuse boxes, etc etc.

wonder why the dryer exception has survived?

[gfretwell]

Not much of a body count to justify changing it.

[KLS]

Beautifully put. :D

[Ralph Mowery]

While it is a good idea, houses and people survived for many years without all the safety equipment.

[S. Barker]

if the grounding jumper is properly in place, then it's just as safe as a 4 wire. IF in fact anyone was actually shocked by a dryer, then it was a dufus installation problem, not a # of wires problem.

steve

for safety its likely worth the effort.

just look at all the other updates required today, GFCI, arc fault, getting rid of K&T to obtain insurance, replacing fuse boxes, etc etc.

wonder why the dryer exception has survived?

[Beachcomber]

Safe is a relative term. The safest installation would be to have the neutral separate from the grounded frame of the dryer, especially since in the US, dryers have 120 V. motors and thus there is always neutral current flowing when the appliance is operating.

The exception was apparently allowed because it is extremely rare for the neutral to become disconnected, which could potentially energize the frame of the dryer to 120 V. Most dryers are installed next to a washing maching, which is more-than-likely to be properly grounded. Thus you would have a possible shock hazard.

But, as mentioned before, most owners of older homes are not going to want to spend the money to rewire the dryer circuit for something that has basically worked fine for 10-40 years, if the 3-wire dryer plug option is allowed.

[Mark]

This is NOT true.

The three wire system, even when properly installed to code is dangerous becasue an OPEN circuit (which can happen) in the 3rd ground/ neutral wire) can end up energizing the metal chassis of the dryer through the 120 volt clock motor or other 120 volt parts in the dryer. If someone then touches say the properly grounded washing machine and the dryer at the same time, they could get a dangerous shock.

That being said, I have a three wire install in my house and it can be made safe with the simple addition of an axtra ground wire connected from the case of the dreyer to a good ground such as a nearby water pipe. I have a ground wire connected between the dreyer and the washer, therefore there can be no voltage across them.

Yes three wire system were code and can be grandfathered to code, but they can still be dangerous and I would add the extra ground wire to be safe. Rewiring for a full 4 prong plug can be expensive if a new cable has to be pulled. Adding an external ground wire is cheap and easy and effective.

Mark