MC4 Crimp Procedure That Passes the Pull Test: Strip Length, Crimp Height, Tool Setting, Assembly and Torque for UL 6703 Solar Connectors
Sep 10, 2026
Summary: A correct MC4 crimp on 10 AWG PV wire uses a 7 mm (9/32 in) strip, a full ratchet cycle in the 10 AWG die of a listed MC4 crimper, strands visible in the contact's inspection window with no strands outside the barrel, the contact clicked into the housing until it locks, and the cable gland torqued to 2.5 to 3 N·m (22 to 27 lb-in). A 10 AWG crimp made that way holds more than 40 lb (180 N) in a pull test; UL 6703 requires 8 lb (35 N) minimum retention, and most utility specs require 30 lb. The connector must be listed to UL 6703 and mated only with connectors its manufacturer lists as intermateable, per NEC 690.33(C). Do not use pliers, a generic terminal crimper, or the wrong die; the joint will pass visually and fail thermally.
What you need
| Item | Spec |
|---|---|
| Connector | UL 6703 male and female, 1000 or 1500 V DC to match the string, 10 to 12 AWG contacts (or 8 AWG contacts and housings for 8 AWG) |
| Wire | PV wire, UL 4703, 2 kV for 1500 V systems, 10 AWG stranded tinned copper, 600 to 2000 V marking as required |
| Crimper | Ratcheting MC4 crimper with 14, 12 and 10 AWG dies, listed or specified by the connector maker; ratchet must complete a full cycle to release |
| Stripper | PV wire stripper set to 7 mm, or an adjustable stripper that does not nick tinned strands |
| Spanner wrenches | Pair, for gland tightening and disassembly |
| Torque | Gland nut 2.5 to 3 N·m; hand tight plus a quarter turn with the spanner is the field equivalent |
Procedure
- Slide the gland nut and the sealing grommet onto the cable first, nut threads toward the cable end. This is the step everyone forgets once.
- Strip 7 mm (9/32 in) of insulation. Too short and strands do not reach the inspection window; too long and bare copper shows behind the barrel. Do not twist the strands.
- Select the contact: male pin goes in the female housing, female socket goes in the male housing. Check the housing marking; the contacts are not interchangeable between housings.
- Load the contact in the 10 AWG die with the open seam of the barrel facing the die's forming anvil, wire barrel in the die, the contact's locating tab against the tool stop. Insert the stripped wire until insulation touches the barrel end and strands show in the window.
- Crimp in one full ratchet cycle. The tool will not release until the die has closed completely; that is the point of the ratchet. Do not open the ratchet release lever to finish early.
- Inspect: strands visible in the inspection window; no strands outside the barrel; barrel closed with no gap at the seam; insulation not crimped under the barrel; contact straight, not bent at the crimp. A crimped 10 AWG barrel measures about 3.0 mm across the flats on most tools. If anything fails, cut it off and start again; a crimp cannot be re-formed.
- Insert the contact into the housing until it clicks. Pull back on the wire with about 10 lb of force; the contact must not move. If it does, the retention clip did not engage; withdraw with the release tool and re-insert.
- Seat the grommet and thread the gland nut onto the housing; tighten to 2.5 to 3 N·m with the spanner. Under-torque lets water past the grommet; over-torque cracks the housing.
- Pull test 10 percent of joints, and every joint on a string over 100 ft: a spring scale or a calibrated pull tester at 30 lb for ten seconds, no movement at the contact or gland.
- Mate the pair until the locking tabs click; confirm the two housings are from the same listed family. Label the string end.
Pull test numbers
| Reference | Minimum |
|---|---|
| UL 6703 contact retention | 35 N (8 lb) |
| Typical utility and EPC acceptance spec | 30 lb (133 N), no movement |
| Correct 10 AWG crimp, measured | 40 to 60 lb before strand failure |
| Pliers crimp, measured | 5 to 20 lb, and rising resistance under load |
The ten faults found in the field
- Gland nut left off the cable and forced on after crimping; grommet split.
- Wrong die: 12 AWG die on 10 AWG wire crushes strands; 10 AWG die on 12 AWG wire leaves a loose barrel.
- Ratchet released early with the lever; barrel not fully formed.
- Strands outside the barrel, creating a corrosion path and a heat point.
- Insulation inside the barrel; no metal contact on part of the barrel.
- Contact inserted backwards or the male contact in the male housing.
- Retention click not achieved; contact backs out under the gland.
- Mixed brands mated: UL 6703 intermateability violated, arc fault years later.
- 1000 V connector on a 1500 V string.
- Gland hand-tightened only; water ingress and corrosion within one season.
Quick answers
What is the strip length for MC4? 7 mm (9/32 in) for 10 and 12 AWG PV wire on standard MC4 and MC4 Evo2 contacts.
How much torque on the MC4 gland nut? 2.5 to 3 N·m (22 to 27 lb-in), with the spanner wrenches; hand tight plus a quarter turn.
Can I crimp MC4 with regular crimpers? No. Use a ratcheting MC4 crimper with the correct die. Other tools do not form the barrel to the listed dimension and fail pull and thermal tests.
How strong should an MC4 crimp be? UL 6703 requires 35 N (8 lb) retention; a correct crimp exceeds 40 lb and most specs test to 30 lb.
Conversions Tech stocks UL 6703 MC4 and MC4 Evo2 connectors, 1000 and 1500 V, 12 to 8 AWG, the ratcheting crimper, spanners and a full tool kit, plus factory-crimped and pull-tested MC4 jumpers from 5 to 100 ft when you would rather not crimp in the field. Read the intermateability rule in 1500 V strings and MC4 Evo2.
