Two circuit wiring for whirlpool tub

[skintdigit]

Hi folks,
I'm installing a whirlpool tub which requires two separate 20 amp/120v circuits, one for the water pump motor, and another for a heated air blower...both with GFCIs. Manufacturer's tech guy was vague on the phone when I called to ask if both circuits needed to be on the same bus. He said the pump and blower need to be on separate circuits and only communicate with each other through the control boxes. OK, l'm thinking, and how do they communicate...sound waves? infra red? smoke signals? No...electricity! So, I'm playing it safe and pulling both circuits from the same bus in the panel so I don't fry a control board somewhere with 240v.
Here's the question. Can I run 12/3 NM-B from the panel and wire the hots to two separate new breakers and share the neutral from both circuits back to the panel? Or will the current produced by two simultaneous loads be too great to safely use the single 12 ga neutral? I guess another way to ask this question is how much current is present in the neutral wire of a single phase, 120 volt circuit with an imposed load of, say, 17 amps?

[Snoonyb]

DO NOT use two single pole breakers off of the same buss.
Use a DP breaker and at the recepticles, pig tail the neutrals.
The current realized at the neutral is the difference in the loads on each of the hots,IE. if the black has a load of 15A and the red has a load of 5A, then the current realized by the neutral would be 10A.

Using a DP breaker insures that ALL voltage will be disconnected when/if service is necessary.

[kactuskid]

The 12/3 circuit you're inquiring about is called a multiwire circuit and since there's a 240 volt potential involved with sharing the neutral, it makes it more dangerous for the DIYer when connecting or working on this type of circuit. I wouldn't even bother with doing it this way. Instead run two separate 12/2-G cables and connect each one to it's own breaker in the panel. If they're on the same buss or opposite busses it won't make a difference since the load is not great. To ensure they're on separate busses depends on how your panel is manufactured, but usually if you install the breakers on the same side of the panel, one on top of the other you will be fine. Usually everyother breaker is on the same buss.

[skintdigit]

Thanks, Snoonyb and kaktuskid. 240 volt potential shouldn't be an issue if I connect both breakers to the same bus, right? I'm trying to avoid 240 to the tub jbox and, more importantly, to avoid 240 to the control box in the tub which coordinates the water pump and blower motor functions. Still leery of how the control box can "communicate" with both 120v. motors safely at the same time if those devices are on separate buses. If I use a DP breaker with a link rod, then I'll have 240 going to the 2 gang GFCI box in the bathroom wall and then 240 at the jbox with receptacles under the tub skirt. I suppose the separate 12/2 runs is the best bet, then. Snoonyb, I think your suggestion requires BOTH buses to acheive the advantage of the differential load on the neutral wire, is this correct? If 12/3 with the hots wired to 2 breakers on the SAME bus is used, would the resulting load on the neutral be the sum of the load on the two hots? If so, this would be overloading the capacity of the 12 ga. neutral. The run is short, around 30 feet, but I had a devil of a time just getting my fish rod up through the cables at the panel and into the attic. With such a tight fit, I was hoping to be able to pull one cable instead of two. Thanks again for your thoughts, folks.

[Snoonyb]

Then use #10 or #8.

[skintdigit]

That's it...10/3 is the answer. Thanks, Snoonyb!

[kactuskid]

DO NOT install a multiwire circuit and connect the hot legs to breakers that are on the same buss. This is illegal and dangerous no matter what wire gauge you install. A multiwire circuit MUST have the breakers installed on opposing buss's.

Staighten 2 cables of romex out flat and wrap some electrical tape around them every 3 feet or so to keep them in place. They'll pull up the chase same as a singe 3 conductor cable and be much safer in the long run.

[skintdigit]

YIKES! If it's illegal I'm sure there is an important safety concern. So I'm back to tandem runs of 12/2 or a multiwire circuit with 12/3 (with hots on opposite busses). The multiwire was the original plan, but I'm afraid of having 240v. potential in the control box which coordinates the two motors. It's a Jason whirlpool tub, and the installation manual is pretty detailed, except that it just calls for two separate 120v. circuits for the two motors, with GFCI protection on each circuit. No mention of concerns about which buss the circuits are on(would the correct term be "phase" for distinguishing voltage from one buss or the other? I do understand that we're talking about single phase, 3-wire power in this application). The multiwire setup seems the most efficient...I'll call the OEM again tomorrow to see if I can get someone on the line who knows whether the multiwire layout will harm the control boxes. Thanks again for the heads up on the buss issue for multiwire circuits

skintdigit

[Snoonyb]

You can lead a horse to water.....
You have received the solution and yet you hesitate, worry it, and still are pondering it.

Now, try using it.

[skintdigit]

Hah! You are absolutely correct, Snoonyb! That's the way my feeble mind works, sometimes. Always trying to understand every aspect of a challenge, even when a practical solution is right in front of my nose(literally, in this case, in the form of the contributors to this board). I'm going the low stress route and pulling two runs of 12/2 taped as kactuskid recommended. I'll worry about the inner workings of jet tub control boxes in another life.
Sometimes I just need to get a "round tuit"
Thanks again for your help, folks.

[HayZee518]

I have a Jacuzzi in my house and I ran two seperate 12/2 to two GFCI circuits - one for the pump motor and one for the tub heater. When the tub is filled with water and you turn on the pump, a flow switch closes allowing the heater to turn on. Air flow is controlled via a siphon tube to create the air bubbles. The buttons that control the on-off operate on air.

[skintdigit]

I wired this one the same way, HayZee, after the advice from board contributors. The unit we installed has a water pump and a heated air blower, but no inline water heater. Needed two separate circuits for the pump and blower. All the functions are electrically controlled via two control boxes...one for pump, the other for heated air blower. Control inputs are via a keypad and led display. Only had two slots left in the panel and didn't want to run the multiwire wiring for fear of cooking a control board in one of the boxes. So we used two runs of 12/2, moved an existing 20 amp circuit to the opposite bus, and powered both of the new circuits from the same bus. The thing's a Cadillac model...more modes and bubbles and flashing lights than I'd ever use, but the lady of the house will enjoy it! Now we're waiting for the glazers to install the 3/8 inch glass for the custom shower we built at the same time...after finishing this project I remembered why I don't like to set tile