Hot Tub wiring

paulhiggsDecember 28, 2009


I am installing an outdoor hot tub and considering the wiring that is needed. The GFCI panel as an 30 and 20 AMP breaker and the instrictions state that a 50amp breaker is needed on the main panel of the house.

When I look up 50 amp services it always suggests that I need #6 guage for the live and neutal and #8 for the earth, however the wiring instructions from the manufacturer show #8 for the live and neutrals and #10 for the ground. The diagrams also show "WIRING ILLUSTRATION 203VAC, 40A, 60Hz" but a 50 amp breaker is shown.

Can anyone help me understand why these would be different?

Is it anything to do with solid or stranded wire?



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It depends on what kind of wire/cable you are using. If you use NM-B or UF-B you need to use the 60° column. If you are running individual wires in conduit, then you can use the 75° column.

There are a lot of rules with a hot tub that need to be followed carefully, if you're not a 110% certain of what you are doing, hire a licensed electrician.

Here is a link that might be useful: Wire Ampacity Chart

    Bookmark   December 28, 2009 at 8:56AM
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Ron Natalie

I assume that was 230VAC not 203 (which would be a rather uncommon residential voltage). The spa does indeed draw 40A continuous with all the pumps and heaters that are allowed to run together running, but the surge of the motor start or whatever mandates 50A. You must follow this recommendation..

Contrary to what Mike is implying, most NM and UF are NOT LEGAL for this purpose. The outside parts of the wiring must have a insulated ground and the sheath of the cable does NOT qualify.

The #8 is correct for the THWN (75°) or (THHN or THWN-2) (90°) you are likely to be legally using for this purpose.

    Bookmark   December 28, 2009 at 10:13AM
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Forgot about the insulated ground, my mistake. Just out of curiosity, why does the ground need to be insulated.

Also I'm curious if could one run NM to the disconnect (say it was mounted on the side of the house) and then individual wires (including the insulated ground) in conduit to the spa? Or does it need to be an insulated ground all the way back to the panel?

    Bookmark   December 28, 2009 at 10:42AM
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Ron Natalie

If you're on the 2008 or later code, they have clarified it that you can run a sheathed cable as long as the ground is in the sheath on the inside part of the run.

Before 2008 it was ambiguous so you were kind of at the whim of your local jurisdiction.

    Bookmark   December 28, 2009 at 12:44PM
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The insulated ground is required by code and that's all I care about. Personally I don't dwell on why in this case.

For a single family dwelling you CAN run NM cable, or any other NEC Chapter 3 wiring method, inside the structure. Once you leave the structure you must follow Art.680 wiring methods and rules.

    Bookmark   December 28, 2009 at 12:46PM
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Ron, I never read that as ambiguous. I was always under the impression that NM was OK for the inside part for spas and pools.

I am not home so I can't look up the actual wording of previous editions right now.

    Bookmark   December 28, 2009 at 12:49PM
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Thanks for all the info provided.
One (hopefully final) question... Most of the 50amp wiring from the main panel will run through the basement of the house, but then it needs to go outside to the GFCI panel. Does some different wire need to be used for the inside and the outside parts?

My other thought was to put in a 100amp outdoor panel, fed from the main 200amp panel of the house (this would give me some additional capabilities for lights etc later on). The GFCI could then connect to this 100amp sub-panel (it would only be about 15' to the GFCI.

    Bookmark   December 28, 2009 at 1:44PM
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Ron Natalie

Petey...the insulated ground on the inside portion of wiring for outside spas/pools was ambiguous and there was lots of arguing about it on the forums. The NEC added text to the 2008 code that made the use of NM explicitly OK in the 2008 code.

    Bookmark   December 28, 2009 at 4:14PM
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Hmmm, I never experienced that. No prob.

    Bookmark   December 28, 2009 at 10:37PM
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