After running two separate circuits for my daughter's dishwasher and waste disposal, I was told that I could have simply run a three wire cable (still 2 breakers) from the panel box and fed the appliances separately. I understand the concept, but, there would be 2 hot wires and only one neutral. Would not that neutral carry twice the current it is designed for? Thanks for explanations and comments. Ivan Vegvary
It depends. This is commonly known as an "edison circuit". If each of the two breakers were on different legs of the 240v service, then the current in the grounded conductor will cancel out, such that if full load is drawn on both of the two hot conductors, the current flow in the grounded conductor (aka neutral) will sum to zero.
If they're on the same leg, then yes, you'll draw 2x the current on the grounded conductor, which would be a code violation.
Using a commercial handle-tie 240v breaker is recommended, as it will ensure:
a) That the two circuits are on opposite legs b) That both circuits must be disconnected simultaneously.
To add to that, if you have two 20 amp circuits on opposite legs, the current in the neutral will always be between
0 and 20 amps. Only the unbalanced portion, ie the difference between the two flows in the neutral. For example, 15 amps on one, 5 amps on the other, you have 10 amps in the neutral.
you really did this the best way. makes future troubleshhoting easier, and its a one time expense, so a little extra now doesnt matter.
plus witheach item on its own breaker service is easier.
My Whirlpool dishwasher and a KitchenAid disposer are on the same 20 amp circuit and never had a problem.
I don't know if it meets code but I can't imagine it is unsafe in any way.
Did the same here, running two 20 amp lines seemed silly to me. I did run them both at the same time right after I installed them to see if it would trip the breaker while I still had the downstairs wall open. No problems showed up with both under load.
Here the disposal only runs while we are cleaning off the plates to put in the dishwasher. The dishwasher isn't turned on until that step is done so in reality they never run at the same time anyway.
John
waste disposal, I was told that I could have simply run a three wire cable (still 2 breakers) from the panel box and fed the appliances separately.
its a one time expense, so a little extra now doesnt matter.
+1 Saving the cost of a single wire and an extra breaker isn't worth the problems that can arise from using Edison circuits. He's dead. They should be, too. (-:
It is NOT recommended. It is required by code. It is mandatory. Doing it any other way is total stupidity
Up here they are called "split" circuits, particularly when feeding a single duplex outlet..
What "problems"? There are certainly advantages beyond saving 2 wires per circuit. Not the least of which is voltage drop mitigation. (up to
50%). You also get to use smaller/fewer boxes. It is only a problem for people who do not understand what they are looking at and they shouldn't be fooling with them in the first place.
The NEC name is "Multiwire circuit"
Statistically, multiwire/Edison circuits don't have a bad track record but I still wouldn't have one in my home. Not worth the risk.
The risk of what exactly?
+1. To an electrician they are absolutely no problem when properly used. Any time there are 2 circuits in a single box, it is the "only" way to be legal.
What risk? And to be legal in Ontario kitchen countertop outlets have had to be "splits" for decades - and the "only" way to do that legally is with a "split" circuit and tied breakers.
Ivan,
For that kind of "Edison" circuit, the two breakers must be on opposite sides of the incoming 240V supply. That way each 120V "hot" leg is out of phase with the other as the AC cycles back and forth. When one leg is positive, the other leg is negative. The neutral never has more than a single load on it.
It's a safe and common way to wire some circuits, but I still prefer to run separate cables for each circuit. That way breakers can be moved around in the panel if needed without fear of overloading the cable (if both breakers were placed on the same phase the neutral would carry twice the load). The cost difference of two cables vs a three-wire cable is usually minimal for most homes.
Anthony Watson
AFAIK, there is no other kind of Edison circuit. The whole point of an Edison circuit *requires* that it be on opposite legs.
Suppose you have a heavy resistive load on leg 1 and a light load on leg 2 and then suddenly lose the neutral. What happens to the voltage across the light load on leg 2? Would 230 volts smoke a small radio on leg 2?
That is what happens when the power company's neutral feeding the house goes haywire.
That's a valid point. If it happens, you could wind up with up to ~240V on the unfortunate load side, something that can't happen if it's a regular circuit.
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