In an old house with no ground wires and metal duplex boxes, we installed a GFCI in the first box in one circuit, and new 3-prong duplexes downstream named A through E. When we plug a load into duplex A or B, no problem. But if we plug a load into any of C through E, the gfci trips and A-E go dead. Would not a leak between neutral and ground somewhere between boxes B and C also cause the GFCI to trip when a load is plugged into A or B? Any ideas about what might actually be happening here?

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    I take it it's the same load you're trying at the various receptacles? – ThreePhaseEel Apr 23 '18 at 4:15
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    The neutral could be crossed with another circuit or ground at B, C or someplace in between. In that case you would have a balanced circuit until there was a load at C or greater, then the circuit would loose balance. I suspect neutral is touching metal box somewhere at B or C. – Tyson Apr 23 '18 at 12:38
  • @ThreePhaseEel, yes we are testing with the same load, a laptop charger. – emichaelb Apr 23 '18 at 15:31
  • @Tyson, but why would adding a load to duplex A not allow some current to flow along the neutral to the ground leak at B-C, thus also trip the GFCI? – emichaelb Apr 23 '18 at 15:31

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