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Thread: Calculating demand load for new service

  1. #1
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    Calculating demand load for new service

    I am calculating the demand load using the optional method with demand factor (220.32) for the main service and have it calculated at 577 amps. Would you throw in a 600 amp disconnect or do you consider it too close to the threshold? The disconnect would be fused and could go to the full 600 rating.
    Also there is no 125% rule for a new main service correct? Didn't see it anywhere but better safe than sorry.

    All thoughts welcome.

  2. #2
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    Also since I am using the optional method and it provides a much lower amperage for the demand load - has anyone had any trouble getting the optional method approved with planning review? I assume that shouldn't be the case even if it is near the max load of the main service. (standard method would push the amperage way up)
    Service is single phase.

  3. #3
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    Quote Originally Posted by profT View Post
    Also since I am using the optional method and it provides a much lower amperage for the demand load - has anyone had any trouble getting the optional method approved with planning review? I assume that shouldn't be the case even if it is near the max load of the main service. (standard method would push the amperage way up)
    Service is single phase.
    Personal opinion, if you've done the residential service calculations, I wouldn't worry about it at all. Sometimes you need to read the customer. Do they have plans for a future ten lane bowling alley? Additions are what may give you troubles.
    Tom
    TBLO

  4. #4
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    I'm with Tom.. read the customer or GC.
    If you are bidding against others then it might be a 600 amp main or even (3) 200 amp panels. In this area if a residence calculates out to 600 amps it usually isn't much of a sell to get the owner to go 800.
    On the other hand, even the optional method may be generous in these times of LED lighting and energy efficient equipment.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  5. #5
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    Quote Originally Posted by profT View Post
    I am calculating the demand load using the optional method with demand factor (220.32) for the main service and have it calculated at 577 amps. Would you throw in a 600 amp disconnect or do you consider it too close to the threshold? The disconnect would be fused and could go to the full 600 rating.
    Also there is no 125% rule for a new main service correct? Didn't see it anywhere but better safe than sorry.

    All thoughts welcome.
    Single family dwelling?

    Apartment building?

    something else?

    I did a new home once that I probably could have installed a single 600 amp disconnect for service - was still less cost to go with 4 200 amp main breaker panels - which would have all been there either way.
    I live for today, I'm just a day behind.

  6. #6
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    This is for an apartment building so there will be no additions or need for an increase in amperage.

    Going with 600 would be much cheaper than 800 due to the size of conductors and length of runs etc.

    I guess I am asking if the optional method is near the 600 threshold (which I don't see as a problem) if they request the standard method we would be at a little over 800 amps which would then require a 1000 amp service which would be overkill and be cost prohibitive. So I am asking is there any reason the optional method (requires just 37% of total load be calculated as the demand load) would draw scrutiny since it is a large building and 600 amps just doesn't "sound" like enough - yet is correct according to the load calcs using this method.

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