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Electronics tech needs help with wire sizing for AC and elevator

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    Electronics tech needs help with wire sizing for AC and elevator

    I am an electronics tech but I fill an electrician's position at a VA hospital. It's a long story why this VA does not use real electricians but that's another thread. Recently an HVAC system has started tripping a 70 amp breaker (3ph, 460V) (elevator also on the circuit). The breaker is located in one building and feeds another building 330 ft away. I've corrected some of the issues and reduced the nuisance tripping to an "acceptable" level (not acceptable to me but the bosses have quit complaining). One of the issues was the panel room was so hot in the area of the breaker (rated 104F but the breaker temp was 110F). That was corrected by adjusting the room's ventilation, the breaker is now at about 95F but I've since learned that other devices were added to the circuit before I came to work here that were never recorded, I just stumbled across them. So now I'm thinking that the 70 amp breaker is no longer adequate and the breaker and wiring should be for 150 amps. I'm basing that on measuring continuous power at 47 amps and non continuous at 91 amps ((47x1.25)+91)). Is this correct?

    Like I said I'm an electronics tech, not an electrician, but I'm all they have right now. There is no funding available to have a contractor come in and deal with this right now, that may be a year away and the affected building is the OI&T building with the medical servers in it. Now I understand the physics of the issue but I'm not so strong on the code and the required calculations. So, the existing wire size is 2 awg with THW insulation (330ft). The current breaker is a 70 amp CH FS340070A. Can I go to a 90 or 100 amp breaker with what I described or am I heading down the wrong road?

    #2
    the elevator AND the hvac unit are on the same 70 A ckt?
    does the hvac serve the elevator room?

    Comment


      #3
      turn off the hvac when elevator runs.
      definitely sounds like a re-wire, but not using 150A ocpd.

      Comment


        #4
        Originally posted by Ingenieur View Post
        the elevator AND the hvac unit are on the same 70 A ckt?
        does the hvac serve the elevator room?
        The elevator and hvac are on the same breaker but the hvac serves the entire 3 story 70+ yr old building. This is also the OI&T building and when the hvac system stops that old building heats up fast.

        I'll add the building power is 120 and 208. That's why the 460 had to be brought in from the nearby building. This is the VA, there is no rhyme or reason to why they do things the way they do.

        Comment


          #5
          Originally posted by RobertKLR View Post
          This is the VA, there is no rhyme or reason to why they do things the way they do.
          If it's Federally owned property it's not subject to local inspections for one things.

          I'm surprised they could get the elevator certified with it hooked up like this but maybe they didn't have to.


          Edit: Find out who the authority having jurisdiction over this property is. Then question them as to any changes you wish to make. Then get any response in writing.

          Allways put the monkey on the other guys back because you are not qualified to make these decisions.
          Last edited by growler; 07-13-17, 01:39 PM.
          The 95% of people that you can't trust give the other 5% a bad name.

          Comment


            #6
            Originally posted by FionaZuppa View Post
            turn off the hvac when elevator runs.
            definitely sounds like a re-wire, but not using 150A ocpd.
            Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
            It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

            Sent from my XT1585 using Tapatalk
            Last edited by GoldDigger; 07-13-17, 02:22 PM.

            Comment


              #7
              Originally posted by growler View Post
              If it's Federally owned property it's not subject to local inspections for one things.

              I'm surprised they could get the elevator certified with it hooked up like this but maybe they didn't have to.


              Edit: Find out who the authority having jurisdiction over this property is. Then question them as to any changes you wish to make. Then get any response in writing.

              Allways put the monkey on the other guys back because you are not qualified to make these decisions.
              I've already done that but getting VA management to weigh in on anything is problematic. I'm always having to go outside the VA to get answers because within the VA there is no functional avenue for technical advice. Right now I've been able to get it operating well enough but I would rather get it right. My normal duties are taking care of the non medical electronics but as I said we haven't had a real electrician here in over 7 years so I've been filling in. When we have money I can get contractors to help out but right now the money is not there.

              Comment


                #8
                Originally posted by GoldDigger View Post
                Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
                It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

                Sent from my XT1585 using Tapatalk
                me being sarcastic

                if the ckt is being overloaded, what other options are there then to provide a new ckt to one or the other.
                personally, HVAC sounds more important, i would install new ckt for hvac and change ocpd for the vator/lift.

                Comment


                  #9
                  Originally posted by GoldDigger View Post
                  Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
                  It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

                  Sent from my XT1585 using Tapatalk
                  I have entertained that thought (I have a plc and parts that could control such a thing) but I'm just wondering if it would be practical to put a 90 or 100 amp breaker in with the existing wiring until the funds are released to get it all done correctly. That could be months away.

                  Comment


                    #10
                    Originally posted by FionaZuppa View Post
                    me being sarcastic

                    if the ckt is being overloaded, what other options are there then to provide a new ckt to one or the other.
                    personally, HVAC sounds more important, i would install new ckt for hvac and change ocpd for the vator/lift.
                    Definitely the hvac is the winner, this is west Texas and it is a very hot summer.

                    Comment


                      #11
                      If you are looking at temporary measures, blowing a fan on the breaker is a classic.
                      Theoretically you are also allowed to upsize the breaker if the ambient temperature is *consistently* high.

                      Sent from my XT1585 using Tapatalk

                      Comment


                        #12
                        Originally posted by RobertKLR View Post
                        I am an electronics tech but I fill an electrician's position at a VA hospital. It's a long story why this VA does not use real electricians but that's another thread. Recently an HVAC system has started tripping a 70 amp breaker (3ph, 460V) (elevator also on the circuit). The breaker is located in one building and feeds another building 330 ft away. I've corrected some of the issues and reduced the nuisance tripping to an "acceptable" level (not acceptable to me but the bosses have quit complaining). One of the issues was the panel room was so hot in the area of the breaker (rated 104F but the breaker temp was 110F). That was corrected by adjusting the room's ventilation, the breaker is now at about 95F but I've since learned that other devices were added to the circuit before I came to work here that were never recorded, I just stumbled across them. So now I'm thinking that the 70 amp breaker is no longer adequate and the breaker and wiring should be for 150 amps. I'm basing that on measuring continuous power at 47 amps and non continuous at 91 amps ((47x1.25)+91)). Is this correct?

                        Like I said I'm an electronics tech, not an electrician, but I'm all they have right now. There is no funding available to have a contractor come in and deal with this right now, that may be a year away and the affected building is the OI&T building with the medical servers in it. Now I understand the physics of the issue but I'm not so strong on the code and the required calculations. So, the existing wire size is 2 awg with THW insulation (330ft). The current breaker is a 70 amp CH FS340070A. Can I go to a 90 or 100 amp breaker with what I described or am I heading down the wrong road?
                        There are a lot of issues associated with this that probably need to be explored to actually "fix" it.

                        I am not even sure it is allowed by code to have an HVAC system on an elevator circuit.

                        Normally you are only allowed a single feeder to a building. it seems likely given your description of the situation that you have more than one.

                        Load calculations are based on the requirements for such calculations found in article 220.

                        No offense, but I am kind of afraid to even offer suggestions given your level of competence. You might end up making it worse just from not knowing what questions to ask, and what is important.

                        Personally I like the idea of just shutting off the A/C compressor while the elevator is starting. It has simplicity going for it. But as another poster mentioned it might create problems with the A/C motor and allowed starts. If the elevator is used a lot you might end up with little or no A/C.

                        #2 copper is good for 115 A depending on what type of insulation it has. My suspicion is that it is AL which is only good for 90 A. that would kind of make sense given the load and the distance the conductor runs.
                        Bob

                        Comment


                          #13
                          One of the exceptions to single feeder is multiple voltage systems, yes?

                          Sent from my XT1585 using Tapatalk

                          Comment


                            #14
                            Originally posted by GoldDigger View Post
                            One of the exceptions to single feeder is multiple voltage systems, yes?

                            Sent from my XT1585 using Tapatalk
                            Among other exceptions.
                            Bob

                            Comment


                              #15
                              Originally posted by petersonra View Post
                              There are a lot of issues associated with this that probably need to be explored to actually "fix" it.

                              I am not even sure it is allowed by code to have an HVAC system on an elevator circuit.

                              Normally you are only allowed a single feeder to a building. it seems likely given your description of the situation that you have more than one.

                              Load calculations are based on the requirements for such calculations found in article 220.

                              No offense, but I am kind of afraid to even offer suggestions given your level of competence. You might end up making it worse just from not knowing what questions to ask, and what is important.

                              Personally I like the idea of just shutting off the A/C compressor while the elevator is starting. It has simplicity going for it. But as another poster mentioned it might create problems with the A/C motor and allowed starts. If the elevator is used a lot you might end up with little or no A/C.

                              #2 copper is good for 115 A depending on what type of insulation it has. My suspicion is that it is AL which is only good for 90 A. that would kind of make sense given the load and the distance the conductor runs.
                              I agree with your assessment of my level of competence. I have extensive electronics training but the technicalities of the electrician field is not part of that training, so no offense taken. I've certainly appreciated the responses so far also. Someone mentioned putting a fan on the breaker and that is what I did until I was able to get the air flow moving like it should through the panel room. These are old buildings, remodeled many times and the ductwork is a mess.

                              There are two feeders to the building in question, one comes straight from the switchgear building (13.2KV) to a transformer for the 208 power but the hvac and elevator are fed from another building across the street which has 460vac.

                              Comment

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