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#82122 - 10/17/02 05:12 PM Another stupid ampacity question
elecbob Offline
Member
Registered: 08/23/02
Posts: 141
Loc: WA
I routinely fuse #8 copper at 40 amps. Table 310-16 says #8 THHN is good for 50 amps. A customer is replacing an existing spa with a spa with a 30 amp 240 v GFI and a 20 amp 120 v GFI. The disconnect box is fed with 4#8 CU conductors from a 50 amp CB in the main panel about 90 feet away. Do I need to replace the #8 CU with #6 CU?
Bob
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#82123 - 10/17/02 05:29 PM Re: Another stupid ampacity question
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6778
Loc: Brick, NJ USA
Bob:
I don't fully understand your question.
Is the spa 240 volt, 3 wire (hot/hot/neut/grd) or 2 wire (hot/hot/grd)??

How does the 120 volt GFi "fit-in"?? If you "tap it off" of the 50 amp feeder, how are you protecting it?? (OCP)

The prime answer is "yes" you can protect 8 THHN Cu at 50 amps per NEC 310-16, before you do any de-rating, if required.

The above is my humble opinion.
John
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#82124 - 10/17/02 06:02 PM Re: Another stupid ampacity question
caselec Offline
Member
Registered: 04/14/02
Posts: 558
Loc: San Jose, CA
Bob

#8 THHN is rated for 50 amps if all of the terminals it is connected to are rated for 75C. If the terminal are not marked with a temperature rating or only rated for 60C then #8 is only good for 40 amps so #6 would need to be used.

Curt
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#82125 - 10/17/02 08:43 PM Re: Another stupid ampacity question
sparky Offline
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Registered: 10/18/00
Posts: 5303
not a stupid Q at all considering the varied interactive formats for derating scattered thru the NEC
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#82126 - 10/17/02 09:01 PM Re: Another stupid ampacity question
elecbob Offline
Member
Registered: 08/23/02
Posts: 141
Loc: WA
There is a 30 amp 2 pole (240 volt) GFI for the heating elements and a 20 amp single pole (120 volt) GFI breaker for the motor. I would be pulling 3#10 (black, red and green)wires and 2#12 (black and white) wires from the GFI breakers to the spa.
I often wonder what the energy cost per hour spent using these things is. I guess ours is not to wonder why. Ours is but to make money hooking up the damn things.
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#82127 - 10/18/02 09:05 AM Re: Another stupid ampacity question
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6778
Loc: Brick, NJ USA
Elecbob:
Didn't put the derating thing in my post to you, sorry.
The cost would be approx.
240x30=7200 watts
1 HP motor= 750 watts
total max of 7950 watts or 8 KW rounded max
At 12cents per KWHr, a whopping calculated 96 cents.
Actual costs will vary based on the local utility rates, and service charges that are added to the monthly billing.

The above disclaimer is for 66wv.
John
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#82128 - 10/19/02 12:01 AM Re: Another stupid ampacity question
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: West Virginia
LOL! Hee hee!



Hey, ya always gotta give yerself an "out", just in case!
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