# Breaker test pins (primary injection tulips)

These are copper alloy pins for primary injection testing of molded case circuit breakers. A test set pushes a high current through each pole of the breaker to check its trip times, and the pin connects the test set's heavy output cable to the breaker's terminal without stripping a real conductor into the lug.

The hex end slides through the hole in the breaker's plastic terminal cover and into the set-screw box lug, where the lug screw clamps on a flat. Behind the hex is a short round neck, then a smooth tangent "tulip" turned straight onto the square bar, so there is no sharp shoulder at the point where a pin levers against the lug mouth and where soft pins bend and crack. Everything behind the tulip is one solid rounded-square section with no holes and no round body. The cable's lug pad lies flat on it and is clamped with vise-grips, which is quick to put on and take off.

## What changed in 1.1.0

There are now seven sizes. The first six follow the Ampteks traditional six-piece set of hex sizes (3/16, 7/32, 1/4, 5/16, 3/8 and 1/2 inch across flats), and size 7 keeps a 5/8 inch hex for large frames. The round body section from 1.0.0 is gone, and the whole pin behind the tulip is now a longer rounded-square section.

## Material and finish

Use C18150 (chromium zirconium copper) or C18200 (chromium copper), precipitation hardened and cold worked to TH04 temper or equivalent. These alloys keep about 80 percent of pure copper's conductivity but are several times stronger than C110, so the hex holds its shape under the lug screw and doesn't bend at the lug mouth. Annealed chromium copper is barely better than plain copper, so the temper matters. Leave the finish bare, degreased and clean, with no plating. Make each pin from one standard square bar (1/2, 5/8, 3/4 or 1 inch), ideally bar that already has radiused corners, so the square is left as stock and only the hex, neck and tulip are machined.

The site's material library has no chromium copper, so the model uses zirconium copper C15000, which has nearly the same density, to show colour and weight.

## Sizes (inches)

| Size | Frames | Hex across flats | Hex length | Neck dia | Square (corner radius) | Full square length | Overall |
|---|---|---|---|---|---|---|---|
| 1 | 15 to 30 A, lugs up to #8 or #6 | 3/16 | 2.00 | 0.230 | 1/2 (0.06) | 5.25 | 8.0 |
| 2 | 40 to 60 A, lugs up to #4 or #3 | 7/32 | 2.25 | 0.265 | 1/2 (0.06) | 5.00 | 8.0 |
| 3 | 70 to 100 A, lugs up to #1 | 1/4 | 2.25 | 0.300 | 1/2 (0.06) | 5.00 | 8.0 |
| 4 | 100 to 125 A, lugs up to 1/0 or 2/0 | 5/16 | 2.50 | 0.375 | 5/8 (0.075) | 4.75 | 8.0 |
| 5 | 150 to 225 A, lugs up to 3/0 or 4/0 | 3/8 | 3.25 | 0.445 | 3/4 (0.09) | 4.50 | 8.5 |
| 6 | 250 to 400 A, lugs up to 350 kcmil | 1/2 | 3.75 | 0.590 | 1 (0.125) | 4.375 | 9.0 |
| 7 | 400 to 1200 A, lug barrels up to 500 or 600 kcmil | 5/8 | 4.00 | 0.735 | 1 (0.125) | 4.625 | 9.5 |

The tulip is 0.50 inch long on sizes 1 to 5 and 0.625 inch on sizes 6 and 7, and the neck is 0.25 inch. The hex tip has a 30 degree chamfer.

## How the sizes were chosen

Each hex's across-corners size fits the largest wire its frame range takes, with a little clearance, so small hexes go with small frames. The hex length is the lug depth, plus the terminal cover depth, plus about a quarter inch, so the tulip stays outside the cover. Lug depths for the larger frames come from published Square D strip lengths (0.65 in on 150 A H-frames, 1.0 in on 250 A J-frames, 1.2 in on 400/600 A L-frames, 1.0 in on 800 to 1200 A frames), while the small-frame engagement of about half an inch is an estimate. Cover depths are partly estimated. The deepest published covers found were ABB Tmax XT high terminal covers, about 2.0 in on XT1/XT2 and 2.4 in on XT3/XT4, and most makers don't publish cover hole depths at all. If your covers are deeper, use the hex length override.

The bending check is made at the lug mouth, using the hex's weakest bending direction, a design yield of 45 ksi and a safety factor of 3, with the load at the middle of the last 4 inches. The allowable load is about 2, 3, 4, 9, 15, 33 and 61 lbf for sizes 1 to 7. The square's section is 3 to 8 times the hex's, so it never limits strength or heating. At 300 percent of the frame rating, the hex warms at well under 1 degree C per second on sizes 1 to 6 and about 1.7 on size 7 at 3,600 A, and instantaneous tests are too short to matter.

## Usage notes

Sizes 1 to 4 are for small frames and light test leads. Support the cable so it never hangs off the pin, because the small hexes can only carry a few pounds.

On 1200 A frames with multi-barrel lugs, use one pin per lug barrel, with one cable on each pin, so each pin carries only its share of the test current.

## Parameters

`size` picks the size (1 to 7). `hex_length` overrides the hex length in inches (0 keeps the size default). `overall_length` overrides the overall length in inches (0 keeps the size default). The pin axis runs along +x with the hex tip at the origin. Dimensions are set in inches, and the model is built in mm.