When you open a motor starter enclosure in the field, you rarely find a blank slate. Most industrial starters ship from the factory partially prewired. For a field electrician, the job isn't building the circuit from scratch; it's completing the control path starting from where the factory left off.
The amount of pre-installed wiring — often called "factory jumpers" — depends entirely on the design standard of the starter: NEMA or IEC.
The NEMA Standard
NEMA starters (common in North American legacy and heavy industrial plants) are typically sold as complete, integrated assemblies. The contactor and overload relay are mechanically and electrically linked at the factory.
Because NEMA starters are often used in "combination" configurations (where a disconnect switch or circuit breaker is in the same box), they frequently include pre-installed control jumpers. You open the enclosure and find the coil return path and often the seal-in circuit already wired.
The IEC Approach
IEC starters (predominant in global markets and modern compact machinery) are modular. The contactor, overload relay, and auxiliary contacts are separate components that snap together on a DIN rail.
While the power path connects automatically via internal bus bars when the overload snaps onto the contactor, the control circuit is almost always an "open book." With an IEC starter, you should expect to land every control wire yourself — from the coil return to the seal-in auxiliary.
The Three Key Factory Jumpers (NEMA)
In a typical NEMA starter, three factory connections save you time and reduce the number of conductors you need to pull to your pushbutton station.
1. The A2-to-95 Jumper (Coil Return) This is the most critical factory connection. It routes the return side of the contactor coil (A2) through the normally-closed (NC) contact of the overload relay (terminal 95). If the motor draws too much current, the overload trips, opening the 95-96 contact and de-energizing the coil.
Following the NEMA/JIC convention, the overload contact sits on the return side of the coil. This factory jumper enforces that standard — and it's why you'll never need to wire this connection yourself on a NEMA starter.
2. The Terminal 3-to-A1 Jumper (Seal-in) On NEMA starters, the built-in holding contact (the normally-open auxiliary used for "sealing in" the circuit) has its output pre-wired to the coil. Terminal 3 (IEC designation: 14) connects directly to coil terminal A1. In the field, you land your START button output on terminal 3 (IEC: 14) — the same node as A1 — and run a wire from terminal 2 (IEC: 13) back to the stop/start junction to complete the seal-in path.
3. The L1-to-Control Tap (Common Control) In "common control" setups, the control circuit runs at the same voltage as the motor (208V or 480V line-to-line). A factory jumper taps power from the L1 line terminal and brings it to the start of the control circuit. This jumper must be removed if you are using a control transformer to step down the voltage for the pushbutton station.
See the Factory Jumpers
The animation below shows the interior of a NEMA motor starter. Press Play to see each factory jumper wire appear with an explanation of what it does.
This is the interior of a NEMA motor starter. Press Play to see the factory jumper wires that come pre-installed.
What the Field Electrician Adds
With the factory jumpers in place, the field electrician only needs to land a few control connections to complete the circuit:
- Control power from the factory L1 tap (or control transformer) to the STOP button.
- Stop-to-Start jumper between the pushbutton station terminals — this often comes pre-installed inside the pushbutton station itself.
- Start output to terminal 3 (IEC: 14) on the holding contact — this is the same node as A1 via the factory jumper.
- Seal-in return from terminal 2 (IEC: 13) back to the stop/start junction.
- Return conductor from OL terminal 96 back to L2 (or the transformer secondary).
The three-phase power conductors (L1/L2/L3 to the starter, T1/T2/T3 to the motor) are separate from the control circuit and are always field-installed.
IEC: The Same Circuit, All Field-Wired
With an IEC starter, the circuit logic is identical — the same coil, overload, and seal-in arrangement. But there are no factory jumpers to start from. Every control wire is yours to land.
By convention (IEC 60204-1), IEC circuits place the overload contact on the hot side of the circuit — before the STOP button. This ensures that if a trip occurs, the entire control string is de-energized from the ungrounded conductor. You have the flexibility to place it where your installation requires, but the hot-side placement is the industry standard for IEC equipment.
IEC starters also use a different terminal numbering system for the auxiliary contacts: 13/14 for the first NO pair, 21/22 for the first NC pair. NEMA starters label the built-in holding contact terminals as 2 and 3.
Beyond the Contactor
In modern automation, Variable Frequency Drives (VFDs), soft starters, and reduced-voltage starters handle motor control electronically rather than with mechanical contacts. These devices don't have the same factory jumper conventions — motor protection is built into their software, and your wiring task shifts to low-voltage digital and analog signals. We'll cover these in future articles.
Summary
Understanding factory prewiring is about knowing where your work begins. On a NEMA starter, you're looking for the jumpers that are already there so you don't wire "around" them. On an IEC starter, you're prepared to build the entire control path from the rail up.
Reading is one thing — wiring it yourself is another. Open the interactive trainer and build this circuit from scratch.
Practice Wiring a NEMA Starter →