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    Max Breaker

    After roughing in a new house and before final, we customarily get what is called a "service release". This is just an inspection with a few circuits connected to allow the POCO to connect power. This is mostly for HVAC to be turned on to acclimate the house for flooring, painting, etc.
    When I was preparing the panel for the service release I asked the HVAC installer what size breaker he needed for his unit as it was not on site when I left. He told me a 30A breaker and that's what I put in.

    Now I'm back doing trim-out and I just thought I would look at the unit to see what the nameplate said. The "Max Breaker" size was 40A. I know the 30A is legal but I don't want to be called back for nuisance tripping. However, this unit has been running for a couple of months and no reported tripping. Since this house is quite a distance for me to drive, do you think I should swap the breaker out for a 40A?
    [COLOR=navy]If you aim at nothing, you will hit it every time![/COLOR]

    #2
    A 40 now is cheaper than latter.

    I only had a couple that wouldn't start on smaller then max OCPD, and they ended up with hard start kits anyway.
    Tom
    TBLO

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      #3
      What is the minimum ckt ampicity? My guess is if it's been running for months your probably good, but as time goes by frequent over heating would likely cause that breaker to trip

      Sent from my SM-G965U using Tapatalk

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        #4
        Originally posted by nickelec View Post
        What is the minimum ckt ampicity? My guess is if it's been running for months your probably good, but as time goes by frequent over heating would likely cause that breaker to trip

        Sent from my SM-G965U using Tapatalk
        MCA was a little over 23A. It was 23.xx, I can't recall exactly.
        [COLOR=navy]If you aim at nothing, you will hit it every time![/COLOR]

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          #5
          Your probably fine I would be able to sleep at night

          Sent from my SM-G965U using Tapatalk

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            #6
            If it will hold the starting surge it will likely be fine. If you are running on some temp service and then later switch to permanent service, there is a chance there is less overall circuit impedance in your permanent service and that could lead to higher starting surge from that arrangement - increasing the chance it trips upon starting.
            I live for today, I'm just a day behind.

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              #7
              I would leave the 30 amp CB. It should never trip under normal conditions.
              Rob

              Moderator

              All responses based on the 2017 NEC unless otherwise noted

              Comment


                #8
                Originally posted by infinity View Post
                I would leave the 30 amp CB. It should never trip under normal conditions.
                NEC allows a 35 amp breaker for 10 HP 480 V three phase motor.

                Many manufacturer selection charts suggest a 25 amp breaker.

                I've seen many connected to a 15 amp breaker and they never trip upon starting, but that don't mean all will hold on a 15 amp breaker either. All depends on starting surge current, which will remain pretty consistent until you make some change to the supply circuit.

                Had a big feed mixer motor at cattle feed yard several years ago - maybe 25 or 30 HP 230 volts. It ran for years on a 100 amp breaker no troubles. Then we happened to replace the supply line to that area with larger conductor - 100 amp breaker would randomly trip at startup - new supply conductors with less resistance meant starting surge increased enough to get into the instantaneous trip range on that breaker. Unfortunately it was a QO breaker and they don't make a 125 amp three pole so it took more than simple swap of a breaker to resolve this issue.
                I live for today, I'm just a day behind.

                Comment


                  #9
                  Originally posted by Little Bill View Post
                  I know the 30A is legal but I don't want to be called back for nuisance tripping. However, this unit has been running for a couple of months and no reported tripping. Since this house is quite a distance for me to drive, do you think I should swap the breaker out for a 40A?
                  What's the downside to swapping it out ? you purchase a new 40 amp breaker but you still have the 30 amp breaker that you remove and those get used all over the place. It's not like it goes to waste.
                  The 95% of people that you can't trust give the other 5% a bad name.

                  Comment


                    #10
                    Leave the 30 and if the customer has a call back or something else for you then change it out. I would not make the extra trip unless you were in the area.
                    They say I shot a man named Gray and took his wife to Italy
                    She inherited a million bucks and when she died it came to me
                    I can't help it if I'm lucky

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                      #11
                      Max breaker?
                      I don't want to break Max.......

                      Sorry mods...........

                      Comment


                        #12
                        Originally posted by Little Bill View Post

                        Now I'm back doing trim-out .
                        Originally posted by Dennis Alwon View Post
                        Leave the 30 and if the customer has a call back or something else for you then change it out. I would not make the extra trip unless you were in the area.
                        I wouldn't make an extra trip to change that breaker either. That would defeat the purpose of the change (save time and money). But if he is there doing a trim out.

                        Edit: you can't buy much gas for the price of a two pole 40 amp breaker ( not to mention the drive time).
                        The 95% of people that you can't trust give the other 5% a bad name.

                        Comment


                          #13
                          Many new units have a voltage range, my current unit has a range of 197-253 volts, MaxOCPD 30 amps, MCA 18.6 amps. I would assume that the 18.6 takes into account the unit running at 197 volts. If it's operating near the top of the range say at 240 volts the current will be much lower than the MCA/125%.
                          Rob

                          Moderator

                          All responses based on the 2017 NEC unless otherwise noted

                          Comment


                            #14
                            Originally posted by kwired View Post
                            If it will hold the starting surge it will likely be fine. If you are running on some temp service and then later switch to permanent service, there is a chance there is less overall circuit impedance in your permanent service and that could lead to higher starting surge from that arrangement - increasing the chance it trips upon starting.
                            It's not a "temp service". That get's replaced by the permanent service when you receive a "service release". As I said earlier, the "service release" just allows the POCO to energizes the service before final is ready. This allows the HVAC to run and also allows finish workers to plug in inside without dragging an extension cord across a finished floor. Also, have to have power of some sort to get a final. So basically, it's the main service without everything hooked up. All that's required for a "service release" inspection is grounds made up in the panel and one 120V GFCI circuit, whether that be one receptacle or several on the same circuit. The impedance doesn't change from "service release" to "final" .
                            [COLOR=navy]If you aim at nothing, you will hit it every time![/COLOR]

                            Comment


                              #15
                              Originally posted by infinity View Post
                              Many new units have a voltage range, my current unit has a range of 197-253 volts, MaxOCPD 30 amps, MCA 18.6 amps. I would assume that the 18.6 takes into account the unit running at 197 volts. If it's operating near the top of the range say at 240 volts the current will be much lower than the MCA/125%.
                              Running current is well under trip range, it is starting current that is going to be a potential nuisance tripping issue. Starting current is going to be impacted by overall circuit impedance during starting conditions. Same HVAC unit may trip the 30 amp breaker in one location because there is a pretty stout source, maybe short service run and short branch circuit length. Another install with same unit may never trip same breaker because the source is higher impedance, maybe has long service run to the source, but same install maybe sees more severe dimming of lights when this unit is starting compared to the first example.
                              I live for today, I'm just a day behind.

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