I just moved into a new house (well, actually it's old - 1920). We don't have a garbage disposal and was interested in in having one installed so I called a plumber. He estimated $650-750 saying that the electrical wiring would be the main cost because the electrical needs to be run directly to the circuit breaker. Is that right? Perhaps I can do the wiring myself?
Yes, you'll need a 20 Amp 120V outlet with just the disposal on it. I don't see why you shouldn't be able to wire it up yourself.
Something else to think about - is your house on a septic tank or a sewer system? Some city regulations don't allow a garbage disposal on a septic tank. Ours is kind of kludged with the switch under the sink because it was an after-inspection add-on to the house when it was built. At least that's what the home inspector told me when I asked him about it.
How updated is your wiring? In an old house, it might still have knob and tube wiring. If this is the case then I wouldn't want to mess with wiring up a disposal.
However, if the wiring has been redone with modern stuff, then its pretty easy. I put one in my 1920s house (with updated wiring) earlier this year.
The main problem I had is that every spot on my breaker box was already full. (See question I asked about this here.) Code does in fact require the disposal to have its own circuit, but for me this was difficult option. Instead I just spliced into the existing kitchen circuit.
By my calculations, a 1/4 HP disposal (which is really all you need) will draw about 1.5 Amps of current.
.25 HP = 186 Watts
186 Watts / 120 V = 1.5 Amps
I calculated the max power draw of all the kitchen appliances plus the new disposal, and it was well under the 20 Amp max of the circuit. It seems silly to dedicate a whole circuit to an appliance that shouldn't draw over 2 Amps.
A double check of the specs on my 1/4 HP disposal indicates it pulls up to 9 Amps! Don't do what I did. Put the disposal on its own circuit.
$650-$750 is a lot to pay. If you're home's wiring can handle it, it's something you can do yourself for about $150 in materials and a few hours of work.
You can tap into an existing outlet possibly, if it is nearby. I am lucky to have a 120V outlet under my sink. I just replaced my disposal today and would also like to state that if you don't own a bottle jack, get one. They aren't expensive but it pays and saves time to get one, especially if you are doing it yourself. It just makes the whole hookup easier. Use the bottle jack with a flat piece of wood (1x4 will do) to help you raise and hold the disposal in place while you use the special tool to screw the disposal socket onto the bracket. Voila!