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Thread: 300 amp motel service neutral

  1. #1
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    300 amp motel service neutral

    So I’m upgrading a motel to support 42kW of added heating load. The units are all 240 1ph. I figured 350 awg cu. for the hots. I should be able to reduce the neutral by 80% right? If so how do I calculate that? What starting point do I use to apply the 80% to?


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  2. #2
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    208/240v ptacs and a/c units dont use a neutral at all.

    42kw is a very small upgrade.. are they changing 9kw ptacs to 12's? Few Panasonic units to the lobby or hallways?
    Electricians do it until it Hertz!

  3. #3
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    These are cadet 3000w wall heaters. I know they don’t use a neutral. That’s why I want to reduce the neutral for the new service but I’m wondering what I apply the 80% to


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  4. #4
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    Quote Originally Posted by DrSparks View Post
    So I’m upgrading a motel to support 42kW of added heating load. The units are all 240 1ph. I figured 350 awg cu. for the hots. I should be able to reduce the neutral by 80% right? If so how do I calculate that? What starting point do I use to apply the 80% to?


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    Look at 250.24(C). The grounded conductor cannot be smaller than the required grounding electrode conductor. For 350 kcmil copper the neutral cannot be smaller than a 2 AWG.
    Last edited by packersparky; 05-14-18 at 09:54 PM.

  5. #5
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    Quote Originally Posted by DrSparks View Post
    These are cadet 3000w wall heaters. I know they don’t use a neutral. That’s why I want to reduce the neutral for the new service but I’m wondering what I apply the 80% to


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    What 80%?

    Grounded service conductor can be as small as the required GEC if the neutral load isn't there.

    Comes down to what is maximum unbalanced load that may be present on the neutral?
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  6. #6
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    Idk I need to reread the whole service call section. I thought I read somewhere about 80% max reduction for neutral. I’m probably going to have to do a load calc for this place. Makes sense about the neutral being no smaller than GEC has to be able to handle short circuit. Got it


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  7. #7
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    Quote Originally Posted by DrSparks View Post
    Idk I need to reread the whole service call section. I thought I read somewhere about 80% max reduction for neutral. I’m probably going to have to do a load calc for this place. Makes sense about the neutral being no smaller than GEC has to be able to handle short circuit. Got it


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    See 250.24(C). Note: 230.23(C), 230.31(C) and 230.42(C), all reference this section for minimum size.

    Actually minimum size is same as minimum supply side bonding jumper though it is same size as minimum GEC in many instances.

    310.15 will require them to be able to have ampacity to handle maximum current they are subjected to, with adjustments where they apply.
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  8. #8
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    Quote Originally Posted by DrSparks View Post
    ]I thought I read somewhere about 80% max reduction for neutral.
    If I'm not mistaken, you're referring to the allowance to reduce a neutral TO 80%, not BY 80%, of the line conductors' capacity.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  9. #9
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    don't know what size service you plan but, FWIW, 350 kcmil is about twice the size needed for the load.
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