Drip loop aquarium setup and electrical safety: GFCI, RCD and stray voltage

Every cord running to your aquarium needs a drip loop, and every aquarium should be plugged into a GFCI (called an RCD outside North America). Those two cheap steps prevent most aquarium shocks and fires. If you have ever felt a tingle in the tank water, stop putting your hands in it until you have found the cause.

Serious shocks from aquariums are rare, but they do happen, and they can kill. You have a heater, filter and lights sitting in or over a large container of conductive water, often with cords running down behind furniture to a power bar on the floor. It's worth twenty minutes to set it up safely.

How to identify it

Signs that something is wrong:

A tingle, buzz or "pins and needles" when you touch the water, especially if you are also touching a metal stand, a tap or a damp floor.
Your GFCI or RCD keeps tripping (cutting the power). It is doing its job: something is leaking current.
A cracked heater tube, water inside a heater, or a pump with a split housing or damaged cord.
Water or white salt crust on cords, plugs or the power bar. Dried salt ("salt creep") conducts electricity and can cause sparks.
A burning smell, scorch marks, melted or discoloured plugs, or a warm power bar.
Fish acting oddly near one piece of equipment, twitching, or avoiding an area. (This is not reliable on its own, but worth noting.)

When it's a problem

Normal: no tingle, cords with drip loops, a safety outlet that you test monthly and that never trips on its own.
Fix this week: no drip loops, no GFCI/RCD, a power bar on the floor, salt creep on plugs, an old heater.
Act now: any tingle, a cracked heater, water in a plug or power bar, or a safety outlet that keeps tripping.
Emergency: someone has been shocked, there are sparks, smoke or a burning smell, or water is pouring onto outlets.

What to do right now

If you feel a tingle, or suspect a fault:

Take your hands out of the water and keep them out. Never test for current with your hand. The amount of current that can stop a heart is tiny (measured in thousandths of an amp), and whether it flows through you depends on your shoes, the floor and what else you are touching. A mild tingle today can be a dangerous shock tomorrow.
Turn the power off before you touch anything. With dry hands, unplug the equipment at the wall, standing on a dry floor. If the plugs or power bar are wet, don't touch them: switch off the circuit breaker (or fuse) for that area first.
If someone is being shocked and can't let go, don't touch them. Cut the power at the breaker, then call emergency services (911 in North America, 999 or 112 in the UK, 112 in the EU, 000 in Australia).
Sparks, smoke or fire: leave it and call the fire department. Never throw water on an electrical fire.
Anyone who received a real shock should be checked by a doctor, even if they feel fine. Shocks can upset the heart rhythm.
Find the faulty item. With everything unplugged, look for a cracked heater, a damaged cord, or water in a plug. Then plug items back in one at a time (into a GFCI/RCD-protected outlet). If the safety outlet trips when one item goes in, that item is faulty.
Throw out the faulty equipment. Don't tape or repair a heater, pump or cord. Aquarium equipment is sealed and can't be safely repaired at home.

Testing for stray voltage: experienced keepers measure stray voltage with a multimeter set to AC volts, one probe in the water and the other on a known ground, with the equipment running, and then unplug devices one at a time to see which one makes the reading drop. Only do this if you already know how to use a multimeter safely around mains power. If you don't, unplug everything, plug things back in one at a time through a GFCI/RCD, and call an electrician if you can't find the cause.

What to do next

Add drip loops to every cord. A drip loop is a U-shaped dip in the cord that hangs lower than the outlet. Water running down the cord drips off the bottom of the U instead of running into the socket. Clip the cord to the wall or stand if it won't stay in a loop.
Get every tank on a GFCI or RCD.
- GFCI (ground-fault circuit interrupter, sometimes "GFI") is the North American name. It compares the current going out with the current coming back. If they differ by about 5 milliamps, meaning current is leaking somewhere, such as through you, it cuts power in as little as 1/40 of a second.
- RCD (residual current device; called a "safety switch" in Australia, sometimes RCCB) is the name in the UK, Europe, Australia and most other places. It works the same way. The ones used to protect people usually trip at 30 milliamps or less.
- You can get one as a wall outlet, a breaker in your panel, a plug-in adaptor, or a power bar with one built in.
Press the TEST button monthly. GFCIs and RCDs can fail without warning. The power should cut off; press RESET to restore it. If it doesn't trip, replace it.
Get power bars off the floor. Mount them on the wall or the inside of the stand, above floor level, away from splashes and below the tank so the drip loops still work. Don't plug one power bar into another.
Clean salt creep and water off cords and plugs (unplugged first). Replace any power bar that is discoloured, cracked, melted or crusted.

Products that help

GFCI or RCD protection (outlet, breaker, plug-in adaptor or protected power bar): the most important safety device for any aquarium.
Cord clips or cable hooks: hold drip loops in place.
Wall-mounted power bar with individual switches: keeps sockets off the floor and lets you switch off one item at a time.
Heater guard: protects the glass tube from knocks and big fish.
Grounding probe: a metal probe in the water connected to ground, meant to trip the GFCI/RCD as soon as current leaks into the water instead of when you reach in. Keepers disagree about them; if you use one, plug it into a GFCI/RCD-protected outlet, and treat it as a backup, never a fix.
Multimeter: for experienced keepers to check stray voltage.
Keep on hand: a spare heater, a torch (flashlight), and a note of where your breaker panel is and which breaker feeds the fish room.

How to prevent it

Unplug before you reach in. Make it a habit: heater and filter off at the wall, then hands in. Plug back in with dry hands when you're done. (Wait for the heater to cool before lifting it out.)
Never let a heater or pump run dry. A dry heater can crack its glass. A pump that runs dry can damage its seals. Both can then leak current into the water.
Inspect equipment at every water change: look for cracks, water inside heaters, and damaged cords.
Replace heaters every few years.
Keep lights from falling in. Use the proper mounting and a lid.
Wear dry, rubber-soled shoes when working on the tank, especially on a concrete basement floor.
Don't overload circuits. A fish room with many heaters may need its own circuit.

Why it happened

Aquarium shocks usually come from submerged equipment that has cracked or whose seals have failed, most often a heater, so current leaks into the water. Nothing happens until something gives it a path to ground, and that something can be you. Water running down a cord into an outlet, salt creep, and power bars on the floor cause the rest. A GFCI/RCD can't stop the leak, but it cuts the power fast enough to make a shock much less likely to be deadly.

When to get help

Call an electrician if the safety outlet keeps tripping with no obvious faulty item, if you have no GFCI/RCD and want one wired in, if outlets are warm, scorched or buzzing, if the tank room is on an old circuit, or if you still feel a tingle with everything unplugged.
Call emergency services for anyone shocked who is unconscious, has chest pain or trouble breathing, or had current pass across their chest, and for any fire.
If a cracked heater has been in the tank, also watch the fish; see heater overheating and stress.

In the game

Multiple Tank Syndrome doesn't have an electrical safety card yet; the closest is the "City power failure" card.