4 wire vs. 3 wire service - Electric power & transmission I have a 3 wire vs. a 4 wire question for you folks out there. My primary transformer has a 12470 volt, 3 phase delta primary - 4160Y2402 secondary. However, my loads on the secondary of the transformer are all 3 phase, 4 wire vs. 3 wire service. REDDOG (Electrical) 23 Jun 09 11:08. electrical - Existing 3 wire service feed to sub panel I know variations of this question have been asked (the closest I could find is here), but I'm still confused. @Tester101 explained if the existing feed to the subpanel is 3 wire with a grounded neutral and two hots and is not electrically connected to your main panel, your sub should have a bonded ground/neutral. Is this an acceptable way to ground the sub panel? How the 3 wire electrical system works - YouTube Click to view on Bing10:14This one covers the single phase panel that uses 2 hot leads and a neutral to get 2 voltages in the same panel. This video is part of the heating and cooling series of training videos made toAuthor: grayfurnacemanViews: 345K Split-phase electric power - Wikipedia A split-phase or single-phase three-wire system is a type of single-phase electric power distribution. It is the AC equivalent of the original Edison three-wire direct-current system. Its primary advantage is that it saves conductor material over a single-ended single-phase system, while only requiring a single phase on the supply side of the distribution transformer.