You're right to be cautious when dealing with a high-leg delta system, especially if you're less experienced with them. While the motor is three-phase and "should" be okay with balanced voltages, the high-leg system introduces some nuances that can affect performance and even cause damage if not understood.Here's a breakdown of what you need to consider and what to check

Understanding the High-Leg Delta System
Three Phase Power

The system provides three-phase power, meaning the motor can operate as designed.

Uneven Voltages

Unlike a standard delta or wye system where all phase-to-phase voltages are equal, the high-leg delta has one phase (the "high leg" or "wild leg") that has a higher voltage to neutral (or ground) than the other two. Typically, the voltages will be: Phase A to B: 480V Phase B to C: 480V Phase C to A: 480V Phase A to Neutral: 240V Phase B to Neutral: 240V Phase C to Neutral:

~415V (This is the high leg) Important - Don't Use the High Leg to Neutral for 120V or 240V Loads

Single-phase loads should never be connected between the high leg (phase C in the example above) and neutral because of the higher voltage. Doing so will damage the equipment. This is where much of the confusion and danger arises from this system.

Does Connection Configuration to the Motor Matter?

In theory, for a perfectly balanced 3-phase motor operating on a perfectly balanced 3-phase voltage supply, the connection of which phase goes to which motor terminal wouldn't matter. However, real-world situations are rarely perfect.

Here's why the configuration might matter on a high-leg system, especially when troubleshooting voltage issues


Imbalance Sensitivity

Motors are more sensitive to voltage imbalances than many people realize. Even small imbalances can significantly increase motor current, heat, and reduce lifespan.2.

Phase Sequencing

While swapping all three leads to the motor will only reverse the direction of rotation, connecting one phase to the wrong terminal relative to the other two phases can cause problems. This is particularly true if there's an existing voltage imbalance due to the high-leg system or other factors.3.

Harmonics

High-leg delta systems can sometimes be more prone to harmonics, depending on the loads connected to the system. Harmonics exacerbate voltage imbalances and can cause motor overheating.4.

Internal Motor Winding Differences

While uncommon, there could be slight manufacturing variations in the internal windings of the motor. If combined with a voltage imbalance, this could lead to disproportionate current flow in one winding compared to the others, resulting in localized heating.

Troubleshooting Steps


Verify the High-Leg Delta Configuration



Identify the High Leg

Use a voltmeter to measure the voltage from each phase to neutral (or ground). The phase with the highest voltage to neutral is your high leg. Mark it clearly. This is critical!

Check Voltages

Carefully measure all phase-to-phase voltages (A-B, B-C, C-A). They should be close to 480V and balanced (within 1-2% ideally, but within 5% is generally acceptable). Also, measure the phase-to-neutral voltages. Document all of these.2.

Measure Motor Voltages and Currents



Voltage at the Motor Terminals

Measure the voltage at the motor terminals while the motor is running (if possible) or at rest. Compare these values to the supply voltages. Voltage drop can indicate wiring issues or overloading.

Motor Current (Amps)

Use a clamp meter to measure the current on each of the three phases feeding the motor. Are the currents balanced? A significant current imbalance is a red flag. Compare to the motor's nameplate FLA (Full Load Amps).

Motor Winding Resistance

If the motor is de-energized, use an ohmmeter to measure the resistance of each motor winding phase to phase. (Disconnect from the power source first!) The resistance values should be very close to each other. Large differences can indicate winding shorts or opens.3.

Check for Grounding Issues



Continuity to Ground

Verify a good ground connection to the motor frame and the electrical panel.4.

Look for Wiring Issues



Loose Connections

Inspect all connections in the circuit (at the panel, disconnect switch, and motor terminals) for looseness, corrosion, or signs of overheating.

Wire Size

Confirm that the wire size is adequate for the motor's FLA and the length of the run.5.

Consider a Motor Analyzer

If you have access to a motor analyzer, it can perform more advanced tests like:

Insulation Resistance (Megger Test)

Checks for insulation breakdown in the motor windings.

Motor Current Signature Analysis (MCSA)

Identifies potential motor faults based on the current waveform.6.

Test the Motor Off-Line

If possible, disconnect the motor from the driven load and run it unloaded. This can help determine if the problem is in the motor itself or the connected equipment.

Regarding the High Leg and Motor Connections



Start with the Existing Wiring

Before changing anything, document the existing wiring configuration. Take a picture and make a diagram!

Experiment (Carefully)

If you suspect the high leg is contributing to the problem, you could try swapping the phases feeding the motor. For example, if phase C (the high leg) is currently connected to motor terminal T1, try connecting it to T2 or T3. Monitor the motor voltage and current carefully after each change. Look for any improvements in balance.

However, don't do this blindly. If you see any signs of arcing, excessive vibration, or extreme current draw, stop immediately and revert to the original configuration. Consider Motor Nameplate

Check the motor nameplate. It should state the voltage and connection type the motor is designed for.

Important Considerations



Safety First

Work with electricity safely. Always de-energize the circuit before working on any wiring. Use proper PPE (Personal Protective Equipment). If you're not comfortable working with electricity, hire a qualified electrician.

Voltage Drop

Excessive voltage drop is a common culprit in motor problems. Calculate the voltage drop in the circuit.

Load

Is the motor overloaded? An overloaded motor will draw excessive current and overheat.

Motor Condition

The motor itself could be failing. Bad bearings, worn windings, or a short circuit can cause voltage and current imbalances.

In summary: While the connection configuration may not be the root cause of your voltage issues, it can potentially exacerbate them, especially on a high-leg delta system. Troubleshooting systematically and carefully monitoring the motor's performance after any changes is key. Flag for review