Continuous Rated Equipment Application

[JasonC]

So I have been trying to come up with evidence to support my side of a design with my PE.

System information

60kw PV system name plate rating at 208V is equal to 166A, Due to it being a PV system, it needs to be corrected for continuous use. This means the corrected current rating is 208A. I am using a 225A Breaker and Enclosure for the primary OCPD. However when it comes to the Disconnect Device (705.22) I am trying to show that a 200A 100% rated switch can be used and not be in violation of code. My PE is under the assumption that because it is a continuous duty system that the output conductors have to be corrected for the 1.25 correction factor and that amperage must be the sizing factor. Which I agree with and wholeheartedly understand. I would agree that if the disconnect was only rated for 80% that I would have to use a 400A switch to comply with code. My argument is that a 100% rated switch has been tested and rated to take up to its name plate rating without the need for a correction factor, the switch has been tested for the additional heat and so on that it would experience at full load continuously.

I know ultimately it is his stamp, and the AHJ has final word. I am trying to save the cost and eye sore of installing a 400A switch when it can be accomplished with a 200A switch legally.

Please correct me if i'm wrong, but also direct me to where I can show that this is correct.

Thank you.

 

[ggunn]

So I have been trying to come up with evidence to support my side of a design with my PE.

System information

60kw PV system name plate rating at 208V is equal to 166A, Due to it being a PV system, it needs to be corrected for continuous use. This means the corrected current rating is 208A. I am using a 225A Breaker and Enclosure for the primary OCPD. However when it comes to the Disconnect Device (705.22) I am trying to show that a 200A 100% rated switch can be used and not be in violation of code. My PE is under the assumption that because it is a continuous duty system that the output conductors have to be corrected for the 1.25 correction factor and that amperage must be the sizing factor. Which I agree with and wholeheartedly understand. I would agree that if the disconnect was only rated for 80% that I would have to use a 400A switch to comply with code. My argument is that a 100% rated switch has been tested and rated to take up to its name plate rating without the need for a correction factor, the switch has been tested for the additional heat and so on that it would experience at full load continuously.

I know ultimately it is his stamp, and the AHJ has final word. I am trying to save the cost and eye sore of installing a 400A switch when it can be accomplished with a 200A switch legally.

Please correct me if i'm wrong, but also direct me to where I can show that this is correct.

Thank you.

I'm afraid I have bad news for you.

I recently went around this tree with Eaton. I was under the impression, same as you, that I could size an unfused disco to exceed the inverter maximum nameplate rating but not 125% of it irrespective of the rating of the OCPD at the interconnection. I was mistaken. Their documentation says "... an Eaton non-fusible switch must be protected by any overcurrent device rated no greater than the ampere rating of the switch." While it is true that under normal operating conditions the current through the switch is limited to the output of the inverter, under fault conditions it is the interconnection OCPD that limits the current from the service, and that must be less than the rating of the switch.

 

[JasonC]

I'm afraid I have bad news for you.

I recently went around this tree with Eaton. I was under the impression, same as you, that I could size an unfused disco to exceed the inverter maximum nameplate rating but not 125% of it irrespective of the rating of the OCPD at the interconnection. I was mistaken. Their documentation says "... an Eaton non-fusible switch must be protected by any overcurrent device rated no greater than the ampere rating of the switch." While it is true that under normal operating conditions the current through the switch is limited to the output of the inverter, under fault conditions it is the interconnection OCPD that limits the current from the service, and that must be less than the rating of the switch.

OK now if I install a 100% rated Breaker and enclosure according to manufacturers specs ahead of the Disconnect device than under fault conditions the equipment would be coordinated. Can I assume that this option would then be legal and compliant. So a 200A 100% rated Breaker for a 166A continuous load with a 200A 100% rated "Utility/Rapid shutdown 705.22" disconnect.

 

[ggunn]

OK now if I install a 100% rated Breaker and enclosure according to manufacturers specs ahead of the Disconnect device than under fault conditions the equipment would be coordinated. Can I assume that this option would then be legal and compliant. So a 200A 100% rated Breaker for a 166A continuous load with a 200A 100% rated "Utility/Rapid shutdown 705.22" disconnect.

If the trip point of the breaker is equal to or less than the rating of the switch, you are OK.

 

[Carultch]

I'm afraid I have bad news for you.

I recently went around this tree with Eaton. I was under the impression, same as you, that I could size an unfused disco to exceed the inverter maximum nameplate rating but not 125% of it irrespective of the rating of the OCPD at the interconnection. I was mistaken. Their documentation says "... an Eaton non-fusible switch must be protected by any overcurrent device rated no greater than the ampere rating of the switch." While it is true that under normal operating conditions the current through the switch is limited to the output of the inverter, under fault conditions it is the interconnection OCPD that limits the current from the service, and that must be less than the rating of the switch.

Use a Square D switch instead of an Eaton switch. "Non-fusible safety switches may carry 100 percent of the nameplatecurrent rating."
https://www.altestore.com/static/datafiles/others/Square_D_Disconnect_Technical_Data_2010.pdf

 

[ggunn]

Use a Square D switch instead of an Eaton switch. "Non-fusible safety switches may carry 100 percent of the nameplatecurrent rating."
https://www.altestore.com/static/datafiles/others/Square_D_Disconnect_Technical_Data_2010.pdf

No help there; Eaton says the same thing. The problem is that the available fault current from the service through the interconnection OCPD exceeds 100% of the rating of the switch.

 

[electrofelon]

The problem is that the available fault current from the service through the interconnection OCPD exceeds 100% of the rating of the switch.

But that is almost always the case. Perhaps I am misunderstanding

 

[ggunn]

But that is almost always the case. Perhaps I am misunderstanding

Perhaps you are. If you have a 25A inverter, a 30A non-fusible disco, and a 35A interconnection breaker, the disco is fine with the 25A inverter current but not with the 35A available fault current from the service. The next size up disco is 60A, so that's what you'll have to install.

 

[electrofelon]

Perhaps you are. If you have a 25A inverter, a 30A non-fusible disco, and a 35A interconnection breaker, the disco is fine with the 25A inverter current but not with the 35A available fault current from the service. The next size up disco is 60A, so that's what you'll have to install.

OK. Your use of the term, "available fault current" was throwing me off. I would consider that improper use of that term. The available fault current will be much higher than 35 amps. Non fusible discos have a standard SCCR rating of 10k, and higher with certain series ratings. But I see the point you are making, that manufacturers seem to want a non fused disco protected at its rating by an OCPD, similar to how the NEC requires this of panelboards in 408.36. I had never heard of this before you mentioned it. I looked at a few other manufacturers to see what they said. I find it ambiguous. The way I read what square D says, you only need this protection when applying the higher than 10k series ratings, but not when you are using the standard 10k SCCR. I am not sure if that is what they intend to say or not. Just to be clear, this is a potential manufacturer requirement not an NEC article 404 requirement.