Sub Panel /Swimming Pool

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Old 10-12-16, 08:21 PM
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Sub Panel /Swimming Pool

Hello Group:

1) I am running four #8 thnn-thwn wires from my service panel to my exterior sub panel in Schedule 80 conduit. I have a 50 amp 220 (not a ground fault) breaker in my service panel feeding my sub panel. I need more breaker spaces than 6 in the sub panel so I want to install a 125 amp sub panel with more circuit space. All breakers in the sub panel will be ground fault. Is it OK per the NEC to use the 125 amp sub panel main breaker as the disconnect, since I am feeding the sub panel with a 50 amp breaker at the service panel?

2) I need to install my sub panel that will service the swimming pool approximately 45 feet away from my house. Is it OK per the NEC if I build a plywood wall to mount the sub panel on? The wall will be constructed of two 4*4 treated posts approximately 4 feet apart with an 3/4" exterior plywood sheet between them. The sheet of plywood will not be the full height of the posts there will be a large gap between the plywood and the ground. The sub panel will be mounted about 4 feet from the ground to the bottom of the sub panel. Below the sub panel wall will be the concrete pad for the pump / pool equipment. The wall will be exposed to all Tennessee weather conditions.

3) When we dug the 18" plus trench for the conduit from the house to where I want to install the sub panel plywood wall, we cut through a couple of flexible gutter drain pipes (solid type no perforation holes). Is it OK to place the schedule 80 conduit underneath the drain pipe where they cross the trench. There are three different places drain pipes cross the trench. I really have no other option running the electrical that would allow me to miss the drain pipes. Yes, I have spliced the drain pipes where they were cut.

4) How do you determine if you require 1 or 2 grounding rods for the sub panel? I understand the Equipotential bond does not connect to the sub panel ground rod, I am just not sure how many I require for the sub panel.

Thank You for your input,

Thank You Dave
Tennessee
 
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Old 10-12-16, 09:31 PM
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I am running four #8 thnn-thwn wires from my service panel to my exterior sub panel in Schedule 80 conduit.
A 50 amp circuit requires three #6 (black, black, white) and a #10 green.
Is it OK per the NEC to use the 125 amp sub panel main breaker as the disconnect, since I am feeding the sub panel with a 50 amp breaker at the service panel?
It is the breaker size that counts not the max amp rating of the panel. So long as it sub panel rating meets or exceeds the supplying breakers it is fine.
Is it OK per the NEC if I build a plywood wall to mount the sub panel on?
That should be Okay.
Is it OK to place the schedule 80 conduit underneath the drain pipe where they cross the trench.
Yes that is fine.
How do you determine if you require 1 or 2 grounding rods for the sub panel? I understand the Equipotential bond does not connect to the sub panel ground rod, I am just not sure how many I require for the sub panel.
Ask your AHJ. If in doubt use two. There is a method of measuring but the equipment is outside the scope of DIY.

Note nominal voltage is 120/240.
 
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Old 10-13-16, 04:20 AM
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sub panel-swimming pool

Thank you for your help ray2047
 
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Old 10-13-16, 04:36 AM
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sub panel swimming pool

From the wire Ampacity chart I used it states - for #8, 90C stranded copper THWN-2 the rating is 55 amp. It does state #8, 60 degree C, NM and UF is rated at 40 amp. The chart was put together by a wire company is it incorrect per the NEC code? What size breaker should I be using for the #8, 90 degree C,THWN-2 stranded copper?
Thank You
Dave
 
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Old 10-13-16, 05:37 AM
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Use a 40 amp breaker in the originating panel for the #8 copper feed.

Ninety degrees centigrade is near the boiling point of water, like somewhere around 195 deg. F.. The 55 amp rating refers to the insulation being able to withstand that temperature for long periods of time. Usage is pretty much limited to conductors in free air such as in overhead strung wiring, or wires resting few enough not to be in layers in a long open tray suspended from the ceiling.
 
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Old 10-13-16, 01:20 PM
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Wire ampacity is always a complicated topic. You can use a 50A breaker with #8 THWN in conduit because you can use the 75C column. In this case the limiting factor is the breaker terminals which never exceed 75C in residential use; THWN is rated to 90C and the conduit is rated to 105C, but you have to use the lowest of all the components in the feeder which is the breaker terminals at 75C. This places the ampacity of the #8 THWN at 45A. By applying the "round-up rule", the code permits you to use the next higher standard breaker size when wire ampacity falls between two standard breaker sizes.

If you were using a cable assembly (NM, UF, SER) you would use the 60C column due to cable assemblies explicitly being capped at 60C by the code regardless of other factors. Unless (there's an exception to every rule...) you are installing a residential service entrance in which case some types of cables can be used up to 90C.

The 90C column is never used directly in residential work, but does occasionally come into play when doing derating calculations on conduits containing multiple circuits.
 
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Old 10-13-16, 05:56 PM
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Sub Panel swimming Pool

Group, Thanks for the help and Information. I appreciate your taking the time to reply.
Dave
 
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