Replacing a 2-gang switch with a 3-gang switch

Our kitchen has a two-gang switch on the wall along the kitchen counter. One switch controls the dishwsher and the other the garbage disposal, obviously on the same circuit. I want to add a switch controlled lighting pendant over the sink. Couldn't I just replace the two-gang switch with a three-gang switch, then wiring the third switch off the the other two, then running wire from there to the pendant?

I am not doing this myself, but before I call my electrician I want to know if this would be the normal option since all I would have to do is widen the hole in the wall to accommodate a three-switch gang, then simply use the power that is already there to control the third switch that would power the light. My thinking is this method would save the electrician time and labor, which in turn would reduce the cost of his services. Or am I overlooking a critical issue somewhere along the way?

Thanks for anyone's insight.

 

You can attach another 2 inch box. But you can also use a duplex switch in one side or the other.

 

One issue is that once you add lighting on the circuit the fastened in place rules kick in. The total of the dishwasher and disposal ratings can't exceed 50% of the circuit. This is sometimes overlooked but you might get caught later.

 

Many DW have a fairly significant heater in them, and a lot of disposers can have up to a 1Hp motor. Combine the two, and you could be getting close to the maximum circuit load. Before you add anything to that circuit, you should add up the total loads listed for the current devices. But, physically, yes, you probably can add another switch. The power and neutral are probably there in the box rather than a couple of switch legs, but you'd have to look to be sure.

 

Why is the dishwasher on a switch? Do you have an old home and the dishwasher was added perhaps after a remodel and the circuit for both the dishwasher and disposal may be the same. An electrician will be able to determine the best course of action since it is his liability at stake. Dishwashers are usually on there own breaker since the heating elements can be 1200-1500 watts and they can run on a 15 amp breaker.

To add another switch or to add wire the 2 gang box may not be big enough. A three gang box is the best way to go but the hole will have to be larger all around to get to what ever is anchoring the box and depending how the existing wire/cables are tied in. If it is all drywall it is an easy patch, if it is tile it could be nearly impossible unless there is access from the other side of the wall.

If it is possible to run a new circuit and wire to the wall, just adding a single gang box, perhaps on the other side if the sink could be easier and faster. The electrician can tell you. Sometimes working with old work and adding new to it is more difficult.

 

FYI - Most codes require a disconnect for a dishwasher but it is not always enforced. Using cord-and-plug is easy to meet the needs for a disconnect but some places want the dishwasher hard wired. In place of the cord and plug the wall switch in sight of the dishwasher becomes the disconnect. Otherwise a breaker lock at the panel is needed.

For new installs a 20 amp circuit usually is good for the dishwasher and disposal. Exception is where the installation instructions call for a dedicated circuit.