How to add an external gfdi

[davidwillis]

Hi, I am setting up an 1800w grid tie system. The inverter I purchased says I need to install an external gfdi (to meet ul codes), but gives no instructions on how to do that. My solar array consists of 8 panels run in series. I have searched for a gfdi, but I can't find one rated to 300v. Also, I am not sure on how it is supposed to be wired. I need to do this as inexpensively as possible, but will need to pass an inspection.

Thanks
David

p.s.

Here is my inverter: http://www.exeltech.com/xlgtproducts.htm

And my panel specs:

Maximum Power (Pmax)*: 224 Watt
Tolerance of Pmax: +10%/-5%
Type of Cell: Polycrystalline silicon
Cell Configuration: 60 in series
Open Circuit Voltage (Voc): 36.6 Volts
Maximum Power Voltage (Vpm): 28.9 Volts
Short Circuit Current (Isc): 8.33 Amps
Maximum Power Current (Ipm): 7.58 Amps

[BB.]

Just to be clear, what is a GFDI?

If you are looking for a DC Ground Fault Interrupter, the inverter you pointed at is a "non-isolated" Grid Tied inverter... I did not find any details/installation instructions with a quick look at the website.... But a DC GFI may not be appropriate for that guy.

-Bill

[davidwillis]

Just to be clear, what is a GFDI?

If you are looking for a DC Ground Fault Interrupter, the inverter you pointed at is a "non-isolated" Grid Tied inverter... I did not find any details/installation instructions with a quick look at the website.... But a DC GFI may not be appropriate for that guy.

-Bill

Ground fault detect & Interrupter is what I thought it meant. All I know is in the instruction manual it said something like this device must be used with an external GFDI device required by ..... some code. I can get the exact wording when I get home. But if I can pass the inspection without it, that would be even better.

[davidwillis]

I have no idea about the virus. It is just a link to the manufacturer of my inverter.

As for the exact wording in my instructions, here it is:

"Warning Compliance to UL1741 Requires the following statement:
this unit is not provided with a GFDI device. This inverter or charge controller must be used with an external GFDI device as required by article 690 of the National Electrical Code for the installation location."

[BB.]

I would still like to see the manual for the Exeltech GT inverter (website seems fine to me--no problems).

But, you can purchase external DC GFI setups:

Midnite Solar 63 amp 150VDC DC Ground Fault Protector
		63 amp 150 Volt DC ground fault protector (GFI - UL listed breaker assy). The 2011 NEC requires a ... on the roof of a dwelling. Now even if you Solarize your doghouse, a ground fault protector is required in order to pass inspection.

The above is around $50... There are others (including enclosures) available too from NAWS (our host).

Ground Fault Protection Circuit Breakers

And if you look around on their website, you will find Outback has DC GF breakers for sale too.

Again, I don't know anything about non-isolated GT Inverters--I would be a bit surprised if the DC GFI does [remove "not"] work correctly with these types of units (vs fully isolated GT Inverters with internal transformers). Not saying non-isolated GT inverters are unsafe--just I wounder if DC GFI's will work with them.

-Bill

PS: I believe these are dangerous to use... But until or unless NEC drops the requirements--You are pretty much required to use them.

[davidwillis]

Well that is interesting. I spoke with my electrical inspector a while ago (before I got the inverter), and he said every thing needs to be UL listed, and have a GFDI. However he my not know about the transformer less inverter.

Now I am even more confused as to how to install this, and get it to pass the inspection.

One other thing, this will be installed on a shed about 150 feet from my house. Since it is not in a building with people living in it, would that make it exempt from needing a gfdi?

[BB.]

The DC GFI is to reduce the chance of fire (it is not the same as the GFI outlets/breakers that you see on 120/240 VAC household branch circuits).

The DC GFI (as far as I know) was an attempt to reduce the chance of "arc faults"... For DC circuits, arc faults are more of a fire hazard than AC--DC arcs will sustain very nicely at lower voltages and currents than AC arcs (DC arc welders are very nice). In reality--the DC GFI (as linked above) just put a 1 amp fuse/breaker between DC return and Earth/Safety Ground. If there is a DC Hot to earth fault, it pops the 1 amp fuse (or some devices will stop operation). I wrote a long paper on why DC GFI's are very unsafe and of limited use as Arc Fault "interrupters".... But it will probably not be useful with the inspector unless they are really into electrical wiring and safety/design issues.

Installing this in an outbuilding would not really matter--unless you can argue that an arc fault would not be a fire hazard (don't think the inspector will buy that).

the 208 NEC was re-written to allow tranformerless inverters that use alternatives to detect DC wiring faults. And the RCD used appears to meet those requirements. Now you have to convince the inspector.

The is sort of the problem with keeping different specifications/codes in sync with each other. I don't know enough about the UL GTI Inverter specs. enough to argue their requirements (I do not have a current version of that code).

But--If your device is UL/TUV/NRTL LISTED, and your building department uses NEC 2008 or later--Or you can bring a copy of NEC 2008 and show them that transformerless GTI inverters are allowed, and alternates to the DC GFI is also allowed (which is probably even in the older code-- J Wiles always argued that NEC does not force engineers to do things in an unsafe manner--So, it the DC GFI listed was just a "suggestion" and should not be used if the engineers believed it to be unsafe)--Then I would makes a copy of the applicable NEC codes and say that this is where your GTI unit falls into.

If they push you to use the DC GFI--It will only work if the 1 amp breaker is left unconnected (i.e., not connected from PV- to earth ground through the breaker).

So as I see it:

1. Convince the AHJ (copy of NEC + GTI Installation Manual) to install without DC GFI (check with Exeltech and see if they have any documents you can give to the AHJ).
2. Install DC GFI and then disconnect ground breaker wire after inspection (note, it may be very difficult or possibly impossible to find a DC Breaker rated for >150 VDC--If inspector looks, they should fail install)
3. Save your money/time and find another project

-Bill

[westbranch]

phone the inspector and have it condemned or dangerous??

[davidwillis]

I finally got my new net metering meter, so I turned on the inverter. It seemed to be working just fine, but then it stops for just a second (the LED goes orange, then back to green... sometimes it goes red then orange then green, sometimes it is really fast, and others I actually hear a relay turn off, then back on in a few seconds). I also noticed (by using an ac amp meter) that there is current going through my grounding wire (about0.10 to 0.15A). So I pulled out the ground wire and measured 61 VAC on between the ground lug, and the ground wire. I don't know what to do. I emailed the company with no response. It is very frustrating though, because it just gets up and running, then shuts off. By connecting an amp meter on the hot wire, I can see that it takes a while to get up to power, and then just as it does, it shuts off.

Any advise?

Thanks

p.s. the manual says red means low voltage on the solar panels (which I can monitor, and it stays over 200 at all times, usually about 225-235 with open voltage at 285). The orange Led is when a utility has resumed valid condition after an abnormal condition.

[davidwillis]

Although it does say the inverter employs a Residual current detection system used to detect ac and dc residual ground current, and immediatly disconnects from the utility. And it complies with IEC62109-2, but it is for fire hasard protection only and is not intended to be used as a GFDI device.