Do I need a ferrule for stranded wire?

A ferrule is highly recommended for stranded wire in screw, spring and push-in terminals. It standardizes the conductor shape, improves clamp contact and prevents stray strands from being cut by the clamp.

What strip length do I need?

Follow the terminal datasheet. Typical strip length is 8 to 12 mm for 5.08 mm pitch blocks. Too short leaves contact area; too long exposes copper outside the clamp.

Can I put two wires in one terminal?

Some terminals are designed for twin-wire entry; others are single-wire only. Use a twin ferrule to fit two stranded conductors into a single-wire block, or specify a twin-entry block for repeated multi-conductor terminations.

AWG 12 is what in mm squared?

AWG 12 is approximately 3.3 mm squared. AWG 14 is about 2.1 mm squared. AWG 16 is about 1.3 mm squared. AWG 18 is about 0.82 mm squared. Always check the terminal datasheet for the actual conductor range.

Can I use solid wire in a screw terminal?

Yes. Solid wire is allowed in screw terminals but cannot be re-used many times without fatigue. Stranded or ferruled wire is more durable for serviceable connections.

What if my conductor is at the upper limit?

If the conductor is near the upper limit of the terminal range, confirm insertion is easy, clamp force is correct, and torque (for screw terminals) is within the rated range. Otherwise step up to a larger terminal or smaller conductor.

Terminal Blocks

Terminal Block Wire Size Guide: AWG, mm² and Ferrules

August 10, 2026 5 min read

Tags:

#AWG to mm2 #ferrule #solid wire #stranded wire #strip length #terminal block #twin wire termination #wire size

Correct wire fit is about more than matching an AWG number to a nominal mm² value. Engineers must check conductor class, strand construction, ferrule dimensions, strip length, number of conductors per clamping unit and the exact range covered by the terminal’s approval. This guide provides a practical starting point while keeping the final decision tied to the selected product datasheet.

Quick Reference: Approximate AWG to mm²

AWG and metric conductor sizes are different systems, so the values below are approximate comparisons rather than exact substitutions. The current column is a rough screening range only; allowable ampacity is governed by the wiring method, insulation temperature, ambient conditions and applicable code.

AWG	mm²	Max Current (Copper, 30°C)	Typical Terminal Pitch
26	0.14	2.2A	3.5mm
24	0.20	3.5A	3.5mm
22	0.34	5A	3.5, 5.0mm
20	0.50	7A	3.5, 5.0mm
18	0.75	10A	5.0, 5.08mm
16	1.5	15A	5.08, 7.5mm
14	2.5	20A	5.08, 7.5, 7.62mm
12	4.0	25A	7.5, 7.62, 10.16mm
10	6.0	35A	10.16mm
8	10.0	50A	Screw terminal >10mm²

1. Ferrules: When They Help and When They Are Required

A wire ferrule, also called a cord-end terminal or bootlace ferrule, is a thin metal sleeve crimped onto a stranded conductor before insertion. Ferrules reduce strand splaying and can make production wiring more repeatable. They are not universally mandatory: many certified terminals accept flexible conductors without ferrules. Use a ferrule when the terminal instructions require or permit it and when the ferrule combination is covered by the intended approval.

Without Ferrule

Stranded wire → strands splay during insertion → some strands outside clamp → reduced contact area → hotspot

With Ferrule

Stranded wire → ferrule crimped on → solid cylindrical profile → clean insertion → all strands clamped → full contact area

Ferrule Standards

Standard	Color Code	Sizes
DIN 46228 Part 1	French blue, gray, black, etc.	0.14–10mm²
DIN 46228 Part 4	Same colors, with plastic collar	0.14–50mm²
UL listed ferrules	No color code	Per UL 486A

Several ferrule color systems are used internationally, and the same color can represent different conductor sizes. Treat color as a production aid only; verify the printed size, packaging and crimp-tool setting.

Ferrule Selection Checklist

Match the metal sleeve to the conductor cross-section and strand class.
Check that the crimped ferrule falls within the terminal’s ferruled-conductor range.
Use the specified strip length so the conductor reaches the full sleeve length.
Use a controlled-cycle crimp tool and the profile recommended by the ferrule supplier.
Do not tin stranded wire before clamping; solder can creep under pressure and reduce contact force.

2. Wire Strip Length

Strip length is determined by the terminal’s clamping geometry, not pitch alone. The values below are typical screening ranges; use the strip-length marking or datasheet for the exact product.

Terminal Pitch	Strip Length	Too Short	Too Long
3.5mm	5–6mm	Wire not clamped	Exposed conductor — shock hazard
5.0mm	6–7mm	Poor contact	Exposed >1mm — fails inspection
5.08mm	7–8mm	Incomplete insertion	Safety violation
7.5mm	8–9mm	—	—
7.62mm	9–10mm	—	—
10.16mm	10–12mm	—	—

No exposed conductor should be visible outside the terminal housing. If copper is visible, re-strip shorter or use a ferrule with an insulating collar.

3. Solid vs Stranded Wire in Terminals

	Solid Wire	Stranded Wire	Stranded + Ferrule
Push-in terminal	✅ Direct push	❌ Must use tool or ferrule	✅
Spring clamp	✅	⚠️ Ferrule recommended	✅ Best
Screw terminal	✅	⚠️ Ferrule recommended	✅ Best
Reusability	Good	Poor (strands deform)	Excellent
Vibration	⚠️ Can fracture	Better (flexible)	Best (gas-tight)

Many spring and push-in designs accept flexible conductors directly when the actuator is used. Ferrules are often recommended for fast, repeatable insertion, especially with fine strands, but the terminal instructions determine whether they are optional, required or not permitted.

4. Twin Wire Entry (Two Wires per Terminal)

Some terminals accept two wires in one clamping point:

Terminal	Twin Wire Capacity	Ferrule Required?
Screw, 2.5mm²	2 × 0.5–1.5mm²	Recommended
Spring clamp, 2.5mm²	2 × 0.5–1.0mm²	Required (one ferrule per wire)
Push-in, 2.5mm²	2 × 0.5–0.75mm²	Required

Twin entry halves the number of terminals needed. Common in PLC wiring (sensor 1 + sensor 2 share a common ground terminal).

Only place two conductors in one clamping unit when that configuration is explicitly approved. Some products accept unequal conductors or twin ferrules; others accept one conductor only. Never assume twin-wire capability from the opening size.

5. How to Specify the Connection Correctly

Record the complete combination on the drawing or work instruction:

Terminal block manufacturer and exact part number.
Conductor standard, material, cross-section/AWG and strand class.
Bare, ferruled or other approved preparation.
Ferrule part number and crimp tool where applicable.
Strip length and insertion inspection criteria.
Screw torque or actuator method.
Number of conductors allowed per clamping unit.

Common Questions

Is 14 AWG exactly the same as 2.5mm²?

No. They are close in cross-sectional area but belong to different sizing systems and may have different outside diameters and strand constructions. Select a terminal approved for the actual conductor designation.

Can I put two wires under one screw?

Only when the product data explicitly lists two-conductor use for those sizes and conductor types. Otherwise, use a distribution terminal, jumper or approved twin ferrule arrangement.

Should stranded wire be solder-tinned before insertion?

Generally no. Under sustained clamp pressure, solder can creep and relax the connection. Use the bare flexible conductor or an approved ferrule as specified by the terminal manufacturer.

Match the Terminal to Your Conductor

GSConn terminal families cover a broad range of conductor sizes and connection technologies. Provide the conductor standard, AWG/mm², strand class, ferrule preference, current and approval market to receive a compatible series recommendation and wiring specification.

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