I have an unusual situation here. I have an older Dell computer that is plugged into an outlet. The monitor that I use with this computer has its own power switch and is also plugged into the same outlet.

If I turn on the computer first and then the monitor, all works okay. However, if I turn on the monitor first and then the computer, a GFCI on a different circuit trips. The neutral wire for this particular outlet is not shared anywhere with the wiring of the other affected circuit except, of course, at the box where all the neutrals are shared. There are additional outlets on this circuit where my Dell is plugged into.

A couple of things to note:

  1. There are several individual circuits coming from the box and because the box is located in a shed away from the house, every circuit has its own GFCI.
  2. Two of the circuits have GFCI breakers while the remaining circuits have GFCI outlets. One of the GFCI breakers is the one that trips.
  3. The computer is plugged into a regular outlet downstream from its GFI outlet.
  4. The separate wires for each of these circuits do run parallel to each other inside the wall.


  • 1
    Where are you on this planet? Why are there several individual branch circuits between the house and the shed, instead of a feeder from the shed to a subpanel in the house? – ThreePhaseEel May 17 '20 at 19:07
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    There aren't several branch circuits between the house and the shed. Maybe I should explain further...From the main electrical box located inside my garage, I had an electrician run a buried cable to the box in the shed. That cable is connected to a 100 amp circuit breaker in the main box. It is from this circuit that the shed gets its power. The box that I referred to in my question was the box located in the shed. And yes, there is a ground rod just outside the shed in addition to the one at the house. Sorry for the confusion. Hope this explanation clears it up. BTW -- no need to be rude. – user155292 May 17 '20 at 19:22
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    Edit your question so it is clear - leaving that info in a comment is not good because not everyone reads all the comments. Btw formatting your question so it is not a “wall” of text will make it easier to read. Perhaps the combined earth leakage current exceeds the rating but not when the monitor is off. – Solar Mike May 17 '20 at 21:47
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    Tell us about the grounds in this circuit. Are any grounds anywhere bootlegged? Was all the wiring done to modern standard? Are any of the circuits wired with 3-conductor (black white red) cable? – Harper - Reinstate Monica May 17 '20 at 23:23
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    Is the breaker only GFCI or is it combination GFCI /AFCI? If you're not sure, post a closeup picture of the breaker panel. – manassehkatz-Moving 2 Codidact May 18 '20 at 1:18

If the GFCIs have a 5mA threshold, the reason might be related to the cable capacitances. Domestic cables can accumulate 200-400 nanoFarad per kilometer, i.e. the GFCI could trip if the summed up downstream cable length is 500m , if the voltage is 120V, 60Hz. Without any devices plugged into the circuit.

The usual PI-filters of switch mode power supplies in PCs and monitors can add more capacitance, increasing the tripping probability. This is why those 5mA GFCIs seem to be too sensitive in some cases, thus providing not more safety then a 30mA GFCI, but instead are the reason for a safety gap if the annoyed user eliminates that 5mA GFCI if it tripped again just before he was to top his high score in the difficult PC game after weeks of failed sessions.

  • I would say it’s more likely with 2 switching power supplies powering up at the same time the leakage could meet the trip threshold for a GFCI or AFCI as AFCI’s do not do well with wave shaping electronics. – Ed Beal May 18 '20 at 14:25
  • Yes, even older switching power supplies do have RFI filters, often a Pi filter with a X2-capacitor between Phase and Ground. If that capacitor is empty when the device is switched on at the net's peak voltage, a relatively huge current spike is contributing to an imbalance between Phase and Neutral current. But long cables with their capacitance do also contribute to imbalances. – xeeka Mar 14 at 16:36

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