PV wire Ampacity question

[topham26]

Hi,
my question is specific to PVwire as it compares to USE-2 wiring.

I am designing a 1000Vdc/string array with a transformer-less (non-isolated) inverter, so I must use PVwire.

Since in the NEC the ampacity values are given by temperature with corresponding wire types, PV wire is rated to 120C rather than 90C, does anyone know about the possibility that I could rate my conductors smaller than what the NEC suggests? With volt drop aside.

could I do this, even if not with respect to the NEC would it be possible no problems occur, or could I even do this with respect to the NEC?

Thanks

Jon

 

[don_resqcapt19]

In general the ampacity of the conductor is controlled by the temperature rating of the equipment and terminations. It is rare where you can use a conductor at its 90?C ampacity.

 

[iwire]

I thought we were limited to 600 volts or less on a string?

Is PV wire rated 1KV?

 

[david luchini]

I thought we were limited to 600 volts or less on a string?

I think the 600V limit only applies to one or two family dwellings (690.7(C)).

Is PV wire rated 1KV?

You can find PV wire rated up to 2kV.

http://www.awcwire.com/Part.aspx?partname=PV-6-266T

 

[topham26]

Here is a video describing the differences between the two, although from a manufacturer and sales perspective.

https://www.youtube.com/watch?v=dDbaJQBdpbc

Basicially:

USE-2 PV wire
600v 1000v
grounded/ungrounded arrays
90C/150C (not120)
either/stranded (for flexibility)
14awg/18awg minimum

and PVwire is UV and flame resistant as well.

 

[don_resqcapt19]

You still can't use either the 90? or the 150?C ampacities for any purpose other than derating.

 

[ggunn]

Ampacity is all about insulation; a copper wire can conduct far more current than what is shown in the ampacity tables before the metal itself is compromised. That said, the heat tolerance of the components the conductor is connected to is a limiting factor as well; in many circumstances a designer cannot even use the 90 degree column, much less a 120 degree column, if it existed. You might be able to get around it by transitioning to higher ampacity (lower temperature) wire before connecting to a fuse block (or whatever), but your transition block must be rated at the higher temperature.

The other thing is that I don't see a 120 degree column in any of the ampacity tables, only 90 and 150 degrees near what you are considering. How would you calculate a 120 degree ampacity?

 

[jaggedben]

You still can't use either the 90? or the 150?C ampacities for any purpose other than derating.

Presumeably he asked his question because his temperature derating is requiring a larger wire size than anything else.