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Thread: Circuit Breaker Sizing

  1. #1
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    Default Circuit Breaker Sizing

    I have two questions:
    1. How can I put my electrical information into the mechanical equipment (MOP, MCA, FLA, and Voltage) so that it will pull through to my electrical information? The load can be pulled through from the mechanical equipment by just having a formula to calculate the load, but it does not look there is a parameter to be put in place for breaker size and a parameter can not be added to the electrical connection. Is there a way to pull the MOP through once mechanical has placed all their information in say a RTU, or if something changes last minute then it will be updated in my schedules as well? I know the load would be, but what about the circuit breaker?

    2. I am trying to get the circuit breaker size for any piece of equipment to come through and show the correct size in the panel schedule, that way you do not have to always resize the breaker information for each piece of equipment. The panel schedule sizes the circuit breaker off a parameter called "Rating", which I have found no way to link to. Rating can be found by going to a device and then going to the tab at the top called "Electrical Circuits" and then look under "Properties". If I change the number under "Rating" then my circuit breaker and wire size will change in my panel schedule, I just want to know if there is a way to link to this information or if you have to always go to the "Rating" and change it every time, and this is also a global change.

  2. #2
    Revit MEP Moderator mjdanowski's Avatar
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    Default Re: Circuit Breaker Sizing

    What I do on my mechanical equipment schedules is:

    - Link in voltage directly to the linked connector parameter.
    - Show kVA for each piece of equipment.
    - Show phase for the equipment (ie. 3 or 1), this is a dumb parameter.
    - Calculate FLA based upon the kVA & phase.

    kVA and voltage are the two things which are linked directly from the schedules to the connector and analysis.

    For question 2, what are you referring to with "linked"?

  3. #3
    Woo! Hoo! my 1st post
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    Default Re: Circuit Breaker Sizing

    I have a similar concern. I would like to see the "Rating" update automatically based on the load on a circuit. Is this possible or does it have to be a manual input?

  4. #4
    Revit MEP Moderator mjdanowski's Avatar
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    Default Re: Circuit Breaker Sizing

    Manual input.

  5. #5
    Woo! Hoo! my 1st post
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    Default Re: Circuit Breaker Sizing

    I know this is super late reply, but I have worked with this issue and wondered if others have found a better solution than I have.

    For your second question, I have been working on an automatic re-sizing of breakers in the panel schedules using calculating values in the panel schedule, rather than using the "Rating" parameter. My formula is terribly long and simple, due to the many different breaker sizes possible. You may be able to use the roundup() function to simplify the formula, but I haven't gotten too deep into the details yet. This formula correctly sizes breakers, but it does not allow you to manually change breaker sizes later or if you add spares/spaces it will lock the breaker value at 0 Ohms, which is not helpful. Any help would be appreciated! Formula is below:

    if(or(Voltage = 120 V, Voltage = 277 V), if((Apparent Load / Voltage) * 1.25 < 20 A, 20 A, if((Apparent Load / Voltage) * 1.25 < 25 A, 25 A, if((Apparent Load / Voltage) * 1.25 < 30 A, 30 A, if((Apparent Load / Voltage) * 1.25 < 35 A, 35 A, if((Apparent Load / Voltage) * 1.25 < 40 A, 40 A, if((Apparent Load / Voltage) * 1.25 < 45 A, 45 A, if((Apparent Load / Voltage) * 1.25 < 50 A, 50 A, if((Apparent Load / Voltage) * 1.25 < 60 A, 60 A, if((Apparent Load / Voltage) * 1.25 < 70 A, 70 A, if((Apparent Load / Voltage) * 1.25 < 80 A, 80 A, if((Apparent Load / Voltage) * 1.25 < 90 A, 90 A, if((Apparent Load / Voltage) * 1.25 < 100 A, 100 A, if((Apparent Load / Voltage) * 1.25 < 110 A, 110 A, if((Apparent Load / Voltage) * 1.25 < 125 A, 125 A, if((Apparent Load / Voltage) * 1.25 < 150 A, 150 A, if((Apparent Load / Voltage) * 1.25 < 175 A, 175 A, if((Apparent Load / Voltage) * 1.25 < 200 A, 200 A, if((Apparent Load / Voltage) * 1.25 < 225 A, 225 A, if((Apparent Load / Voltage) * 1.25 < 250 A, 250 A, if((Apparent Load / Voltage) * 1.25 < 300 A, 300 A, if((Apparent Load / Voltage) * 1.25 < 350 A, 350 A, if((Apparent Load / Voltage) * 1.25 < 400 A, 400 A, if((Apparent Load / Voltage) * 1.25 < 450 A, 450 A, if((Apparent Load / Voltage) * 1.25 < 500 A, 500 A, if((Apparent Load / Voltage) * 1.25 < 600 A, 600 A, if((Apparent Load / Voltage) * 1.25 < 700 A, 700 A, if((Apparent Load / Voltage) * 1.25 < 800 A, 800 A, if((Apparent Load / Voltage) * 1.25 < 1000 A, 1000 A, if((Apparent Load / Voltage) * 1.25 < 1200 A, 1200 A, if((Apparent Load / Voltage) * 1.25 < 1600 A, 1600 A, if((Apparent Load / Voltage) * 1.25 < 2000 A, 2000 A, if((Apparent Load / Voltage) * 1.25 < 2500 A, 2500 A, if((Apparent Load / Voltage) * 1.25 < 3000 A, 3000 A, if((Apparent Load / Voltage) * 1.25 < 4000 A, 4000 A, if((Apparent Load / Voltage) * 1.25 < 5000 A, 5000 A, 6000 A))))))))))))))))))))))))))))))))))), if(or(Voltage = 208 V, Voltage = 480 V), if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 20 A, 20 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 25 A, 25 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 30 A, 30 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 35 A, 35 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 40 A, 40 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 45 A, 45 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 50 A, 50 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 60 A, 60 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 70 A, 70 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 80 A, 80 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 90 A, 90 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 100 A, 100 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 110 A, 110 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 125 A, 125 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 150 A, 150 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 175 A, 175 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 200 A, 200 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 225 A, 225 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 250 A, 250 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 300 A, 300 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 350 A, 350 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 400 A, 400 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 450 A, 450 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 500 A, 500 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 600 A, 600 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 700 A, 700 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 800 A, 800 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 1000 A, 1000 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 1200 A, 1200 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 1600 A, 1600 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 2000 A, 2000 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 2500 A, 2500 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 3000 A, 3000 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 4000 A, 4000 A, if((Apparent Load / (Voltage * sqrt(3))) * 1.25 < 5000 A, 5000 A, 6000 A))))))))))))))))))))))))))))))))))), 20 A))

  6. #6
    I could stop if I wanted to
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    Default Re: Circuit Breaker Sizing

    Jesus. How many projects do you have to use that on before you make up the amount of time it took to create/troubleshoot the equation?

    I just created a circuit schedule that includes breaker size and load, then made a calculated value to determine if the load is <80% of the breaker rating. If it's greater than that, the field in the schedule turns red and I adjust the breaker size inside the schedule. Quick and easy, and a good QA/QC startegy during design.
    Autodesk Revit MEP 2015 Certified Professional #408406

  7. #7


    Default Re: Circuit Breaker Sizing

    I'm replying to an old thread, I know, but it's not like these electrical requirements havegone away in the last seven years. If you're not opposed to investing more money in additional software, I have an add-in for Revit that provides both of the features requested in the original post.

    1. We have the ability to specify FLA, MCA, and MOCP on equipment, either in the family or in the instance, depending upon your workflow preferences. The breaker the equipment is connected to then uses those values to size the breaker and the wire. This page in our documentation shows how to set that in the family:
    http://www.designmaster.biz/docs/ele...connection.htm

    2. For circuits that do not have equipment connected to them, we size them automatically based upon 125% of the connected load. If the load changes, the breaker size changes, too. It basically assumes everything is continuous, which is safe and easy but wrong. We eventually hope to separate load types into continuous or noncontinuous so we can size correctly for breakers with noncontinuous loads. For situations where that needs to be addressed, you can manually override the breaker size that is calculated. This page in our documentation shows how you specify the breaker sizing for a circuit:
    http://www.designmaster.biz/docs/ele...rcuit_edit.htm

    You can download a free trial of the add-in from our website.
    http://www.designmaster.biz/revit/free-trial.html
    David Robison

    Design Master Electrical RT: Electrical calculation software for Revit MEP.
    http://www.designmaster.biz/revit/

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