Contactor Terminal Numbering Across IEC, NEMA and UL: A1/A2, 13/14, 95/96

Every terminal on a contactor carries a number or letter, and those markings are not decorative. They are a compressed wiring instruction: A1 and A2 are the coil, 13/14 is a normally-open auxiliary contact, 21/22 is normally-closed, 95/96 is the overload relay’s trip contact. Read them correctly and a panel can be traced, tested and modified without a drawing. Misread them and a stop circuit gets wired through a normally-open contact, or a PLC input ends up on the wrong side of a trip contact.

This guide covers the whole terminal language of a contactor — power poles, coil, auxiliary contacts and overload relay — across IEC 60947, NEMA and UL conventions, including where the three systems genuinely differ and where they only look different. It deliberately goes beyond the power-circuit markings alone: if you only need L1, L2, T1, T2 on the main poles, that is covered in what L1, L2, T1 and T2 mean. What follows is the rest of the device.

Quick Answer: Three Layers, Three Conventions

The important structural fact: contactors use two different numbering philosophies at once. Auxiliary contacts follow a rule you can decode and extrapolate. Overload relay trip contacts use a fixed historical pair that you simply have to know. Mixing the two up is the origin of most terminal-related wiring errors.

The Auxiliary Contact Rule: Tens Digit Is the Contact, Units Digit Is the Function

IEC auxiliary contact numbering is systematic. The tens digit identifies which auxiliary contact it is (1, 2, 3, 4 …). The units digit identifies the function and which side of that contact you are on:

• units 1 and 2 — normally closed (NC) contact
• units 3 and 4 — normally open (NO) contact
• units 5 and 6 — early-make or late-break contact (special timing function)
• units 7 and 8 — special-purpose contact, function defined by the manufacturer

So contact number 1 has an NC pair at 11/12 and an NO pair at 13/14. Contact number 2 has 21/22 (NC) and 23/24 (NO). Contact number 3 has 31/32 (NC) and 33/34 (NO). This is why 21/22 is universally NC on IEC-pattern contactors while 13/14 is universally NO — and why an auxiliary block labelled 43/44 is an NO contact belonging to contact number 4, not “the 43rd terminal”.

The contact number does not tell you whether the contact is physical (a real block clipped onto the front or side) or integrated into the contactor body. Both are numbered the same way, which is convenient: a 21/22 on a side-mounted block behaves exactly like a 21/22 moulded into the frame, and both are normally closed at rest.

Power Poles: Odd Line, Even Load

The main poles carry the load, and two marking systems coexist. The letter system is what most buyers see on contactors sold internationally:

The numeric system is older European practice and is still printed on many DIN-rail and modular devices. Its logic is the same one that governs auxiliary contacts: odd on the line side, even on the load side. That consistency is worth remembering, because it is the only part of the power-pole marking that carries a rule rather than a label.

What the markings deliberately do not tell you is polarity or phase sequence. A three-phase contactor will close happily with L1/L2/L3 swapped; the motor simply runs backwards. On a reversing assembly that is the whole point of the second contactor, which is why the reverse unit’s load terminals are wired in swapped order — as shown in reversing contactor arrangements.

The Coil: A1, A2, and Why There Are Two A2 Terminals

Every IEC contactor coil has A1 and A2. The markings are the same under NEMA and UL practice, which makes the coil the one part of the device that is genuinely international.

Three details cause most of the confusion:

• Two A2 terminals. Large frames often provide two A2 terminals internally connected, one on each side, so a control wire can land on whichever side is convenient. They are electrically the same point — nothing needs bridging.
• DC coils and polarity. On DC coils, A1 is conventionally the positive terminal. A flyback diode or a diode-type suppressor fitted the wrong way round will short the control supply the first time the coil is energised, so the A1/A2 orientation matters when suppression is added. See coil surge suppression for the device-specific rules.
• Coil voltage is printed separately from the terminal designation — usually on a sticker or moulded into the coil former, e.g. “220–230 V 50 Hz”. The A1/A2 marking says nothing about voltage; that is why a 24 V coil and a 230 V coil look identical from the front. The voltage classes are covered in contactor coil voltage.

Overload Relay Terminals: 95/96 and 97/98 Break the Rule

A thermal overload relay does not follow the 1–2 / 3–4 auxiliary rule. It uses a fixed historical pair:

95/96 opens when the relay trips, which is why it is wired in series with the coil in a conventional starter: the trip removes coil voltage directly, without relying on any control logic. If the same contact is instead wired to a PLC digital input, the trip no longer stops the contactor by itself — the PLC has to act on it. That is a design decision, not a wiring accident, and it belongs in the drawing.

The 97/98 alarm contact is a frequent omission. It exists so a trip can be reported without breaking the control circuit, which is what you want on a plant where an unannounced trip is the expensive part. The internal contact arrangement is described in how a thermal overload relay works.

Where IEC, NEMA and UL Actually Differ

For most of the device, the three systems agree. The differences are concentrated in four places:

• Power pole marking. IEC technical literature favours 1/3/5 → 2/4/6; NEMA and North American product markings overwhelmingly use L1/L2/L3 → T1/T2/T3. Many export-market contactors print both.
• Auxiliary contact marking. IEC devices carry the tens/units numbering. NEMA-style definite-purpose and HVAC contactors frequently label auxiliary contacts simply “NO” and “NC” with no numbers at all, especially on small frames where the auxiliary is integral and not field-configurable.
• Overload relay. The 95/96 and 97/98 convention is European in origin and now essentially universal, including on UL-listed devices. It is the closest thing to a global standard on a contactor.
• Nothing at all for the coil. A1/A2 is used across all three systems.

Practical consequence: on an IEC device you can decode an unlabelled terminal from the number. On a NEMA-style definite-purpose contactor you cannot, and you should trace continuity rather than trust the print. The construction differences behind that are covered in definite purpose versus general purpose contactors.

Six Numbering Traps That Cause Real Wiring Errors

If a device is already wired and behaving incorrectly, the fastest diagnostic is continuity at rest: every NC pair should read closed, every NO pair open, with the coil de-energised. That single test catches most of the traps above before any control logic is suspected. For the wider wiring sequence, see how to wire a contactor.

Reading a Complete Device: Worked Example

Take a four-pole frame with one integral NO auxiliary and a clip-on NC block, carrying these markings: 1/2, 3/4, 5/6, 7/8 on the power side, A1/A2 at the bottom, 13/14 on the integral auxiliary and 21/22 on the clipped block.

• Four power poles, numbered in the old European scheme: 1-2, 3-4, 5-6, 7-8, with odd line / even load. Suitable for three phases plus a switched neutral, or four poles for a two-circuit load.
• Coil at A1/A2, voltage from the coil label, not from the terminal print.
• 13/14 is NO, contact number 1 — the natural seal-in or feedback contact.
• 21/22 is NC, contact number 2 — the natural interlock or “stopped” feedback contact.
• No 95/96 on the contactor itself: the overload relay is a separate block that bolts onto the load side and brings its own 95/96 and 97/98 terminals.

That reading is the whole value of the numbering system: from the print alone, the available functions and their rest states are known before a meter is connected. The contactor’s role relative to relays and breakers — and why it carries auxiliary contacts at all — is set out in auxiliary versus main contacts.

Frequently Asked Questions

What does 13/14 mean on a contactor?

It is a normally-open (NO) auxiliary contact. The “1” is the contact number and the “3/4” indicates an NO function, so 13 and 14 are the two terminals of the same NO contact. It closes when the coil is energised.

Is 21/22 normally open or normally closed?

Normally closed (NC). Units digit 1 or 2 indicates an NC contact, so 21/22 is closed at rest and opens when the contactor picks up. It is the standard choice for an electrical interlock or a “contactor is off” feedback signal.

Why does my overload relay use 95/96 instead of 21/22?

Overload relays predate the harmonised auxiliary numbering and kept their own fixed pair: 95/96 for the NC trip contact and 97/98 for the NO alarm contact. The convention is now used worldwide, including on UL-listed devices.

What is the difference between A1/A2 and L1/T1?

A1/A2 is the coil — the control circuit that operates the contactor. L1/T1 (or 1/2) is a main power pole that carries the load current. They are electrically isolated from each other and must never be interconnected.

Can I use any auxiliary contact for the seal-in circuit?

You need an NO contact, because the seal-in path must be open when the contactor is at rest and closed when it picks up. 13/14 or 23/24 are the usual choices; an NC pair such as 21/22 will make the contactor drop out as soon as the start button is released.

Do NEMA contactors use the same terminal numbers as IEC contactors?

Partly. The coil (A1/A2) and the overload relay (95/96, 97/98) are the same. Auxiliary contacts on NEMA-style definite-purpose frames are often marked only NO and NC without numbers, and the power poles carry L1/L2/L3 → T1/T2/T3 rather than 1/3/5 → 2/4/6.

The Practical Takeaway

Learn one rule and one exception. The rule: on IEC auxiliary contacts, the first digit identifies the contact and the last digit identifies the function — 1/2 NC, 3/4 NO — which makes every number on the device decodable. The exception: overload relay terminals 95/96 and 97/98 carry fixed historical functions that the rule does not predict, and confusing them disables motor protection. Everything else — A1/A2 for the coil, odd-line/even-load on the power poles — is consistent enough to trust. For frames where this numbering applies across the range, the LC1-D series contactors page lists the pole and auxiliary configurations available, and the AC contactor category covers the full range.