Install Mid-Circuit Interrupters in PV Array
The Tesla Mid-Circuit Interrupter (MCI) is used within PV strings and arrays to meet the Rapid Shutdown requirements of NEC Article 690.12 (2017 and 2020 editions). For information on how the Tesla MCI functions with Powerwall+ as a Photovoltaic Rapid Shutdown System (PVRSS), see Appendix E: Solar Assembly Rapid Shutdown.
Always connect an MCI to one end of a series string or mounting plane sub-array string. Whether the MCI is connected to the “first” or “last” module in a series string is not important. The quantity and placement of additional MCIs within the string varies by the type of PV panel used (see table below).
The following table lists the systems that have been certified as UL 3741 PV Hazard Control Systems or PV Rapid Shutdown Arrays (PVRSA) when installed together with Powerwall+ and Tesla MCI in accordance with the compliance instructions linked in the table. This certification is in accordance with the NEC, Article 690.12 (B), and defines the required MCI counts as shown in the table. Refer to the applicable PVHCS datasheet for detailed listing instructions.
|Tesla ZS Systems (ZS Comp, ZS Span, ZS Ramp, ZS Seam)
|Tesla TxxxS modules (where xxx = 405 to 450 W, increments of 5)
|1 MCI per 3 modules1
|ZS PVHCS datasheet
|Tesla TxxxH modules (where xxx = 395 to 415 W, increments of 5)
|1 MCI per 3 modules
|Hanwha Q.Peak Duo Flat PV modules:
|1 MCI per 3 modules
|Tesla Solar Roof
|Solar Roof V3 Modules (SR60T1, SR72T1, SR72T2)
|1 MCI per 10 modules
|Solar Roof PVHCS datasheet
|Other Listed Modules and Mounting Systems
|Systems using certified PV modules and mounting systems other than those defined above are covered by Tesla's UL 3741 certification if they are in compliance with the PVHCS listing instructions
|Generic PV Array PVHCS datasheet
1 Exception: Tesla solar modules installed in locations where the max Voc for three modules at low design temperatures exceeds 165 V shall be limited to two modules between MCIs.
Installation Best Practices
- Ensure that Tesla MCIs are not stored prior to installation in environments with moisture or dirt
- Install the Tesla MCI in line with the PV modules using standard Staubli Type MC4 certified compatible connectors
- Ensure the MCI is minimum 12.7 mm (½ in) from glass or backside of a PV module
- For flat plate solar panel installations, ensure the MCIs do not directly contact the roof. For Solar Roof installations, see the Solar Roof Installation Manual for proper mounting guidance
- For easier servicing of flat plate solar panel installations, install the MCIs on the perimeter of the array if possible
- Always secure the MCI with appropriate wire management
- Ensure no more than 5 MCIs are connected per PV string
- Ensure that total DC circuit
length, from + MPPT terminal to - MPPT terminal (including module wire leads,
jumper wires and all wiring within the array boundary for any individual
string), does not exceed 160 m (525 ft) for single strings or 120 m (394) for
- Total DC circuit length refers to the entire round trip wire length, from inverter to the roof, then back to the inverter
- Ensure paralleled strings are the same length, or as close in length as possible (if the paralleled strings are different lengths, it is likely the MCIs will not function properly; this likelihood increases the greater the difference in paralleled string lengths)
- Keep a completed string diagram indicating the layout of the array and the placement of each MCI (either a paper copy, electronic copy available in the field, or both)
- Connect the positive and negative leads of the MCI to the corresponding positive / negative MC4 terminals of the PV modules or Solar Roof modules.
- For flat plate solar panel
installations, attach the MCI under the module frame.
- To attach the MCI using
ZEP Home Run wire clips, install the (2X) clips to the module frame and
clip both ends of the MCI leads, then slot the MCI underneath the metal
frame.NoteFor MCI-2, place the clips at least 2 inches (51 mm) from the MC4 connector, but no more than 6 inches (152 mm) from the connector.
- To bolt the MCI to an
existing hole in the frame, align the MCI through hole with the frame
and use the appropriate mounting hardware as defined in MCI-1 Mounting Hardware Sizing . NoteThis option is only available for MCI-1.NoteFollow all module manufacturer’s instructions before mounting the MCI to the module frame. Ensure there is at least ½ in (12.7 mm) between the MCI and the module substrate, and only mount the MCI using existing holes in the module frame.NoteFor rail PV systems, use any of the mounting holes to mount the MCI directly to the rail (see MCI-1 Mounting Hardware Sizing for mounting hardware sizes) or use the manufacturer’s module level power electronic mounting bracket and mount the MCI to the bracket.
- To attach the MCI using ZEP Home Run wire clips, install the (2X) clips to the module frame and clip both ends of the MCI leads, then slot the MCI underneath the metal frame.
- For Solar Roof installations,
mount the MCIs directly to the roof, above the Tile Footlaps and positioned at a
slight angle as pictured below. Use the appropriate mounting hardware as defined
in the table below. NoteFor MCI-2, attach each lead of the MCI to the corresponding Staubli MC4 connector, and place an MC4 cap on each of the remaining MC4 connectors.CAUTIONDo not twist the MC4 connectors on MCI-2. Twisting the connectors damages the electrical contacts inside, likely resulting in MCI failure.
|Wood Screw (No. 8)
|Screw (up to M4 (5/32"))
|Bolt (up to M8 (5/16"))
|Screw (up to M4 (5/32"))