Stray Voltage

[narwal]

Re: Re: Most of you are wrong.

Re: Re: Most of you are wrong.

I didn't mean to distort your post, but that single sentence:
"Grounding probe is NOT a MUST, GFCI is not either, but a GFCI has the potential of saving your life, not sure I'd have the same confidence in a grounding probe."

Is wrong regardless of the context. Both ARE a must no matter what.

You mention thing with "cord outside" but that is irrelevant. Anything which plugs in and is in the tank OR sump can be a problem.

"So if there is no electrical cord or piece of electrical equipment physically touching the water, why would either a grounding probe or a GFCI be necessary?"

Yes, I totally agree, but it is highly unlikely that anyone will have a setup that requires no AC power. Don't forget that water is a good conductor, and that anything in the sump will also have a path of water to the main tank.

" If you could run your system as I've highlighted above, but without a heater, that would be the situation and there would in fact be little requirement for grounding probes and GFCIs.

True. But who would have a system like that? And again - it doesn't address the issue of equipment in the sump.

I can't understand why you seem so dead set against GFI's and ground probes. They are not expensive, do no harm, and have the potential to prevent accidents. Compared to the cost of our investments in our tanks they are very cheap insurance and a huge safety feature.

 

[stugray]

This topic has been covered extensively on this thread:

http://www.reefcentral.com/forums/showthread.php?s=&threadid=1549593

Oh and Narwal:


I agree with almost everything you have said, but be careful....

"The flow of current is ALWAYS along the route of least resistance"

That is not true and is a common misconception about electricity.

Electricity follows ALL PATHS to ground, NOT just the path of least resistance.
It just so happens that MOST of the electricity flows along the path of least resistance.

Stu

 

[narwal]

OK

OK

Yes Stu, you are correct.

But we are talking about reefkeeping and safety - and too much information can be confusing.

Besides, this isn't an electrical theory forum so I stayed away from related topics like virtual grounds, zero point reference, phantom grounds and ground loops.

 

[Rickyrooz1]

I added the ground probe today, all the readings on the voltmeter (AC and DC) were 0.00!

 

[tmz]

<a href=showthread.php?s=&postid=15115750#post15115750 target=_blank>Originally posted</a> by Rickyrooz1
I added the ground probe today, all the readings on the voltmeter (AC and DC) were 0.00!

Don't let that mislead you. When you install a ground probe all the volotage runs to ground so it should be zero. It changes to amps /current. So unless you measure those with an amp meter you really haven't found out if there is current in the tank.

 

[tmz]

Hello again narwal.

I can't understand why you seem so dead set against GFI's and ground probes. They are not expensive, do no harm, and have the potential to prevent accidents. Compared to the cost of our investments in our tanks they are very cheap insurance and a huge safety feature. posted by narwal in response to Mike1134

I don't know why some others are set against them. First , gfci is key. After that I am personably reluctant about ground probes in two potential scenarios:

Heater malfunctions which do not always trip a gfci.

Faulty grounds and shorts in light fixtures due to salt creep or faulty wiring which can throw a lot of current through you on it's way to a grounded tank if you happen to brush against the fixture while your hand is in the water.

I'm also not to sure about the effect of current/amperage vs voltage (particularly the ubiquitous induced voltage)on marine organisms.

BTW earlier on you indicated that isolating equipment on separate gfcis is not a good strategy. Why?

Thanks

 

[gabbagabbawill]

<a href=showthread.php?s=&postid=15115956#post15115956 target=_blank>Originally posted</a> by tmz
When you install a ground probe all the volotage runs to ground so it should be zero. It changes to amps /current. So unless you measure those with an amp meter you really haven't found out if there is current in the tank.

why do you say this? Do you know what you are talking about? ohm's law states I=V/R, rather Current=Voltage/resistance... if your Voltage=0, then using this equation, how could you have any measurable current?

For an ammeter to be installed correctly, it would need to have the probes set to measure AMPS and go BETWEEN the ground probe and ground.

If you are to find ANY voltage or current on a true ground, then something is not connected correctly.

This is not to say that you may be able to measure voltage or current on two separate ground planes, which would be possible, but you should not be dealing with this in any normal setup.

NARWAL is pretty much correct in everything he says. Still, I prefer to use a ground probe + GFCI.

There will always be induced current or voltage with any submersed motor/ pump. This is unavoidable without a ground probe. I like to think that the aquarium inhabitants are much happier when this induced voltage equals zero by implementing a ground probe.

Still, you should always check your equipment and replace if and when you encounter a failure that could pose an electrical hazard.

 

[Mike31154]

I'm not dead set against GFCIs. As mentioned in my second post I use two of them on my system. I was merely attempting to present that the statement MUST is a little absolute. There are always choices and alternatives. And there are no guarantees even with these items. You need to be aware of safety when working around electricity and water, no argument there. If you measure excessive stray voltage in your system, it's best to determine the culprit and work to remedy the situation. Safety devices will keep you relatively safe in the meantime.

The OP measured 1.8 and subsequently 0.8 volts in his system after doing some maintenance on his return pump. Neither of those voltage levels are particularly dangerous, much too low of a potential to produce a current capable of harming a healthy human being.

 

[MeReefBeef]

Where is this stray voltage you guys speak of coming from?

 

[gabbagabbawill]

Stray Voltage by definition is the occurrence of voltage between two objects that should not have any voltage difference between them. In this case, the two objects we speak of are the Aquarium Water and Earth Ground.

I have done some thinking about this and I believe that I have rationalized the reasons to have a ground probe;

First, I believe that we are essentially creating a ground plane or system ground with the aquarium water itself.

If you go with the assumption that all electrical devices with an AC mains are relative to an earth ground, then the ground plane in the aquarium is actually a floating ground UNLESS it is electrically connected to the Earth Ground.

With a floating ground, it is possible to have a ground potential or voltage difference with reference to Earth Ground.

Because water IS a conductor, it is subject to electromagnetic induction that is caused by the changing magnetic fields created by the pumps, heaters, lighting and other electrical devices that are in close proximity to the water. This is one place where the voltage difference between the aquarium's ground plane and the Earth Ground comes from (the other source of stray voltage is a failed device, heater, pump, etc).

In order rid ourselves of this induced voltage, we must ground the aquarium water to Earth ground, completing and connecting the circuit that we have created (the entire aquarium system is, in effect, an electrical circuit).

If you combine this with a GFCI and/or circuit breaker, then it will be possible to detect and immediately remedy a fault within this circuit by removing the mains voltage, thus greatly lowering the risk of electrocution or fire.


Some definitions, most of which below, I have copied from Wikipedia for reference:

Earth Ground - In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth.

Ground Plane - In electrical engineering, a ground plane is an electrically conductive surface.

Floating Ground - A system ground that is not actually connected to Earth ground.

System Ground - The ground plane within a circuit that may or may not be connected to an earth ground.

Ground Potential - The difference in Voltage between the System Ground and Earth Ground.

Electromagnetic induction - The production of voltage across a conductor situated in a changing magnetic field or a conductor moving through a stationary magnetic field.