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I'm installing a manual transfer switch to feed a 240V subpanel from either generator or the main panel. No devices other than the main panel are bonded. Since the neutral is not switched, can I bypass the transfer switch with the neutral and ground wires and connect the neutrals from the main panel and the generator directly to the subpanel?

Does the pictured wiring meet code?

proposed wiring

  • Have you read the installation instructions that came with the transfer switch? – Tester101 Aug 23 '14 at 12:28
  • Duplicate of diy.stackexchange.com/questions/44417/… ? – keshlam Aug 23 '14 at 20:03
  • This is not a duplicate question of 44417, which actually asks how neutral and ground are handled with a bonded generator. Ironically, I answered that question that you pointed me to :) Specifically, I am asking if the unswitched neutral must pass through the transfer switch housing. Can I run separate neutrals from the main and the generator directly to the subpanel as pictured? – user3158036 Aug 24 '14 at 16:11
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2014 NEC 300.20 (A) "Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and where used the grounded conductor and all equipment grounding conductors shall be grouped together". Also see 2014 NEC article 702.

  • Thanks for the code quote...of course the interpretation is the challenge. First, I'm using PVC conduit,not metal raceways. Since this is a 240V system, the bundle returning to the main would be flux neutral (no induction) if the loads on the 120V legs are balanced. Is it reasonable to run the neutral with the bundle? This would make the bundle flux neutral if the loads were not balanced. – user3158036 Aug 25 '14 at 1:50
  • The enclosures are not steel? – user24125 Aug 25 '14 at 2:34
  • Interesting... I can't count how many steel switch boxes I have opened that did not contain a neutral conductor. The romex wire from the fixture to the box is used to carry the hot, the switched hot back to the fixture (appropriately identified), and the ground. No neutral. In fact, that is how I wired every ceiling fixture in my most recent permitted and approved addition. Without looking it up, I wonder if the quote is taken out of context or meant for a specific application? – Jimmy Fix-it Aug 25 '14 at 2:47
  • If the loads on the sub panel are line to neutral loads for general and intermittent use. How can you be sure that the load on the feeder from the generator or from the main panel remain balanced at all times? You Of course try to balance the loads but the only way that they could be is if they were all line to line 240 volt loads. – user24125 Aug 25 '14 at 2:49
  • A steel switch box that contains a switch loop is balanced hot in switch leg out the same Ko or raceway. The magnetic field from the two cancel each other out. I'll try to find a reference. I had asked that question many years ago and that was always the answer. – user24125 Aug 25 '14 at 4:26
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The neutral does not have to pass through the switch housing. Many wiring diagrams will show it passing through because a common conduit is the norm. The switch housing must be bonded to the system ground, your diagram does not show that.

  • You are correct. I neglected to add the ground wire to the transfer switch in the diagram. Thanks for point that out. Oddly, the transfer switch does not have a grounding lug, but can add one. – user3158036 Aug 25 '14 at 0:45

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