I posted this a few years back. Maybe it'll help:
ZZAAPPed Again!! (Shocked by Tank)
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If you've been in this hobby for a while, chances are you've been shocked by something connected to your tank(s). Especially anyone who has any kind of salts in their tank water. Wet electrical equipment and/or equipment with salt buildup (salt-creep) give optimal chances of someone receiving a shock. A lot of people use surge protectors on their tanks. While these surge protectors will protect your equipment from surges in your service lines, they won't necessarily protect anyone from being shocked. To achieve personal protection from mild to fatal shocks, there is the GFCI. These protective devices used to be out-of-range price-wise for most hobbyists. Now, they're very affordable and can be easily found in most hardware and department stores.
Here's an excerpt from doityourself.com which explains the function and types of GFCI protective devices:
The GFCI
A "GFCI" is a ground fault circuit interrupter. A ground fault circuit interrupter is an inexpensive electrical device that, if installed in household branch circuits, could prevent over two-thirds of the approximately 300 electrocutions still occurring each year in and around the home. Installation of the device could also prevent thousands of burn and electric shock injuries each year.
The GFCI is designed to protect people from severe or fatal electric shocks Because a GFCI detects ground faults, it can also prevent some electrical fires and reduce the severity of others by interrupting the flow of electric current.
The Problem
Have you ever experienced an electric shock? If you did, the shock probably happened because your hand or some other part of your body contacted a source of electrical current and your body provided a path for the electrical current to go to the ground, so that you received a shock.
An unintentional electric path between a source of current and a grounded surface is referred to as a "ground-fault." Ground faults ground-fault. Ground faults occur when current is leaking somewhere, in effect, electricity is escaping to the ground. How it leaks is very important. If your body provides a path to the ground for this leakage, you could be injured, burned, severely shocked, or electrocuted.
Some examples of accidents that underscore this hazard include the following:
* Two children, ages five and six, were electrocuted in Texas when a plugged-in hair dryer fell into the tub in which they were bathing.
* A three-year-old Kansas girl was electrocuted when she touched a faulty countertop
These two electrocutions occurred because the electrical current escaping from the appliance traveled through the victim to ground (in these cases, the grounded plumbing fixtures). Had a GFCI been installed, these deaths would probably have been prevented because a GFCI would have sensed the current flowing to ground and would have switched off the power before the electrocution occurred.
How the GFCI Works
In the home's wiring system, the GFCI constantly monitors electricity flowing in a circuit, to sense any loss of current. If the current flowing through the circuit differs by a small amount from that returning, the GFCI quickly switches off power to that circuit. The GFCI interrupts power faster than a blink of an eye to prevent a lethal dose of electricity. You may receive a painful shock, but you should not be electrocuted or receive a serious shock injury.
Here's how it may work in your house.. Suppose a bare wire inside an appliance touches the metal case. The case is then charged with electricity. If you touch the appliance with one hand while the other hand is touching a grounded metal object, like a water faucet, you will receive a shock. If the appliance is plugged into an outlet protected by a GFCI, the power will be shut off before a fatal shock would occur.
Availability of GFCIs
Three common types of ground fault circuit interrupters are available for home use:
* Receptacle Type: This type of GFCI is used in place of the standard duplex receptacle found throughout the house It fits into the standard outlet box and protects you against "ground faults' whenever an electrical product is plugged into the outlet Most receptacle-type GFCls can be installed so that they also protect other electrical outlets further "down stream" in the branch circuit.
* Circuit Breaker Type: In homes equipped with circuit breakers rather than fuses, a circuit breaker GFCI may be installed in a panel box to give protection to selected circuits The circuit breaker GFCI serves a dual purpose - not only will it shut off electricity in the event of a "ground-fault," but it will also trip when a short circuit or an overload occurs Protection covers the wiring and each outlet, lighting fixture, heater, etc. served by the branch circuit protected by the GFCI in the panel box.
* Portable Type: Where permanent GFCls are not practical, portable GFCls may be used One type contains the GFCI circuitry in a plastic enclosure with plug blades in the back and receptacle slots in the f rant. It can be plugged into a receptacle, then, the electrical product is plugged into the GFCI. Another type of portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCls.
