Ungrounded PV systems

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c_picard

Senior Member
Location
USA
So I'm about to install my first ungrounded PV system, and I have a pretty basic question. Are there any specific labelling requirements on the DC side? I'm running under the assumption that each conductor has some potential to earth ground, therefore is "hot". I certainly won't be marking anything white or grey, I know, but is a simple (+) and (-) sufficient to satisfy NEC PV source circuit labelling requirements?

Oh, and I'm just talking about terminations, not the labelling of DC cables or conduits.
 

iwire

Moderator
Staff member
Location
Massachusetts
As far as the why .......... why not?


This is from the 2008 NEC, be sure to check the 2011 as you are a MA guy.

690.35 Ungrounded Photovoltaic Power Systems. Photovoltaic
power systems shall be permitted to operate with
ungrounded photovoltaic source and output circuits where
the system complies with 690.35(A) through (G).

(A) Disconnects. All photovoltaic source and output circuit
conductors shall have disconnects complying with 690,
Part III.

(B) Overcurrent Protection. All photovoltaic source and
output circuit conductors shall have overcurrent protection
complying with 690.9.

(C) Ground-Fault Protection. All photovoltaic source and
output circuits shall be provided with a ground-fault protection
device or system that complies with (1) through (3):

(1) Detects a ground fault.

(2) Indicates that a ground fault has occurred

(3) Automatically disconnects all conductors or causes the
inverter or charge controller connected to the faulted
circuit to automatically cease supplying power to output
circuits.

(D) The photovoltaic source conductors shall consist of the
following:

(1) Nonmetallic jacketed multiconductor cables

(2) Conductors installed in raceways, or

(3) Conductors listed and identified as Photovoltaic (PV)
Wire installed as exposed, single conductors.

(E) The photovoltaic power system direct-current circuits
shall be permitted to be used with ungrounded battery systems
complying with 690.71(G).

(F) The photovoltaic power source shall be labeled with the
following warning at each junction box, combiner box, disconnect
disconnect,
and device where energized, ungrounded circuits
may be exposed during service:

WARNING
ELECTRIC SHOCK HAZARD.
THE DC CONDUCTORS OF THIS
PHOTOVOLTAIC SYSTEM ARE UNGROUNDED
AND MAY BE ENERGIZED.

(G) The inverters or charge controllers used in systems
with ungrounded photovoltaic source and output circuits
shall be listed for the purpose.
 

ron

Senior Member
I know the code allows ungrounded systems, but I haven't been able to find a listed inverter (in the US) that is ungrounded.

I'm responding to an RFP now that asked for ungrounded PV, but I have to tell them they can't have it, because the AHJ will not allow non-UL listed stuff in his jurisdiction.
 

c_picard

Senior Member
Location
USA
Here's a link to a Solar Edge letter of compliance...

http://www.solaredge.com/files/pdfs/products/inverters/csa-etl-compliance-solaredge-products.pdf

It's an ETL listing, but still valid.

This is a small residential job, here's an article about the potential benefits of the Solar Edge system.http://www.solaredge.com/files/pdfs/solarpro-john-berdner-interview.pdf

As stated, this is a first for me, but seems interesting...I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Here's a link to a Solar Edge letter of compliance...
I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!

I gather you are using Solar Edge optimizers. I don't know much about these things, but I'm a little unclear as to what it is about using these that requires an ungrounded system.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
As stated, this is a first for me, but seems interesting...I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!

If the NEC would allow 1,000 VDC strings, you'd see longer. I've worked on a number of projects where there were a dozen or more panels in a string, and the only reason there were that few is the 600 volt limit.
 

c_picard

Senior Member
Location
USA
Yeah, I haven't seen documentation just yet, and I'm not sure why the main inverter is set up ungrounded.
I gather the whole grounding thing is pretty unique to the U.S. Solar Edge is Israeli I think.

...a little background; I'm not used to seeing strings of more than 12 likely because it get's so damned cold up here in New England! That and because most of the inverters I've used were limited in their input voltages, for example PV Powered's limit is well below 600Vdc. This job coming up maxes out at 550Vdc, cutting it mighty close.

I'll post any info I come across, so long as it's not "Confidential and Proprietary"
 

c_picard

Senior Member
Location
USA
690.47(B), 250.169

690.47(B), 250.169

Evidently this is the first SolarEdge inverter installed in the US, so I don't feel so bad about not knowing the specifics on ungrounded systems.

We got some questionable intel from tech support today when we asked about a GEC requirement....we were told one wasn't needed. We installed one anyhow, and I just looked over 690.47(B), seems like we made the right call.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Ah, sounds like you're running some pretty high voltage panels. Most of the work I'm involved with is battery-backed, so the charge controller interfaces to the array and most charge controllers are limited to 150 VDC. Which means a 45 volt panels is a bit much.

Kaneka makes a very sweet 1 meter square amorphous panel with a Voc of 67 volts that I'd love to use, but can't because 1 is too low and 2 is close to too high.

And for anyone who cares, MidNite Solar now makes a higher voltage charge controller, as does Xantrex / Square-D.
 

c_picard

Senior Member
Location
USA
The powerboxes have a safety feature that limits their output to 1Vdc for each module connected when the inverter is offline. You need a Solaredge inverter which is "paired" to the set of powerboxes on initial startup. Also each powerbox communicates via the inverter to give the real-time monitoring of output.
 

c_picard

Senior Member
Location
USA
Optimizers communicate via DC circuit, sort of like ethernet over power I gather...I've seen this used with other monitoring systems, but on the AC side.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I don't think that is correct. They use it (grounded array) for DC ground fault detection.
No, they don't. They use a pair of ammeters on the DC+ and DC- and compare them. If there is a difference, there is a ground fault and an alarm/shutdown results.

I went to an SMA session on the TL inverters. IIRC, the array must be ungrounded because in a TL design, the AC neutral is not isolated from the DC side and if the DC- were grounded it would connect the neutral to ground.
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Just to clear this up for anyone who's confused, most SMA inverters in this country have transformers and use a grounded conductor for GFDI.

The transformerless models are a newer product; personally I haven't seen one yet. They have an ungrounded array and do GDFI as described by ggunn. Other mfrs also are introducing transformerless models.

The array still needs an EGC, so most details of installation are not different, aside from wire color.
 
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