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

[bcroe]

The transformerless inverter basically uses the PV array to pump up an AC output voltage in the + direction relative to the neutral, with the - of the array temporarily referenced to ground internally and then uses that same panel with the + now referenced to ground instead to pump up a negative voltage to drive the AC line negative with respect to neutral. (For an inverter with only a 240V AC output it is a little more complicated than that, but the principle is the same.

if the installer actually bonds the negative to the ground at any point in his wiring, then the inverter will not work, and will actually blow a fuse or trip an internal breaker to indicate the fault.
If the installer does not bond the negative to ground (or to either the AC EGC or AC neutral) then during the operation of the inverter the + and - leads will both change voltage with respect to ground, although of course the difference between them will stay constant at the panel Vmp voltage.
To deliver AC out a transformerless inverter which has a buck regulator design must get a DC voltage from the panel which is greater than the peak to peak AC output voltage (for a 240V output). For 240V AC that comes to about 350V DC.

I hear what you are saying. To operate in the "transformerless" mode the voltage of the
entire array would have to shift from + ground reference to - ground reference and back
each line cycle. This would appear as a square wave of hundreds of volts magnitude on the
array wiring, making a HORRENDOUS radio interference generator & antenna. Some of the
AC output current would be flowing in the array. I don't know what happened when panels
first became available, but I don't believe such a design has been produced for a long time.

These days high frequency ferrite cores are able to provide isolation without the use of
a huge 60 HZ iron core. The array voltage reference to ground is fixed; EMI filters may
be applied as needed to the input & output. I'm going to suggest, a "transformerless"
inverter is one where the input & output circuits are NOT isolated; current may flow between
them. Same as small radios of the 50s & 60s.

That brings us to today; PV inverters operate with one input lead at ground potential.
Was the rule, if one conductor is not bonded to ground in the inverter, the array disconnect
must break both leads? Fronius does not bond an input to ground; they place a 1A fuse
between an input lead and ground. A ground fault will blow that fuse and the voltage be
detected by the inverter. By this theory these inverters must disconnect both leads, which
probably is never done (except here). And probably not bonded on any other inverter with
GFI function.

I'm now suggesting the above is incorrect. The rule is, or should be stated, that any
inverter with non isolated input-output (current can flow between them) require both
array leads to disconnect. Isolated inverters with one input REFERENCED to ground
(but not necessarily BONDED) require only the other lead be disconnected. Failing
that, I suspect most private installations are not compliant. Bruce Roe

[sensij]

Bruce,

You might to read this to get a better understanding of how modern transformerless (AKA, non-isolated, aka ungrounded) inverters work. Yes, it is required that any disconnect and OCPD on the DC side is on both the DC+ and DC- in those circuits.

HX_Guy,
If the bare ground wire to the electrode hasn't been attached yet, and you don't care to wait for the installer to bond it, you could just get rid of it. It would only have been required if you had an inverter with a transformer. The green equipment ground conductor should connected all the way to the ground bus in your main service panel, and is sufficient grounding for your system. The green wire is the only ground called out by your permit, #10 THWN-2. You can verify that it is connected properly by checking the resistance between the AC neutral (white) and the ground bus in the inverter (with the power off, of course). It should be a very low number.

Edit:
@#$%, I just looked at the next page of your permit and see that the GEC is called out. It really isn't required for a SolarEdge inverter as long as the grounds are connected to your panel ground, but since it is on your permit, I understand why you might want to keep it.

[HX_Guy]

If the bare ground wire to the electrode hasn't been attached yet, and you don't care to wait for the installer to bond it, you could just get rid of it. It would only have been required if you had an inverter with a transformer. The green equipment ground conductor should connected all the way to the ground bus in your main service panel, and is sufficient grounding for your system. The green wire is the only ground called out by your permit, #10 THWN-2. You can verify that it is connected properly by checking the resistance between the AC neutral (white) and the ground bus in the inverter (with the power off, of course). It should be a very low number.

Sensij, the 3-line diagram in the permit does in fact show that the inverter needs to have a bare ground wire running to the electrode so for inspection purposes, it's probably good to leave it.

EDIT: Haha looks like you're edit beat my reply.

[HX_Guy]

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

[foo1bar]

Amy, your first method was correct, the 200A panel is going to be derated to 175A since the solar is using a 60A breaker.
A separate permit was required for this, which we got, but again the installer said that is something that APS (our power company) need to come out and do because the power from the street to the main service panel needs to be shut off to do it.

Your POCO wil replace the main service panel breaker?

That's rather nice of them.

I thought my POCO was pretty nice. But I think they'd just shut off the breaker, pull the meter, and come back in 2 hours to put the meter back after your electrician was done replacing the breaker.
(BTW - If it were me, I would make sure it's torque'd per manufacturer's specs.)

[bcroe]

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"

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

There is a stack of 10 different colors of electrical tape here to solve such problems. A
lot of wires are "taped" the end foot (back into the conduit) to the color needed. Works
for humans, and the electrons don't care. Beyond that are wire labels. Bruce Roe

[HX_Guy]

There is a stack of 10 different colors of electrical tape here to solve such problems. A
lot of wires are "taped" the end foot (back into the conduit) to the color needed. Works
for humans, and the electrons don't care. Beyond that are wire labels. Bruce Roe

If the inspector is ok with that, I'm good with it! Heck I'm good with how it's now, doesn't really matter to me...I can tape it off myself just for future safety, I just want it to pass inspection tomorrow.

[SunEagle]

There is a stack of 10 different colors of electrical tape here to solve such problems. A
lot of wires are "taped" the end foot (back into the conduit) to the color needed. Works
for humans, and the electrons don't care. Beyond that are wire labels. Bruce Roe

I agree with you Bruce. Worse case is that the inspector ask for the white wires to be taped at both ends with black tape.

The same thing is done all the time with a black insulated wire being colored coded (Black, Red, Blue for 120/208V systems or Brown, Orange, Yellow for 277/480V systems. In both cases the 4th wire has white tape on it and is designated the Neutral wire.

[sensij]

I agree with you Bruce. Worse case is that the inspector ask for the white wires to be taped at both ends with black tape.

The same thing is done all the time with a black insulated wire being colored coded (Black, Red, Blue for 120/208V systems or Brown, Orange, Yellow for 277/480V systems. In both cases the 4th wire has white tape on it and is designated the Neutral wire.

No, it is not code compliant. There are specific conditions allowed in code for a white wire to be remarked. See 2011 NEC 200.7. Code is not written to help electrons get from point A to point B. It is written for people. My suggestion to re-mark in this case is not to create a compliant installation, but an attempt to make the non-compliance less obvious to the AHJ.

[SunEagle]

No, it is not code compliant. There are specific conditions allowed in code for a white wire to be remarked. See 2011 NEC 200.7. Code is not written to help electrons get from point A to point B. It is written for people. My suggestion to re-mark in this case is not to create a compliant installation, but an attempt to make the non-compliance less obvious to the AHJ.

I am not sure if NEC 200.7 (C) can be used for this situation or not. It can sometimes get a little fuzzy when you see one thing and then read about it in the code as not being acceptable.

Attached is a combiner box used in a solar pv array. The DC wires coming from the panels are white and yellow insulated and the wires going to the inverter are black insulated with white and yellow tape. It (along with 11 others) passed inspection.

PV Combiner panel.jpg

[HX_Guy]

Hey guys, real quick on a different note, what do you recommend for making the left side conduit bushing water tight? My installer just used what looked like a anti-short bushing and today we got some rain, and sure enough, I checked the combiner box and there was water inside (I shut off the system this morning before it started to rain as a pre-caution).

Could I just put some silicon caulking on the outside of the bushing to seal it tight? Would that be ok?

[SunEagle]

Hey guys, real quick on a different note, what do you recommend for making the left side conduit bushing water tight? My installer just used what looked like a anti-short bushing and today we got some rain, and sure enough, I checked the combiner box and there was water inside (I shut off the system this morning before it started to rain as a pre-caution).

Could I just put some silicon caulking on the outside of the bushing to seal it tight? Would that be ok?

You might have to replace it with a compression fitting for cables. Like this Hubbell fitting. http://www.cesco.com/b2c/product/120...FUQV7Aodyk0AIQ

By the way what is that single red wire for?

[sensij]

I am not sure if NEC 200.7 (C) can be used for this situation or not. It can sometimes get a little fuzzy when you see one thing and then read about it in the code as not being acceptable.

Attached is a combiner box used in a solar pv array. The DC wires coming from the panels are white and yellow insulated and the wires going to the inverter are black insulated with white and yellow tape. It (along with 11 others) passed inspection.

Remarking black insulation as white is OK, in fact, it is specifically allowed by 200.7(A)(3). Anyplace else in the circuit, the conductor will appear black, and be treated as unknown voltage.

Re-marking white insulation as black can only be done under a few conditions, the most common if which is if that conductor is part of cable, which is 200.7(C)(1). That is why it can be OK to use NM cable to wire a light switch, and just mark the white wire black. Anyplace else in the circuit where it is not marked, a visible white conductor not inside a cable would be seen as grounded, and may be misinterpreted as safe, or connected incorrectly. Of course, checking the voltage first is always a good practice, but code sometimes helps when good practice is inconsistent.

[bcroe]

Bruce, You might to read this to get a better understanding of how modern transformerless (AKA, non-isolated, aka ungrounded) inverters work. Yes, it is required that any disconnect and OCPD on the DC side is on both the DC+ and DC- in those circuits.

Thanks for that information. I seem to agree with this. As for inverters, the issue
is input-output ISOLATION, and it would be less confusing if everybody used
the same and consistent description, instead of using the round about and NOT
conclusive term "transformerless".

"Inverters that include an isolation-transformer as part of the listed product are
specifically designed and tested for use with grounded PV systems and are
often referred to as isolated inverters or transformer-isolated inverters."

I see the SolarEdge-Optoimizer system is not isolated. So a dual pole disconnect
switch would be required. That also explains why a specific inverter input voltage
must be maintained. "SolarEdge has developed a unique utility-interactive
PV system that consists of module-level dc-to-dc power optimizers coupled with
proprietary non-isolated inverters."

I note, they mention floating vs bonded conductors. Here the Fronius neg is
NEITHER. The array negative isn't FLOATING, because its connected by a
very low impedance (fuse) to ground. It isn't BONDED, because the fuse can
be blown open and in fact is expected to do so for a fault. This issue is not
addressed in the document.

It is addressed here. Its pretty obvious if there is a ground fault in my array,
or just some leakage current over dozens of panels, there could be hundreds
of volts on either array lead. Working on the inverter DC wiring would not be
safe just because a single pole disconnect switch was opened. This all became
obvious when some array wiring had to be relocated, and the ground fuse blew.
Now there are disconnects for every array current carrying wire. This
issue seems to generally ignored. Bruce Roe

[SunEagle]

Remarking black insulation as white is OK, in fact, it is specifically allowed by 200.7(A)(3). Anyplace else in the circuit, the conductor will appear black, and be treated as unknown voltage.

Re-marking white insulation as black can only be done under a few conditions, the most common if which is if that conductor is part of cable, which is 200.7(C)(1). That is why it can be OK to use NM cable to wire a light switch, and just mark the white wire black. Anyplace else in the circuit where it is not marked, a visible white conductor not inside a cable would be seen as grounded, and may be misinterpreted as safe, or connected incorrectly. Of course, checking the voltage first is always a good practice, but code sometimes helps when good practice is inconsistent.

I agree with you. HX-Guy will probably have to replace it with a black insulated wire unless the Inspector says different.

I also agree with you that it doesn't matter what the color of the wire you first need to check with a meter to see if it is alive or dead.