Grounded conductors

[earshavewalls]

Several Residential PV installations have been going into our City for the past 4 years. I am the plan check engineer who checks each of these plans prior to permitting. I happened to go out in the field with the Supervising Inspector and one of the regular inspectors and discovered something that I had to comment on. PV systems with a grounded conductor have been installed using a white insulation for the grounded conductor (DC side). When entering the combiner/DC disconnect section of standard inverters, this puts the AC conductors in the same enclosure with the DC conductors. According to the 2010 California Electrical Code (based on the 2008 NEC), Article 200.6(D), "Where grounded conductors of different systems are installed in the same raceway, cable, box, auxiliary gutter, or other type of enclosure, each grounded conductor shall be identified by system."

I immediately instructed the installer and the inspectors that, at least at this point in the system, the grounded conductors of each system (DC and AC) shall be distinguished in accordance with CEC 200.6(D)(1) thru (3). This can be a special challenge on a commercial installation where there are multiple voltages present (120/208 and 277/480 are most common). When you throw a PV system into the mix, you may need to go to the third option in 200.7(A)(2): "A conductor with three continuous white stripes on other than green insulation."

I know that this has not been checked or corrected in ANY of the PV systems that were installed before this issue came up. The transformerless inverter systems are ungrounded systems, so this is not an issue, as long as the insulation is a color other than white, gray, or green. We have not had issues with these systems, only the transfomer-type inverter systems.

Of course, this is NOT an issue with micro-inverters or AC modules, as ALL of the installed wiring will be AC.

Since this came up here, I imagine this may come up elsewhere.

Just thought I would drop this on the forum to see what turns up.

Wayne
In Magic Mountain Land

 

[fmtjfw]

An additional marking on the DC grounded conductor can be used to distinguish it from the AC grounded neutrals. Using a wire tag with a "DC" might do the trick or a colored tape other than white, gray, black, red, or green.

**DRAFT**
2014 draft has White for grounded DC conductors, Red for ungrounded Positive, and Black for ungrounded Negative. It also suggests labeling like "+", "-", "pos", "neg" ... for ungrounded DC
**DRAFT**

 

[jaggedben]

When entering the combiner/DC disconnect section of standard inverters, this puts the AC conductors in the same enclosure with the DC conductors. According to the 2010 California Electrical Code (based on the 2008 NEC), Article 200.6(D), "Where grounded conductors of different systems are installed in the same raceway, cable, box, auxiliary gutter, or other type of enclosure, each grounded conductor shall be identified by system."

If an inspector said this to me in the field, I would be strongly tempted to take a small piece of USE-2 off my truck, splice it to the end of the DC grounded conductor, wrap some white tape around it, and say "There, I've complied with 200.6(6.)." :thumbsup:

Seriously, I think this is a case of unwarranted over-enforcement. I don't say that lightly. First of all, in a standard disco/combiner, the conductors are readily identifiable from where they are terminated, and any qualified individual opening the box knows to expect both AC and DC conductors. Furthermore, and more significantly, if an installation complies with 690.4(B), then the conductors are already physically separated and identified as necessary. 690.4(B) has the same intent as 200.6 as far as preventing mis-identification. So if an installation complies with 690.4(B), is it really necessary to enforce 200.6 on top of that?

If you didn't accept my joke method above (and, actually, why shouldn't you?) then you'd be requiring installers to carry a not-so-readily-available alternative conductor on their trucks for every string inverter installation. That really strikes me as a uncalled-for additional layer of red tape.

Now I will grant you that a lot of installers may bring the AC and/or DC conductors into the 'wrong side' of the combiner/disco and thus violate 690.4(B). But I would strongly encourage you to be a stickler about that instead of this.

This can be a special challenge on a commercial installation where there are multiple voltages present (120/208 and 277/480 are most common). When you throw a PV system into the mix, you may need to go to the third option in 200.7(A)(2): "A conductor with three continuous white stripes on other than green insulation."

Realistically I see this hardly ever being an issue. The only AC conductors that would typically need to be in the vicinity of the DC conductors would be those of the voltage that the inverter(s) is connecting at, and that would rarely if ever be more than one system voltage.

 

[ggunn]

Several Residential PV installations have been going into our City for the past 4 years. I am the plan check engineer who checks each of these plans prior to permitting. I happened to go out in the field with the Supervising Inspector and one of the regular inspectors and discovered something that I had to comment on. PV systems with a grounded conductor have been installed using a white insulation for the grounded conductor (DC side). When entering the combiner/DC disconnect section of standard inverters, this puts the AC conductors in the same enclosure with the DC conductors. According to the 2010 California Electrical Code (based on the 2008 NEC), Article 200.6(D), "Where grounded conductors of different systems are installed in the same raceway, cable, box, auxiliary gutter, or other type of enclosure, each grounded conductor shall be identified by system."

I immediately instructed the installer and the inspectors that, at least at this point in the system, the grounded conductors of each system (DC and AC) shall be distinguished in accordance with CEC 200.6(D)(1) thru (3). This can be a special challenge on a commercial installation where there are multiple voltages present (120/208 and 277/480 are most common). When you throw a PV system into the mix, you may need to go to the third option in 200.7(A)(2): "A conductor with three continuous white stripes on other than green insulation."

I know that this has not been checked or corrected in ANY of the PV systems that were installed before this issue came up. The transformerless inverter systems are ungrounded systems, so this is not an issue, as long as the insulation is a color other than white, gray, or green. We have not had issues with these systems, only the transfomer-type inverter systems.

Of course, this is NOT an issue with micro-inverters or AC modules, as ALL of the installed wiring will be AC.

Since this came up here, I imagine this may come up elsewhere.

Just thought I would drop this on the forum to see what turns up.

Wayne
In Magic Mountain Land

Why is the grounded conductor more of a concern than the ungrounded one? The PV ungrounded conductor (positive) is often black, as is the AC "hot" conductor.

 

[SolarDude]

But per NEC 2011 which California will adopt eventually. Art. 206.6 (A)(6) A single conductor, sunlight-resistant, outdoor-rated cable used as a grounded conductor in photovoltaic power systems, as permitted by 690.31, shall be identified at the time of installation by distinctive white marking at all terminations. So in NEC 2011 we are back to using white for the grounded conductors???

 

[jaggedben]

We've always been required to have white markings for grounded conductors.