JMS-F SunSpec Certified Rapid Shutdown Device Installation
In this tech tip video, SMA Solar Academy Senior Technical Trainer Mike Mahon demonstrates the installation of the JMS-F line of SMA-compatible SunSpec-certified rapid shutdown receiver. These devices, when paired with the US-41 models of the Sunny Boy or CORE1 inverters, provide easy, reliable, module-level shut down to meet all the 2017 NEC rapid shutdown requirements.
For more information about commissioning the Sunny Boy US-41 click here.
For more information on installing the Sunny Boy US-41 click here.
Is it possible to have more than one rapid shutdown initiator switch? Is the rapid shutdown initiator switch just a multipole mushroom button dry contact that we could piggyback with some other signaling or is it more involved?
Ron, when using SunSpec for rapid shutdown, ANY device that interrupts the connection of the inverter on its AC terminals to the grid can act as the rapid shutdown initiator. The SunSpec certified transmitter board in the Sunny Boy or CORE1 US-41 inverter will then stop transmitting the SunSpec signal (on the DC conductors) to the SunSpec receivers in the array, and this will cause the PV system to go into shutdown mode very rapidly. The inverter’s AC breaker, the main service AC breaker, or a standard AC disconnect switch between the inverter breaker and the inverter’s AC terminals are appropriate choices of initiator. While all of the devices just listed can be the initiator, code would recognize the one that is labeled properly (e.g. 2020 NEC 690.56(C)(2)) as the true initiator. Code allows only one initiator if there is a single PV system at the site.
Just a question about the shutdown procedure for the Sunny Boy 5.0. I haven’t completed install of my system yet (diy) and am still studying as I install. I am using the JMS-F units, one for each 330 Watt module in the 2 arrays with 8 modules per array connected in series, so 2 DC inputs to the inverter. On the AC side I have the output L1, N, L2 and a Gnd also, all 10 AWG CU stranded wire going to a Square D disconnect switch, 240 VAC 30 amp 2 pole, to be an EMERGENCY DISCONNECT switch, with L1 and L2 being connected to the switch itself, the N a pass thru and the Gnd connected to the metal Square D box for safety and then on out with the L1,L2,N and G to the house 240 VAC 200 AMP breaker box. All this was just to let you know what I had. My question concerns the shutdown of the modules. I understand if I open the circuit on the AC side by moving the handle of the Square D emergency shutdown switch to the off position I kill the AC to the inverter (or shutting the breakers off in the breaker box), that should cause the inverter to cause the Rapid Shutdown system to block the modules from sending DC on to the inverter. If I haven’t shut the AC off though and just shut the Photovoltaic Array DC Disconnect Switch off, I still have 240 VAC on the output terminals in the lower section of the Inverter from the house breaker box. The Sunny Boy operators manual stipulates that shutting the DC Disconnect Switch off still leaves a DC voltage on the input lines from the solar panels that could be hazardous. I take this to mean that the DC Disconnect Switch only prevents the AC portion of the Inverter from producing AC. Of course the manual doesn’t know I have the JMS-F Rapid Shutdown system installed. But since the 240 AC from the house breaker is still present, does this have an effect on the JMS-F operation? I know any sane person would shut the AC off first then shut the DC Disconnect SW off. But you never know who’s going to be messing with your system.
Sam – After you have turned on the SunSpec rapid shutdown transmitter in the inverter during commissioning, the loss of AC voltage on the inverter terminals will signal the inverter to stop transmitting the rapid shutdown “keep alive” signal. Very quickly this will cause the JMS-F units to send the array into shutdown and low voltage (under 30VDC) will be present on the DC connection plug in the Connection Unit section of the inverter. Similarly, once the transmitter is enabled in the inverter, turning off the DC disconnect will prevent the rapid shutdown “keep alive” signal from making it to the array, and the JMS-F units will send the array into shutdown, rapidly reducing the DC voltage on the plug inside the inverter, even with AC voltage remiaining on the inverters AC terminal plug. Without the JMS-F units and not enabling the SunSpec transmitter, turning off only the DC disconnect would result in open circuit voltage (much higher than shutdown voltage) being present at the DC connection plug – that is what the manual is describing.
Is it compatible with SMA 110KW core 2?
Hasan, SMA does not include a SunSpec certified rapid shutdown transmitter in the CORE2, so the JMS has not gone through compatibility testing with that inverter. The JMS-F is certified for use only with the Sunny Boy US-41 and CORE1 US-41 lines.
The shutdown module says it will not operate with less then 14 volts. Using 100 watt panels it may not enable the panel at times. Am I understanding that correctly? Why are 2 100 watt panels not able to be used with 1 device? Thank-you for your feedback.
Greg – Please make sure you are looking at the most current datasheet The minimum voltage of the JMS-F device is 10V. It is possible that low voltage modules would be close to this voltage. SMA does not manufacture the JMS-F device, you can contact JMTHY to inquire if two series connected 100W modules could be connected to one device. Please note that the device power, voltage and current limits cannot be exceeded, and code limits voltage to below 80V within the array when Rapid Shutdown is triggered. So if the modules you are considering could have a Voc of over 40V each in the coldest temperatures, this setup would not be code compliant.
With the installation of these rapid shutdown devices, can the SMA Secure Power Supply option still be included and function while remaining NEC 2017 compliant?
Jonathan – The SunSpec transmitter in SMA inverters is configured to stop transmitting when the inverter loses AC power. This is done to allow any AC disconnect to serve as the Rapid Shutdown initiator. Use of the SunSpec shutdown does prevent the Secure Power Supply functionality of the Sunny Boy US line from working.
Um… I have sunspec. Modules installed and SPS working… Is this possible with the TS4-R-F? I originally wanted the T4S-A-Os but my installer got spooked by the “9 volt solution”… So I just have these now… But SPS is working for me… What is different with my system?
Garrett – This should not be occurring if installed according to SMA instructions. With SunSpec transmitter turned on in the inverter, when grid power is lost, the array should go into shutdown. If the SunSpec transmitter is not turned on, the array should remain in Shutdown mode at all times, with or without the grid. I recommend contacting SMA service at Service@SMA-America.com to ensure that you are complying correctly with code, or discuss with your installer.
What about this info from a SMA technical note:
This can be achieved if the following conditions are met:
1. The inverter model is SBx.x-1SP-US-41 with a firmware package of 3.01.11.R or higher
2. The inverter operating parameter for Rapid Shutdown Mode has been correctly set to:
TS4 Shutdown
3. Therearetwo9-Voltbatteriesconnectedinseries(18-Voltsintotal)connectedtothehighvoltage
side of the Secure Power Supply Switch (as shown in Figs. 1 and 2)
4. The user manually activates the Secure Power Supply switch
Under these conditions, when the utility grid is disconnected, the 9-Volt batteries energize the rooftop gateway, which releases the TS4-R-O devices from their rapid shutdown condition and therefore allows the inverter to commence operation from the DC inputs, assuming there is sufficient sunlight available.
Joshua – note in the Purpose section of that note that it applies only when the TS4-R-O (non-SunSpec) units are used for rapid shutdown, not the SunSpec receivers JMS-F.