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  • Subpanel Clearances from other electrical equipment

    I've read through NEC Article 110: Requirements for Electrical Installations and I can't find the answer.

    Here is a pic of the subpanel being installed. Before I finish mounting, strapping conduit, and running cabling through, can anyone throw me any red flags if the location will be a possible problem to AHJ.

    2015-11-21 20.00.38.jpg

    It's within an attached garage, 125amp rated 8/16 fed with #6/3 with no main disco, 50amp breaker at main panel.

    Obviously not a lot of room on the left side near the PV inverter AC conduit. I told the installer I didn't like the AC conduit sticking that far out from the side, but I didn't want to haggle over 2 inches as he said something about needing that much room for the bend. But was annoying considering I already moved the surface mount receptacle over 18" to the right to make room for the panel.

  • #2
    Originally posted by cebury View Post
    Here is a pic of the subpanel being installed. Before I finish mounting, strapping conduit, and running cabling through, can anyone throw me any red flags if the location will be a possible problem to AHJ.
    I don't think so - there's no restrictions on having a panel near an outlet or the inverter.

    It's within an attached garage, 125amp rated 8/16 fed with #6/3 with no main disco, 50amp breaker at main panel.
    If it's close enough (no significant voltage drop) and no derating needed due to high temperatures, that's probably fine. (Oh - and it's #6/3 +ground right?)

    Whether you're OK at the main panel is yet another question - but I'll assume your installer already has figured that out.

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    • #3
      Thank you.

      Originally posted by foo1bar View Post
      If it's close enough (no significant voltage drop) and no derating needed due to high temperatures, that's probably fine. (Oh - and it's #6/3 +ground right.
      It's a 70' run point to point from our upgraded 200a panel.

      I haven't talked with ahj about what ambient temps are used here in town, but I know it gets way hot up in attics. Two EC I've talked with stated or implied I'm overthinking/worrying about the details (derating rules) too much. "Drag 6/3+g Romex and your good for for 55a maybe even 70+". But I've seen the Manuf specs for Romex: ampacity is always from the 60 column, even tho it's states rating at 90. That means it's never above 55a unless in very cold ambient temps, rt?

      The EC wired the main breaker with 50a.

      I plan on installing a 30a EV charger, which means it will draw consistent current for hours at a time. I put in 50a so I could leave room for a spa down the road. Obviously can't do both at same time.

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      • #4
        The component which is most dramatically affected by attic heat is not the wiring but the circuit breakers. They will not be damaged by the heat, but will trip at a much lower current level than their rating if placed in a high ambient temperature.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by cebury View Post
          Thank you.


          It's a 70' run point to point from our upgraded 200a panel.

          I haven't talked with ahj about what ambient temps are used here in town, but I know it gets way hot up in attics. Two EC I've talked with stated or implied I'm overthinking/worrying about the details (derating rules) too much. "Drag 6/3+g Romex and your good for for 55a maybe even 70+". But I've seen the Manuf specs for Romex: ampacity is always from the 60 column, even tho it's states rating at 90. That means it's never above 55a unless in very cold ambient temps, rt?

          The EC wired the main breaker with 50a.

          I plan on installing a 30a EV charger, which means it will draw consistent current for hours at a time. I put in 50a so I could leave room for a spa down the road. Obviously can't do both at same time.
          I am not sure on your city, but my city inspector said 60Amp or lower is fine without issue, but the wire must be big enough for 60Amp. I would suggest to check with them in order to use the largest possible breaker to the sub.
          5KW Enphase system.

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          • #6
            The main purpose of the clearance is to allow a person to work and get away in the event of an explosion or fire. You cannot get away with what they do in China and Arab countries.

            MSEE, PE

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            • #7
              Originally posted by solarz View Post
              I am not sure on your city, but my city inspector said 60Amp or lower is fine without issue, but the wire must be big enough for 60Amp. I would suggest to check with them in order to use the largest possible breaker to the sub.
              If I'm reading the NEC correctly, the romex 6/3+g wires are rated from the 60 degree ampacity columns, which means 55amp before derating from heat (ambient or conduit fill), which means the breaker can be 60amp to protect the 55amp distribution line -- which is probably what your AHJ said.

              I'm fine with 50amp for now, since it's derated ~17% (55*.83) = 45.65 and next size up breaker is 50amp (or round down at 45).

              If my EC is correct, the AHJ won't care and might allow 60amp. I'll save that for down-the-road if needed, but I'd probably be running THHN #3 by that time if I really did ever pull 60amps at once.

              Do the electricians agree with my understanding thus far?
              Last edited by cebury; 11-23-2015, 04:10 PM. Reason: Corrected mis-calculation

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              • #8
                Originally posted by inetdog View Post
                The component which is most dramatically affected by attic heat is not the wiring but the circuit breakers. They will not be damaged by the heat, but will trip at a much lower current level than their rating if placed in a high ambient temperature.
                Ahh, thanks for the info. In case you can't tell, the picture is in my attached garage, though it looks like an attic space.

                Unless you are saying that mid-section heat on wires affects the endpoint panel breakers which are located outside of said hot areas. I always thought said derating was purely to prevent exceeding insulation specs and melting wires.

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                • #9
                  Use an LB

                  Originally posted by cebury View Post

                  Obviously not a lot of room on the left side near the PV inverter AC conduit. I told the installer I didn't like the AC conduit sticking that far out from the side, but I didn't want to haggle over 2 inches as he said something about needing that much room for the bend. But was annoying considering I already moved the surface mount receptacle over 18" to the right to make room for the panel.
                  I get that it is easier and cheaper for the installer to use a conduit bender and no fittings to make that swing, but it wastes space and looks poor. A $6 LB (conduit body) will allow for a 90 degree turn and free up lots of space.

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                  • #10
                    Originally posted by cebury View Post
                    If I'm reading the NEC correctly, the romex 6/3+g wires are rated from the 60 degree ampacity columns, which means 55amp before derating from heat (ambient or conduit fill), which means the breaker can be 60amp to protect the 55amp distribution line -- which is probably what your AHJ said.

                    I'm fine with 50amp for now, since it's derated ~17% (55*.83)*1.1=50.2 equals the max OPCD size.

                    If my EC is correct, the AHJ won't care and might allow 60amp. I'll save that for down-the-road if needed, but I'd probably be running THHN #3 by that time if I really did ever pull 60amps at once.

                    Do the electricians agree with my understanding thus far?
                    From 240.6(A)
                    (A) Fuses and Fixed-Trip Circuit Breakers.
                    The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200...

                    From 240.4(B)
                    (B) Overcurrent Devices Rated 800 Amperes or Less.
                    The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be provided all of the following conditions are met: <easy conditions to meet>

                    From 334.80 Ampacity.
                    The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of a 60°C (140°F) rated conductor.

                    I'm not sure about your 1.1 factor in the calculation, but for the purpose of adjusting and correcting, you can start with the 90 deg ampacity (75 A). As long as the adjustments and corrections don't drop the ampacity to 45 A or below, a 50 A breaker to protect those conductors should be compliant.
                    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                    • #11
                      Originally posted by sensij View Post
                      From 240.6(A)

                      I'm not sure what calculation you are performing with the 1.1 factor, but as long as the corrected and adjusted ampacity is above 45 A, using a 50 A breaker to protect those conductors should be found compliant.
                      My calculation was absolutely incorrect (it's "next size up" not "no more than 10% over"). I just figured it out in the NEC and came to update my post when I found yours! Appreciate the clarification.

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                      • #12
                        Originally posted by Sunking View Post
                        The main purpose of the clearance is to allow a person to work and get away in the event of an explosion or fire. You cannot get away with what they do in China and Arab countries.

                        Ha! that reminds me of this one:


                        If you follow the main page to here, the discussion of exactly HOW dangerous this is gets interesting for those of us outside the industry (wannabe's).

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