is a PVGFC necessary?

Dapdan
Dapdan Solar Expert Posts: 330 ✭✭
Hey all,

I am about to clean up my installation with some midnite boxes and breakers and was wondering if a PVGFC was really necessary for an off-grid type installation. Anybody practical experiences would be gratefully accepted.

Cheers...
Damani

Comments

  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: is a PVGFC necessary?

    Well it is the law now. i will leave it at that as i would never advocate breaking the law.
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: is a PVGFC necessary?

    It is part of the US NEC. This may or may not applied to your location. If your array voltage is above 24 volts, then you may want to look into it. I have a 12 volt system, so I do not use a PVGFC. As 12 volts will not electrocute a person.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: is a PVGFC necessary?

    Throwing new fangled on systems by law/NEC regulations without an understanding their need--I don't agree with this.

    First question--what is the DC GFI supposed to protect against?

    An AC GFI is capable of detecting and shutting down a branch circuit with ~10-15 mAmps of leakage current (0.010 to 0.015 amperes). This is the amount of current that is "safe" around humans. Above that amount--applied in the correct locations of a human--it can stop the heart.

    Very good reason for AC GFI, very simple and reliable circuit, and only required where AC outlets are located near wet locations (sinks, tubs, outside, swiming pools, etc.)... Where hot to ground shorts are possible.

    AC GFI's are not required everywhere or on permanently wired equipment (that I am aware of). Can be a pain on those types of systems, because leakage currents in excess of 15 mAmps are very possible because of capacitive coupling--and the changes of injury/death to users is near zero.

    DC GFI's--Open a circuit when current exceeds 1 amp... OK--roughly 100x that needed to kill a person--so protecting against electrocution is not reliable.

    Protection against shorts and fires? Normally, the wiring is protected by appropriate fuses/breakers (i.e., 15 amp breaker on 14 awg wiring).

    If, there was a ground fault--not all faults are detected or protected against (ground fault to "-" lead--not protected, and, in fact, may bypass the GFI 1 amp detection circuit). Even if the GFI is activated--the GFI is still present (solar panels are still energizing the circuit up stream of the breaker)--so the majority of the circuit is still an electrocution hazard.

    I do not understand what DC GFI is supposed to protect against... Interestingly enough--if GFI protection circuit was not present on Grid Tied inverters--the system would be safer because the PV would be floating/isolated with respect to ground. You could grab either the + or - lead (not both) while standing in a puddle of water and not get shocked because there is no return path--whereas with a "DC GFI" protected system--you could end-up dead (note: DC off-grid systems are almost always ground referenced--so adding DC GFI does not affect the electrocution hazard there).

    In the end, as Halfcrazy said, you don't argue with the law unless you have a very good reason not to do it (and there are some good reasons not to)... However, if you have an inspector or insurance company requiring DC GFI--are you willing to document and argue (possibly with a lawyer) the issues--or just give in to get along. :confused:

    In the end, install the circuitry and understand that no additional safety is provided by the setup. You still need to treat all wiring with respect (as if it is energized) until you can prove otherwise.

    -Bill

    And as N3qik says--this is a US requirement... Your area's requirements are probably different (or don't even address the hardware in question).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: is a PVGFC necessary?

    BB

    The PVGFC is to sense a short to the panel frame, this will then trip the PVGF breaker indicating a problem with the array. This, I can see on a grid/off-grid array over 48 volts.
  • Dapdan
    Dapdan Solar Expert Posts: 330 ✭✭
    Re: is a PVGFC necessary?

    Hey all,

    First off, thanx to all you guys for your welcome input. I currently reside in Barbados and currently those codes dont apply to off grid type systems and we dont have an option in respect of grid tie (local elec comp is just talking about it, i dont see it happening for years to come). My system is currently a 24V system and i am looking at cleaning up my wiring and installing protective DC breakers and make it more maintenance friendly. My research into Midnite solar equip lead me to the recommendation for PVGFC and hence my question. I currently use C60 and C40 CC but looking to upgrade to the a new MPPT version (hopefully the classic) and hence run a higher PV voltage (35v to 70v) and step down accordingly at the CC.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: is a PVGFC necessary?

    as far as the nec is concerned, that isn't law even in the usa until your local government enacts it as such. i can say wiles confuses me somewhat on the issue as he makes references to roof mounted pvs and the grid and i'm not all that interested in wiles' opinions as law anyhow. i don't know your full circumstances so you be the judge on it and know that it as a safety device couldn't hurt. a bit of lightning protection couldn't hurt too.
  • Dapdan
    Dapdan Solar Expert Posts: 330 ✭✭
    Re: is a PVGFC necessary?

    hey niel,

    getting some arrestors and capacitors for lighting protection is part or my plan. I am preparing my naws shopping lists hopefully one of the guys there will give me a discount ;)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: is a PVGFC necessary?

    N3qik,

    Actually, I don't see how a short from the panel guts (say it is broken by a baseball) to frame ground will be protected by the average 1 GFC protection circuit... The only thing that will "protect" such a short is if there are series fuses/breakers in each panel string (only required/useful if more than 2 strings in parallel).

    As I understand (and I may be wrong) the DC GFC protection circuit is installed in after the combiner before the solar charge controller (or GT Inverter).

    A broken panel to frame short would not, necessarily, provide a current path through the 1 amp "GFC" sense circuit breaker. A panel break may involve both the local ground and local power leads shorting to the frame--bypassing the frame ground. And even then, the panels and the +/- wiring are still energized by the local cells and paralleled panels. So, you still have both a fire and shock hazard with the exposed circuits at the solar panels and with respect to their wiring to the DC GFI breaker.

    The only circuit that has been "opened" is the path from the PV array to the solar charge controller...

    A + connection to earth ground connection between the DC GFI breaker and the charge controller or a + to earth short on the battery bus side does not trip the DC GFI detect or de-energize the Battery Bus power from the + lead. And--the "DC Battery Bus" side is where a human involved short is most like to occur...

    Before I say much more--I have to find Jim/Crewzer's post on the the DC GFI connection plan. It has been roughly a year since I last looked at it--so I don't quite remember where the ground protection is made...

    Ah found it (inbetween the Wind-Sun site having problems--at least for me)--a discussion of the issues with DC GFI/GFP.

    Grounding and GFI/GFP

    I still don't like it or see a valid reason for DC GFI/GFP.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dapdan
    Dapdan Solar Expert Posts: 330 ✭✭
    Re: is a PVGFC necessary?

    bill,

    There doesnt seem to be a simple answer and reading all of the tech stuff from your ref. thread is also causing dizziness. I am really more unsure now and seem to be tending to leaving it out (in respect of cost considerations). would this be an il-advised decision?

    Cheers
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: is a PVGFC necessary?

    if memory serves me correctly i think it was supposed to be a 'just in case' between the dc and ac sides of things coming together. wires have been known to come down onto roofs and serves more as a what if protection device. if i'm wrong on this then somebody chime in and correct me.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: is a PVGFC necessary?

    I agree this GFI/GFP does cause disorientation.

    I personally do not see there is anything to gain in adding a DC GFI/GFP or where overall safety of the system will be improved by adding such a device.

    Normally, I am against adding complexity and components to a system--adds cost and can make the system more unreliable and harder to debug problems. Also, it can make it a pain to install and wire--especially if people are confused about the requirements and the wiring directions.

    I am not an expert in this field, and I have no special knowledge about the NEC thoughts behind the issue (other than in the links you have read).

    However, I am always willing to listen and learn.

    If somebody has good reasons for adding the DC GFP to your off-grid system--I am all ears.

    I am am just "some guy" behind a keyboard. So--it is important that you (or the local person installing your system) 100% understand the wiring requirements and why, or why not, you would choose to install a DC GFP.

    If it were my system--I would be studying the issue more myself just to be sure (I will take another look, but I don't have a lot of free time or access to the NEC to dig deeply into the issue)--I certainly am not an authority on proper practices...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dapdan
    Dapdan Solar Expert Posts: 330 ✭✭
    Re: is a PVGFC necessary?

    Thank you for all your assistance Bill. I will continue my research. I tend to like the simple approaches myself.

    Cheers...
    Damani
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: is a PVGFC necessary?

    It will tell you that you wired something wrong.

    boB :D
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: is a PVGFC necessary?

    2008 NEC Article 690.5 generally requires ground fault protection for grounded DC PV arrays.

    There are two exceptions:

    (1) Ground-mounted or pole-mounted PV arrays with not more than two parallel source circuits and with all DC source and DC output circuits isoltaed from buildings shall be permitted without GFP.

    (2) PV arrays installed on other than dwelling units shall be permitted without GFP where the equipment grounding conductors are sized in accordance with 690.45.

    Links to recent GFP article by John Wiles: http://www.nmsu.edu/~tdi/pdf-resources/CC123.pdf

    HTH,
    Jim / crewzer