Garbage Disposal / Dishwasher

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  #1  
Old 09-27-05, 08:08 AM
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Garbage Disposal / Dishwasher

Greetings,

Working on renovating my kitchen and recently came into a problem I'm sure will be easy for the guys in this forum. I have a 12-2 run from the breaker to a blue box near the sink. From there I have two 12-2 runs to beneath the sink that are to be plugged into a split 20A recept - One half on a switch (in the box), the other half on all the time for the dishwasher.

So far everything makes sense except that in the blue box near the sink I also have another switch (separate 15A circuit) controlling a light above the sink. The problem I have is that the 20A switches I've found to use for the disposal don't seem to match the 15A light switch (thickness, appearance, etc.) it would be next to, or the rest of the switches in the house for that matter. When I asked for help finding a non industrial 20A switch at Home Depot this is what the associate there told me:

"You can use a 15A switch here because there's never more than 15A being drawn through the switch if it's only controlling your 8.5 amp disposal. Even if the whole circuit itself is on a 20A breaker."

Now this makes perfect sense to me but the concept of having a 15A switch on a 20A breaker doesn't seem right - even though only 8.5 amps would be passing through the switch. What if the disposal went crazy or faulty or whatnot and needed to pop the breaker - wouldn't this cook my switch first, burning down my home and killing my wife and unborn child? =)

So my question is: Is this maneuver legit, should I just make this a 15A circuit to be shared between the disposal and dishwasher, or should I keep looking for a 20A switch that matches?

Many Thanks!
 
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  #2  
Old 09-27-05, 09:17 AM
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According to electrical code you size the switch to match the load, not the circuit ampacity. You are perfectly okay and safe to use a standard 15A toggle switch for the disposal. It is actually very common to use a 15A switch on a 20A circuit provided the switched load does not exceed 15A.

Circuit breakers have two trip mechanisms: a thermal trip which trips on overload and a magnetic trip which trips on short circuits (like you describe). This secondary function of the breaker will interrupt the current before the wiring and switches experience overheating in the event of a line-ground fault. The motor inside your disposal has internal overload protection as well. There are a number of lines of defense in a properly installed circuit.
 
  #3  
Old 09-27-05, 11:31 AM
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Ipbrooks, This switch is controlling a motor load, so the rating of the motor cannot exceed 80% of the switch rating, which in this case is 15*0.8=12 Amps. see NEC 404.14(A)(3). But your answer is still correct for this case, since the motor is only drawing 8.5 Amps.
 
  #4  
Old 09-28-05, 07:20 AM
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Thank you both very much for your help with this.
 
  #5  
Old 09-28-05, 08:31 AM
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Good point Dave, thanks.
 
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