Romex for microinverters?

[Andy Cazzato]

I have a customer whose house was wired during original construction for a string inverter using Romex for DC conductors between the roof mounted modules and the inverter in the garage. The romex runs thru the attic and inside sheetrock walls. An entire of subdivision of homes is wired this way.

To my knowledge, Romex has never been allowed for DC conductors without metal conduit. This house would require considerable time and material to abandon the Romex and run conduit externally thru walls and over roofs to connect the modules to the string inverter location. The inverter is a Xantrex ST which has failed and cannot be repaired, so a replacement string inverter would also add to the cost of adding external conduit.

If we convert this system to microinverters will the Romex be allowed to carry AC (240Vac, 7.1 A max) without conduit or would new metal conduit be required regardless?

In case you're curious, these new homes were inspected and passed by the City of Watsonville, CA between 2001 and 2003 with the solar built in.

Andy Cazzato
Santa Cruz Solar

 

[dereckbc]

Have you read and understand 690.31


690.31 Methods Permitted.

(A) Wiring Systems. All raceway and cable wiring methods included in this Code and other wiring systems and fittings specifically intended and identified for use on photovoltaic arrays shall be permitted. Where wiring devices with integral enclosures are used, sufficient length of cable shall be provided to facilitate replacement. Where photovoltaic 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.

 

[GoldDigger]

Have you read and understand 690.31

690.31 Methods Permitted.

(A) Wiring Systems. All raceway and cable wiring methods included in this Code and other wiring systems and fittings specifically intended and identified for use on photovoltaic arrays shall be permitted. Where wiring devices with integral enclosures are used, sufficient length of cable shall be provided to facilitate replacement. Where photovoltaic 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.

Andy:
And do you also understand that there is an ongoing debate as to whether "output circuits" refers also to the AC output of a string or micro inverter or only refers to DC after combiners, fuses, disconnects, etc. The question boils down to whether all of that sentence refers only to DC or not.
Your AHJ will have his own interpretation of this, so best to find that out if you can without bringing down undue trouble.

If you run PV wire instead, your options are a little more flexible under the 2011 code, which is coming soon to a California near you. The AHJ may allow you to jump the gun on this just a bit.
I am assuming that when you say you will need to run conduit outside the house it is because you cannot run conduit inside the attic and down the walls?

Note that an attic may or may not be "readily accessible" and putting wires in a chase to restrict access may be enough to avoid this particular provision. There are lots of other applicable sections to watch out for too.

 

[ggunn]

I have a customer whose house was wired during original construction for a string inverter using Romex for DC conductors between the roof mounted modules and the inverter in the garage. The romex runs thru the attic and inside sheetrock walls. An entire of subdivision of homes is wired this way.

To my knowledge, Romex has never been allowed for DC conductors without metal conduit. This house would require considerable time and material to abandon the Romex and run conduit externally thru walls and over roofs to connect the modules to the string inverter location. The inverter is a Xantrex ST which has failed and cannot be repaired, so a replacement string inverter would also add to the cost of adding external conduit.

If we convert this system to microinverters will the Romex be allowed to carry AC (240Vac, 7.1 A max) without conduit or would new metal conduit be required regardless?

In case you're curious, these new homes were inspected and passed by the City of Watsonville, CA between 2001 and 2003 with the solar built in.

Andy Cazzato
Santa Cruz Solar

I don't know much about the NEC before 2008, but under that version and later of the code the homes woulda shoulda have never passed inspection with DC wiring not in conduit. I am fairly certain that Romex for the AC wiring from microinverters will be OK, though, assuming the conductor count and wire sizing for ampacity is adequate.

 

[GoldDigger]

In case you're curious, these new homes were inspected and passed by the City of Watsonville, CA between 2001 and 2003 with the solar built in.

Not sure what the CA code cycle was in 2003, but I would bet that it lagged by at least two years.

 

[shortcircuit2]

I have a customer whose house was wired during original construction for a string inverter using Romex for DC conductors between the roof mounted modules and the inverter in the garage. The romex runs thru the attic and inside sheetrock walls. An entire of subdivision of homes is wired this way.

To my knowledge, Romex has never been allowed for DC conductors without metal conduit. This house would require considerable time and material to abandon the Romex and run conduit externally thru walls and over roofs to connect the modules to the string inverter location. The inverter is a Xantrex ST which has failed and cannot be repaired, so a replacement string inverter would also add to the cost of adding external conduit.

If we convert this system to microinverters will the Romex be allowed to carry AC (240Vac, 7.1 A max) without conduit or would new metal conduit be required regardless?

In case you're curious, these new homes were inspected and passed by the City of Watsonville, CA between 2001 and 2003 with the solar built in.

Andy Cazzato
Santa Cruz Solar

Welcome to the forum...

My 2002 NEC has no article 690 restrictions on Romex as a wiring method. In California you are under the 2008 NEC currently and you are required to provide protection by raceway as outlined above. Micro inverters can be wired with Romex inside the building in dry locations.

Under the 2008 NEC, after the DC disconnect the only restriction on Romex use is again over 30 volts and readily accessible....

 

[jaggedben]

Photovoltaic source and output circuits are DC circuits by definition. A microinverter output circuits is not subject to any restrictions on those circuits.

There is no restriction on the use of romex for any 240V AC circuit. There's some restrictions on location (e.g. no wet locations). And the ground is often not adequate for the solar GEC (#8). The latter may be problem in an existing home.

Golddigger calls this a 'debate' but in my opinion it's just that some people haven't looked at the definitions in the beginning of 690. Unfortunately that includes some AHJs.

 

[dereckbc]

Unfortunately that includes some AHJs.

There are Two Golden Rules when dealing with AHJ. The rules are:

1. AHJ is always correct.
2. When AHJ is incorrect refer to rule #1.

 

[Andy Cazzato]

re: romex for microinverters

re: romex for microinverters

Andy:
And do you also understand that there is an ongoing debate as to whether "output circuits" refers also to the AC output of a string or micro inverter or only refers to DC after combiners, fuses, disconnects, etc. The question boils down to whether all of that sentence refers only to DC or not.
Your AHJ will have his own interpretation of this, so best to find that out if you can without bringing down undue trouble.

If you run PV wire instead, your options are a little more flexible under the 2011 code, which is coming soon to a California near you. The AHJ may allow you to jump the gun on this just a bit.
I am assuming that when you say you will need to run conduit outside the house it is because you cannot run conduit inside the attic and down the walls?

Note that an attic may or may not be "readily accessible" and putting wires in a chase to restrict access may be enough to avoid this particular provision. There are lots of other applicable sections to watch out for too.

GoldDigger: After posting I heard from the AHJ. He thinks this was overlooked by his department in the "early days" of 2001. He concurs that the DC Romex is unsafe as installed originally, but that it would be acceptable to use it for the AC output of microinverters.

Yes, new conduit would have to run outside for DC because there are too many obstacles inside the house.

 

[ggunn]

Golddigger calls this a 'debate' but in my opinion it's just that some people haven't looked at the definitions in the beginning of 690. Unfortunately that includes some AHJs.

Just because some people are uninformed, that doesn't keep them from debating.