HDMI triggering the Ground Fault Circuit Interrupters via Projector

Question

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.

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.