[MikeinFlorida]

I have several questions about putting in new sub panel. Background: I have 200 Amp service to the house. I am remodeling the kitchen and need to put in several new circuits to meet the changes. Access to the main panel is difficult and currently full. The sub panel would be 50 feet from the main. For these reasons it would be easiest to run the kitchen wiring to the new sub panel. I did a sub panel load calculation. The lighting and small appliance load was 3210 VA. The in-place load was 20,652 VA. (These loads included a wall oven, a cook top, microwave, dishwasher, disposal, large and small refrigerator, and a remote cook top vent.) Demand at 75% yielded 15,489 VA, and the largest motor (the dishwasher), at 25%, 330 VA. My total load came to just under 80 AMPS. However, I want to put in a 100 AMP sub panel to allow for any future expansion. Does this seem reasonable?

The run for the feeder will have to be through the attic. I’m in Florida and it does get above 120F in the attic in the summer. I used Table 310-16 to determine the correct conductor size. My understanding of the code is that the 60C column must be used to determine the ampacity values. In this case, #2 Cu will work. I also believe that I need to use the correction factor based on the attic temperature. Using #2 CU THHN or THHW, the calculation was .75 (at 56-60C) times 130 (the allowable ampacity for #2 CU THHN or THHW). The answer is 97 AMPS. Is that close enough to 100? If I used Al wire, what would be the correct size?

I also did the voltage drop calculation using the #2 Cu. The drop to the sub panel was 1.8% and the total drop to the farthest branch (the cook top) was 1.95%. Because this was under the 5% max drop, I think this is not an issue?

I used Table 250-95 to determine the grounding conductor size. For 100 Amps, the table said #8 Cu was the answer. I didn't see a temperature correction factor, but I planned on using #6 Cu to compensate. Is this adequate? I plan to isolate the neutral and grounding wire in the sub panel. I understand the neutral/grounding will only be on the same bus in the main.

I planned on running SCHD 40 PVC for the conduit. Because there will be four wires, I used the 40% fill calculation. Using 2/2/2/6 CU, the math was .3426 inches. 1" PVC at 40% was .346. Seems I could use that, but to make the pull easier I was going to use 1.5" PVC. Is that right?

For the pull, what is the easiest tool to use? I understand that the conduit must be complete before the pull. I was intending to put a nylon rope inside the PVC before/as I glue it, to help make the pull. Good idea or is there a better way?

Finally, in the main, I will use a double pole 100 Amp breaker. I was going to place it in a different row form the AC breakers. Does it matter where it "sits” on the main?

What did I miss? Thanks in advance for the help.

[Washington1]

I have several questions about putting in new sub panel. Background: I have 200 Amp service to the house. I am remodeling the kitchen and need to put in several new circuits to meet the changes. Access to the main panel is difficult and currently full. The sub panel would be 50 feet from the main. For these reasons it would be easiest to run the kitchen wiring to the new sub panel. I did a sub panel load calculation. The lighting and small appliance load was 3210 VA. The in-place load was 20,652 VA. (These loads included a wall oven, a cook top, microwave, dishwasher, disposal, large and small refrigerator, and a remote cook top vent.) Demand at 75% yielded 15,489 VA, and the largest motor (the dishwasher), at 25%, 330 VA. My total load came to just under 80 AMPS. However, I want to put in a 100 AMP sub panel to allow for any future expansion. Does this seem reasonable?

The calculation is off, but yes a 100A sub will work

The run for the feeder will have to be through the attic. I'm in Florida and it does get above 120F in the attic in the summer. I used Table 310-16 to determine the correct conductor size. My understanding of the code is that the 60C column must be used to determine the ampacity values. In this case, #2 Cu will work. I also believe that I need to use the correction factor based on the attic temperature. Using #2 CU THHN or THHW, the calculation was .75 (at 56-60C) times 130 (the allowable ampacity for #2 CU THHN or THHW). The answer is 97 AMPS. Is that close enough to 100? If I used Al wire, what would be the correct size?

The answer is 107A Yet a #2CU will work fine in your condition. If you want to use Alum, then go 1/0 note: I'm not taking alum into consideration through-out this post

I also did the voltage drop calculation using the #2 Cu. The drop to the sub panel was 1.8% and the total drop to the farthest branch (the cook top) was 1.95%. Because this was under the 5% max drop, I think this is not an issue?

1.9% looks good

I used Table 250-95 to determine the grounding conductor size. For 100 Amps, the table said #8 Cu was the answer. I didn't see a temperature correction factor, but I planned on using #6 Cu to compensate. Is this adequate? I plan to isolate the neutral and grounding wire in the sub panel. I understand the neutral/grounding will only be on the same bus in the main.

#8 will work see Table 250.122 The Neutrals, and grounding conductors will be separated at the sub-panel--good answer!

I planned on running SCHD 40 PVC for the conduit. Because there will be four wires, I used the 40% fill calculation. Using 2/2/2/6 CU, the math was .3426 inches. 1" PVC at 40% was .346. Seems I could use that, but to make the pull easier I was going to use 1.5" PVC. Is that right?

1 ¼ is the minimum size.

For the pull, what is the easiest tool to use?

Everyone has a way of doing things. If you choose a nylon rope, then this should work fine. I would use a fish tape. I would invest in some listed lubricant (soap) for the pull. Yet, if you go 1.5” PVC the pull shouldn't be that bad, and you may not need the lub. Just note that you can not have more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes.

I understand that the conduit must be complete before the pull.

True

I was intending to put a nylon rope inside the PVC before/as I glue it, to help make the pull. Good idea or is there a better way?

I would vac the line through--if you are set on using rope. The rope can also be pulled through using a fish tape. Yet, if you have a fish tape, then you may as well use it to pull your feeders.

Finally, in the main, I will use a double pole 100 Amp breaker. I was going to place it in a different row form the AC breakers. Does it matter where it "sits” on the main?

Nope


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[MikeinFlorida]

Saw where my Load calculation was wrong and you calculated 107A for the temp adjusted. I have another sub panel to put in later so I was curious where I went wrong on those. Thanks