I'm a new homeowner - please be patient. I know nothing about anything. I just purchased a Bosch compact stackable washer/dryer. The washer , which says it is 220-240V, plugs into the back of the dryer. The dryer, which says it is 220-240V, has a wire cord already attached with 4 prongs. My laundry closet has a 220V outlet with 3 prongs. I had wanted to put a new electrivcal cord on the dryer, but the people at Bosch said it would invalidate to warranty. My question is this: Can I just install a 4-prong outlet in the laundry closet (there are only three wires coming from the wall), or do I need an electrican to come in and re-wire the laundry closet with a four-wire line? Is it safe if I just put in the 4 prong outlet without the expense/hassle of getting the electricain to run the 4-wire line? Thanks for the help...

 

No, you can't do that per the NEC. For a 120/240-V appliance, you need to rewire to provide 4 wires: two hots, one neutral, and one ground. Otherwise, with just three conductors (which used to be permitted), the neutral is used as a ground, too.
Doug

 

If the manufacturer of the appliance will not allow the installation of a three-wire cord set, then the only option is to have an electrician install a new four-wire circuit. This is a strange situation however, because most manufacturers do allow a three-wire cord set to be installed and the installation manual will provide directions for both methods. The new four wire circuit will be a safer option though.

 

OK, let me correct what I previously posted.

The current NEC allows a dryer to use a 3-conductor connection IF the receptacle is existing from prior to the 1996 code. However, if the branch ckt feeding the dryer has to be reworked, then it has to be upgraded to 4-conductors.

And, for a new dryer designed for 4-conductors, there will not be a bonding jumper between the neutral and the metal frame of the dryer; the NEC requires the dryer to be modified to add the bonding jumper - and that may be be frowned upon by the appliance manufacturer (Bosch, in this case).

A washer is not allowed the same exception as a dryer. (And, a 240-V washer is a little unusual.) So, technically, your washer (and therefore the dryer, which your washer plugs into) would need a 4-wire connection to comply with the NEC.

The best solution is to upgrade to a 4-conductor receptacle. And while you're at it, check the amp draw of the washer/dryer combination, and, if necessary, increase the amperage of the conductors and breaker.
Doug