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04-30-2013, 10:57 AM #1
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.
Similar Threads:Last edited by Robert Foster; 04-30-2013 at 11:15 AM. Reason: try to add pic
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04-30-2013, 01:22 PM #2
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
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05-03-2013, 07:27 AM #3
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05-03-2013, 03:19 PM #4
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05-06-2013, 11:02 AM #5
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?
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05-06-2013, 12:41 PM #6
Re: distribution panel serving HVAC system
In my area, that box would be marked "240V only".
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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
www.allsafehome.ca
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05-10-2013, 05:25 PM #7
Re: distribution panel serving HVAC system
It would all depend on if this panel is a disconnect or a sub-panel.
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05-11-2013, 11:17 AM #8
Re: distribution panel serving HVAC system
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.
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05-11-2013, 12:21 PM #9
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".
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05-11-2013, 11:06 PM #10
Re: distribution panel serving HVAC system
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.
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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?
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05-12-2013, 01:29 AM #11
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.
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05-12-2013, 06:28 AM #12
Re: distribution panel serving HVAC system
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05-12-2013, 10:44 AM #13
Re: distribution panel serving HVAC system
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.
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05-12-2013, 05:25 PM #14
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