Inverters and 240.87
- Thread starter Danielt
- Start date
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
240.87 applies to circuit breakers 1200A and larger (240.67 is for fuses 1200A and larger). If the inverter has a fuse or circuit breaker output and is 1200A and larger, it must comply.
- Location
- Illinois
- Occupation
- retired electrician
Can the inverter even source enough fault current for this to be an issue? As I recall, they typically cannot source enough current to operate the output side OCDP in the instantaneous trip range.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
PV systems are designed that way intentionally. Conductors and OCPD are sized so that conductors cannot be damaged and OCPD cannot be tripped by the maximum inverter output current.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
The 4000A breaker will need to have ERMS to be compliant, irrelevant on being fed from an inverter.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
It seems to me that this would be covered by (B)(5)
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
This is really not an inverter or a PV question in my opinion. It's evidently something that any manufacturer of any type of equipment containing 1200A or higher rates circuit breakers would need to be aware of.
This poses the "look inside the box" question. Can an AHJ look inside a piece of UL Listed equipment and point to something and say, this does not comply with the NEC? The answer is no, see NEC 90.7. The CB inside a UL Listed inverter is assumed to comply with the NEC when the inverter is installed in accordance with the manufacturer's installation instructions.
Wow, great point. But is UL listing assumed to meet current NEC code? I would think the UL test is just to make sure the equipment does what it says, in this case safely inverting the voltage. Do they also look for code requirements like arc-energy reduction? Or does the NEC just not apply?
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Generally they are separate spheres and the NEC does not apply. Which I think can be said in this case. But there is also some harmonization of UL standards and the NEC and ways they look to each other. I would be somewhat surprised if there wasn't already something in UL standards about arc-energy reduction. That seems like a 'standardsy' thing that's making it's way into the NEC and not vice versa. But I could be wrong.
So the bottom line is how to make sure the installation complies with 240.87? Require info that the UL listing confirms compliance, or say that 240.87 doesn't apply as the OCDs are part of UL approved equipment (90.7)? Seems like the Code needs some clarification on this.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
This.
(Sorry if I wasn't clear before.)
No, the code is pretty clear. See first sentence of second paragraph of 90.7.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
The inverter manufacturer doesn't know if you will use one of the alternate compliance methods for 240.87, so if they don't install arc flash reduction maintenance switch in the 4000A CB, that doesn't relieve the designer / installer to still comply with 240.87
This is incorrect. The designer does not have to evaluate what is in the UL Listed box for NEC compliance. That is made very clear in 90.7 and applying 240.87 would require evaluating the internal OCPD. When a UL Listed device requires extra outside equipment to be installed it will state so in the installation documentation. For instance, the installation documentation for inverters that can be interconnected to ungrounded utility sources will often have as an additional requirement the installation of an external ground fault detection device since the inverter usually does not have one included.