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    NEC 517 violation

    Why would code reject this?
    Attached Files

    #2
    But be ok with this?
    Attached Files

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      #3
      Why would an engineer or designer submit such sorry prints for bids or comments?

      Roger
      Moderator

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        #4
        No division of service between essential, life safety, critical, and equipment branches?

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          #5
          Originally posted by roger View Post
          Why would an engineer or designer submit such sorry prints for bids or comments?

          Roger
          They are mine, rough mouse sketches, drawn up in an hour. Mostly for discussion purposes before going "official"

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            #6
            Originally posted by Russs57 View Post
            No division of service between essential, life safety, critical, and equipment branches?
            Bingo.

            But- why would you need division if two independent systems are going to be in place? Failure of either will not effect the other.

            Comment


              #7
              Lemme guess:
              Because the electrical industry is still practicing "segregation"!

              Comment


                #8
                Originally posted by topgone View Post
                Lemme guess:
                Because the electrical industry is still practicing "segregation"!
                Codes reasoning, as best as I can figure is that should fault happen on one branch it does not effect that other. However, by having two separate systems as seen here no common mode or simultaneous failure can take place either. Yet 517 wants me to believe this does not meet the practical safeguards of life and property.

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                  #9
                  Is there a specific 517 ref for this?

                  ~RJ~

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                    #10
                    Originally posted by mbrooke View Post

                    Bingo.

                    But- why would you need division if two independent systems are going to be in place? Failure of either will not effect the other.
                    But failure of half the receptacles or lights in an OR is still a big issue. Doctors have to take time figuring out where to move plugs, and how to work with partial lighting.

                    (One OR once lost emergency power, but still had power to all normal power receptacles. Of course everything was plugged into the EM receptacles, so the doctors never even realized that the white receptacles still had power. )

                    Add that to the fact that large HVAC equipment and elevators are much more likely to fault, or to have large current surges, which in turn could trip an upstream breaker. And all in all, the less equipment and wiring you have on the output of an ATS, the more reliable the system is going to be.

                    However, I do agree that with all the newer requirements for selective coordination, this shouldn't be the issue it used to be. If an AHU or condenser trips a circuit breaker, it theory it would only be the branch breaker serving that unit.

                    However, there are still a lot of older systems that may not be coordinated because they were installed before the NEC requirements were added.

                    Comment


                      #11
                      Originally posted by steve66 View Post

                      But failure of half the receptacles or lights in an OR is still a big issue. Doctors have to take time figuring out where to move plugs, and how to work with partial lighting.

                      (One OR once lost emergency power, but still had power to all normal power receptacles. Of course everything was plugged into the EM receptacles, so the doctors never even realized that the white receptacles still had power. )


                      How does the current code address this issue?

                      Comment


                        #12
                        Originally posted by mbrooke View Post

                        How does the current code address this issue?
                        IMO, the code only addresses the issue indirectly. It does this by allowing the configuration in your second post, but not the one in the first post.

                        The less you have on a critical or life safety branch, the less likely a fault will occur and take out the entire system.

                        I think it would be a good idea to give doctors and staff drills where power outages are simulated. But I don't know of any facilities that do that, and its obviously outside the scope of the NEC or any building codes.

                        Comment


                          #13
                          Originally posted by steve66 View Post

                          IMO, the code only addresses the issue indirectly. It does this by allowing the configuration in your second post, but not the one in the first post.
                          It addresses it by mandating a certain percentage of receptacles be on the normal branch or a second critical branch. The idea is that if critical branch failed with utility power available, doctors and nurses can still transfer everything to the normal branch.


                          The less you have on a critical or life safety branch, the less likely a fault will occur and take out the entire system.
                          Not if you have selective coordination I'd think.

                          I think it would be a good idea to give doctors and staff drills where power outages are simulated. But I don't know of any facilities that do that, and its obviously outside the scope of the NEC or any building codes.

                          I know ICUs in some hospital practice blackout / med gas out protocols where they run down what to do and how to go about mechanically ventilating patients.

                          Comment


                            #14
                            Mbrooke, I'll admit to not knowing why you are asking questions of the good members of this forum that you already know the answers to. You come across as wanting to "reinvent the wheel" and /or proving that NEC/AHJ/NFPA are wrong and you are right. Good luck with all of that.

                            To me, you seem more interested in the cheapest solution. From where I sit, as a maintenance engineer in a hospital, I would think your "due diligence" should be aimed at providing a system most likely to insure delivery of power in the face of the worst calamity. Perhaps I have an unrealistic expectation or have misread your intent? Regardless, on to the designs you have proposed.

                            In your first design you have a 4,000 amp main feeding a pair of 2,500 breakers. IIRC all three of these breakers will require ground fault protection on them. You are not required to have ground fault protection on the 2,500 amp generator breakers. You may NOT have ground fault protection on the load side of any ATS so none of the breakers in the East or West switchgear may have that protection. Now what happens if you have a serious ground fault (call it a bolted connection) on the HVAC load on the East/Orange branch. At best you only trip the 2,500 amp breaker feeding normal power to the East/Orange switchgear (my experience has shown you will trip all normal power breakers). So now your East generator starts, ATS transfers, and you re-energize your bolted fault on your HVAC load. What happens? You might like to think the generator delivers nominal voltage to all loads until the 400 amp HVAC breaker clears the fault (and that severe under voltage to sensitve medical equipment will cause no harm). You might like to think nothing could explode or ignite before that 400 amp breaker trips. Remember that 400 amp breaker will carry 2,000 to 4,000 amps for a cycle or two at least. If impedance of wire limits current at the fault it may take a good deal longer to clear. Next thing you know that generator breaker trips and you just lost half of your life safety, critical, and equipment power to your entire facility. Don't think individual HVAC OPC devices will save you when some idiot just core drilled through your HVAC feeder. Only you can decide what design choices you can live and sleep with.

                            If you want to please me simply replace the purple and orange panels feeding the OR iso panels with breakers, have said breakers feed an ATS, have that ATS feed the OR iso panels. Now each iso panel has normal and emergency as an option on each pole of that ATS.

                            I'll stop now as I'm doubting you care what I think. If I'm wrong I'll be glad to comment on what I see as weak points in design two.

                            Comment


                              #15
                              Originally posted by Russs57 View Post
                              Mbrooke, I'll admit to not knowing why you are asking questions of the good members of this forum that you already know the answers to. You come across as wanting to "reinvent the wheel" and /or proving that NEC/AHJ/NFPA are wrong and you are right. Good luck with all of that.

                              To me, you seem more interested in the cheapest solution. From where I sit, as a maintenance engineer in a hospital, I would think your "due diligence" should be aimed at providing a system most likely to insure delivery of power in the face of the worst calamity. Perhaps I have an unrealistic expectation or have misread your intent? Regardless, on to the designs you have proposed.

                              In your first design you have a 4,000 amp main feeding a pair of 2,500 breakers. IIRC all three of these breakers will require ground fault protection on them. You are not required to have ground fault protection on the 2,500 amp generator breakers. You may NOT have ground fault protection on the load side of any ATS so none of the breakers in the East or West switchgear may have that protection. Now what happens if you have a serious ground fault (call it a bolted connection) on the HVAC load on the East/Orange branch. At best you only trip the 2,500 amp breaker feeding normal power to the East/Orange switchgear (my experience has shown you will trip all normal power breakers). So now your East generator starts, ATS transfers, and you re-energize your bolted fault on your HVAC load. What happens? You might like to think the generator delivers nominal voltage to all loads until the 400 amp HVAC breaker clears the fault (and that severe under voltage to sensitve medical equipment will cause no harm). You might like to think nothing could explode or ignite before that 400 amp breaker trips. Remember that 400 amp breaker will carry 2,000 to 4,000 amps for a cycle or two at least. If impedance of wire limits current at the fault it may take a good deal longer to clear. Next thing you know that generator breaker trips and you just lost half of your life safety, critical, and equipment power to your entire facility. Don't think individual HVAC OPC devices will save you when some idiot just core drilled through your HVAC feeder. Only you can decide what design choices you can live and sleep with.

                              If you want to please me simply replace the purple and orange panels feeding the OR iso panels with breakers, have said breakers feed an ATS, have that ATS feed the OR iso panels. Now each iso panel has normal and emergency as an option on each pole of that ATS.

                              I'll stop now as I'm doubting you care what I think. If I'm wrong I'll be glad to comment on what I see as weak points in design two.
                              Yeah, you're right! As much as possible, we design things to fit every requirement our clients need, We must be careful to follow what the regs stipulate. It must be made clear that the regs are "minimum" requirements also. But, a more careful investigation on every design could be best served if designers listen to others' point of view, IMHO. Just saying though!

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