What size conduit to use.

[paulhiggs]

For the wiring of my GFCI to the hot-tub, I need to run the following
20A #12 Blue
20A #20 Red
30A #10 Blue
30A #10 Red
Neutral #10 White
Ground #10 Green

What size conduit should I run these THWN conductors in?

Thanks
Paul

[HayZee518]

All in the same conduit? 5 conductors derate all of them by 80%
12 ga at 80% = 16 amp
10 ga at 80% = 24 amp
Take a gander at this site.

http://www.spadepot.com/spacyclopedia/wiring-hot-tub-spa.htm

[paulhiggs]

Wow, thats quite some reduction. My run from the GFCI to the tub will be about 20 feet. I'll run the 20Amp using #10 and the 30Amp, Neutral and Ground using #8. The tub only has a single inlet. Will also use 1" PVC.

[HayZee518]

Even if you run 20 amps on 10 ga wire you still have to derate the cable at 80% if you run all the conductors in one pipe! this is NOT voltage drop. The length is so short voltage drop doesn't factor into this. four or more conductors' amperage is reduced by 80% due to internal heating.
Did you take a look at that site I mentioned?

[mrcaptainbob]

Conduit size...

Would running a larger size conduit be better? Say 1.5"? Would that help heat dissipation?

[HayZee518]

It isn't a case of conduit size. You could have a 4 inch conduit and have multiple circuits running inside it. the rule says up to 3 conductors the rating is for 100% load. 4-6 conductors the ampere rating is dropped by 80%. So even if he ran 6 number 6 thhn/thwn conductors fused at 20 amps, the current rating is reduced by 80% because of the number of conductors.

[paulhiggs]

Thanks for these clarifications. I thought it might have been related to interference rather that actual heading. Its a little strange that Caldera makes a tub that requires 6 conductors when such a restriction exists.
The conduit will run under the deck, not buried.

My last thought is to run two conduits, each 3/4". In one I will put the two 20A hots and ground and the second will have the 30A hots and neutral. Then, very close to the tub, put a box that can bring together these two conduits and merge them into a single 1" liquidtight to the actual tub. That liquidtight part will only be 2-3 feet.

Does that sound reasonable? Any other recommendations?

[HayZee518]

run the two conduits into the hot tub service box, then once inside do whatever you need to with them. with the one inch conduit you run into the same de-rating problem. what are the two 20 amp circuits for? what is the 30 amp circuit for? I'm assuming the 30 is for the heater.
did you look at the site page for spas?

[normel]

For derating use the 90C amperage values: for 12ga it is .8 x 30 = 24; for 10ga it is .8 x 40 = 32. You are OK to use the wire sizes you have selected with the breakers (20A and 30A) you need.

[paulhiggs]

Yes, I looked at the spa webpage that was provided. There is a small box that mentions tubs from Caldera which have two CFCI's (240V 20A and 240V 30A). I'm not sure what each is for "inside the tub", but you can look at the wiring diagrams for the Geneva (which I have) online at

http://www.calderaspas.com/pdfs/301850_Utopia_Manual_Rev_C_09.pdf

[paulhiggs]

Hopefully my last question on this.
Should I use solid or stranded THWN for the hots and neutral (I'll use a bare-solid for the ground)?

[normel]

Hopefully my last question on this.
Should I use solid or stranded THWN for the hots and neutral (I'll use a bare-solid for the ground)?

Use stranded.. it will be easier to pull. You must use an insulated ground to feed a hot tub.... and per my previous post, you CAN run all of this in the same conduit using #12 and #10; the ground will need to be #10 also.