Bonding Neutral and Ground at Main Panel
Bonding the neutral and ground wires in the main electrical service panel is necessary for safety and compliance with the National Electrical Code. This bonding serves critical functions like completing the fault current path and limiting the voltage difference between the neutral and ground wires.
In this article, we’ll cover the purpose of neutral-ground bonds, where they should be installed, hazards caused by improper bonds, and tips for DIYers and electricians dealing with panel modifications.
We’ll also answer common questions about proper grounding methods and when to call a professional for help. By the end, you’ll surely have a solid understanding of neutral-to-ground bonds in main and sub-panels.
Understanding the Basics of Neutral and Ground Wires
Before learning about bonding neutral and ground wires, it helps to understand the role and purpose of these two conductors in electrical systems:
- Neutral Wires – The neutral wire provides the return path for electric current after it passes through a load. Neutral wires carry current during normal operation. They are usually insulated with white or grey insulation.
- Ground Wires – The ground wire provides a safe path for any stray fault current to flow to the ground. This prevents electric shock. Ground wires do not carry current under normal conditions, but only in a fault scenario. They are bare or green-insulated.
The significant difference is that neutral wires carry load current continuously, while ground wires only carry current in a fault. Neutral is the current return, and safety ground is the shock protection.
What Does Bonding Neutral and Ground Mean?
Bonding refers to electrically connecting the neutral wire and ground wire at a single point in the system. This connection is made inside the main electrical service panel using a bonding screw, jumper wire, or other permanent means.
The neutral wire is the return path for the electric current after it passes through a load. The ground wire provides a safe path to the ground for any stray electrical fault current to prevent shocks.
For example, in most generator setups, the ground wire is connected to a grounding electrode system. This protects the generator and other connected electrical equipment from damage due to electrical faults or lightning strikes.
Why Should You Bond Neutral and Ground in the Main Panel?
There are two key reasons for bonding neutral and ground in the main service panel:
Completes the Fault Current Path
Bonding the neutral and ground wires provides a complete path to flow any ground fault or short circuit current. This allows enough current to flow to trip the circuit breaker, safely de-energizing the circuit.
A ground fault might not draw enough current to trip the breaker without bonding in the main panel. The current could then pass through the earth and piping systems, creating a dangerous shock hazard.
Limits Neutral to Ground Voltage Rise
The bond also limits the voltage difference between the neutral and ground wires. This provides a stable reference to the ground potential for the electrical system and connected equipment.
Significant voltage differences between neutral and ground can damage sensitive electronics. The neutral-ground bond keeps voltages close, preventing equipment damage.
Where Should You Bond Neutral to Ground?
The National Electrical Code only permits the neutral wire to be bonded to the ground wire in one location – at the main electrical service panel. This is where the primary overcurrent device or main circuit breaker is located.
Sub-panels and all other distribution points downstream must keep the neutral isolated from the grounded conductor.
Why Not Bond Neutral and Ground at Other Locations?
It is also important to realize that you should bond the ground and neutral only at the main panel. Here are reasons why you should not bond neutral and ground anywhere else:
Can Create Objectionable Neutral Currents
Bonding neutral and ground wires in a sub-panel or other points creates an alternative path for the neutral current to flow back to the source. This can result in the neutral current splitting between the neutral and ground wires.
Ground wires are not intended to carry current during normal operation. Any stray neutral current on the grounding conductors is considered an “objectionable current” and can lead to shock hazards if the ground path is lost.
Defeats Purpose of Ground Fault Protection
Ground fault currents can circulate between the two bonds when bonding neutral and ground downstream instead of properly tripping the breaker.
Any neutral-to-ground bonds after the main panel can render ground fault breakers useless.
Can Create Ground Loops
Multiple neutral-to-ground bonds can allow currents to circulate between the bonds, creating ground loops. These can introduce noise and unwanted voltages in a system.
Step-by-Step Guide to Bonding Neutral and Ground
Follow these steps to bond neutral properly and ground wires:
- Locate the main service panel where the main breaker or service disconnect is positioned. This is the only location where neutral and ground should be bonded.
- Identify the neutral bus bar and the ground bus bar. In some panels, the bus bars may be combined.
- Remove any existing bonding straps, screws, or jumper wires between the neutral and ground bus bars. You can discard these.
- Connect a bonding jumper wire between the neutral and ground buses using an appropriate lug, screw, or clamp. You should size the wire per NEC requirements, often #8 AWG or larger copper.
- Ensure the connection between the bonding jumper and bus bars is tight and permanent. It should not be removable.
- Attach the incoming neutral service entrance wire to the neutral bus bar.
- Attach the grounding electrode conductor from the ground rods/water pipe to the ground bus bar.
- Double-check that all neutral wires are connected only to the neutral bus and that all ground wires only connect to the ground bus.
- Verify you only have one neutral-to-ground bond at this main panel. Remove any additional bonds.
- Clearly label the panel as containing the neutral-ground bond to avoid improper alterations later.
That covers the proper procedure for bonding neutral and ground wires at the main panel. Now let’s look at some common examples of residential and commercial services.
Bonding in a Residential Main Panel
A standard residential main electrical panel typically has a neutral-ground bonding jumper installed. This connects the neutral bus bar to the ground bus bar, joining the two together at a single point.
Some key steps when working in a residential main panel:
- Confirm only one neutral-to-ground bond exists. Remove any additional bonding straps or wires.
- The incoming neutral service wire must connect to the neutral bus only.
- The grounding electrode conductor from the ground rods only goes on the ground bus.
- Subfeed circuits to sub-panels or outbuildings must have neutral and ground isolation – no bonds in sub-panels.
Bonding in a Commercial or Industrial Main Panel
Larger commercial buildings and industrial facilities have extensive electrical systems with multiple service entrances and distribution equipment. However, the same requirement holds true – only bond neutral and ground in one main panel or service disconnect.
Some tips when dealing with complex commercial services:
- Clearly identify and label the neutral-ground bond location. The main panel is not always readily evident.
- Disconnect and remove any bonding links downstream from the main service disconnect in distribution panels.
- Keep the neutral bus isolated from the enclosure and ground bus in all distribution and branch circuit panels.
- Route a separate ground conductor, phase, and neutral wires to keep paths isolated.
Ground Rod Connections at Main vs Sub Panels
Both main panels and sub-panels need proper connections to the grounding electrode system. However, there are some important distinctions:
Main Panel Grounding Electrode Connections
The grounding electrode conductor from ground rods, Ufer ground, or other electrodes must connect directly to the ground bus bar in the main panel only.
This bonds the grounding electrodes to the neutral-ground bond location.
Sub-Panels Grounding Electrode Connections
Sub-panels should connect their grounding electrode conductor to a separate isolated ground bus bar, not the neutral bus. A wire connects the ground bus bar to the main panel’s ground.
This keeps ground rods referenced to the main panel bond location while keeping the sub-panel neutral and the ground isolated.
When to Call an Electrician
Improper neutral and ground bonds can have serious consequences like fires, equipment damage, and shock hazards.
Consult a licensed electrician if you are unsure whether your system is bonded correctly or notice any of the following:
- More than one neutral-ground bond in a system
- Bonds in sub-panels or downstream equipment
- Unlabeled panels where the main bond location is unclear
- GFCI or AFCI breakers tripping without an apparent cause
- Tingling sensations or small shocks from touching appliances
Common Questions About Neutral-To-Ground Bonds
Here are some additional questions that often come up:
Should I Remove the Neutral-Ground Bond From My Main Panel?
No, the main panel should have a neutral-ground bond installed for safety.
Removing it would be hazardous and violate electrical code requirements.
What Size Wire Should I Use for the Neutral Ground Bond?
Follow NEC guidelines for the minimum required wire size. In a 200A residential panel, #8 AWG copper is common. Upsize as needed for larger amperages.
Where Exactly Should I Make the Neutral-Ground Connection?
Bond them on the neutral and ground bus bars directly. Do not make the connection off the bus using a wire pigtail, as this can come loose.
Can I Use the Panel Enclosure as the Ground Bus Bar?
Yes, when the panel enclosure is electrically conductive. You would bond the neutral wire directly to the metal panel can with an appropriate lug or screw.
Should I Isolate the Neutral and Ground in My Main Panel?
No, you should have one neutral-to-ground bond installed as required by the NEC code. Isolating them in the main panel would pose a serious hazard.
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