How would you explain it to someone with no knowledge of electrical outlets and the risks? Is the risk higher for a saltwater tank than something like a computer in a non-GFCI plug? Thanks!
Depending on several factors it takes roughly 50mA to cause your heart to lose syntonization. The chambers start working against each other and little to no blood gets pumped. This is called fibrillation
To put into 50mA perspective, a typical cellphone charger charges at a rate of 1,000-2,000mA but at 5V there is not enough electrical pressure to reach your heart. 110V is plenty of electrical potential to reach your heart.
There are 3 types of conductors in a modern home:
A) The ungrounded current carrying conductor (hot wire)
B) The grounded current carrying conductor (neutral wire)
C) The equipment grounding conductor (EGC or “ground”)
Your residential convenience circuits are typically 15 or 20 amp 15,000-20,000mA but require about twice that to trip the breaker instantaneously.
So what a GFCI (Ground Fault circuit interrupter) does is measure the current on both the current carrying conductors at the recepticle. If you remember from HS electronics, the current is the same at all point in a series circuit but not in a parallel circuit.
When the GFCI senses a difference of as little as 5mA for as little as 200 ms it disconnects both the hot and the neutral.
Why is this important? Because in order for there to be the amperage differential, something has to be energized that shouldn’t be.
This next statement is a gross simplification but true. The 50-100mA that it takes to kill you wiill NEVER trip the 15A circuit breaker.
In our hobby, the point of the GFCI is to kill your fish tank before your fish tank kills you.
Have a 2nd GFCI circuit just for your return pump or circulation pump, have a battery backup for a circulation pump, there are several strategies to protect your tank from a ground fault.
As for your 2nd question, the only reason the salt water tank is more dangerous than a computer is that your computer is generally painted or plastic and has some level of insulation which will reduce or eliminate the electrical potential (pressure or voltage) and salt water is an excellent conductor of electricity. Also, you are very rarely standing sitting or kneeling on a wet surface when working on a computer but in areas like bathrooms, kitchens, fish tanks and to a lesser extend garages and yards, working on wet surfaces is quite common.
You asked for the time and I told you how to build a clock. That’s the best I could do. Sorry.