Wire Ferrules — When You Need Them and How to Crimp Them Correctly

If you have ever tightened a stranded wire in a terminal and watched the fine strands splay out around the screw, you already know why wire ferrules exist. A ferrule is a small metal tube that gathers the strands together and turns a flexible conductor into a solid end that the terminal can grip securely. In this article you will see when you need a ferrule, how to choose the right size and how to crimp it properly.

What a wire ferrule is

A ferrule (also called a bootlace ferrule or cord end terminal) is a tube made of tinned copper. Most have a plastic collar at one end — it protects the wire insulation from bending, and its colour indicates the size. The ferrule is placed over the stripped end of the wire and pressed with crimping pliers, so the strands are compacted into one solid "pin".

Why you need one

• The strands don't splay. Without a ferrule some strands stay outside the terminal, and a loose strand can touch the neighbouring terminal and cause a short circuit.
• The screw doesn't cut the wire. With fine strands, the pressure of the screw can break some of them — the cross-section is reduced and the joint starts to heat up.
• The connection doesn't loosen. Stranded wire "settles" under the screw over time. A crimped ferrule keeps its shape and the contact stays tight.
• Faster and cleaner installation. The crimped end goes into the terminal in one move, without tidying up strands.

When it is required and when you don't need it

Always use a ferrule when:

• you connect a stranded (flexible) wire — for example flexible single-core wire or a cord — to a screw terminal of a circuit breaker, RCD, contactor, relay or terminal block;
• you work in a distribution panel with many connections next to each other;
• you connect two wires into one terminal — then use a twin ferrule;
• the device manufacturer explicitly requires it in the instructions.

You don't need one when:

• the wire is solid (single-core rigid) — it is already solid;
• you use a cable lug (ring or fork), because that is a different type of terminal.

Never tin the end of a stranded wire with solder instead of using a ferrule if it goes into a screw terminal. The solder gradually "flows" under the pressure of the screw, the connection loosens and starts to heat up.

How to choose the right size

The ferrule is chosen by the cross-section of the wire in mm² — 0.5, 0.75, 1, 1.5, 2.5, 4 and so on. If the wire is 1.5 mm², you need a 1.5 mm² ferrule. A larger ferrule will not crimp tightly, and the strands won't fit into a smaller one.

Be careful with colours. The collar colour is only a visual aid and is not the same across all manufacturers. The two most common systems are:

• 0.5 mm² — orange (common code) / white (DIN 46228-4)
• 0.75 mm² — white / grey
• 1 mm² — yellow / red
• 1.5 mm² — red / black
• 2.5 mm² — blue / blue
• 4 mm² — grey / grey

Our ferrules follow the first system: 0.5 mm² orange, 0.75 mm² white, 1 mm² yellow, 1.5 mm² red, 2.5 mm² blue and 4 mm² grey. The rule is simple: go by the mm² number, not the colour — especially if you mix ferrules from different suppliers.

What a code like E1508 means

Many ferrules are marked with a code of the form E + cross-section + length. For example E1508 means a ferrule for 1.5 mm² with an 8 mm long metal barrel, and E4012 — for 4 mm² with a 12 mm length. The length tells you how much to strip the wire.

Twin ferrules

When two wires have to go into one terminal, don't twist them together or push them in separately. Use a twin ferrule — it has a wide opening for two wires of the same cross-section. It is chosen by the cross-section of one wire: for two 1.5 mm² wires you need a 2×1.5 mm² twin ferrule, and for two 2.5 mm² wires — a 2×2.5 mm² one.

What to crimp with

A ferrule should only be crimped with ferrule crimping pliers. Ordinary pliers or cable lug crimpers squash it unevenly and the connection is unreliable.

The most convenient are self-adjusting ratchet pliers, such as the ferrule crimping pliers 0.08–6 mm². The jaws adjust themselves to the ferrule size, and the ratchet won't let you open them before the crimp is complete — so every ferrule is crimped with the same force. They produce a square profile that fits easily into both screw and spring terminals.

How to crimp — step by step

Step 1 — Strip the wire to the length of the metal barrel. For most ferrules up to 2.5 mm² this is 8 mm. Use wire strippers so you don't cut the strands.

Step 2 — Lightly twist the strands in the direction of their lay so they go in easily and none are left outside.

Step 3 — Insert the wire into the ferrule until the insulation stops against the plastic collar. The ends of the strands should reach the end of the metal tube or protrude only very slightly (up to 0.5–1 mm).

Step 4 — Place the ferrule in the pliers in the slot for the correct size (with self-adjusting pliers — simply in the jaws), so that only the metal barrel is crimped, not the plastic collar.

Step 5 — Squeeze fully until the ratchet releases the pliers.

Step 6 — Check. Pull the wire — the ferrule must not rotate or slip off. No strands should be visible outside it, and the insulation should sit inside the collar.

The most common mistakes

• Ferrule too large — it crimps loosely and the wire slips out.
• Wire stripped too long — bare copper is left between the collar and the insulation.
• Wire stripped too short — the strands don't reach the end and the terminal clamps an empty tube.
• Crimping on the plastic collar — the collar cracks and the metal is left under-crimped.
• Two wires in a single ferrule — use a twin ferrule.

If you are just starting out

The easiest option is a kit with both pliers and an assortment of ferrules — for example HSC8 crimping pliers with insulated ferrules or crimping pliers with 1200 ferrules in a case. If you already have pliers, the E-400 kit of 400 ferrules covers the most commonly used sizes.

Related articles

• How to choose the right cable size
• Circuit breaker curve B, C or D — how to choose the right one
• Heat shrink tubing — how to choose the diameter and install it correctly

Browse all cable terminals and ferrules and crimping tools in the store.

Important: Electrical installations must be carried out by a qualified electrician. The information in this article is for educational purposes only.