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Ask 'Dr. Spa' Q & A Message Board

Ask 'Dr. Spa' Q & A Message Board archives

Re: Wiring Up a Sundance Optima

I have a major concern with it. I don't know where you got your research that says #8 THHN is approved for 60 amps, but I just confirmed with my copy of the 2005 NEC which states in Table 310.16 that #8 THHN is only good up to a maximum ampacity of 55 amps before the application of derating factors. Your tub ships from the factory set for 50 amp operation, in which case the recommended #8 would probably be sufficient. Sundance does not recommend the #8 if you change the jumper settings for 60 amp operation.

For the record, #8 THHN (or equivalent) has an ampacity of 55 amps. #6 THHN has an ampacity of 75 amps. Although your tub actually draws a maximum of 48 amps normally, a hot tub (or any major product with motors) will draw higher amperage briefly on motor start-up. That's why such products are subject to the so-called 125 percent rule. Everything (wire, breakers, disconnect) must be sized to meet this rule. Your choice of #8 fails this test and we haven't even begun to inquire as to dearting issues.

I would suggest that you re-jumper back to 50 amp operation with this wire. If you have severe de-rating issues, you may even want to jumper back to 40 amp operation for now, at least until you properly size your wire.

I must admit that I am slightly puzzled that you undersized this portion of the circuit when you plainly heeded our other advice about upsizing the wire on the long run.

Here's a golden rule about wire: Size matters.


: So the outcome was no further bonding was
: needed as there was nothing metal near the
: spa which might become energized. Inspector
: said I could ground to the grounding rod I
: drove in but it simply wasn't needed.

: But he the inspector did have an initial wiring
: concern. I used #4 THHN from the house to
: the outside 60 AMP GFCI (~70') - overkill so
: no problem here; and then #8 THHN (~12')
: from the GFCI to the spa. Inspector said the
: wire was too small and wouldn't rate to 60
: AMP. I showed him the Optima wiring guide
: which recommended #8 and that max draw is 48
: AMPS. I also found research on wiring that
: indicated that #8 could handle 60 AMPS. He
: let it go (approved it) but suggested I
: contact Sundance to confirm the wire size. I
: set the jumper so the spa knows it has 60
: AMPS and I can run both pumps and the heater
: at the same time without an issue.

: Anyone see an issue with using #8 THHN?

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