Split Bolt Connectors: Sizing, Torque, Taping, and Where the NEC Won’t Let You Use One

The split bolt is the oldest connector in the truck and still the most misused. Sized and torqued correctly, insulated properly, and kept out of the places the NEC excludes it from, it is a fast, reusable, inspectable splice or tap. This guide covers selection, installation, and the code boundaries — and links to our copper split bolt line, which crosses directly to Burndy SERVIT® KS, ILSCO IK, Blackburn Type H, and NSI N-series.

How a split bolt is rated

Every split bolt carries two numbers that matter: the range for equal main and tap (both conductors the same size, from the largest the saddle accepts down to the smallest that still seats) and the minimum tap with one maximum main (the smallest tap you can land beside a full-size run). A "6 AWG" split bolt might accept 6–10 AWG as equal conductors and take a #16 tap beside a #6 run. Manufacturers also publish whether the range is solid, stranded, or both — UL recognizes solid and stranded configurations at #8 and smaller, but stranded only at #6 and larger for many designs.

Selecting the right size

1. Identify both conductors. Run size and tap size, solid or stranded, copper or aluminum.
2. Pick by the larger conductor first. The run must sit inside the equal-range; then confirm the tap is at or above the minimum-tap figure for that connector.
3. Copper only unless dual-rated. Copper-alloy split bolts (Burndy KS, ILSCO IK, Blackburn H, our 610-series) are for copper and copperweld conductors. Aluminum or Cu/Al combinations need a dual-rated body with a spacer (Burndy KSU, ILSCO SK, Blackburn HPS/HPW) — NEC 110.14(A) prohibits mixing dissimilar conductors in a connector not identified for it.
4. Temperature and voltage. This class is rated 90°C and 600 V; the copper-alloy families are also UL 467 listed for grounding and bonding and suitable for direct burial in earth or concrete.

Installation and torque

1. Strip insulation to roughly the connector length plus 1/4". Do not nick strands.
2. Wire-brush the conductors bright. Oxide is resistance.
3. Seat the run in the bolt saddle, lay the tap alongside it (or in the pressure bar's opposite groove on designs with a two-groove bar), and hand-run the nut.
4. Torque to the value on the connector or its datasheet. Typical UL 486A-class values for the maximum conductor combination: 80 in-lb (#10–#8 bodies), 165 in-lb (#6–#4), 275 in-lb (#2), 385 in-lb (1/0–2/0), 500 in-lb (3/0), 650 in-lb (250–350 kcmil), 825 in-lb (500 kcmil). Smaller combinations in the same body take less — consult UL 486A Tables 7-4 to 7-6 or the manufacturer chart. A torque wrench is the difference between a listed connection and a guess.
5. Do not re-torque after the insulation goes on; split bolts do not have a break-off head, so torque discipline is on the installer.

Insulating the connection

A bare split bolt is an exposed conductor. NEC 110.14(B) requires splices to be insulated to at least the equivalent of the conductor insulation. Field practice: two layers of rubber (self-fusing) tape to fill the voids around the bolt, then two half-lapped layers of vinyl electrical tape over it — or a snap-on insulating cover sized to the connector, which saves tape and time and is reusable. On grounding conductors and bonding jumpers, covering is optional unless the spec calls for it.

Where the NEC will not let you use one

• Buried or encased grounding electrode conductor splices — no. NEC 250.64(C)(1) restricts GEC splices to irreversible compression or exothermic weld. A split bolt on a buried GEC fails inspection. Use a UL 467 irreversible compression connector instead.
• Concealed splices without a box — no. A split bolt splice in a branch or feeder circuit must be in an accessible box or enclosure (NEC 300.15, 314.29).
• Aluminum in a copper-only body — no. See 110.14(A) above.
• Where it is a good fit: service-entrance and feeder taps in troughs and wireways; bonding jumpers on equipment and structures; grounding electrode conductor taps that remain accessible; temporary power; motor and lighting taps in accessible enclosures; utility and telecom ground bars; and repair splices where a compression tool is not on site.

Split bolt vs. insulated multi-tap vs. compression

Cross-reference by size — Burndy KS, ILSCO IK, Blackburn H, NSI N — is in the companion table: Split Bolt Cross-Reference Chart. Every product page in the collection carries its own verified crosses and torque figure.