How to add an external gfdi

[BB.]

Yea, we cannot host large files--generally just a page or two. Anyway, posting a copyrighted text here would not be a good idea anyway.

I will send you a PM.

-Bill

[davidwillis]

David the first time I clicked your message I got the warning I got the warning it was unsafe, After I posted again it seemed ok so I deleted that post. When you get the Exeltech inverter in operation hope you can give some feedback on it and let us know how well it works. I was a little interested in one but most of the solar dealers don,t seem to be selling it yet. solarvic

It looks like it should do a good job if I can figure out the GFDi. I got what I think is a good price for it ($850 including shipping).

[Chuck46]

This is what he is talking about http://www.outbackpower.com/docman/1...pter_REV_A.pdf Hope this helps

Chuck

OOps the llink doesnt work but its on outbacks site

[Cariboocoot]

Link works fine for me.

There's a big difference between the <150 Volt arrays typically used with battery-based systems as the >300 Volt arrays often found on straight GT inverters. I haven't seen a GFDI for the high Voltage arrays. MidNite has one good for up to 300 Volt but not beyond that. Their breakers fit nicely in their boxes, btw.

Like Bill, I don't agree with this NEC regulation. Not that my opinion matters one whit.

[BB.]

David sent me the first ~19 pages of the manual--and the following is contained within:

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 GFDIdevice as required by Article
690 of the National Electrical Code for the installation location.


The XLGT Grid Interactive Inverter is a transformerless inverter, and as such, it is required to
be used in an Ungrounded Array Photovoltaic Power System as referenced by Article
690.35 of the 2008 National Electric Code. Article 690.35 does not require a GFDI device, it
does specify an updated list of requirements, and the XLGT Grid Interactive Inverter contains
all the necessary components to meet this new NEC2008 requirement.

Residual Current Detection (RCD)

The XLGT Grid Interactive Inverter employs a Residual Current Detection System used to
detect AC and DC residual ground current, and immediately disconnect from the utility
source. The RCD System is designed to comply with IEC62109-2 the International Standard
for Safety of power converters for use in photovoltaic power systems.

RCD technology addresses the specific needs of transformerless ungrounded systems, in
which an array grounding failure point could result in an AC ground current flow, a DC ground
current flow, or a combination of the two, which is the more likely case. RCD technology is
designed as a fire hazard protection system only, and is not intended to be used as a GFDI
device in any form.

RCD General operation

On initial power up the array is tested to ensure that Ground Impedance Is greater than
1kOhm/volt, or a minimum of 500kOhms, the XLGT will NOT engage the utility connection
breaker if this minimum value is not met. This test is indicated by the two green blinking
lights, if successful, the unit will then click the relay closed, and then check the Utility
conditions to attempt a grid connection. If this test is not passed, a red flashing light will
indicate a failure to meet the minimum ground impedance, and service by a qualified service
personnel may be required to fix this situation.

Upon successful start up, grid connection, and power generation, if a failure of array ground
isolation, resulting in ground fault current either AC current or DC current is detected, the
RCD will open the Utility relay and cause the system to cease power export. The RCD fault
is indicated by an alternating green and red flash. Only qualified service personnel should
clear any ground fault condition that exists. Only pressing the Reset button will clear the
RCD Detection, and allow the XLGT to resume grid interaction operation.

And later on:

WARNING! Connecting either leg of the PV Array will cause the XLGTto
become inoperative.

Electric Shock Hazard. The direct current circuit conductors of this
photovoltaic power system are ungrounded, but maybe energized with
respect to ground due to leakage paths and/or ground faults.

...

PV Array wiring
Because of the transformerless design of this inverter, neither leg of the PV is connected to
the ground terminal.

So, the DC GFI (as linked above) is not needed and if [DC GFI] used as directed, [the DC GFI] will cause the GT Inverter to shutdown.

The GT Inverter includes an RCD circuit--Which should meet the requirements of NEC 690 (alternative designs are allowed).

It appears that your local AHJ (authority having jurisdiction) must be following NEC 2008 or later (not all places do--You may have to do a bit of tap dancing to get them to allow a transformerless design GTI).

The first warning is from UL1749--Which does put the DC GFI into their requirements (and I think is a very dangerous requirement). The RCD does do the function of stopping current flow (turning off the inverter) if there is a Ground Fault in the DC Array Wiring.

At least, that is my reading of the documentation and requirements.

-Bill

[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

[davidwillis]

I thought I would post the response from Exeltech.

Hello David,

The warning statement you referenced is required in our manual for the inverter to meet UL1741 compliance. If you'll continue to the paragraph immediately following that warning statement, we indicate that our XLGT is designed to operate in with an un-grounded PV array, and further references Article 690.35 wherein our inverter does not require a GFDI to be code-compliant.

This is an example where the UL1741 Safety Standard (latest revision was released in 2005) is out of step with the National Electric Code. In this case, the NEC exemption prevails.

I've attached the latest copy of the XLGT Installation Manual from our website. It was just updated today. (Changes didn't impact anything you mentioned.)


Dan

I hope that is good enough for the inspector

[BB.]

Good luck David...

That is pretty much what I believe the "proper" answer to be too. Now it is up to the inspector (and if he/she was already keyed in on the DC GFI requirement--It may take some time to get a change in their thought processes).

-Bill

[Cariboocoot]

This is an example where the UL1741 Safety Standard (latest revision was released in 2005) is out of step with the National Electric Code.

Why am I not surprised?

Thanks for getting to the bottom of this. Let us know how "compliant" the AHJ is.