Open a motor control panel built in Ohio in 2005 and trace the overload relay contacts. Open an identical-function panel built in Stuttgart that same year and trace them again. The circuits do the same thing. The overload protection works the same way. But the 95-96 contact is wired into a different part of the control circuit — and both installations are correct.
This is not a wiring error, a regional shortcut, or a sign that someone improvised. It is the result of two engineering standards arriving at two defensible answers to the same question: where should the overload relay's normally-closed contact interrupt the coil circuit?
The Contact in Question
Every thermal overload relay has a set of normally-closed auxiliary contacts designated 95-96 per IEC 60947-1 terminal marking conventions. These contacts sit in series with the contactor coil. When the relay's heaters detect sustained overcurrent and the bimetallic mechanism trips, the 95-96 contact opens, the coil circuit breaks, and the contactor drops out. The motor stops.
The contact is bidirectional — terminal 95 can be the input or the output. What matters is that it appears somewhere in the series path between the hot conductor and the coil return. The question is where in that path.
Two answers have become standardized.
OL Contact Position in the Control Circuit
Return-Side Placement: The NEMA Convention
In the North American tradition governed by NEMA standards, the 95-96 contact is placed on the return side of the coil — between the coil's A2 terminal and the return conductor (L2 in a line-voltage circuit, X2 in a transformer-fed circuit).
The control circuit path reads:
L1 → STOP (NC) → START (NO) → Coil A1 ... Coil A2 → OL 95 → OL 96 → L2
This is how NEMA-rated motor starters ship from the factory. Allen-Bradley 509-series, Eaton Freedom/AN16, Square D 8536, Siemens Class 14 — all of them leave the production line with two internal jumper wires already installed: A2 to 95 and 96 to L2. The electrician in the field never touches these connections. The overload protection is pre-wired as part of the assembly, and the field wiring is limited to the hot-side control chain (STOP, START, seal-in) and the power terminations.
This convention exists for practical reasons, not arbitrary ones.
Factory prewiring eliminates a failure mode. If the OL contact must be field-wired, it can be forgotten. A motor starter with 95-96 left unconnected will run without overload protection — the coil energizes through the STOP/START chain and the OL contact is simply not in the circuit. The motor runs until something burns. By prewiring the return path at the factory, NEMA starters make this mistake structurally impossible.
Troubleshooting is cleaner on the return side. A ground fault on the return conductor does not mask the behavior of the OL trip. The OL contact opens, the coil loses its return path, and the contactor drops — regardless of what else is happening on that side of the circuit. The failure mode is unambiguous.
This convention is documented across NFPA 79 (Industrial Machinery), NEMA ICS 2 (Industrial Control and Systems: Controllers, Contactors, and Overload Relays), and referenced in NEC Article 430 motor circuit provisions. It is what most North American trade programs, apprenticeship JATCs, and electrical training curricula teach as the standard configuration.
Hot-Side Placement: The IEC Convention
IEC 60204-1 — the international standard for Safety of Machinery, Electrical Equipment of Machines — takes the opposite position. The 95-96 contact is placed on the hot side of the coil circuit, between the hot conductor and the first control device (typically the STOP button).
The control circuit path reads:
L1 → OL 95 → OL 96 → STOP (NC) → START (NO) → Coil A1 ... Coil A2 → L2
The OL contact is now the first device the current encounters after leaving the hot bus. The engineering rationale is different from NEMA's, and it is equally sound.
The OL contact interrupts the ungrounded conductor. In a ground fault scenario where the return conductor accidentally contacts the grounded enclosure, a return-side OL contact might not cleanly de-energize the coil — the fault provides an alternate return path that bypasses the open contact. With the OL on the hot side, a trip opens the circuit upstream of everything else. No current reaches the coil, the STOP button, or the START button, regardless of what faults exist downstream.
Arcing energy is lower. When the OL trips and the contact opens under load, the inductive kick from the coil creates an arc across the separating contacts. On the return side, the full coil inductance drives this arc. On the hot side, the arc energy is the same in magnitude, but the contact opens before the coil — the stored energy dissipates through the coil's own resistance and any suppression network rather than across the OL contact gap.
The convention aligns with IEC 60204-1 Section 9.4 and the broader CE marking requirements for machinery sold within the European Economic Area. Equipment bearing a CE mark and intended for the EU market will almost universally use hot-side OL placement.
You will encounter this convention on European-origin machinery (Schneider Electric, ABB, Siemens AG equipment designed for the EU market), on any CE-marked equipment imported into North America, and increasingly on new installations in US and Canadian plants that source from global OEMs. The trend line in North America runs toward IEC conventions as supply chains become more international.
Side by Side
| | NEMA (Return-Side) | IEC (Hot-Side) | |---|---|---| | OL position in circuit | After coil, before return | Before STOP, after hot | | Factory prewired? | Yes — NEMA starters ship this way | No — requires field wiring | | Ground fault behavior | Neutral-side, no fault interaction | Hot-side, better fault isolation | | Primary standard | NFPA 79, NEMA ICS 2 | IEC 60204-1 | | Common in | North America | Europe, global OEMs, newer NA installs |
Both Are Correct
There is no wrong answer here. In both conventions, the motor stops when the overload trips. The 95-96 contact opens, the coil loses excitation, the contactor drops, and the motor is disconnected from power. The protection function is identical.
What differs is the failure mode under fault conditions and the practical logistics of installation. NEMA's approach optimizes for field reliability — fewer wires to forget, fewer ways to install the starter without protection. IEC's approach optimizes for fault isolation — the contact position provides cleaner de-energization when something else in the circuit has already gone wrong.
Neither placement violates the National Electrical Code. NEC Article 430 requires overload protection but does not dictate the contact position within the control circuit. The choice is governed by the applicable machinery standard (NFPA 79 for domestic, IEC 60204-1 for international), the plant's engineering specifications, or the Authority Having Jurisdiction.
What to Look For in the Field
When you open a panel and need to identify the convention in use, trace the 95-96 wires:
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If terminal 95 or 96 connects to a coil terminal (typically A2), you are looking at return-side placement — the NEMA convention. The OL return path runs from the coil through the relay and back to the return bus.
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If terminal 95 or 96 connects to the hot conductor or the first control device (typically the STOP button's input terminal), you are looking at hot-side placement — the IEC convention. The OL sits upstream of the entire control chain.
Check the schematic on the inside of the panel door. The OL contact symbol — two bars with a diagonal slash — will appear either between the coil and the return rail (NEMA) or between the hot rail and the first control device (IEC). The position on the schematic matches the position in the field wiring.
If you maintain equipment from multiple OEMs or work in a plant that has been expanded over decades, expect to find both conventions in the same facility. This is normal. Neither needs to be "corrected" to match the other.
Reading is one thing — wiring it yourself is another. Open the interactive trainer and build this circuit from scratch.
Wire both conventions yourself →