How to check crimp terminals on wires?

A good crimping of a terminal on a cable increases the usable life time of the connection and avoids micro cuts when using the cable in a car or an aircraft.

When do you check wire terminal crimps ?
During the manufacturing cycle and at each change of processing settings, including :

Checking the first batch manufactured
Check for each new setup of machines or crimping pliers (tool exchange)
Check each coil change (if terminals are supplied in a coil)
Interim checks (every 1000 crimps for example)
Check the final crimp

There are 2 types of control: visual inspection and a tensile test.

A / Visual control: This is to visually check that the terminal is properly positioned on the wire. The lug rings must be tightly wrapped around the cable, no strand shall be out of the crimping. The cable end must appear at the end of the terminal and should not be folded or bent.

Wiretest 2

Wiretest T1

B / Tensile test: This very simple test is used to verify the correct crimp pull out force. Tensile tests are performed on a motorized test machine called a 'crimpt tester ' or' terminal pull tester' that performs this tensile test. These tests are destructive. They are performed either on pieces issued from the manufacturing process and prepared for these trials, or on samples made with wire of the same section (in the case of very long harnesses that canot been inserted on the machine.

The testing machine is equipped with a special receptacle for maintaining the terminal or utilizing a self closing grip. The cable is held by a special tool designed for not injuring the jacket. It can be a bit eccentric or self closing. Self closing grips can also be used in the case of high capacity, forces higher than 200 lbs (1000N).
The testing machine generally provides tension at a constant speed of 2 inch per min until failure of the crimp or the cable. It is also possible to use manual testers for small wires. The test sample is passed if the value found is above a reference value.

To define the reference value, there are general standards such as CEI760, or standards specific to certain industries (rail, aerospace, automotive).

The main values used are given, for guidance, in the following table :

		Minimum pull strength
Wire size (AWG)	Wire size (mm²)	MIL-T-7928		UL 486		MIL-DTL-22520G
AWG	mm² (1 wire)	Lb	N	Lb	N	Lb	N
26	0,128	7	31			5	22
24	0,205	10	45			8	36
22	0,324	15	67	8	36	12	53
20	0,519	19	85	13	58	20	89
18	0,75	38	169	20	89
16	1,31	50	223	30	134	50	223
14	2,08	70	312	50	223	70	312
12	3,31	110	490	70	312	110	490
10	5,26	150	668	80	356	150	668
8	8,37	225	1001	90	401	220	979
6	13,3	300	1335	100	445	300	1335
4	21,15	400	1780	140	623	400	1780
2	33,62	550	2448	180	801	550	2448
1	42,41	650	2893	200	890	650	2893
0	53,49	700	3115	250	1113	700	3115
00	67,43	750	3338	300	1335	750	3338
000	85,01	825	3671	350	1558
00000	107,22	875	3894	450	2003	875	3894