PV wiring in conduit

[Grouch]

Hi all,
Looking at section 690.31(A) (2008 NEC), it says "where PV source and output circuits operating at maximum system voltages greater than 30 volts are installed in readily accessible locations, circuit conductors shall be installed in a raceway".

The 30 volts... are they talking about the Voc for each solar module, the Vmp for each solar module, or the total Voc for the entire string of series connected modules?

 

[Grouch]

or the total Voc for the entire string including any temperature correction factors for the voltage?

 

[LarryFine]

I would say it refers to whatever qualifies as line-to-line within each raceway.

Nominal voltage, like 24v and down vs. 36v and up.

 

[jaggedben]

Maximum system voltage is Voc multiplied by temperature coefficient for the design low temperature.

Otherwise, Larry has it correct. Read the definitions of PV source and output conductors at the beginning of 690.

If you are not using micro-inverters or optimizers then your source circuits will be strings. If you are using micro-inverters or optimizers then your source circuits are just one panel.

Note that rooftops are usually not readily accessible.

 

[Grouch]

so assuming we're in a readily accessible location, and we have a string / central inverter (not microinverters)... it's pretty much guaranteed that the max system voltage (Voc x temp. coefficient) will always exceed 30 volts? Just 2 solar modules in series and the voltage will already be greater than 30 volts.

 

[LarryFine]

Just 2 solar modules in series and the voltage will already be greater than 30 volts.

Then you'd have below 30v from each panel, and above 30v after they combine.

 

[Grouch]

Thanks. So rooftops are not considered readily accessible as jaggedben mentioned? you don't need the PV conductors (source and output) in conduit / raceway?

 

[electrofelon]

Around here, readily accessible is typically considered to be within reach, or about 8 feet.

 

[jaggedben]

Nowadays the max voltage on a single panel is typically well in excess of 30V.

The code definition for readily accessible specifically calls out portable ladders as an example of what would not be needed to reach the location. So generally unless a rooftop has a permanent staircase or ladder to it, it's not readily accessible. Admittedly commercial rooftops are more likely than residential to be readily accessible.

 

[Grouch]

Got it. Thanks guys for the help.

 

[Carultch]

Nowadays the max voltage on a single panel is typically well in excess of 30V.

The code definition for readily accessible specifically calls out portable ladders as an example of what would not be needed to reach the location. So generally unless a rooftop has a permanent staircase or ladder to it, it's not readily accessible. Admittedly commercial rooftops are more likely than residential to be readily accessible.

How does this apply for rooftops with permanent ladders and/or staircases that enable ready accessibility? Obviously, you can't have every inch of your wiring inside a raceway, because the modules require you to exit the raceway, to connect to them. Is it OK to have the wiring external to the raceway, as long as it is in a location controlled by key locks, that only qualified personnel can access?

 

[jaggedben]

How does this apply for rooftops with permanent ladders and/or staircases that enable ready accessibility? Obviously, you can't have every inch of your wiring inside a raceway, because the modules require you to exit the raceway, to connect to them. Is it OK to have the wiring external to the raceway, as long as it is in a location controlled by key locks, that only qualified personnel can access?

For the case of single modules it's basically a code violation to modify the product such that the leads are in a raceway. So they get a pass. Also the 30V limit is obsolete and should probably have an exception.

I think it was always illegal, although very often overlooked, to have string inverters on such rooftops.

It's important to note that an optimizer output circuit is not a PV source or output circuit, so it is arguably not subject to this rule. In the 2008 NEC that might be vague since such things didn't exist when it was written.

 

[Grouch]

Adding to this thread. Once your wiring on the rooftop is inside conduit...
1) Does it make sense to use USE-2 or PV wire inside the conduit? or should you use regular THHN wire?
2) Does the code even allow USE-2 or PV wire inside conduit?

 

[Carultch]

Adding to this thread. Once your wiring on the rooftop is inside conduit...
1) Does it make sense to use USE-2 or PV wire inside the conduit? or should you use regular THHN wire?
2) Does the code even allow USE-2 or PV wire inside conduit?

1. For strings over 600V, you usually have to continue the use of PV wire in conduit, because what else carries the higher voltage rating? On 600V and less strings, you have an advantage to switching to THWN-2 wire inside conduit, due to it being smaller in diameter, generally less expensive, and allows you to use smaller conduits. The drawback is that you have to introduce an enclosure where the splicing happens, because no part of the THWN-2 wire can leave the conduit/raceway/enclosure system.

2. PV wire, yes. USE-2, the short answer is "usually yes", but it is nuanced. Outdoor conduit = always yes. Conduit inside a building? It has to carry an additional rating that allows it to be used inside a building. USE-2 wire that doesn't carry other ratings, is not permitted inside buildings. However, in practice, most USE-2 wire carries additional ratings such as RHW-2, that permit it to be used just like any other building wire., provided that you account for its larger diameter.

 

[Grouch]

Awesome! good stuff, thanks.