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Thread: Test question

  1. #1
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    Test question

    A combination load consisting of 15KVA of resistance heat and a motor rated 1.2KVA is served by a 240v branch circuit. What is the minimum required rating for this branch circuit?


    I get 84 amps. Test booklet says the answer is 90. What say you guys?

  2. #2
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    Quote Originally Posted by blueheels2 View Post
    A combination load consisting of 15KVA of resistance heat and a motor rated 1.2KVA is served by a 240v branch circuit. What is the minimum required rating for this branch circuit?


    I get 84 amps. Test booklet says the answer is 90. What say you guys?
    You have to size it according to breaker sizes. Look at 240.6
    If you aim at nothing, you will hit it every time!

  3. #3
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    Quote Originally Posted by Little Bill View Post
    You have to size it according to breaker sizes. Look at 240.6


    Thanks I was thinking it was asking for load to be considered when sizing the ocpd.

  4. #4
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    Quote Originally Posted by blueheels2 View Post
    I get 84 amps.
    Perhaps I need more coffee this morning. But I don't see how you came up with 84.

    Taking the motor at 125% of 1.2 KVA gives you 1.5 KVA. Add 15 KVA for the heaters and you are up to 16.5 KVA. If this is single phase, then 16.5 KVA / 240 V = 68.8 amps. If this is three phase, then divide again by 1.732 and you get 39.7 amps.

    Please explain your math, while I go pour myself another cup of wake up juice.

    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  5. #5
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    15000 + 1200= 16,200 ÷ 240= 67.5 x 1.25 because it's a continuous load gives you 84.375A.

    Edited to add you calculated the motor as continuous but the heaters are considered continuous as well based off of 424.4 (b) I think.

  6. #6
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    Quote Originally Posted by blueheels2 View Post
    15000 + 1200= 16,200 ÷ 240= 67.5 x 1.25 because it's a continuous load gives you 84.375A.

    Edited to add you calculated the motor as continuous but the heaters are considered continuous as well based off of 424.4 (b) I think.
    Yes, fixed space heating is considered a continuous load. That said, there is no 85 amp breaker, so you must go to the next size up which is a 90 AMP.

    That also said I do not see how you could put both of those loads on the same circuit, unless they were a package deal like an HVAC unit.

    Edited to add... When posting test questions, it is incredibly important to post them completely as written... Not saying you didn't, just that even a missing, in the wrong place could change the answer
    Electricians do it until it Hertz!

  7. #7
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    Quote Originally Posted by JFletcher View Post
    Yes, fixed space heating is considered a continuous load. That said, there is no 85 amp breaker, so you must go to the next size up which is a 90 AMP.

    That also said I do not see how you could put both of those loads on the same circuit, unless they were a package deal like an HVAC unit.
    I would agree. This is just the questions you have to answer to get a license in NC.

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