Technical Bulletin

Megohm Testing for Homeowners

Why insulation resistance testing protects your home, your safety, and your investment

Most homeowners never think about the insulation inside their electrical system — until something goes wrong. Wires degrade. Moisture gets in. Connections loosen. And when insulation fails, you get shorts, fires, and equipment damage that costs thousands to fix. Megohm testing catches these problems before they become emergencies.

1 What Is Megohm Testing?

Also called insulation resistance testing, a megohm test sends a high DC voltage (typically 500V or 1000V) through your electrical circuits and measures how much current leaks through the insulation. The result is expressed in megohms (MΩ) — millions of ohms.

Think of it like a blood pressure check for your electrical system. Healthy insulation has high resistance — meaning almost no current leaks through. Degraded insulation has low resistance — meaning electricity is finding paths it shouldn't, generating heat and creating fire risks.

The Bottom Line

1 MΩ per 1,000 volts of operating voltage is the minimum acceptable reading. For a 240V residential circuit, that means at least 0.25 MΩ. We don't accept that minimum — we flag anything under 1 MΩ for a residential system.

2 Why Your Home Needs It

Aging WiringHomes over 30 years old often have insulation that's dried out, cracked, or degraded
Moisture DamageAttics, crawl spaces, and exterior walls expose wiring to humidity and leaks
Pest DamageRodents chew wire insulation — we've found bare copper inside walls
Generator ConnectionTransfer switch and feeder cables need verified insulation integrity
Panel UpgradesBefore any major work, we test existing circuits for safe load handling
InsuranceMore insurers requiring electrical inspections for older homes

3 Recommended Testing Schedule

Every 5 Years

Full home insulation resistance test — all homes 25+ years old

Every 3 Years

Generator feeder, transfer switch, and main panel — homes with standby generators

Before Purchase

Complete inspection including megohm testing — especially homes 30+ years old

After Water Damage

Emergency testing on all affected circuits

Before Major Renovation

Baseline test to verify circuits can handle added load

4 What Happens During the Test

A typical residential megohm test takes 1-2 hours. We test every major circuit — outlets, lights, appliances, HVAC, and generator connections if applicable.

1

Power down circuits being tested (brief outages, 5-10 minutes per area)

2

Connect megohmmeter to each circuit

3

Apply 500V DC and measure resistance

4

Document every reading with circuit labels

5

Flag readings below 1 MΩ for repair

6

Provide written report with recommendations

Warning Signs — Test Now

• Frequent breaker trips with no obvious cause

• Burning smell from outlets or switches

• Discolored or warm outlet covers

• Lights flickering throughout the house

• Home is 30+ years old and never tested

What It Costs vs. What It Saves

A residential megohm test costs $300-$600. Compare that to an electrical fire ($15,000-$50,000), generator repair ($2,000-$8,000), or replacing a circuit system ($5,000-$15,000). The test pays for itself the moment it catches one problem.

Schedule a Megohm Test →