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Thread: Maximum amperage of circuits in service panel

  1. #1
    Join Date
    Jun 2003
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    3

    Maximum amperage of circuits in service panel

    I've been racking my brain trying to find this in the code book, but I have a customer who has a 100 amp service and all but two slots are full. He wants a total of three circuits added. One of them is for a 50 amp hot tub. I just need to know what amperage will this panel max out?

  2. #2
    Join Date
    Jun 2003
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    3

    Re: Maximum amperage of circuits in service panel

    I for got to mention, he'd rather go for a sub-panel if it's feesable.

  3. #3
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    Feb 2003
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    Massachusetts
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    Re: Maximum amperage of circuits in service panel

    Originally posted by slapnuts:
    I have a customer who has a 100 amp service..........just need to know what amperage will this panel max out?
    Just a guess, 100 Amps.

  4. #4
    Join Date
    Feb 2003
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    Florida
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    7,286

    Re: Maximum amperage of circuits in service panel

    If the service is 100-amps, then most likely the service entrance conductors are only rated for 100-amps. The 100-amps was originally calculated for the total demand load that the dwelling would draw.

    To add a load as large as 50-amps will most likely require you to upgrade the service to handle the additional load. To be sure, calculate the total connected load of the existing system, apply the demand factors, and add in the new circuit loads. If you come out larger than about 24,000 volt-amps, you will need to increase the service size.

    If you come in below 100-amp service load, the circuits can be added to the panel unless you exceed 42 circuits or the total amount of circuits allowed per the manufacturers specifications of the panel. You may also add a sub-panel off the service panel if desired.
    Bryan P. Holland, MCP

  5. #5
    Join Date
    Jul 2003
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    4

    Re: Maximum amperage of circuits in service panel

    each bus is rated at 100 amps...so 200 amps total,see 408.15 NEC 2003...but the total load is based on the calculated load for each space.

  6. #6
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    Feb 2003
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    N.C.
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    Re: Maximum amperage of circuits in service panel

    The service will "max out" when it reaches 100 amps long enough. The number of breakers and the sum of the face value of these breakers have no bearing on the situation. You need to do a load calculation with the known loads being used on a daily basis.

    In reality, I would suggest a service upgrade. A typical home with a Hot Tub has out grown a 100 amp service.

    Roger
    Moderator

  7. #7
    Join Date
    Feb 2003
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    Bremerton, Washington
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    6,661

    Re: Maximum amperage of circuits in service panel

    Roger is correct an upgrade should be considered. Adding one or two more circuits, 20 A is no problem. The hot tub would most likely be the major load on the panel if added.
    Moderator-Washington State
    Ancora Imparo

  8. #8
    Join Date
    Feb 2003
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    3,172

    Re: Maximum amperage of circuits in service panel

    sbshvac: I am sure you want to reconsider your math. This is what many think, that the current adds up. You are measuring the same current twice.

  9. #9
    Join Date
    Jun 2003
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    3

    Re: Maximum amperage of circuits in service panel

    Thanks all for the input. I figured he would need an upgrade, but I just wanted a second opinion to make sure since I couldn't find it in the book.

  10. #10
    Join Date
    Mar 2003
    Location
    Nord'est Wisconsin et Paris France
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    Re: Maximum amperage of circuits in service panel

    i work on few homes have hot tubs there with 50 amps feeder to hot tub and i have a habit to change over the service from 100a to 200a to advoild the conflect ( sorry for spelling) and have more room to upgrade as need few of my comster were little suprsed what i say to change over from little 100 to 200 and i say best thing i always do is check the load what they use it everyday including central air or whatever is the largest load on it then sum it up and many time it was pretty close to the limit with 100 amp service and one house i did work on not too long ago i have to up grade from 200 to 400 amp service ( a suprise have big hot tub and swimming pool there ) so that slove my headache there


    but really best way to be ahead of game if heard word hot tub best bet to check the service to see have room only 2 house i work on i left on 100 due that comuster have mostly gaz fired devices including hot tub that was my first one to hear a gaz fired unit


    merci marc
    Marc
    master electrician
    Wisconsin and Paris France

    "Pas de problème, il marche n'est-ce pas?" (No problem, it works doesn't it?)

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