electic redundancy with GFI

[salt lick]

I am planning the wiring for my tank. what I intend to do is have two heaters and two circulation pumps paired-up on different GFI outlets. if one circuit shorts and trips the GFI, the other will still provide circulation and heat till I return home... Do you tink this will work? Or will the short take out the other GFI's as well?

[salt lick]

the GFI's are independant, wired in parrallel not in series

[pacmans]

Hi Salt lick
I am not sure what you mean by parallel are you feeding both GFI's with the same hot wire (Black) L1 off the line side of the GFI?
pacmans

[IFLY2HIGH]

I wanted to do the same thing, but was confused and worried about one GFCI possibly tripping the other GFCI wired right next to it. You can wire a GFCI to GFCI. Mine had the regular input terminals to where you hook up the feed wire and then can hook up an aditional outlet. The GFCI has another set of screws that anything connected to them was covered by the GFCI.

I was worried that the GFCI wired after the FIRST GFCI would end up tripping them both out. So I decided to wire them in completely different boxes. I have a new circuit running to my fish tank (Double outlet box = 4 outlets). I use two heavy cords comming from the 2 wall sockets to the inside of my tank. Inside, I have 2 plastic electrical boxes. There both wired with a GFCI and a socket. The socket is not protected by the GFCI. I only wanted the GFCI for my return pump, heater, and my Lightwave 401. If there was a fault I didn't want the entire system to go down, but still wanted protection on certain devices.

HTHS

[badgers]

if wired in parrallel the two GFI's will be independant.

[pacmans]

Hello all
Don't mean to through a wrench into the plan but I have to say this.
If the fault were of significant sieze then both GFI's could turn off if both circuits were run off the same breaker in the main supply panel ,just thought I would throw that in there.
So parallel off a common circuit is not really the best way to go If you want a degree of isolation.

As for the GFCI (ground fault circuit interupter) these are designed for personal safety and should be checked according to the instructions because they fail to trip from time to time.


hope that helps
pacmans

[Frick-n-Frags]

I was going to throw in my 2 cents last night, but the "tripping both from a large 'line side' fault" thought keeps bugging me so I had to think about it some more.

The GFI trips when differential current appears across the monitored node. That is to say,"the current flow into one wire better equal the current flow out the other wire or it trips" If a parallel path on the equipment side is created for one of the supply lines BACK to the supply, the differential current increases and the GFI trips because some of the current is diverted (or shunted as we like to say) down this third path and things don't add up back at the GFI.

So OK, so you shatter your heater and you really load the supply. So for an instant we have a big voltage drop between L1 and L2. Now, what impact will the lower voltage across L1 and L2 have as it is momentarily applied across the monitored nodes of GFI # 2 who is peacefully running it's equipment. I say the equipment gets a brownout, but remember whoever-the-heck's law about current into a node MUST equal current out of a node, and if one were to consider all the equipment on the GFI#2 as the node, the same current out, must be the same current back and I don't see the GFI tripping. If I am to believe my own drivel, then I would say the multiple parallel GFI's will work OK.

Help me pacmans. Does this make sense? maybe I am missing something? Maybe if you faulted one circuit into the other GFI's secondary circuit you would (or probably should) trip both of them. This is a brain buster. Do you want some triple pass Berlin coffee to help you think better? I know it works for me :) I know, let's just start a "RIO's suck, Oh no they don't" fight and just sleaze out of this thread, heh heh.

[salt lick]

Several of you seem to think they will behave independently, even if current leaks thru the water. I'll buy that. So how many of you subscribe to the dual heater and pumps philosophy?

[salt lick]

Pacman has a point, if the short draws enough current (short to ground) then the breaker will trip. So I think I will pull two independant wires from two new breakers to feed the GFI's.

[pacmans]

Hello
A GFI measures the difference in potential between L1 to the neutral line of the circuit if a leakege of I believe
1 milli amp occures the GFI should trip but I would not stake my life on one as I have gotten a tingle from a GFI protected circuit before that is why the manufacturer recomends testing them.
but it is better than nothing and I will leave it at that.

When the GFI's are wired so that breaker # 1 say feeds one GFI and breaker # 2 feeds the second GFI then if a fault occures on one or the other GFI you should in theroy still have one circuit in operation.

Unless this potential fault is so big(sparkes shooting everywhere) that it blows the main breaker to the house:D

But seriously if you are worried about a problem with a fault then have someone local look at the layout and run a few tests it may be worth it considering your investment

I would be glad to but I am to far away:(

Hey Frick-n-frags I think I need a shot of that triple pass berlin java just to keep up:D

I think what your getting at is could the salt's continuity or ability to carry current trip the other GFI, all I can say is if it did then there would or should have been a leakedge there to begin with and should have tripped it anyway before it got to that point.

Hope this helps and makes some sense
pacmans

[badgers]

GFI does not measure the potential between L1 and the neutral. It really does not measure anything. There is a circular coil of wire around the hot and neutral leads. The ends of this coil are connected to the trip mechanism. When equal the magnetic fields in the two wires cancel each other. When unequal there is an alternating magnetic field which cuts through the wires of the coil. When an alternating magnetic field cuts through wires it creates a current. This current trips the device.
the coild size shape and windings are designed to activate the device at a current imbalance of 5ma + or - 1ma.
the test button is a resistor that should only trip the device when power is on.
There are some ballasts and other quirky electircal devices that use capacitors and or coils. These some times can trip GFIs because of a harmonic in tune with the resonant frequency of the cap or a coil creating a back emf. There is a quality difference in GFIs and some cheap GFIs trip when they should not.

[Frick-n-Frags]

I get it! Really, the point is keeping one pumpset going no matter what. What the GFI's do at this point doesn't really matter if the whole shebang is off. Me being lazy, I have extension-corded my way through the drop ceiling from all over to sneak a bunch of high powered light into the system without popping breakers. I would probably add the redundant pumpset right to that, done, can't hurt, if I had one.

Here's another wrench:
I wonder how many more times you lose your power than short out your equipment, and if you did have a short, what are the chances of the breaker tripping faster than the GFI?

Independent generator (dun dun DUNNNNN) That is your only answer. You must install a prohibitively expensive complex generator system that is triggered like a UPS. This is the only way to reach redundancy Nirvana. You must comply. We have the girl.
(dun dun DUNNNNNNNN DUUUUUUNNNNNNN)

[Frick-n-Frags]

Wow, parallel typing, what a hoot.

[Frick-n-Frags]

Mr. badgers, what kind of lighting designer are you? Could you help out with a bunch of HID ballast questions, like what are the main differences in the transformer component of a mercury vapor and a metal halide ballast without the capacitor-resistance whatever module. Could you refer me to some sources of real hard core HID and flourescent ballast theory (I want sooo bad to reverse engineer an Icecap. There is no $20 worth of components in one of those (sorry big bro)but I would rather just build my own.) I used to bug the crap out of the engineers here at Nela park trying to spec out a blue shifted MH 10 years ago, but no one would listen....

Just what does a 220v 250w mercury vapor ballast do for that bulb that plugging it straight into the wall (220 of course) doesn't do.

These are the things i want to know so we can break the backs of all these rip-off lighting mfrs.

[pacmans]

Originally posted by badgers
if wired in parrallel the two GFI's will be independant.

Hello
Well I debated replying to this but here goes

Salt lick
I think you got the message and my motto is Kiss and that seems to be universal no matter were you come from.
Grab another breaker if ya want additional isolation
nuf said.

Badgers
Measure may have been a bad choice of words but sensing
(if thats a better word to use) a current through a series of cutting magnetic fields sounds a little mystical for my taste and most people fear electricity on the whole so why complicate it.

The above mentioned quote is Ok to ya just missed the breaker for a degree of additional isolation of the 2 GFI's.

When you take appart a component in detail as you did it is great but most people are thinking measure, it's human nature.
When you come right down to it measuring or sensing a magnetic field and creating a current from an imbalance, the difference in potential between L1 and neutral still just gives you a
1 or a 0
ya might say it's logical.

Frick-n-Frags
I thought the gen set was a praticular good one
but why not put the ups with it:D


see ya
pacmans

[badgers]

pacmans, I am sorry, I did not mean to attack your choice of words. IME when using the word measure people imagine a little current meter and a little switch that goes off when the imaginary meter hits 5ma.

sorry if I offended you.