Wire Length Measurement Guide

One of the most common problems leading to wire harness redesign is a harness that is not the right length, either too short to reach all terminals or too long to be routed cleanly. This article explains how MiniProto measures wire lengths for harnesses designed using the harness design tool (custom drawings provided will be interpreted as noted in the drawing).

General Guidelines

1. Wire lengths are measured along the exposed length of wire.

2. Any part of a wire covered by a connector, protector, or heatshrink (even if transparent) is treated as unexposed and therefore not part of the wire length.

3. Splices generally measure approximately .50-.75in (12.7-19.1mm) of exposed copper with .25in (6.4mm) of heat shrink overlap with either side of the wire insulation.

4. If in doubt, a first article photo may be requested at no cost to the customer. Email support@miniproto.com to request.

Simple Harness Examples

In this simplest of examples, the black wire length is measured along all exposed length of wire between each connector.

Some connectors, such as this XT60, have optional snap-in protectors. Since these cover the wire, the length is measured from where the wire exits the protector.

Heat Shrink Examples

An unprotected XT-60 harness still requires heat shrink, which is applied per guideline 3. A Molex Perma-Seal terminal on the other end, though transparent, still covers the wire, so the length is measured from the end of the integrated heat shrink as shown.

The heatshrink applied per guideline 3 measures approximately .25in (6.4mm) here.

Spliced Examples

In a more complex example, the two blue dimensions measure approximately .25in (6.4mm) while the orange dimension measures approximately .50in (12.7mm).

The red wire lengths would therefore be measured as above.

This example includes a barrel connector with integrated strain relief and a wrapped two conductor cable. The length is measured as shown as this translates to the “exposed length of wire” principle.

Additional Notes

Unfortunately, it can often be difficult to determine the overall length of the harness (including the connectors). MiniProto provides the best available datasheet for each connector in the online configuration tool by clicking the button shown below.** **

If any questions remain, please do not hesitate to contact support@miniproto.com with any questions. We are happy to provide assistance, measurements, pictures, and even fully labeled first article inspection photos on request.