What a supply-side connection is
A supply-side connection (often called a line-side tap) ties the solar or storage output into the service conductors between the utility meter and the main service disconnect, instead of into a breaker on the panel’s busbar. Because the power never passes through the busbar, the 120% rule doesn’t apply. It is covered by NEC 705.11, which the 2020 NEC rewrote as “Supply-Side Source Connections” and the 2023 NEC renamed “Source Connections to a Service.”
When to use one
- The panel fails the busbar rule and derating the main isn’t possible
- The panel has no open breaker spaces
- The system is larger than the busbar can take, even at 120%
- The existing panel is obsolete or recalled and the customer isn’t replacing it yet
What 705.11 requires
- Output rating: the sum of the power sources’ continuous output current on a service can’t exceed the ampacity of the service conductors (sources controlled by a power control system under 705.13 are handled separately).
- Conductors: sized to 705.28, and not smaller than 6 AWG copper or 4 AWG aluminum.
- Connections: made with listed connectors suitable for the purpose (230.46 in the 2020 and 2023 editions for splices and taps on service conductors), without overfilling the enclosure, and following the equipment manufacturer’s instructions where the tap is made inside existing equipment.
- Overcurrent protection: the 2020 NEC requires it within 10 ft of conductor length from the connection for dwellings (16.5 ft for other buildings). The 2023 NEC dropped those distances and points to Part VII of Article 230 instead. “Conductor length” includes every bend, so the real distance is shorter than it looks.
- Disconnect: a service-rated, lockable disconnect with fuses or a breaker, usually a fused AC disconnect beside the meter.
- Grounding and bonding: treated like service equipment: bring the neutral to the disconnect and bond it there per Article 250.
Section numbers inside 705.11 moved between 2017, 2020 and 2023; cite the edition your jurisdiction has adopted.
Coordinate with the utility
- Some utilities don’t allow taps inside the meter socket or a meter-main; others require a specific tap box.
- Making the tap usually means pulling the meter or cutting service, so book the utility disconnect before the install day.
- The interconnection application should show the supply-side connection on the one-line diagram.
What to show on the plan set
- The tap location and method on the line diagram, with the listed tap connectors named
- Conductor sizes from the tap to the fused disconnect, and the conductor length
- The fused disconnect’s rating and fuse size, and the neutral and bonding connections
- The source directory (705.10) and the labels at the service equipment
- The equipment location on the site plan
How Ballast Solar handles it
When a panel fails the busbar check, Ballast Solar offers the supply-side tap as one of the fixes and checks the 705.11 requirements for your adopted edition. See also rapid shutdown and the plan set checklist.
Questions
What is a supply-side tap for solar?
A connection of the solar or storage output to the service conductors between the utility meter and the main disconnect, under NEC 705.11. It avoids the busbar, so the 120% rule doesn’t apply.
How far can the disconnect be from a supply-side tap?
Under the 2020 NEC, the overcurrent protection must be within 10 feet of conductor length from the connection for dwellings, or 16.5 feet for other buildings. The 2023 NEC removed those distances and refers to Article 230, Part VII.
What is the minimum wire size for a supply-side connection?
6 AWG copper or 4 AWG aluminum, and sized to NEC 705.28.
Do I need the utility for a line-side tap?
Usually yes. The tap is made on service conductors, so the meter is typically pulled or the service cut, and some utilities restrict taps in meter sockets. Check the utility’s interconnection requirements.
This guide explains the code for planning purposes. The adopted edition, local amendments and the AHJ’s interpretation govern; the contractor of record is responsible for the design.