NEC 705.11 Supply-Side Tap (Line-Side Connection) Engineering & Wire Sizing
Everything electricians and DIY permit applicants need to know about NEC 705.11 Supply-Side Taps: minimum 6 AWG copper wire mandate, 10-foot tap conductor length limit, UL-listed IPC connectors, and fused AC disconnects.
1. NEC Code Rules & Electrical Engineering Breakdown
NEC 705.11(B) Minimum Conductor Size (Never Smaller Than 6 AWG Cu!): Even if you are only connecting a small 20A solar inverter via a Supply-Side Tap, NEC 705.11(B) strictly prohibits using tap conductors smaller than 6 AWG copper or 4 AWG aluminum on the supply side of the service disconnect because fault current ahead of the main breaker is limited only by the utility street transformer!
NEC 705.11(C) Maximum 10-Foot Tap Length to Fused Service Disconnect: For single-family dwellings, the supply-side tap conductors from the point of connection on the service entrance wires to the new Solar Fused Service Entrance Disconnect must not exceed 10 feet (3.0m) inside a raceway.
UL-Listed Connectors Required (NEC 705.11(E)): Splices or taps on service entrance conductors must use connectors explicitly listed for "Service Entrance / Supply-Side Tap" use (such as Ilsco KUP-L-Tap IPCs or NSi Polaris Grey/Black multi-tap blocks)—never standard split-bolts without listing.
2. Field Calculation Worksheet & Amperage Table
NEC 705.11 SUPPLY-SIDE TAP HARDWARE CHECKLIST ------------------------------------------------------------------ 1. Tap Connectors: UL-Listed Insulation Piercing Connectors (Ilsco IPC) or Polaris 2. Tap Conductors: Min 6 AWG Cu THHN/THWN-2 (Up to 60A) or 3 AWG Cu (100A) 3. Tap Length: ≤ 10 Feet in EMT / Rigid / Schedule 80 PVC Conduit 4. Disconnect: 60A or 100A Service-Entrance Rated Fused AC Switch (with Class R/J Fuses) 5. Grounding: Neutral bonded to Enclosure inside the Fused Service Switch (NEC 250.24)
3. Recommended UL-Listed Hybrid Hardware
Run Interactive NEC 220 Critical Loads Sizer →Inspector & NEC Compliance FAQ
Why must the AC disconnect on a Supply-Side Tap be FUSED and Service-Entrance (SE) rated?
Because a Supply-Side Tap connects ahead of your main breaker, there is zero overcurrent protection between the utility transformer and your tap wires! The new disconnect IS a Service Entrance Disconnect and must contain current-limiting fuses (not an unfused pull-out) and a neutral-to-ground bond.
Does adding a Supply-Side Tap violate the "Six Disconnect Rule" in NEC 230.71?
Under the 2020 and 2023 NEC 230.71, new services cannot rely on 6 switches in a single enclosure, but NEC 230.82(6) and 705.11 explicitly permit an external supply-side solar/storage disconnect mounted in a separate enclosure adjacent to the main service.