Voltage NOT problem, CURRENT is!

This is Jean's "I have a migraine, so what else can go wrong anyway" little
sermon on electricity in our tanks, and how you get shocks.

The voltage of _anything_ used in your tank is more or less irrelevant.  THE
CURRENT is what shocks you and/or your fish. The current flow can be found
using Ohm's Law, E= I / R.  The fuse (if any) in your circuit limits the
amount of current that can flow.  A Ground Fault Interrupter (they use a
different term in UK) is an extremely fast acting switch that "sees" a flow
of current that is abnormal in that some current is going to the Ground
(Earth in UK) and not flowing to the Neutral wire.  It shuts things down
before you even perceive that you are getting a shock.

The water in our tanks is a VERY good conductor of electricity.  It has lots
and lots of Electrolytes in it.  Water in Sea Water Tanks is an even BETTER
conductor of electricity. 

Folks sell nice neat electrodes that are supposed to conduct any stray
voltage directly to ground.  Nice idea, but it is pretty much useless.
 Voltage does not just roam around your tank, shocking things at random.
 Voltage is the electrical equivalent of pressure.  Current is the electrical
equivalent of the amount of water flowing. High voltage (pressure) with low
resistance gives high current.  High voltage with high resistance gives low
current flow.  How much current can you get? Depends upon resistance and
voltage.  If you are barefoot, standing on a wet concrete floor, and reach
into a salt water tank that has a direct short to the mains, you will
probably die. You have made a very low resistance path for electricity,
through your body.  _Your blood makes a really good low-resistance path for
current._ (Which is, by the way, why you always feel a shock much more
severely if you have a cut on the finger that is in the water - lots more
current flows through the blood in the cut.) 

HOW MUCH CURRENT is dangerous? Well, 5 milliamperes can be felt, 10 hurts, 15
REALLY HURTS, 30 will freeze you on to the current source.  "Freeze on" means
that the amount of current flowing through your muscles is great enough to
take  control of the muscles away from your nerves.  Take my word for it, you
do NOT want to be frozen on.   Not a pleasant situation.   Painful, usually
fatal.  Reason? You can't get loose, you start to sweat at the point of
contact (hand, foot, etc.) and your electrical resistance goes down, more
current flows, resistance drops more, eventually either your heart is stopped
or your breathing is stopped, and you are gone. Or, you are lucky as heck and
(a) someone sees what is happening, and they throw a flying drop kick to you
and knock you loose from the circuit, or (b) your weight pulls you free, or
(c) someone flips the switch and disconnects you from the current. 

How to test for stray voltages:  Grip one prong of one of those little neon
circuit testers in your hand, touch the other prong to the cover glass, then
to the water itself.  The light will glow brightly at a current flow too
small for you to feel it.  A really bad voltage leak will usually light the
neon bulb just by touching the cover glass.  (Bet you didn't know that there
is almost always a very thin film of water on that cover, connecting with the
water in the tank?)

If you get a light, first disconnect the heater, then try again.  If no
light, your heater is the problem. If still lights, try turning the tank
lights off. Same results, same conclusion.  If it still lights, keep
unplugging things until it no longer lights. By simple trial and error you
will find out what the problem is.  Heaters often leak, power heads often
leak, lights usually leak.  (Lights are especially bad when they first turn
on in the morning.  There is often a thin film of water covering all surfaces
of the light, a film that quickly evaporates from the heat of the light.)

Now, why do I not believe in those neat little expensive grounding
electrodes?  Well, they just provide a path from the current to the ground.
 If the leakage is from the other end of the tank, everything in the tank
between the electrode and the leakage source is getting shocked.  Tell me,
what did you gain?  Remember, the voltage is a pressure thing, and it is not
just an evil being, wandering around the tank aimlessly, looking for things
to shock!!  The flow of electricity, the current, will always take the lowest
resistance path to the ground, or to the neutral wire.  Frankly, I think
grounding electrodes are a lot like those water softening magnets.

If you have a ground fault interrupter in your tank circuit, and you put one
of those little electrodes in your tank, guess what happens when you get a
leak?  That's right, the GFI goes off,  and so does all of the electrical
supply to your tank.  Everything on the GFI circuit goes off, and that may
include your pump, air pump, CO2 solenoid, heaters, lights, etc.   Yep, it
worked, but what did you gain? Yes, you did NOT get electrocuted.  _Good

Before someone really gets annoyed with me, you can be quite effectively
electrocuted by the batteries in a 12-volt flashlight. Yes, I did say 12
volts. Palm to palm shock, two cut fingers, get yourself shorted to the
batteries, they will produce sufficient current to shock the heart and stop
it.  With a 12-volt car battery, it is easier, because it can produce a
higher current (lower resistance inside the battery than the batteries in a
flashlight.) THIS HAS HAPPENED.

Anyway, I am no more afraid of a 220 volt shock in a tank than a 12 or 24 or
whatever volt shock. In fact, I am more worried about the 24 volt heating
cable! We tend to think, "Only 24 volts, big deal."   It depends on how you
are hooked up to it!  It also depends quite a bit on whether the 24 volt
current source is completely isolated from the 120-240 volt main line.

More useless information.  See that bare copper wire tacked to the pole
holding the big transformer that supplies electricity to your house?  The
wire that disappears underground at the base of the power pole?  That gadget
is a ground for a "Faraday Shield," which is a copper screen in that transform
er that is between the 7,200 volt (common voltage, could easily be different)
power line and your house.  Seems those copper windings in the transformer
act like a capacitor, which makes a capacitative coupling that, without the
Faraday Shield, would couple that 7,200 volts to your house wiring.  Yes, it
CAN happen that the Faraday Shield ground cable somehow gets disconnected.
 Things can get really _lively_ around the home!  Everything zaps you!
 Normally just really annoying, perhaps scary, sometimes quite painful.  Not
enough current  to kill you, but sufficient voltage to completely break down
the natural resistance of dry skin. 

Anyway, if you think you are being zapped by your tank, get a neon tester and
see.  I have seen folks convinced that they were getting zapped, when there
was no voltage at all on anything  they touched.  They were imagining it. 

Hope this long, tangled rant proves helpful!