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Thread: Determining Service size and compatibility of Commercial Service

  1. #1
    Join Date
    Jun 2018
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    Nashville,TN
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    Determining Service size and compatibility of Commercial Service

    Friends, I'm new to the forum and am a residential home inspector and mechanical engineer. I typically decline commercial work as I am less familiar but looked at a 6000 SF commercial office building built in 2006 likely to the 2000 IBC for friend who is looking to purchase the building. To be clear we have no intention of doing any electrical work and he will get an electrician when and if needed.

    The main breaker of the service is an 800 max. Seimans Sentron Series unit Model # MD63F800. It is a 3 phase system with 2-350 kcmil copper wires entering all 3 lugs. Depending on the wire temp rating it looks like the 350 service wiring is rated at 310/350 Amps x2 would be 610/700 Amps which is not up to the 800 breaker protection. I am sure this is not the correct way to look at this. Also I see 3 dials at the lower section of the breaker graduated from 1low to 8high...which are all set at 1low. Is the amp rating of the breaker adjustable using these dials?

    Long and short i want to properly report the service size and confirm the compatibility of the service wiring with the over current protection....Thanks in advance...Bill

  2. #2
    Join Date
    Feb 2003
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    That 800A frame circuit breaker has an interchangeable trip plug from 500A to 800A. It would have been likely on the bottom depending on how the breaker was oriented in the enclosure.

    The 350kcmil copper is good for 310A per set, so you have 620A worth without considering any deratings that may be needed for that service / feeder due to ccc or temperature or underground or etc.

    Do you have a picture of the breaker? Look at this one https://i.ebayimg.com/images/g/azoAA...h9/s-l1600.jpg
    Last edited by ron; 06-09-18 at 11:23 AM.
    Ron

  3. #3
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    Yes I do have a photo that looks exactly like the photo you posted but the dial arrows at the bottom are set at 1Low. Would this mean the overcurrent protection on my breaker is set at 600 Amps and your photo 800 Amps as your photo is at 8high? Thanks In advance Bill

  4. #4
    Join Date
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    The picture I linked to was for a circuit breaker that was a 600A trip (thermal or long time) and the dials (lo to hi) were for the adjustable instantaneous (magnetic) part of the tripping characteristics to accommodate things such as transformer or motor inrush.

    The wire and panel ampacity would be equal to or greater than the 600A trip.

    https://testguy.net/uploads/lsig-curve-explained.jpg
    Ron

  5. #5
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    Jun 2018
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    Nashville,TN
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    I would post the pic of my breaker but its too blurry. My breaker also is labeled 600 A Magnetic Adj. in the lower section of the breaker where the dials are. Looks like mine is a 600 A trip also which matches the wire size ratings properly....Thanks Ron

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