PV Rapid Shutdown Switch

[Jacobb951]

From my understanding, firefighters usually kill the power (utility) to a building once they arrive, via service disconnect or by removing the Meter from the socket.
Both of these methods will cause a Grid-Tied solar system to shutdown (Initiating the built in Rapid Shutdown Function).

For Grid-Tied systems, I feel like it doesn't make sense to have Rapid Shutdown Switch, it seems redundant as these systems need Grid voltage to operate in the first place. Am I wrong?

 

[don_resqcapt19]

From my understanding, firefighters usually kill the power (utility) to a building once they arrive, via service disconnect or by removing the Meter from the socket.
Both of these methods will cause a Grid-Tied solar system to shutdown (Initiating the built in Rapid Shutdown Function).

For Grid-Tied systems, I feel like it doesn't make sense to have Rapid Shutdown Switch, it seems redundant as these systems need Grid voltage to operate in the first place. Am I wrong?

The rapid shutdown is not just for the AC output from the system...it also covers the DC output from the panels and 690.12(B)(1) requires the voltage outside of the array to be reduced to 30 volts or less within 30 seconds of the shut down being activated.

 

[Carultch]

From my understanding, firefighters usually kill the power (utility) to a building once they arrive, via service disconnect or by removing the Meter from the socket.
Both of these methods will cause a Grid-Tied solar system to shutdown (Initiating the built in Rapid Shutdown Function).

For Grid-Tied systems, I feel like it doesn't make sense to have Rapid Shutdown Switch, it seems redundant as these systems need Grid voltage to operate in the first place. Am I wrong?

The DC side is permanently energized in sunlight, even when the AC is shut off, and you'd need to cover it with an opaque tarp or wait for sunset to shut it down completely. Anywhere that NEC2017 and later applies, the NEC effectively requires devices that shut off the outputs at the module level, with an allowable standby voltage of up to 30V after shutdown is initiated, for communication and diagnostics purposes. The NEC doesn't explicitly state that you need module-level rapid shutdown, but if you read between the lines in 690.12, the voltage constraints imply module-level rapid shutdown. Theoretically, you could connect sub-30V modules all in parallel instead of series and still comply with this rule despite no shutdown at all on the DC side, but it is unlikely you will ever see this in practice as very few (if any) products exists that could work this way.

Generally, one disconnect, strategically placed, is permitted to satisfy multiple requirements with the same device. It is common for utilities to require an outside-mounted disconnect, and it is logical for this device to double for rapid shutdown initiation. Your fire department may require additional locations to initiate rapid shutdown, but the NEC alone has very simple criteria for what kinds of devices qualify. See 690.12(B)(2)(C). For a system capable of off-grid operation (islanding), you may need a separate switch dedicated to rapid shutdown, as it would continue to operate its off-grid loads if all you did was shut off its connection to the grid-tied side.

The previous installment of rapid shutdown in NEC2014 was extremely vague on what kinds of initiation devices were intended, what location requirements they have, and how many (if multiple) would be permitted. It's a good thing that 2017 has more guidance, so everyone involved can understand the intent.

 

[Jacobb951]

The rapid shutdown is not just for the AC output from the system...it also covers the DC output from the panels and 690.12(B)(1) requires the voltage outside of the array to be reduced to 30 volts or less within 30 seconds of the shut down being activated.

The DC side is permanently energized in sunlight, even when the AC is shut off, and you'd need to cover it with an opaque tarp or wait for sunset to shut it down completely. Anywhere that NEC2017 and later applies, the NEC effectively requires devices that shut off the outputs at the module level, with an allowable standby voltage of up to 30V after shutdown is initiated, for communication and diagnostics purposes. The NEC doesn't explicitly state that you need module-level rapid shutdown, but if you read between the lines in 690.12, the voltage constraints imply module-level rapid shutdown. Theoretically, you could connect sub-30V modules all in parallel instead of series and still comply with this rule despite no shutdown at all on the DC side, but it is unlikely you will ever see this in practice as very few (if any) products exists that could work this way.

Generally, one disconnect, strategically placed, is permitted to satisfy multiple requirements with the same device. It is common for utilities to require an outside-mounted disconnect, and it is logical for this device to double for rapid shutdown initiation. Your fire department may require additional locations to initiate rapid shutdown, but the NEC alone has very simple criteria for what kinds of devices qualify. See 690.12(B)(2)(C). For a system capable of off-grid operation (islanding), you may need a separate switch dedicated to rapid shutdown, as it would continue to operate its off-grid loads if all you did was shut off its connection to the grid-tied side.

The previous installment of rapid shutdown in NEC2014 was extremely vague on what kinds of initiation devices were intended, what location requirements they have, and how many (if multiple) would be permitted. It's a good thing that 2017 has more guidance, so everyone involved can understand the intent.

First off, thank you both for your responses.

Common grid-tied solar systems (Solaredge, Enphase) have built-in, module level, rapid shutdown. These systems will automatically perform Module-level shutdown when the inverter(s) doesn't sense grid power. This is performed without a separate initiation device, happens during power outages.

From my understanding, Firefighters will always shutdown Utility power to a building, before attempting to fight a fire. For homes with Grid-tied solar systems on the property, doing this will Automatically perform Module-level Rapid shutdown. So having a secondary, dedicated device doesn't seem necessary to me, at least for solar systems that perform automatic, module level shutdown.

To summarize, I suppose my question is this...If automatic module-level, rapid shutdown function is built in to the system, why should a separate device be required?

 

[acrwc10]

".If automatic module-level, rapid shutdown function is built in to the system, why should a separate device be required?

You are correct, it shouldn't be required,,,,,But,,, some utilities and some solar companies require them.

 

[wwhitney]

You are correct, it shouldn't be required,,,,,But,,, some utilities and some solar companies require them.

I.e. the NEC doesn't require the separate device if the main service disconnect does the job. Of course, if there's an ESS and MID installed so that the PV continues operating when the main service disconnect is thrown, then a separate device would be necessary (I infer).

Cheers, Wayne

 

[don_resqcapt19]

First off, thank you both for your responses.

Common grid-tied solar systems (Solaredge, Enphase) have built-in, module level, rapid shutdown. These systems will automatically perform Module-level shutdown when the inverter(s) doesn't sense grid power. This is performed without a separate initiation device, happens during power outages.

From my understanding, Firefighters will always shutdown Utility power to a building, before attempting to fight a fire. For homes with Grid-tied solar systems on the property, doing this will Automatically perform Module-level Rapid shutdown. So having a secondary, dedicated device doesn't seem necessary to me, at least for solar systems that perform automatic, module level shutdown.

To summarize, I suppose my question is this...If automatic module-level, rapid shutdown function is built in to the system, why should a separate device be required?

They will if there is a readily available service disconnect. The standard operating procedure document for many fire departments prohibits the pulling of a meter to disconnect power. This is prohibited for two reasons...first pulling a meter while the service is energized is not safe and second, many firefighters do not understand the difference between self contained meters which when pulled will interrupt the flow of power and CT meters that will not interrupt the flow of power when pulled.

If the module level shutdown provides the reduction of the DC voltage to 30 volts or less outside the array boundary and to 80 volts or less within the array boundary, there should be no need for any additional equipment as 690.12(C)(1) permits the service disconnect to be the activation for the required rapid shutdown.
Where the service disconnect is inside the one or two family dwelling the initiation device for the rapid shutdown must be installed at a readily accessible location outside the building pre 690.12(C).