Decoding the 3 Phase 220V Wiring Diagram Symbols

While modern US NEC designations use 240V (or 208V for Wye systems), legacy equipment, international IEC grids, and Latin American standards frequently label this topology as a 3 phase 220V wiring diagram. Motor nameplates typically read 220/240V, meaning the physical wiring sequence remains identical across these nominal voltages. Before tracing the physical wires, you must translate the schematic symbols into physical components.

A standard Direct-On-Line (DOL) motor starter diagram relies on five core symbols:

  • Q1 (Disconnect/Breaker): Represented by a square with a diagonal line or a switch symbol. This is your 3-pole main disconnect.
  • KM1 (Contactor Coil): A rectangle or circle labeled with the coil designator. This is the electromagnetic relay that switches the high-current power.
  • 13/14 & 21/22 (Auxiliary Contacts): NO (Normally Open) and NC (Normally Closed) switches mechanically tied to the contactor, used for the control circuit and holding logic.
  • F2 (Thermal Overload Relay): A rectangle with a bimetallic strip zigzag inside. This monitors current draw and trips the control circuit if the motor overloads.
  • M (Motor): A circle with an 'M' and a 3-phase designation (often showing U, V, W terminals).
Nomenclature Note: When reading IEC vs. NEMA diagrams, IEC schematics (like those from Schneider Electric TeSys) separate the power and control circuits visually, whereas NEMA diagrams often draw them on a single ladder logic line. The physical wiring is the same.

Terminal and Pin Mapping: Physical Device vs. Schematic

The most common point of failure for DIYers and junior technicians is mismatching the schematic labels to the physical terminal screws on the contactor and overload block. Below is the exact pin mapping for a standard IEC-style DOL starter (e.g., Schneider LC1D09 contactor paired with an LRD overload).

Schematic Label Physical Terminal Function Standard US Wire Color (240V Delta/Wye)
Line In (Q1) 1/L1, 3/L2, 5/L3 Main power entry from breaker to contactor Black (L1), Red (L2), Blue (L3)
Line Out (KM1) 2/T1, 4/T2, 6/T3 Switched power out to overload relay Black, Red, Blue (with phase tape)
Overload In (F2) 1/L1, 3/L2, 5/L3 Power entry to thermal bimetallic sensors Black, Red, Blue
Overload Out (F2) 2/T1, 4/T2, 6/T3 Protected power out to motor peckerhead Black, Red, Blue
Coil (KM1) A1, A2 Contactor electromagnetic coil power Red (A1), Black/White (A2)
NO Aux (KM1) 13, 14 Normally Open contact for seal-in circuit Red (control voltage)
OL Trip (F2) 95, 96 NC contact to break control circuit on overload Black (control voltage)

Node-by-Node Trace: Source to Load (Power and Control)

To wire this safely, you must trace the power circuit and the control circuit separately, while maintaining a strict, unswitched ground path. According to NFPA 70 (NEC) Article 430, the ground must never pass through a switching device.

The Power Circuit Trace

  1. Source: 3-phase 220V/240V enters the 3-pole disconnect breaker. Terminals: Line side.
  2. Breaker Load Side: Three conductors (Black, Red, Blue) exit the breaker and land on the contactor's 1/L1, 3/L2, and 5/L3 terminals.
  3. Contactor Load Side: When the coil energizes, power flows through the main contacts and exits at 2/T1, 4/T2, and 6/T3.
  4. Overload Line Side: These three wires land directly on the thermal overload relay's 1/L1, 3/L2, and 5/L3 terminals.
  5. Overload Load Side: Power passes through the bimetallic strips and exits at 2/T1, 4/T2, and 6/T3, traveling directly to the motor's U, V, and W terminals in the peckerhead.

The Control Circuit and Ground Path

The control circuit operates the A1/A2 coil. In a 220V control setup, you pull one phase (e.g., L1) through a fuse, into the Start pushbutton (NO), through the Stop pushbutton (NC), and through the Overload's 95/96 NC terminals, finally landing on A1. The A2 terminal returns to L2. The auxiliary contacts 13/14 are wired in parallel with the Start button to "seal in" the circuit once released.

Polarity and Ground Path: 3-phase 220V Delta systems have no neutral. The Equipment Grounding Conductor (EGC) — a bare copper or green wire — must run directly from the panel's ground bar to the motor housing ground lug. Never switch, fuse, or route the EGC through the contactor or overload relay. If a phase faults to the motor casing, the EGC provides the low-impedance path back to the source to trip the breaker instantly.

Meter Verification: Proving the Circuit Dead and Live

Never assume a diagram matches the physical reality of a panel. Use a CAT III or CAT IV multimeter (like those detailed in Fluke's three-phase testing guides) to verify your work.

De-Energized Checks (Lockout/Tagout Applied)

  • Contactor Poles: Set meter to continuity (Ω). Place probes across 1/L1 and 2/T1. It should read OL (Open). Manually press the contactor plunger with an insulated tool; the meter should drop to < 0.5 ohms. Repeat for L2/T2 and L3/T3.
  • Overload Trip: Measure continuity across 95 and 96. It must read < 1 ohm. Press the manual "Trip" button on the overload; the meter must immediately read OL.
  • Ground Integrity: Measure resistance from the motor peckerhead ground lug to the main panel ground bar. It must read < 1 ohm.

Energized Checks (PPE and Arc Flash Boundary Required)

  • Line Voltage: Set meter to AC Volts. Measure L1-L2, L2-L3, and L1-L3 at the breaker load side. You should read between 220V and 240V on all three legs. A variance greater than 2% between legs indicates a utility or transformer issue that will destroy the motor windings over time.
  • Coil Voltage: When the contactor is pulled in, measure across A1 and A2. It should match your control voltage (e.g., 220V or 24V, depending on the coil spec).

Decision Tree: Sizing Wire, Breaker, and Overload for a 5HP Motor

Sizing components for a 3-phase motor is not as simple as matching the nameplate Full Load Amps (FLA). You must follow NEC Article 430, which separates conductor sizing from short-circuit breaker sizing. Below is the decision path for a standard 5 HP, 220V/230V, 3-Phase induction motor.

Component Calculation Rule (NEC) Math for 5HP (FLA = 15.2A) Concrete Pick / Part Number
Wire Size 125% of Motor FLC (Table 430.250) 15.2A × 1.25 = 19A 10 AWG THHN Copper (Rated 35A @ 75°C, provides voltage drop margin and mechanical strength over 14 AWG).
Short-Circuit Breaker Max 250% of FLC for Inverse Time (Table 430.52) 15.2A × 2.5 = 38A 40A 3-Pole Breaker (NEC allows rounding up to the next standard size if the exact calculation doesn't match a standard breaker).
Thermal Overload Sized to motor nameplate FLA (typically 115% max trip) Target trip: ~17.5A Schneider LRD20 (Adjustable range 12A to 18A). Set the physical dial exactly to 15.2A.

Final Default Recommendation: If you are wiring a 5HP 3-phase 220V motor and the nameplate confirms a 15.2A FLA, do not overthink the breaker sizing. Pull 10 AWG THHN in conduit, install a 40A 3-pole breaker, and use an LRD20 overload relay dialed to 15.2A. This combination guarantees the breaker will hold through the motor's high inrush current (Locked Rotor Amps) during startup, while the overload relay will accurately protect the windings from thermal damage during a mechanical jam.