Ungrounded Inverter

[Zee]

Anybody with experience installing an ungrounded inverter in the USA? I have a home-owner with an existing array from 2004 that needs a new inverter. I would like the POWER ONE PVI-3.0 (aka Aurora). It utilizes some sort of "sophisticated detection circuit" to identify a ground fault, and then shut down operation . It does require an ungrounded array however. My understanding is that PV Wire is a must and that is not a possibility (existing array). I also believe all conduit needs grounding bushings (not sure???) Is this realistic given code req.s?

 

[jaggedben]

Anybody with experience installing an ungrounded inverter in the USA? I have a home-owner with an existing array from 2004 that needs a new inverter. I would like the POWER ONE PVI-3.0 (aka Aurora). It utilizes some sort of "sophisticated detection circuit" to identify a ground fault, and then shut down operation.

Typically this type of circuit uses ammeters to compare the current on the positive and negative and interrupts operation if they do not match.

My understanding is that PV Wire is a must and that is not a possibility (existing array).

Because the panel leads are not PV wire? Or because replacing non-PV-wire home runs on the array is not something you want to do?

I also believe all conduit needs grounding bushings (not sure???)

Grounding bushings are a must for anything that is over 250V or serves as a DC GEC. So they are must for grounded systems as well.

Is this realistic given code req.s?

I'd say it depends on the PV wire question.

Also you don't mention whether there is a combiner. If so that would have to be re-configured.

 

[ron]

Although ungrounded arrays are okay in the NEC, I've never seen a UL listed inverter that accepts ungrounded arrays.

The install schematic for the one you mention shows grounded arrays

http://www.power-one.com/sites/power-one.com/files/pvi-3.0_3.6_4.2-outd_us.pdf

 

[Zee]

Thanks Jaggedben,

Good points as usual.
Interesting about the ammeters interrupting the circuit.
Yes, Both the solar panel leads and the homeruns are USE-2 and i do not want to replace - nor can I!
Yes, gr. bushings are required always and there is no similar extra req. for ungrounded systems.

It turns out disconnecting all conductors pos and neg is the 2nd major req for ungrounded systems. Probably why you mentioned the CB probably needing reconfiguration.

I look forward to building one of these ungrounded systems.

This won't be it. I will be using the POWER ONE inverter after all, but a GFDI protected one (isolated), hence a grounded system will be used.
DUAL MPPT's. Very cool. I can add 7 very different panels to existing old array! I don't have to break the chain of old panels to insert my new panels. I can leave that dirty old system on one MPPT and add mine to the next. So when that one fails.... mine will still be operational!

BTW - I have been using PV Wire on ALL systems, so it won't be hard to switch to ungr. systems. I see no reason to not use the safest conductor insulation when working with 600 VDC. It is a matter of a couple bucks on a resid. system.

 

[Zee]

Ron, thanks, I haven't seen one IN PERSON yet either.
Yeah I finally determined that they do have grounded inverters.

I thought you may be interested to know that I do see at least 2 UNGROUNDED inv.s (!) in suppliers catalogs:
1. SMA 8000 9000 10000 TL (transformerless aka ungrounded)
2. Power One has small resid. sized inv.s (3 KW and other sizes.)

And yes, they are UL listed. Which is nice....

 

[Zee]

Followup.
So I installed a Power One Aurora PVI-3.8-I -OUTD-US-NG inverter.
(Negative ground)
It has failed after 10 days.

 

[ggunn]

Anybody with experience installing an ungrounded inverter in the USA? I have a home-owner with an existing array from 2004 that needs a new inverter. I would like the POWER ONE PVI-3.0 (aka Aurora). It utilizes some sort of "sophisticated detection circuit" to identify a ground fault, and then shut down operation . It does require an ungrounded array however. My understanding is that PV Wire is a must and that is not a possibility (existing array). I also believe all conduit needs grounding bushings (not sure???) Is this realistic given code req.s?

Although the negative DC conductor in an ungrounded array is not grounded, all non energized metal parts (racking, conduit, etc.) still need to be grounded via an equipment grounding conductor.

 

[ggunn]

Although ungrounded arrays are okay in the NEC, I've never seen a UL listed inverter that accepts ungrounded arrays.

What about SMA's transformerless inverters?

 

[Zee]

Although the negative DC conductor in an ungrounded array is not grounded, all non energized metal parts (racking, conduit, etc.) still need to be grounded via an equipment grounding conductor.

Thanks GGUNN.
I most definitely always bond equipment and run EGC as usual.