How Do You Bond a Neutral and Ground in a Main Panel?

Understanding the neutral-ground bond in a residential panel is one of those topics that trips up handymen, DIYers, and even some early-career electricians. Get it right and the safety system works exactly as designed. Get it wrong and you either lose ground fault protection or create dangerous parallel current paths. This guide covers what the main bonding jumper does, why it lives in the main panel and nowhere else, and why homeowner DIY here is a bad idea in a Toronto or GTA home.

How is neutral and ground bonded in a main panel?

In an Ontario residential main service panel, the neutral bus and the ground bus are connected together by a listed main bonding jumper — typically a green screw, a strap, or a short conductor supplied with the panel. This single intentional bond is the reference point for the entire home’s grounding system. In any downstream subpanel, the neutral and ground buses must be separated, with grounds landing on a dedicated ground bar bonded to the subpanel enclosure and neutrals landing on an isolated (non-bonded) neutral bar. The bond happens once, at the main, and never again.

This is not a DIY task. Panel work is licensed-contractor territory under the Ontario Electrical Safety Code. This article explains the principle so you understand what a licensed electrician does, not so you attempt it yourself.

Why the bond exists

Two purposes:

• Establishes a common reference potential. Bonding neutral and ground at the service entrance holds them at the same voltage relative to earth.
• Provides a fault current path. If a hot conductor faults to a metal appliance chassis, the ground conductor carries fault current back to the main panel and through the bond to the neutral, allowing the breaker to trip. Without the bond, the fault current has no low-impedance path back and the breaker will not trip quickly enough.

Related: what happens if a house has no ground wire and what does the bare copper wire do.

Why the bond happens ONLY at the main panel

If neutral and ground are bonded a second time in a subpanel (or anywhere downstream), current returning from loads on the shared circuits divides between the neutral conductor and the ground conductor. This creates a parallel neutral path that:

• Puts normal load current on the ground bus and ground conductors.
• Energizes appliance chassis and metal boxes with a small but persistent voltage.
• Prevents GFCI protection from working correctly (GFCIs measure the difference between hot and neutral, and a parallel path invalidates the measurement).
• Creates shock and fire risks that are hard to diagnose after the fact.
• Fails ESA inspection immediately.

This is the reason the single-point-bond rule is one of the most fundamental safety rules in the entire OESC. See what is a subpanel and when do I need one for the subpanel side.

What the bond looks like inside a main panel

Common physical implementations of the main bonding jumper in Ontario residential panels:

• Green bonding screw. A green painted screw that threads through the neutral bar into the panel enclosure. Simplest and most common.
• Bonding strap. A metal strap linking the neutral bar to the ground bar (or the enclosure).
• Factory-installed jumper wire. A short green insulated conductor with lugs on each end, connecting the neutral and ground buses.

The panel manufacturer specifies which method to use, and a licensed contractor selects the correct hardware for the specific panel model. The screw or strap that ships with the panel in the little bag of parts is the correct piece.

Grounding electrode conductor and system grounding

The main bonding jumper is one half of the story. The other half is the grounding electrode conductor (GEC), which connects the panel’s ground bus to the earth via one or more grounding electrodes:

• Ground rods driven into the earth outside the house.
• Metallic water service pipe (if metallic all the way to the street).
• Concrete-encased electrode (Ufer ground) in newer builds.
• Building steel where applicable.

Ontario also requires bonding of metallic water service piping and, in most cases, metallic gas piping. These bonds ensure any voltage that could appear on metallic building systems is at the same potential as the electrical system.

Subpanels: keep them separate

In every subpanel installed after the main:

• The green bonding screw is removed or the bonding strap is left off.
• Grounds land on a ground bar that is directly bonded to the enclosure.
• Neutrals land on a separate neutral bar that is isolated from the enclosure.
• A four-wire feed from the main panel supplies the subpanel: two hots, one neutral, and one ground.

Any subpanel that shares a two-hot-and-one-neutral feed without a separate ground (like an outdoor shed panel wired with only three conductors) is either legacy work needing correction or a subpanel that qualifies for a rare exception. Modern OESC requires the four-wire feed in almost all cases.

Common bonding mistakes we find

• Green bonding screw left in place on a subpanel. Very common on DIY-installed subpanels.
• Neutral and ground both landed on the same bar in a subpanel that has separate bars available.
• Main bonding jumper missing entirely on a main panel, leaving the system without a proper bond.
• GEC (grounding electrode conductor) undersized, corroded, or disconnected from the ground rod.
• Missing bonding on metallic water service.
• DIY-added ground rod bonded to a subpanel, creating a second grounding path.

All of these fail ESA inspection and create real safety issues. Related: what are the signs of a bad ground wire.

Why this is not a DIY job

• Panel work requires opening the deadfront and exposing live bus bars.
• Torque specs, listed hardware, and grounding conductor sizing all matter.
• An incorrect bond creates a silent failure mode that only shows up during a fault — too late.
• Most panel work must be performed by an ECRA/ESA-licensed contractor under the OESC.
• ESA inspection is required for any service or panel change involving bonding.

Expert tip from our ESA-licensed electricians

The single most common DIY subpanel mistake we correct in the GTA is the green bonding screw left in on a subpanel install. The homeowner or handyman follows a YouTube video, installs the subpanel with the factory-shipped hardware, and never removes the bonding screw. The subpanel works, but a hot fault will now push current through the ground conductor back to the main in parallel with the intended neutral path, energizing chassis along the way. If you have any subpanel in your home installed by anyone other than a licensed contractor with an ESA notification on file, ask an electrician to open it and check the bonding on their next service call. It is a two-minute check that catches one of the most dangerous silent defects a home can have.

Related reading from ezsmart.ca

• What Is a Subpanel and When Do I Need One?
• What Does the Bare Copper Wire Do?
• What Happens If a House Has No Ground Wire?
• What Are the Signs of a Bad Ground Wire?
• How to Fix a Loose Wire in the Breaker Box

Contact us

Want a Toronto or GTA home’s main-panel bonding and subpanel separation verified by a licensed electrician? Call ezsmart at 416-838-9006 or use our contact page. An ESA-licensed electrician will inspect and correct any bonding defects under a proper notification.