Any issues with adding fuses to my DC Negative inside the combiner box?

HX_Guy · January 2015

It was discovered that since my inverter is transformerless, both the DC+ and the DC- need to have fuses. The combiner box I purchased only has the DC+ fused, but the DC- is going straight to the PV- bus bar.

The simplest solution I can see if adding fuse holders on the DC- wires. There are 4 fuse holders already in the box and I only need 3 of them on the DC+ side, so I would need to add 2 more, which I believe there is space for on the DIN rail.

Are there any potential issues you guys see which this plan?

westbranch · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Where di you find that little bit of info (fused Neg.)?

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

westbranch wrote: »

Where di you find that little bit of info (fused Neg.)?

It was pointed out to me on another solar forum. The information is actually in the SolarEdge inverter installation manual and also on my permit.

From SolarEdge:

Note: In rare cases where three or more strings of power optimizers are wired in parallel, fusing will be required to protect the wiring between the power optimizers and the inverter. Because the circuit conductors are not grounded, fuses would be required in both the negative and positive conductors. The recommend fuse size of 20 Amps is calculated using the 15 Amp continuous output current limit of the power optimizer multiplied by 1.25 in accordance with NEC Articles 210.19 and 240.4.

From my building permit:

Additionally, this article here talks about the NEC code requirements: http://ecmweb.com/nec/wiring-methods-pv-systems-and-nec

In a transformerless inverter, neither the positive nor negative conductor has a bond to ground. The result is that you no longer have a grounded current-carrying conductor. This requires both conductors in each circuit to be protected with OCPDs and have disconnecting means as required in Art. 690, Part III.

westbranch · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Oh, right! Solar Edge with each panel having its own (optimizing?) inverter... forgot you had those

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

westbranch wrote: »

Oh, right! Solar Edge with each panel having its own (optimizing?) inverter... forgot you had those

It's not just for SolarEdge, the SMA Sunny Boy TL inverters and some ABB (Power One) are also transformerless and would require the same thing.

BB. · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Interesting. Learn something new every day.

-Bill

Ethan Brush · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

How code compliant does this have to be? You have an issue using white conductors as ungrounded conductors and they cant be re identified unless in a cable assembly. Regarding the original question, note the 2008 NEC didnt specifically say that a fuse was needed in each ungrounded conductor in an ungrounded system, in case you are still on '08

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Ethan Brush wrote: »

How code compliant does this have to be? You have an issue using white conductors as ungrounded conductors and they cant be re identified unless in a cable assembly. Regarding the original question, note the 2008 NEC didnt specifically say that a fuse was needed in each ungrounded conductor in an ungrounded system, in case you are still on '08

Havn't had the inspection yet and honestly I don't know how it's going to go. My installer for some reason thinks my inverter is "grounded"...when I told him yesterday via text that the white wire needs to be changed to black, he said to not touch anything as the the system is grounded and white is the correct color. I'm wondering if the inspection will even know which way it's supposed to be (traditionally it seems the transformer based, grounded inverters were the norm and that is what they are used to to seeing, including the white wire).

As for changing the white wire to black, I was thinking something like this...what do you think? It's black heat shrink wrap that would mask the white cable completely inside the disconnect.

Ethan Brush · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

HX_Guy wrote: »

Havn't had the inspection yet and honestly I don't know how it's going to go. My installer for some reason thinks my inverter is "grounded"...when I told him yesterday via text that the white wire needs to be changed to black, he said to not touch anything as the the system is grounded and white is the correct color. I'm wondering if the inspection will even know which way it's supposed to be (traditionally it seems the transformer based, grounded inverters were the norm and that is what they are used to to seeing, including the white wire).

As for changing the white wire to black, I was thinking something like this...what do you think? It's black heat shrink wrap that would mask the white cable completely inside the disconnect.

Your installer doesnt seem up to speed on his PV or electrical theory. If you have a transformerless inverter, the array must be ungrounded because there is no isolation between the dc side and the AC side (which is almost always a grounded system). Thus if you ground one of the array conductors, you have a direct short between an AC "hot" conductor and the grounded PV conductor. I would have to check the wording in article 200, but Im pretty sure the coloring coding would need to be a "continuous outer finish" and you cant just re identify at accessible points.

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Ethan Brush wrote: »

Your installer doesnt seem up to speed on his PV or electrical theory. If you have a transformerless inverter, the array must be ungrounded because there is no isolation between the dc side and the AC side (which is almost always a grounded system). Thus if you ground one of the array conductors, you have a direct short between an AC "hot" conductor and the grounded PV conductor. I would have to check the wording in article 200, but Im pretty sure the coloring coding would need to be a "continuous outer finish" and you cant just re identify at accessible points.

This is the installer's first use of a SolarEdge system and probably his first use of a transformerless inverter, he normally uses Fronius inverters which are traditional, transformer based, grounded systems.

That would really suck for him if the inspector says the whole cable needs to be replaced, it's a 50' run through flexible metal conduit...through the wall and through the attic.
My plan was to heat shrink wrap it before the inspector came out...that shrink wrap goes from 10mm to 5mm and the 6AWG cable is 6mm, so it would be a very tight fit, may not even be able to tell that it's not the original finish.

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

By the way, I don't think it's going to be an issue with the white cable in the combiner box, since it's on the roof, and the inspector here doesn't go on the roof..all inspections are done from ground level.

The problem though is going to be inside the disconnect box at the inverter, if they open that up.

Vic · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Hi HX,

You sure have been through a lot on this project.

I am not a real Code Jock ... so guess that the Combiner shown in the OP is a six position box? Even if it is, a real Bus Bar may be required for mechanical support of the breakers. And having a Positive bus and a Negative bus closely spaced may well not pass ... ALL of this is up to the Inspector, as you know.

There might be an issue with the entry of the ground cables that enter the Combiner, as that bushing does not look rain-tite to me ... not even sure about the bare stranded ground cable ...

Sometimes the Listing of these boxes are very specific as to configuration ... But again it is all up to the inspector.
EDIT: Just was your last post ... well then all of this may well be moot, although some adherence to NEC will be in your favor ...
Good Luck, Vic

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Thanks Vic, it sure has been pretty challenging...learned a lot though!

The inspector here doesn't go up on the roof, so I'm not worried about the combiner box not passing inspection.

The DIN rail will fit 6 fuse holders, I went up on the roof and checked, so they would have mechanical support. I was also told that it wouldn't be a problem with having the negative and positive bus bars that close to each other and it's pretty common to do that actually, but I still think I would feel better with having wires from down from each negative fuse holder to the negative bus bar already installed there.

For the bushing, are you talking about on the left side of the box where the black PV wire and the bare ground cable enter into the box (the gray bushing)? You're right, it's not very water tight at all, the cables move in and out pretty easily. Not sure what the best solution would be, maybe some silicon sealant on the outside to seal it up? Would that work?

gww1 · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

I would never aurgue with people that on this subject I know are much smarter then me so take what I say as from the uninformed. I ran all white wire and color coded the ends where they connect. I have and never will be inspected but believe that I did it based on reading that it would be ok. I can't remember if it was in the outback insalation manual or if it was when I was looking at nec codes. I may have it wrong but something makes me believe it was ok. I don't feel like searching everything I looked at before to find what made me believe this and it is not impossible that I dreamed it. It would suck to be inspected and find this is a problim.
Good luck
gww

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

This is so ridiculous...should I really be fighting my installer to follow code? The inspection has been scheduled for tomorrow and I just sent him a text...

"Are you sure you don’t want to change the white wire to black? it’s definitely supposed to be any other color but white since it’s considered a “hot” wire, the DC Negative is not grounded because this is a transformerless inverter"

No reply back yet.

I actually just looked at the 3-line diagram on the permit and even that says, can't believe I missed it until now.

DC:
POSITIVE = RED
NEGATIVE = BLACK
GROUND = GREEN

Ethan Brush · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Let us know how the inspection goes.........

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Ethan Brush wrote: »

Let us know how the inspection goes.........

Will do. It was supposed to be today but got rescheduled for tomorrow.

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Made the change to the combiner box, worked out nicely and looks quite professional.

New parts...

Cut off the last leg as only 3 fuses are needed.

Old combiner box setup with unfiused DC-

Took out the old fuses off the DIN rail

Put in new 20A fuses

westbranch · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

so what happened to wire #4 in the old setup?

BB. · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

One caution... These touch safe fuse holders (at least some of them, don't know this one specifically) should not be popped open when under load (do not use them for a disconnect when under load/power).

They can sustain an arc.

http://solectria.com//site/assets/files/1481/solectria_fuse_servicing_for_disconnects_for_dc_combiners_white_paper.pdf

If a fuse is in need of replacement while the PV array is still connected to the combiner, that fuse will remain live and presents an electrical shock risk and arc flash hazard. It is imperative that the fuse be completely de-energized from all sources before attempting to replace the fuse.
...
For string combiner boxes, satisfying the new requirement NEC 690.16(B) is simple. The “touch safe” fuse holders enable the safe removal of the fuse from all energy sources. However, these fuse holders are not load break rated and are explicitly labeled “Do not open under load.” Opening a fuse holder under load presents a dangerous arc flash hazard. Solectria Renewables’ DISCOM disconnecting string combiner has an integrated DC disconnect. To service the fuse simply turn off the DC disconnect on the front of the string combiner and, after the absence of current is verified with a DC clamp meter, open the fuse holder and remove the fuse. The combination of a DC disconnect and “touch safe” fuse holders in DISCOM disconnecting string combiners provide a convenient method for quickly maintaining the fuses within the combiner box and meeting NEC 690.16(B).

-Bill

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

westbranch wrote: »

so what happened to wire #4 in the old setup?

Oops, forgot to post the rest of the pictures.

Ready to re-install in combiner box

And finished product

Before and after

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

BB. wrote: »

One caution... These touch safe fuse holders (at least some of them, don't know this one specifically) should not be popped open when under load (do not use them for a disconnect when under load/power).

They can sustain an arc.

http://solectria.com//site/assets/files/1481/solectria_fuse_servicing_for_disconnects_for_dc_combiners_white_paper.pdf

-Bill

Yeah I've read about not doing that. Luckily with this SolarEdge system, when you shut off the inverter or switch off the DC disconnect at the inverter, the power from the panels drops down to 1V x panels per string. So the 16 panel string is 16V, the 11 panel string is 11V etc. I was able to comfortably work up there with the wires while the sun was hitting them. (I did verify with the voltmeter that it was in fact low voltage, didn't just assume that if the inverter was off it was safe).

westbranch · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Darn, just in the last 2 days I saw the remnants of a fuse open under load, all that is left is the blackened plastic... BAD! It was inside a MN box of some sort. just cant locate it...

OK I see red wire #4 is your #1 on the left side of the box and it is taped off in the lower left corner ???

HX_Guy · January 2015

Re: Any issues with adding fuses to my DC Negative inside the combiner box?

Yeah, it's just taped off to look cleaner, but the #1 is now not connected to anything (it's corresponding white negative wire was too short to reach the fuses so I didn't use the #1 connectors, only #2, #3, and #4. #2 negative is also too short but the negative for that one is the wire coming through the conduit.

Any issues with adding fuses to my DC Negative inside the combiner box?

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