Hi –
I’m wiring a cabin with an off-grid PV 12 volt DC system, and I’m wondering if a standard GFI will work (in a location less than 6′ away from a sink.)
Thanks for your help
Edited 12/10/2007 2:08 pm ET by bva
Hi –
I’m wiring a cabin with an off-grid PV 12 volt DC system, and I’m wondering if a standard GFI will work (in a location less than 6′ away from a sink.)
Thanks for your help
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Replies
Welcome to Breaktime!
Filling out your profile is useful sometimes to place your questions in geographical context.
Now then, your question at hand:
Uhhhhhh.
>> off-grid PV 12 volt DC system <<
I don't know what that is - 12 vdc lighting and outlets? Never heard of a 12 v GFI, within 6' of a sink or not. 12vdc has no earth ground.
I suspect there are others here also with the same problem, but they are staying quiet.
I, on the other hand, am not afraid to show my ignorance.
Jim
What exactly are you looking protect with a GFI circuit. What devices are being powered?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
I don't know - I'm checking into it
Why? I don't know much about using 12V for infrastructure wiring, but it seems to me that the hazards that GFIs protect people from don't exist with 12V.
Scott.
Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”
I don't know, but it seems like 12v could kill someone - if an appliance fell (or was pushed) into a sink, or ---
<<I don't know, but it seems like 12v could kill someone - if an appliance fell (or was pushed) into a sink, or --->>I was working installing cab's in an off-grid house about 15 years ago and had to squeeze in through a bin cab I had built under a little DC fridge. some how I assumed that those 12 volt wires weren't very dangerous and accidentally crossed a wrench onto a couple of them. Sparks like fireworks right over my shoulder and no way to move more than six inches! Learned something that day. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
Nobody ever got electrocuted by a car battery. Lots of amps, but low voltage. (Tho' I wouldn't put my tongue on one!)
I can't imagine you'd need a GFI w/ a 12V system. Consider: No exterior 12V lighting systems have the low voltage side GFI protected. Campers don't have GFI protection on the low voltage circuits, tho' they do on the high voltage outlets.
Mike HennessyPittsburgh, PA
Edited 12/10/2007 8:09 pm ET by MikeHennessy
Thanks, Mike - makes sense.
but like they say, it's not the volts that gets you but the amps.
I was kind of wondering the same thing though. As I understand it anything under 30 something volts is low voltage and not really checked by BIs but am wondering if there's enough amps to warrant the GFCI.
"Currents of approximately 0.2 A are potentially fatal, because they can make the heart fibrillate, or beat in an uncontrolled manner.""In general, for limb-contact electrical shocks, accepted rules of thumb are: 1-5 mA is the level of perception; 10 mA is the level where pain is sensed; at 100 mA severe muscular contraction occurs, and at 100-300 mA electrocution occurs.""At currents as low as 60 to 100 milliamperes, low-voltage (110-220 volts), 60-hertz alternating current traveling through the chest for a split second can cause life-threatening irregular heart rhythms. About 300-500 milliamperes of direct current is needed to have the same effect."http://hypertextbook.com/facts/2000/JackHsu.shtml
yep, and we're talking 2 volts and your quote is ref.ing something about standard house voltage of 110-120v.
Like Mike said, nobody ever eleotrocuted by a car battery.
I saw someone on CSI get electrocuted by a car battery. There were big long blue snappy sparks like lightning flying all over.
and this was on TV?
Yeah, I was cracking up.
I found the script, no one died, it was a ruse for a robbery. Seriously, there were 12 foot long sparks.
Name of the show was Suckers.
http://www.crimelab.nl/transcripts.php?series=1&season=4&episode=13
So was it like the hoaky Flash Gordon (original) sparks or like a lightning bolt?
More like lightning bolts zipping along the wet walkway around the pool. With lots of buzzing noise. I was expecting some exotic power supply, or high voltage transformer, but it was just a car battery connected with jumper cables.
Too bad you can't get that kind of perfomance out of a battery when it's it's freezing rain, 1" of ice to scrape and you left the headlights on.
Oh, wait you can... on TV.
"I saw someone on CSI get electrocuted by a car battery. There were big long blue snappy sparks like lightning flying all over."
Actually, this is like something I have always wanted to do. My Lovely Assistant and I both love Halloween -- we tend to scare more kids away from the house than not sometimes. You know, scarry sounds, chainsaws, creepy lighting, costumes, etc.
My plan is to enclose the front of our porch with jail cell bars made out of EMT, and hook them into one pole of a car battery. Put a "High Voltage" sign on the bars. Hook the other battery pole up to wires in some gloves that will be part of some sort of Frankenstein's Monster costume. When the kids approach, I would proceed to drag my gloved hands over the bars, creating impressive, tho' harmless, sparks, convulse and shriek. At this point, kids start to rethink how much they want that candy. ;-)
Got the idea from something similar I found on the Net while looking for Halloween ideas. Ain't the Internet grand?
Mike HennessyPittsburgh, PA
OK, now I may be inspired to do my "Vlad the Impaler" front yard decoration... lots of small stuffed dummies in halloween costumes... impaled on 10' stakes... have to walk through a forrest of bodies to get to the door... BAHAHAHAHAHAHAHAHA!Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
HOORAY!!!!!
piking is making a come back...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
OK! Yet another great Halloween idea from your Breaktime friend, Vlad the Impaler!
Now I really am going to have to do that.
Mike HennessyPittsburgh, PA
There is a Wiki entry on GFCIs which lists types and includes types for pulsating DC, but I don't see any for straight direct current.
The entry is at: http://en.wikipedia.org/wiki/Residual-current_device
and includes the following (along with a lot more):
In the United States and Canada, a residual current device is also known as a ground fault circuit interrupter (GFCI), Ground Fault Interrupter (GFI) or an appliance leakage current interrupter (ALCI).
...
Standard IEC 60755 (General requirements for residual current operated protective devices) defines three types of RCD depending on the characteristics of the fault current.
* Type AC: RCD for which tripping is ensured for residual sinusoidal alternating currents.
* Type A: RCD for which tripping is ensured:
o for residual sinusoidal alternating currents,
o for residual pulsating direct currents,
o for residual pulsating direct currents superimposed by a smooth direct current of 0.006 A, with or without phase-angle control, independent of the polarity.
* Type B: RCD for which tripping is ensured:
o as for type A,
o for residual sinusoidal currents up to 1000 Hz,
o for residual sinusoidal currents superposed by a pure direct current,
o for pulsating direct currents superposed by apure direct current,
o for residual currents which may result from rectifying circuits, i.e.:
+ three pulse star connection or six pulse bridge connection,
+ two pulse bridge connection line-to-line with or without phase-angle monitoring, independently of the polarity.
--------------
There is a magazine called "Home Power" which specializes in off grid power. There might be some type of resource on their web site at:
http://www.homepower.com
Edited 12/10/2007 7:34 pm ET by CaseyR
Thanks - whew! that's a lot of information. I'll try the homepower website.
Lowest human body resistance at dc measured at 12 Vdc (14 V lead acid) is about 600 ohms, drops to 400 V at higher voltage, and this is with both hands immersed in a satruated salt solution.
I=e/R= 14/600 = 23 mA, below electrocution threshold.
There is a recorded (reported by Indemnity ins. corp of SF) electrocution at 18 Vac, 60 Hz, have never been able to find the specifics of that case.
Dry body hand to hand resistance is typically 50kohms, 5 kohms simply sweaty.
14/5000 = 2.8 mA
Commercial gfi trip at 4 to 6 mA, so one of those would not trip (even in a grounded 12 V system) unless you were pretty well immersed in salt water, thus would be a waste of $$.
Thanks -
It sounds like you did your homework and like I don't have to worry about it.
Thanks to all you responders, and have a happy (and safe) Halloween!
Yeah, dry skin is normally a pretty good insulator. However, if you break the skin or get contact with mucus membranes, that is a different matter. Eons ago when I was taking electrical engineering courses, we had a mandatory safety lecture designed to try and scare us safe. The lecturer claimed that because such a small amount of current directly across the heart could screw things up, you could get electrocuted by a dry cell if you swallowed it and it got lodged just so as to put the current through your heart. Seems unlikely, but maybe under totally improbable conditions, it could happen.
Standard GFI work on a 12V DC system? Nope. But I wouldn't think you'd need a GFI for a 12V system.
Now, if you have an inverter system providing 120V AC to outlets then you'd need to meet code re GFIs on outlets near a sink, and, so long as the inverter weren't too "noisy", standard GFIs would work.