Stray current and stray voltage (wiki)

[syncro]

Is this correct, clear and concise? Any other questions this should answer? This is what I've gleaned from reading this forum and others. Hopefully it will help the next person. Post here or feel free to edit directly at http://www.theaquariumwiki.com/Stray_current

Stray current refers to unintentional electricity flowing through the aquarium water. Malfunctioning and deteriorating equipment are the usual sources and can represent a danger to the aquarist and livestock. Stray current is closely related to stray voltage - a voltage potential between the aquarium water and ground.

== Stray current vs stray voltage ==
In typical household circuits, current is far more dangerous than voltage.

Stray voltage is an electrical potential difference between the water and earth ground. A voltage difference does not indicate any electricity is actually flowing through the water. It indicates the possibility of current to flow if a suitably low resistance path between the water and ground is introduced. So stray voltage on its own is not directly harmful. It is common to have some stray voltage as pumps can induce a voltage potential with their rotating magnets.

Stray current refers to flowing electricity. It is typically harmful to humans at and above 6mA [1]. A properly functioning tank should not exhibit any measurable stray current (< 1mA). Stray current may or may not trip a GFCI receptacle depending on the path it takes.

== Symptoms ==
* shock and/or tingling when touching the water, in particular on cuts
* shock and/or tingling when touching the water and a metal lighting fixture
* GFCI outlet tripping
* odd behaviour from fish or coral
* possible cause of Head and Lateral Line Erosion (HLLE) disease
* erroneous readings from pH probes

== Sources ==
* Damaged/malfunctioning equipment
This introduces stray voltage when an energized part or wire is exposed to the water. For example, a cracked housing on a pump/heater or a worn electrical cord with exposed wire. This is dangerous as the full current of the outlet may flow if the aquarist touches the water and a ground (like a grounded metal fixture).
* Pumps and powerheads
These use magnets to couple the drive shafts and the rotating magnets create a moving magnetic field with induces a voltage (and small current) in the water. A typical aqarium pump may generate up to 50v of stray voltage. This is harmless as the current generated is very small (< 1ma, below both human perception and the sensitivity of a common multimeter).
* Lighting
Some lighting can induce a stray voltage and current similar to pumps. Ensure the lighting reflectors are grounded.
* Static electricity
May be source of a small amount of stray voltage (several volts).

== Identifying ==
* Inspection
** Remove all equipment (perhaps as part of regular cleaning and maintenance)
** Inspect cords for worn, chewed or damaged sections
** Inspect where the cord enters the equipment. Is it secure and undamaged
** Look for cracked housings on pumps
** Look for water inside glass heaters

* Measuring
WARNING - This procedure deals with mains power and is potentially fatal. If in doubt, contact an electrician. Consider performing a visual inspection as decribed above instead.
** Ensure all equipment is connected to a GFCI outlet. While this is not required for to measure current it will significantly reduce the risk of harm and/or death if a mistake is made.
** Ensure you have a clear, dry area to work. Reduce the risk of accidentially touching anything in particular the water or ground.
** Turn on all electrical equipment in contact with the water
** Configure the multimeter to measure current (mA)
** Some multimeters have multiple probe sockets, ensure your probes are in the correct sockets for measuring current
** For older multimeters without auto-ranging: select the highest range
** Place black probe in the third (ground) prong of the GFCI outlet (or an attached three prong extension cord)
** Place red probe in the water
** For older multimeters, if the meter reads 0 select the next lowest range and repeat until the meter reads non-zero or you select the lowest range.
** If the multimeter reads 0ma, you are done, there is no stray current
** Disconnect equipment one by one (don't forget float switches)
** When the current reading drops, the last piece of equipment you disconnected is a source of stray current
** Immediately replace all equipment contributing to stray current

== Recommendations ==
An aquarium should have no detectable stray current. Eliminate all sources of stray current. Consider installing a ground probe (in conjunction with a GFCI outlet) to identify stray current sooner. Stray voltage can be safely ignored provided there is no stray current.