Understanding Ground Bars
Ground bars, also called neutral bars, are widely used in both residential and commercial electrical service panel boards. Their purpose is to terminate all the white return wires (or white wires) from the multiple load circuits in the building.
Ground Bars and Circuit Overloads
Ground bars don’t actually have a lot to do with circuit overload protection. That job is performed by the circuit breaker. Besides the white wires inside the panelboard that terminate at the ground bar, there are black wires (also termed “hot” wires) that are protected from overload by the circuit breakers in the electrical panel board.
The circuit breaker’s role is to sense the current in the hot wire and “trip” if the current is exceeded for too long. Most Circuit Breakers perform this current sensing by an element inside the circuit breaker that will heat up as the current rises. Ultimately, the heating effect in the circuit breaker triggers the spring-loaded circuit breaker to “trip,” turning off that circuit using a bi-metallic trigger to release the spring energy holding switch contact closed.
The white neutral wires, the ones connected to the ground bar, are not protected by a circuit breaker because it is only necessary to interrupt a circuit at one point to break current flow.
Ground Bars and Voltage Isolation
The black, ‘hot’ wire is generally 110 volts (for a single, phase alternating) and the white neutral wire, anchored within ground bar in the electrical panel board is zero volts. Therefore, the danger for shock (which is defined as voltage induced current flow into the human body) is minimized.
As a result, it is the black wire again, that is designed to stop both current flow and the presence of voltage in the circuit.
It is extremely important to point out that a ground bar does still carry current even if the voltage at the location of the ground bar is essentially zero. All the current used in appliances throughout the entire building eventually goes through the ground bar and back to the current source: the utility line.
All electrical current has to come from somewhere and go somewhere. It is a similar concept as water coming from your garden hose. While there is always water pressure (which would equate in this analogy to voltage) there may not always be current (which would be water flowing out of the hose).
Thereby, ground bars are simple mass wire termination devices that allow many neutral wires to be terminated in the electrical service panel with very little space and costs.
Construction of Ground Bars
In the United States, ground bars are mainly bade from tin plated aluminum (grades 6061, 6005, 6105, 6063).
Brass neutral ground bars are popular in many countries but conductivity of brass is about 28% that of copper while aluminum is 43% that of copper. Therefore for cost reasons, aluminum is a much lower choice.
Tin plated ground bars are compatible with both aluminum wiring and copper wiring. Aluminum wiring today is made of a harder alloy than many years ago which allows it to compete in reliability with copper wire IF used in Dual Rated aluminum connectors. However, only aluminum wire connectors are compatible with both aluminum and copper wires.
