You are absolutely on the right track. This is a classic symptom of a failing or failed neutral connection, either at the service entrance, in the meter box, or (less likely but possible) at the transformer supplying the house. Here's a breakdown of why and what to do next

Why a Bad Neutral Causes This:
Imbalanced Loads

Homes are generally wired with a split-phase 120/240V system. This means you have two 120V "legs" that are 180 degrees out of phase with each other, creating the 240V needed for larger appliances. The neutral wire provides the return path for the 120V circuits.

Neutral's Role

The neutral should carry the difference in current between the two legs. If the loads on each leg are perfectly balanced, the neutral carries very little current.

Loss of Neutral - Chaos! When the neutral connection is compromised, it can't effectively carry this return current. This forces the voltage to find another path, often through other 120V circuits. The result is: One leg sags in voltage

The heavily loaded leg (the one where the motor is starting) "pulls down" the voltage because it's struggling to get a return path.

The other leg spikes in voltage

The voltage from the loaded leg is, in effect, being "pushed" onto the other leg because the neutral isn't doing its job of providing a stable reference.

Damaged Appliances

This unbalanced voltage can wreak havoc on sensitive electronics and shorten the lifespan of motors and other appliances. The low voltage can cause motors to overheat as they struggle to start and run. The high voltage can damage electronic components.

Your Diagnostic Steps Were Excellent!

You correctly identified the following: Voltage Imbalance Under Load

This is the key symptom.

Good Voltage at Service Entrance (Main Off)

This means the problem is downstream of the utility's connection point but upstream of the panel itself.

Next Steps (Safety First!)

1.

IMMEDIATELY Inform the Homeowner

This is a dangerous situation. Explain that there's a serious electrical fault that needs to be addressed urgently to prevent further damage and potential fire hazards. Advise them to minimize the use of large appliances until the problem is resolved. Tell them NOT to attempt any DIY repairs.2.



TURN OFF THE MAIN BREAKER! This will help prevent further damage while you continue to investigate and more importantly, keep the system safe.3.

Inspect the Service Entrance Neutral Connection

This is the most likely culprit.

Visual Inspection (Before Touching Anything)

Carefully examine the neutral connection at the service entrance. Look for:

Corrosion

Green or white powdery residue.

Burning/Arcing

Blackened or melted insulation.

Loose Connections

Anything that doesn't look tightly secured.

Damaged Wiring

Nicks, cuts, or breaks in the wire insulation.

If you suspect a faulty neutral at the service entrance and you are NOT qualified to work on the utility side of the meter, stop here and contact the utility company! If you are qualified and authorized to work on the service entrance carefully test the neutral connection. With the main breaker OFF (double-check!), check for continuity from the neutral wire in the panel to the neutral connection point at the meter or service entrance. A high resistance reading (significantly above 0 ohms) indicates a problem. Check the tightness of the neutral lug. It needs to be properly torqued according to manufacturer specifications.4. Inspect the Meter Box Neutral Connection

If the service entrance connection looks good, the next most likely place is the neutral connection in the meter box. The process is similar to step 3, but again, be extremely careful and only proceed if you are qualified and authorized to do so.

Contact the utility company immediately if you are not!5. Consider Calling the Utility Company

They have specialized equipment and expertise to check the transformer and the connections up to the service drop. They are the only ones who can safely address problems with their equipment. Tell them you suspect a service neutral issue based on your measurements.6.

Double-Check the Grounding Electrode System

While less likely to be the primary cause, a poor or missing grounding electrode system (ground rod, water pipe connection, etc.) can exacerbate the effects of a neutral problem. Ensure the grounding electrode system is properly installed and has a low resistance to ground. This usually requires a specialized ground resistance meter.

Important Cautions



Electricity is dangerous! If you are not thoroughly familiar with electrical safety procedures, do not attempt any troubleshooting beyond visual inspection. Working on service entrance equipment can be especially hazardous. This is the utility's responsibility in many jurisdictions. Always de-energize the circuit before working on it. Use a reliable voltage tester to confirm that the circuit is dead. Follow all applicable electrical codes and regulations. If in doubt, call a qualified electrician.In summary, your diagnosis is spot-on. Focus on the service entrance and meter box neutral connections. Contact the utility company if you suspect problems with their equipment or if you are not qualified to work on service entrance wiring. Flag for review