Overview: A colleague of mine took her HP laptop from Canada (19.5 V, 1.4 A DC rated) to work in Brazil and experienced ground fault trips on the outlets when she connected an HDMI to a projector during a presentation. Please see my key points for more detail.

Key Points:

  • Brazil uses Type N connections
  • During the presentation her laptop was not connected to the wall and instead was on battery
  • However due to the different wall outlet she did borrow a charger for her time in Brazil (but did not have it plugged in during presentation)
  • The other Brazilian colleagues use Dell laptops rate at the same voltage and current but do not have this issue
  • The HDMI cable was their cable (incase there is a difference between Canadian and Brazilian make)
  • The fault did not happen immediately but after (as she described) 5 minuets
  • This issue occurred twice until they decided to switch to another (Brazilian) laptop at which point it did not occur.

Research: I did some research to see what could be the case and found that people experience a lot of HDMI issues that may be caused by incorrect grounding or pre-charged circuits from DVR's to TV's. I feel this might be relevant so here is a link to a forum response on CNET.

My possible explanations: Considering that this was tripping a GCFI instead of an overcurrent breaker my guess is that it's not a "drawing too much power" issue but instead a difference in grounding between the Canadian equipment (laptop) and the Brazilian equipment (HDMI and projector). I also believe that perhaps these differences are creating a charge to build upon an insulated part which is reaching a critical flashover point and then being discharged through the case to ground and perhaps this explains why there is a time delay.

  • \$\begingroup\$ You mentioned that a change in laptops fixed the problem. I suspect the one laptop has a noisy power supply. The HDMI cables are all the same-or should be. Laptops are often powered by a desktop power supply. This is grounded so it can trip a GFCI breaker if it had a defect-or is just noisy. \$\endgroup\$
    – user105652
    Feb 15, 2018 at 15:11
  • \$\begingroup\$ @Sparky256 But don't you find it odd that her laptop wasn't connected to a power supply? As I mentioned it was being fed off it's battery. Are you suggesting that her laptop developed a charge build up prior to connection which could have been transferred to the projector's power leads? She was using a power supply they provided while she was there so maybe it set her up for failure. I'll add that as a key point. \$\endgroup\$ Feb 15, 2018 at 15:25
  • \$\begingroup\$ Was the laptop connected to something else? Network? If the laptop was completely isolated from everything but the HDMI then there must be some traces of mains power on the HDMI coming from the projector. \$\endgroup\$
    – Daniel P
    Feb 15, 2018 at 22:19
  • \$\begingroup\$ Also, a GFCI doesn't care if you put a "foreign" current on the earth wire (it's not even connected to the earth wire) but measures if there is a loss on the mains, so if the GFCI trips it means that mains current as leaked (to earth or to another part that is not on that same GFCI). \$\endgroup\$
    – Daniel P
    Feb 15, 2018 at 22:25
  • \$\begingroup\$ I find it interesting that you state it is some traces of main power on the HDMI as I never thought about that, it is really curious to me that it only happened with the laptop she brought with her. \$\endgroup\$ Feb 16, 2018 at 2:04

1 Answer 1

  1. A GFCI breaker will trip if there is an imbalance between the 'hot' lead current and the neutral return current. This means that somewhere in that path some current is leaking to ground.

  2. This can be to chassis ground in a grounded device. A refrigerator, a desktop power supply, etc. Cheap power supplies for LED's that use half-wave rectifiers can also trip a GFCI breaker.

  3. A two-wire AC plug does not have a ground, and by UL standards must be double insulated with a plastic or fiberglass case. If such a device causes a GFCI breaker to trip, it most likely has an internal short in its power supply.

  4. If a 3 prong plug is used it is a grounded device. A 3 prong desktop power supply often has the (-) negative common output grounded to Earth ground. If A GFCI breaker trips while using this setup, the power supply may not be the fault, but logic says it probably is.

  5. If it is a appliance with a 3 prong plug and it repeatedly trips a GFCI breaker, then most likely the appliance has a short-or partial short-to a metal chassis that is Earth grounded.

  6. That it why it is so important that 3 prong plug devices go into a grounded AC outlet, else a severe shock hazard is possible.

  7. There are arc-fault breakers designed to pick up tiny leakage currents before they become a fire or shock hazard. They are recommended for old houses and apartments where old aluminum wiring is present, and chaffing of poor quality insulation is possible.

  8. Also aluminum wire can be a fire hazard if overloaded such that it burns the insulation, but not enough current flows to trip a conventional breaker. An arc-fault breaker can detect this and shut off the power.

  9. Note that equipment that normally works ok can be an issue if it is a device that connects to other devices via a HDMI or USB cables, as now they share signal grounds, if not Earth grounds. If both plug into separate outlets there is a chance of Earth ground imbalance. Not an arc per se but a leakage path through the electronics, some of which have a resistor/capacitor connection to chassis/Earth ground.

  • \$\begingroup\$ I'm sorry, I understand how GFCI breakers work for the most part, which is why i was so confused why simply changing one laptop for another without connecting any power supply or anything else was causing them to trip - even worse with a time delay. Could you perhaps guide me to which of these points you feel would be possible causes here and why? I do not see all of these points as relevant to the question. \$\endgroup\$ Feb 16, 2018 at 2:03
  • \$\begingroup\$ Paragraphs 1, 3, 4, and 5 could contain the true answer, which is unknown without experimentation. There is no 'trick' to this other than tracking down that which always fails (trips the GFCI breaker). I added paragraph 9 for some clarity. \$\endgroup\$
    – user105652
    Feb 16, 2018 at 2:25
  • \$\begingroup\$ Paragraph 9 was something I had completely forgotten about, and since the laptop was not connected to a power supply perhaps there was a grounding issue between the two devices. Thanks for sharing your knowledge. \$\endgroup\$ Feb 16, 2018 at 12:00

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