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  1. #1
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    Default distribution panel serving HVAC system

    Weird Question, but I am scratching my head as to why in an otherwise very well built and "clean" house this morning a distribution panel was fed with only a three conductor cable. There was no metallic conduit between the distribution and main either. If all the circuits in the distribution panel are serving a single HVAC system can the fourth conductor be omitted? This was a large, high end, new heat pump including humidification and electronic air filter all fed through this distribution panel.

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  2. #2
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    Default Re: distribution panel serving HVAC system

    IF ALL the loads are 230 volt single-phase, the third conductor would be the equipment ground. There would be no need for the neutral.

    "Get correct views of life, and learn to see the world in its true light. It will enable you to live pleasantly, to do good, and, when summoned away, to leave without regret. " Robert E. Lee

  3. #3
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Robert Foster View Post
    Weird Question, but I am scratching my head as to why in an otherwise very well built and "clean" house this morning a distribution panel was fed with only a three conductor cable. There was no metallic conduit between the distribution and main either. If all the circuits in the distribution panel are serving a single HVAC system can the fourth conductor be omitted? This was a large, high end, new heat pump including humidification and electronic air filter all fed through this distribution panel.
    I have seen that a number of time. I'm not certain, but if the panel only has room for the circuit breakers used to the system, then it may be to code. If there is room for other breakers then I suspect that it is wrong.


  4. #4
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Mark Reinmiller View Post
    I have seen that a number of time. I'm not certain, but if the panel only has room for the circuit breakers used to the system, then it may be to code. If there is room for other breakers then I suspect that it is wrong.
    Perfectly Legal.
    There is no code requirement to run a grounded ( neutral) conductor to a sub panel.


  5. #5
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    Default Re: distribution panel serving HVAC system

    I agree that there is no need for a "Neutral", grounded conductor to be run for loads that are in the 240 Vac family. However there is a requirement that there be a receptacle with 25' of the unit to be used for when repairs are necessary. Is there a receptacle present and where does it get its power from?


  6. #6
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    Default Re: distribution panel serving HVAC system

    In my area, that box would be marked "240V only".

    - - - Updated - - -

    Make sure you report that as a '240 volt only' panel. It is basically a cluster of disconnects.

    John Kogel, RHI, BC HI Lic #47455
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  7. #7
    Daniel Mack's Avatar
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    Default Re: distribution panel serving HVAC system

    It would all depend on if this panel is a disconnect or a sub-panel.


  8. #8
    Daniel Mack's Avatar
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Robert Meier View Post
    Is there a distinction between the requirements for either in the NEC? Would a sub-panel with only 240 volt loads require a neutral?
    NEC 100, definition of a feeder, requires all circuit conductors, including the neutral, be used until the final branch circuit over current-device is used. At this point it would be OK to use a 2 pole breaker without the neutral for (for example) 240 volt equipment not needing a neutral. Certainly this does not in any way disqualify an adequate grounding (not the neutral) means.

    Research the definition between grounding and grounded for more clarity.

    So, a sub-panel would require all circuit conductors originating from the feeder panel, a multi wire branch circuit would not.


  9. #9
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    Default Re: distribution panel serving HVAC system

    That definition is simply stating the following (I will start downstream and work upstream):

    Branch circuit conductors are those conductors which are between the device (receptacle outlet)/appliance/etc and the first overcurrent device (breaker/fuse) upstream - that breaker/fuse is the branch circuit overcurrent protection.

    Feeder conductors are the conductors terminating at the branch circuit overcurrent protection device and the preceding overcurrent protection device.

    "All" the conductors installed as described for "feeder" conductors are feeders. That definition is not stating which or how many conductors are required to be there, only that the conductors between those two overcurrent devices are "feeders".

    Jerry Peck, Construction / Litigation Consultant
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  10. #10
    Daniel Mack's Avatar
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Robert Meier View Post
    Here's the definition that you've mentioned from Article 100 of the NEC. Where does it say that a neutral is required for a feeder? A 3, 3wire system doesn't even have a neutral so are you saying that a 3, 3W system cannot have a feeder?
    Obviously, if a neutral is not in the 3 phase system, it is not one of the conductors; however, all the conductors in the system of origin must be included in the sub-panel feed. For example, one can not feed a 240 volt sub panel from a 3 phase 480 volt delta system.

    - - - Updated - - -

    Quote Originally Posted by Jerry Peck View Post
    That definition is simply stating the following (I will start downstream and work upstream):

    Branch circuit conductors are those conductors which are between the device (receptacle outlet)/appliance/etc and the first overcurrent device (breaker/fuse) upstream - that breaker/fuse is the branch circuit overcurrent protection.

    Feeder conductors are the conductors terminating at the branch circuit overcurrent protection device and the preceding overcurrent protection device.

    "All" the conductors installed as described for "feeder" conductors are feeders. That definition is not stating which or how many conductors are required to be there, only that the conductors between those two overcurrent devices are "feeders".
    Please forgive my understanding of your answer but according to your conclusion, I can feed a 12 circuit 120 volt sub panel from one leg of a 120-277 volt wye system?


  11. #11
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    Default Re: distribution panel serving HVAC system

    Daniel, "system of orgin"? That is what is leading you to draw conclusions not stated or implied in the code mentioned.


  12. #12
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Daniel Mack View Post
    Please forgive my understanding of your answer but according to your conclusion, I can feed a 12 circuit 120 volt sub panel from one leg of a 120-277 volt wye system?
    Daniel,

    Huh?

    The discussion has been about a 240 volt ONLY panel ... how did you get distracted over to a 120 volt circuit?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  13. #13
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Jerry Peck View Post
    Daniel,

    Huh?

    The discussion has been about a 240 volt ONLY panel ... how did you get distracted over to a 120 volt circuit?
    I have been thoroughly researching this and I have ended up unconvinced of my own argument. Here is what I have found in the code:

    250.24(C) Grounded Conductor Brought to Service Equipment.
    Where an ac system operating at less than 1000 volts
    is grounded at any point, the grounded conductor(s) shall
    be routed with the ungrounded conductors to each service
    disconnecting means and shall be connected to each disconnecting
    means grounded conductor(s) terminal or bus. A
    main bonding jumper shall connect the grounded conductor(
    s) to each service disconnecting means enclosure. The
    grounded conductor(s) shall be installed in accordance with
    250.24(C)(1) through (C)(4).

    Which only applies to the service entrance conductors

    It is now required to install the neutral of a multi-wire branch circuit in a switch box of the system.

    It seems there is an inconsistency between the main panel and the sub-panel in the NEC Certainly if I was the AHJ on the inspection, I would not approve this application because it is in a residence and a DIY homeowner could think the grounding conductor could be used as a neutral but that would be my call.

    Technically, the neutral is not required in the OP. I stand corrected and will submit a code change recommendation concerning residential applications. This is not a good practice for a home.


  14. #14
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    Default Re: distribution panel serving HVAC system

    Quote Originally Posted by Daniel Mack View Post
    I have been thoroughly researching this and I have ended up unconvinced of my own argument. Here is what I have found in the code:

    250.24(C) Grounded Conductor Brought to Service Equipment.
    Where an ac system operating at less than 1000 volt is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A
    main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(4).

    Which only applies to the service entrance conductors
    You are correct that does only apply to a service.

    It is now required to install the neutral of a multi-wire branch circuit in a switch box of the system.
    This requirement was added because the manufactures of dimmers and motion sensors were using the ground for neutral internally in the devices. This is no longer allowed and the manufactures will be adding neutral conductors to these devices. Thus the requirement for the neutral conductors in switch boxes

    It seems there is an inconsistency between the main panel and the sub-panel in the NEC Certainly if I was the AHJ on the inspection, I would not approve this application because it is in a residence and a DIY homeowner could think the grounding conductor could be used as a neutral but that would be my call.
    There is no inconsistency. If you are installing a feeder that only serves 240 loads why install a neutral? Think about the larger commercial and industrial facilities. There are feeders ran that only serve a motor,or a larger air handling unit,or a piece of production machinery. Think about all the extra wasted time/materials & money on the requirement for a useless neutral.

    If that panel is installed to only serve 240 volt loads it is perfectly fine.
    An AHJ CAN NOT reject the install unless the jurisdiction has something in writing and adopted into law stating the requirement for the neutral.
    Keep in mind the NEC and the IRC are NOT design codes.


    Technically, the neutral is not required in the OP. I stand corrected and will submit a code change recommendation concerning residential applications. This is not a good practice for a home.

    Thats the way to go about it !


    I do not think it will go any where, but I do encourge everyone to write for code changes that they do not like

    I personnally wrote 12 proposals for the 2011. I had 3 propsals accepted


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