Negative Conductor in a Photovoltaic System

[BearState]

We are working on a Photovoltaic System. We are running two postive wires and two negative wires in a conduit. Is the negative conductors considered as current carrying? and if so, I think by code we'll have derate the conductors. Please advise.

Thank you.

 

[Dennis Alwon]

I am bumping this up as I too would like to know. My guess is yes but depending on the insulation of the conductor it may not matter as wire at 90C will be derated but not enough to affect the practical ampacity.

 

[don_resqcapt19]

This would be just like running two hots and two grounded conductors...they are all current carrying conductors.

 

[tallgirl]

Which conductors are they, because you may be under that wonderful 156% rule that makes wires get really big really fast.

What you do not want to do with PV conductors is scrimp on conductor size because you can. Make sure you check all of your voltage drop calculations and keep a running tally of where you're losing performance. Because if you don't, you may find yourself in trouble with any performance warranty you have.

 

[BearState]

Thank you for all your response. That helped me a lot.

 

[K8MHZ]

Which conductors are they, because you may be under that wonderful 156% rule that makes wires get really big really fast.

What you do not want to do with PV conductors is scrimp on conductor size because you can. Make sure you check all of your voltage drop calculations and keep a running tally of where you're losing performance. Because if you don't, you may find yourself in trouble with any performance warranty you have.

156 percent rule?

Please elaborate. We will be wiring up four inverters in our class lab starting tomorrow. One will have a battery back up. Also, I am donating some of the wire and would like to be sure about the AWG requirements.

 

[iwire]

156 percent rule?

The 125% required twice by 690.8.

 

[rgomes26]

You want to keep in mind that even though you're using -2 90*C conductors, many of the terminals in PV systems are listed for 75*C so keep that in mind for your derating.

Another common mistake I see installers make using USE-2 and PV Wire is that they neglect to re-identify their grounded conductors.

 

[K8MHZ]

The 125% required twice by 690.8.

I wonder if my instructor caught that. Just to be sure, (A) (1) takes us up to 125 percent and (B) (1) takes it up that other 125 percent (1.25^2 = 1.5625), correct?

 

[don_resqcapt19]

You want to keep in mind that even though you're using -2 90*C conductors, many of the terminals in PV systems are listed for 75*C so keep that in mind for your derating.

You can still use the 90? ampacity for derating.

Another common mistake I see installers make using USE-2 and PV Wire is that they neglect to re-identify their grounded conductors.

And if it is #6 or smaller you can't re-identify it...you must use white or gray.

 

[K8MHZ]

You can still use the 90? ampacity for derating.

And if it is #6 or smaller you can't re-identify it...you must use white or gray.

200.6 (2) seems to allow an exception for single conductor cable in PV systems. It says all we have to provide is 'distinctive white markings at all terminations'.

 

[iwire]

I wonder if my instructor caught that. Just to be sure, (A) (1) takes us up to 125 percent and (B) (1) takes it up that other 125 percent (1.25^2 = 1.5625), correct?

That is my understanding.

I designed a couple of 500 KW systems and as Tall Girl points out the wire sizes get big fast by the time you do the 125% + 125% and the ambient / on the roof derating.

 

[K8MHZ]

That is my understanding.

I designed a couple of 500 KW systems and as Tall Girl points out the wire sizes get big fast by the time you do the 125% + 125% and the ambient / on the roof derating.

Wow.

So, If I have 100 A (#3 Cu) I need to bump that up to 156.25 A. Now, if I figure the roof temp to get up to 125 F, I now have to throw in a .67 correction factor. That takes us to 233.31 A ??? Now we are up to a 250kcmil conductor???

Did I do that right?

 

[don_resqcapt19]

200.6 (2) seems to allow an exception for single conductor cable in PV systems. It says all we have to provide is 'distinctive white markings at all terminations'.

You are correct, I missed that. It is 200.6(A)(6) in the 2011 code.

 

[K8MHZ]

You are correct, I missed that. It is 200.6(A)(6) in the 2011 code.

Of course, the key word is 'distinctive'. I wonder how many PV installers get gigged because their marking fails to have a special style, quality or attractiveness?

 

[tallgirl]

Of course, the key word is 'distinctive'. I wonder how many PV installers get gigged because their marking fails to have a special style, quality or attractiveness?

We're talking about men, here. A length of white tape or heat shrink is plenty "distinctive".

Now, if it were women doing the installs, they'd have pretty ribbons and maybe some glitter and everything would smell nice.

 

[K8MHZ]

We're talking about men, here. A length of white tape or heat shrink is plenty "distinctive".

Now, if it were women doing the installs, they'd have pretty ribbons and maybe some glitter and everything would smell nice.

Posts copied. Copy will be given to Lisa, the only girl in our class. I'm pretty sure she will get a chuckle out of it. I did.