Electrical Connectors

Electrical Connectors

Conductors are useless without good connections to hold everything together. Thus, having both properly sized cables and terminations suitable for the equipment you want to power is absolutely vital to keep your equipment running. This is where electrical connectors come in.

The use of specially designed connectors for finely stranded conductors has become especially in recent editions of the NEC (National Electric Code). For example, all of our SO cable is considered finely-stranded according to the 2011 NEC, so they require connectors identified for their particular strand class (e.g. class D, G, H, etc.).


Terminating Finely Stranded Cables

Due to the increased usage of fine-stranded conductors in recent years, the 2008 NEC introduced new codes for the connectors of such conductors. The definition of “fine-stranded” may vary, but the 2011 NEC requires the identification of connectors for conductor classes with higher strand counts than class B and class C conductors (article 110.14). Thus, conductor stranding class B and C conductors do not require specially identified connectors, but specially identified connectors are required for class D, G, H, K, and M conductors.

The American Society for Testing and Materials (ASTM) is an internationally recognized organization that sets the standards for conductor stranding. The NEC follows ASTM standards for conductor stranding.

Please refer to “Conductor strand classes” below to see table 10 (a new table in chapter 9 of the 2011 NEC) that lists class B and class C copper and aluminum conductor strand counts.


Types of Electrical Connectors

Just like how there are many types of cables for various applications (fixed or portable, welding, battery, marine, communication, light or heavy duty, elevator, etc.), there are also many different types of connectors. However, it’s helpful to group connectors into two general categories:

Terminal Connectors

These electrical connectors are attached to the ends of conductors and connect cables to circuit or equipment terminals.

USB and household power plugs are common examples of terminal connectors.

Splice Connectors

These electrical connectors join two or more wires together and can be used anywhere along the length of a cable.

These types of connectors are often used as a method to repair wires by removing the damaged portion and splicing together the newly created ends. There are special tools you can use, such as twist-on (wire nut) or T-tap connectors, but you can also splice a cable by manually twisting the ends together and using solder and heatshrink to protect the conductors.

NEC 110.14(B) further specifies that soldered splices must be mechanically and electrically secure prior to soldering. It must also be covered by insulation with the same ratings as the insulation on the conductors or an insulating device (e.g. heat shrink) identified for use with wire splices.


Pressure (e.g. Crimp or Screw) or Solder Connections

For a connector to work, there first has to be a secure connection between the conductor and the connector itself. You will either have crimp, solder, or screw contacts in the connector to secure the conducting wires. An example of a single conductor crimp connector is shown below.

How to Crimp a Lug Connector (Using the TH0007 Crimper)

Crimping a lug connector step 1
Crimping a lug connector step 2
Crimping a lug connector step 3
Crimp integrity

STEP 1 Place terminal in jaw of crimper. Place stripped wire in terminal.

STEP 2 With crimper on solid surface, strike crimp ram with hammer 1-2 times.

STEP 3 When hammer impact feels solid, the crimp is complete.

NOTE: Some crimpers come with a gauge, but with variations in wire, terminal wall thickness and material used, this feature is a recipe for bad crimps. Using the force method above will guarantee perfect crimps every time. Once the terminal completely envelopes the wire, the crimper will not move and when struck will feel "solid". See guaranteed crimp quality photo above.


How to Select Electrical Connectors

Always consult a licensed electrician if you are not sure about a wiring issue, but we also recommend looking at the latest UL White Book and article 110.14 in the NEC for more information on connector sizing. “Wire Connectors” are covered under section ZMKQ in the 2012 UL White Book.

The following ratings should be marked either on the connector itself or the unit container.

Wire Size

Electrical connectors are rated to accept a specific range of conductor sizes. Wires too large or too small lead to poor connections.

Current (Ampacity) and Voltage

It should go without saying that the ampacity of a connector should be equal to or higher than the ampacity of SOOW wire itself for a given voltage rating (e.g. x amps at y volts).

Remember to size a conductor according to the the weakest link (such as a terminal or some other device) connecting to that conductor. Similarly, the rating of equipment terminals may limit the ampacity rating of the connector to the equipment terminal.

Conductor Material

Not many connectors are rated for use with aluminum and copper conductors in direct contact without some sort of adapter. A current running through a circuit with copper and aluminum in direct contact will cause the metals to corrode, quickly fail, and possibly start a fire due to the higher resistance in the corroded area.

Marking For use with
CU Copper Only
AL Aluminum Only
AL-CU or CU-AL Copper-Copper
Aluminum-Aluminum
Direct physical contact between copper and aluminum conductors are not permitted
AL-CU (intermixed - dry locations) Copper-Copper
Aluminum-Aluminum
Intermixed and direct physical contact between copper and aluminum conductors are allowed

Conductor Strand Class

The definition of “fine-stranded” may vary, but the 2011 NEC requires conductor strand classes higher than class B and class C to use connectors identified for use with that specific strand class (article 110.14). Thus, specially identified connectors are required for conductors with a strand class higher than class B and C (e.g. D, G, H, I, K, or M). This is because loose strands that fail to make a connection with the intended contact surface are more likely to result when terminating finely stranded conductors.

Table 10 in chapter 9 (shown below) is a new addition to the 2011 NEC, and is reproduced from UL Standard 486 A-B.

Conductor Size Number of Strands
Copper Aluminum
AWG or kcmil mm2 Class B Class C Class B
24 - 30 0.20 - 0.05 a - -
22 0.32 7 - -
20 0.52 10 - -
18 0.82 16 - -
16 1.3 26 - -
14 - 2 2.1 - 33.6 7 19 7b
1 - 4/0 42.4 - 107 19 37 19
250 - 500 127 - 253 37 61 37
600 - 1000 304 - 508 61 91 61
1250 - 1500 635 - 759 91 127 91
1750 - 2000 886 - 1016 127 271 127

aStrand counts vary.

bAluminum 14 AWG (2.1 mm2) is not available.


Number of Conductors

Unless otherwise marked, only use a single conductor for a connector. Sometimes the number of conductors is identified in parenthesis in front of the wire size rating. Some connectors will have separate wire size ranges for single conductor and multiple conductors. For example, your typical household power plug uses a connector that can hold either two or three conductors (i.e. two- or three-prong power plugs).

Torque Tightening

Make sure a connector is torqued properly (i.e. screwed on with enough force) or you’ll end up with loose connections which will fry your terminals.

Insulation Temperature

If the insulation temperature rating is too low the insulation may get easily damaged and burned, exposing the conductors inside and leading to premature wear and failure.