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PV Wire on Ungrounded systems
- Thread starter Zee
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SolarPro
Senior Member
- Location
- Austin, TX
It is explained in this UL white paper:
http://www.ul.com/global/documents/offerings/industries/wireandcable/techcorner/PVWire.pdf
In summary:
"when compared to USE-2 wire, PV wire has superior sunlight resistance and low-temperature flexibility in addition to a thicker insulation or jacket and a proven level of flame resistance."
http://www.ul.com/global/documents/offerings/industries/wireandcable/techcorner/PVWire.pdf
In summary:
"when compared to USE-2 wire, PV wire has superior sunlight resistance and low-temperature flexibility in addition to a thicker insulation or jacket and a proven level of flame resistance."
BillK-AZ
Senior Member
- Location
- Mesa Arizona
Kind of circular reasoning.
The reason given in the UL document is: "Per the NEC, USE-2 wire is suitable for use in grounded PV arrays only but PV wire can
be used within both grounded and ungrounded PV arrays."
Does not answer why USE-2 600V wire is not suitable for ungrounded systems, but 600V PV wire is suitable.
Granted, there are a lot of benefits to the use of PV wire.
The reason given in the UL document is: "Per the NEC, USE-2 wire is suitable for use in grounded PV arrays only but PV wire can
be used within both grounded and ungrounded PV arrays."
Does not answer why USE-2 600V wire is not suitable for ungrounded systems, but 600V PV wire is suitable.
Granted, there are a lot of benefits to the use of PV wire.
SolarPro
Senior Member
- Location
- Austin, TX
The mechanical characteristics of PV wire are more robust that those of USE-2. PV wire is more resistant to nicks and abrasion. It's also more flexible and has improved fire resistance.
Basically, PV Wire is intended for PV applications by design. The outdoor-rated conductors that were used in the US for PV source circuits prior to the introduction of listed PV wire were the best products available. However, they were not designed specifically for PV applications. That's the way I think of it.
Basically, PV Wire is intended for PV applications by design. The outdoor-rated conductors that were used in the US for PV source circuits prior to the introduction of listed PV wire were the best products available. However, they were not designed specifically for PV applications. That's the way I think of it.
Much appreciated SOLARPRO and BILLK-AZ,
Yes, I agree PV wire is better in so many ways.
Heavy insulation, T performance and UV resistance.
(I happen to use it exclusively - gr. or ungr. system)
Still..... it seems there is no explicit reasoning given for why Code requires PV WIRE only on ungr. sys.s.
Again i have always wondered... why specifically for ungr. sys.s??
It implies - to me - that ungr. sys.s are less safe?
Yet, am I right in viewing these ungr. systems as inherently safer?
1. Neither pos. or neg. have potential to ground (floated array),
2. they still have Ground Fault Protection
3. they incorporate the latest technology
4. and are often Arc fault protected.
Yes, I agree PV wire is better in so many ways.
Heavy insulation, T performance and UV resistance.
(I happen to use it exclusively - gr. or ungr. system)
Still..... it seems there is no explicit reasoning given for why Code requires PV WIRE only on ungr. sys.s.
Again i have always wondered... why specifically for ungr. sys.s??
It implies - to me - that ungr. sys.s are less safe?
Yet, am I right in viewing these ungr. systems as inherently safer?
1. Neither pos. or neg. have potential to ground (floated array),
2. they still have Ground Fault Protection
3. they incorporate the latest technology
4. and are often Arc fault protected.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
I'm with you Zee. I don't think there's any logical reason for it. Just a certain ingrained bias against ungrounded systems in this country, is my guess. I think that ungrounded PV systems are in fact a bit safer. To my mind an array that has a ground fault is dangerous regardless of whether it started as a grounded or ungrounded system. Also, when a ground-fault fuse blows then what do you end up with? ... An ungrounded system, that's what. 690 even requires a warning label on inverters that says this.
Ergo, to my mind, whatever is good enough for grounded systems should be good enough for ungrounded systems, and vice versa.
SolarPro, I think we all know that PV wire is more robust than USE-2. If it's that much safer, maybe the code should just require it for all PV arrays. It would cost us a bit more money but simplify our supply chains.
(Then there's the vendor that just shipped me a bunch of USE-2 that they had labeled 'PV Wire' on the box. But that's another issue...)
Ergo, to my mind, whatever is good enough for grounded systems should be good enough for ungrounded systems, and vice versa.
SolarPro, I think we all know that PV wire is more robust than USE-2. If it's that much safer, maybe the code should just require it for all PV arrays. It would cost us a bit more money but simplify our supply chains.
(Then there's the vendor that just shipped me a bunch of USE-2 that they had labeled 'PV Wire' on the box. But that's another issue...)
shortcircuit2
Senior Member
- Location
- South of Bawstin
PV wire is not the only option on ungrounded systems...it is just the most economical product to install to comply with 690.35(D)
SolarPro
Senior Member
- Location
- Austin, TX
Yes, the Code making panel clearly wanted to hold ungrounded PV systems to a higher standard. That's a bit ironic given the ground fault detection blind spot subsequently discovered in transformer-isolated central inverters. If you wanted to protect against the chance of having an undetected first fault in a grounded source circuit conductor, specifying PV wire, which offers better mechanical protection, wouldn't be a bad place to start.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Also, when a ground-fault fuse blows then what do you end up with? ... An ungrounded system, that's what.
Au contraire. If the fuse has blown because of a ground fault you have a system which is grounded at the point where the fault occurred which caused the fuse to blow. Of course, you also have a system which is shut down on the AC side.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
However, since the fault could be in the middle of a string, you could have a system in which neither the positive nor the negative lead are grounded.
That matters for handling the wires, but from the insulation strength viewpoint the potential relative to ground is limited.
Sent from my XT1080 using Tapatalk
That matters for handling the wires, but from the insulation strength viewpoint the potential relative to ground is limited.
Sent from my XT1080 using Tapatalk
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Au contraire. If the fuse has blown because of a ground fault you have a system which is grounded at the point where the fault occurred which caused the fuse to blow. Of course, you also have a system which is shut down on the AC side.
Yes, that's true. But my point was that it behaves no differently from a system that was configured as ungrounded.
I appreciate the thinking, guys.
Until I see otherwise, it does seem as if the NEC people are "testing" these ungrounded systems for a couple years and viewing them cautiously, so they have applied more stringent safety standards in the meantime.
Really, i have no problem with that, PV Wire should be used on all solar - IMHO.
It is a real issue also, I repair older grid-tie systems all the time, where the grounded inverter has failed. My best replacement option is an ungrounded new inverter......a bit of a Code conundrum since these were wired with USE-2. Anywho, thanks.
Until I see otherwise, it does seem as if the NEC people are "testing" these ungrounded systems for a couple years and viewing them cautiously, so they have applied more stringent safety standards in the meantime.
Really, i have no problem with that, PV Wire should be used on all solar - IMHO.
It is a real issue also, I repair older grid-tie systems all the time, where the grounded inverter has failed. My best replacement option is an ungrounded new inverter......a bit of a Code conundrum since these were wired with USE-2. Anywho, thanks.
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