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Understanding Neutral Bars
(also known as ground bars, or earth bars)

Information about what is a neutral bar and how it useful in service panels.

Neutral bars are widely used in residential and commercial electrical service panels to terminate all those white 'neutral' or 'return' wires from the many load circuits in the building.

The black 'hot' wires are protected from overload by circuit breakers in the panel which typically sense the current in the 'hot' wire and 'trip out' if current is exceeded for too long. Current sensing is usually by an element in the circuit breaker that heats up when current is too high. As the element heats more for higher currents and gathers more heat when currents exist for extended overload periods, it mimics the wiring in the buildings circuits which would themselves heat up, causing a potential fire hazard.

The heating effect in the circuit breaker is used to trigger the spring loaded circuit breaker 'trip', turning off that circuit using a bimetallic "hair" trigger to release the spring energy holding switch contacts closed, when that certain total heating effect is reached.

The white neutral wires are not protected by a circuit breaker as it is only necessary to interrupt a circuit at one point to break current flow. That takes care of heat build up from overloads in wiring. The other safety consideration is that of voltage isolation.

As the 'hot' black wire is 110 volts (for single phase, alternating) and the white neutral wire, anchored at the panel is essentially 0 volts, the danger for shock (voltage induced current flow in the human body) is minimized.

Consequently the black 'hot' wire is the one chosen to stop both current flow and the presence of voltage in the circuit.

It is important to note that a neutral bar does still carry current even if the voltage at the location of the neutral bar is essentially zero with respect to ground.

A variable amount of the current used in appliances all over the building goes through the neutral bar and back to the current source, the utility line.

All current has to come from somewhere and go somewhere like water FLOWING in a hose pipe. Whereas water PRESSURE (voltage) may be present with no current (no water flow when the tap or spray gun is shut off).

The exception to this is when the two split phases are balancing out forward and reverse flow in the center leg. This happens when the two split phases are working in series so 230 / 2 = 115VAC  and no current needs to flow though the neutral if the current is equal in both legs.  

Neutral Load Balancing in typical residential USA single phase utility transformer systems use a split single phase load tap which creates two independent 115 VAC sources, which can be used in series to get one extra 230 VAC output.   

The center tap is the neutral (white) “return” line and almost always has current flowing in it unless on rare occasions the current load in line A is identical to line B in which case the forward and reverse currents at the neutral bar cancel each other out, so no current flow occurs.

Most of the time the loads in the building are not balanced so whatever is out of balance is flowing through the neutral bar.

The more random loads that are turned on will make it more statistically likely that more of the increased load current will cancel out at the neutral. However the imbalance still could be substantial but always likely to be much smaller than the total current load. The wiring of buildings helps to distribute the loads between lines.    

Really big loads, ranges, dryers and A/C are 230VAC so do not spoil the load sharing of 125VAC.

Add to this the large numbers ring loop ground wires terminated at the same neutral bar, there is considerable heat sinking guaranteed by these normally non-current carrying , cold copper ground wires.

These ground wires anchor the neutral voltage to zero volts or specifically local ground. They also provide short protection to all appliances.         

Consequently, The neutral bar used on split single phase panels can be made extremely lightweight since it will not to see currents that are very high and will not get as hot as a power distribution bar or power collection bar which could have full ampacity of each wire flowing at the same time and without any load canceling nor any ground wires dumping heat.

Though both of these wire connector types, Neutral Bars and Power Bars, are covered by UL486A/B testing, the neutral bar has to be UL Recognized only and additionally tested in the final panel design to verify the statistical load assumptions.

Whereas, a UL Listed General Use Multi hole “Power Bar” connector may be used for non-balanced, non-mixed live/ ground applications at full conductor rated current, per wire hole, up to the rated temperature rise of the connector (75C or 90C).

Nevertheless when wiring multi-wire connectors, keeping input and output current wires close to each other, and “pair matched” in expected current flow, helps to reduce the temperature rise by minimizing the total distance and concentration of current in conducting metal.         

Center Split Tap Single Phase Transformers use a “potential divider” construction and so both legs can be 230VAC  / 2 = 115 VAC each.  The Line A / Line B load current imbalance flows back and forth to the utility transformer at the center tap.   This is not a 2 phase system. Most of the time some current flows in the center tap. Two random black wires, even though they measure only 115VAC each to ground, can be 230 VAC between them, if different lines, so watch out!

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Neutral bars are simple mass wire termination devices that allow many (often white) neutral wires to be terminated in the service panel with little space and cost.

In the USA neutral bars are mainly made from tin plated aluminum (grades 6061, 6005, 6105, 6063 are common).

Brass Neutral bars are popular in many countries but conductivity of brass is about 28% that of copper while aluminum conductivity is 43% that of copper so on a cost per amp basis, aluminum is much lower cost, especially considering that aluminum weighs much less than brass or copper and costs much less per pound than brass or copper.

Tin plated neutral bars are compatible with both aluminum wiring and copper wiring. Aluminum wire today is made of a harder alloy than many years ago which enables it to compete in reliability with copper wire IF used in Dual Rated aluminum connectors such as tin plated aluminum neutral bars sold by LugsDirect.com. Generally only aluminum wire connectors are compatible with both aluminum and copper wires.

So what does it mean to say that the voltage on a neutral bar is "essentially zero"? Is the potential the same as ground (earth) then? Yes and no.

Electrical codes dictate that the neutral circuits and the ground circuits be bonded at only one point, the main entry point. This might mean in the main panel or incoming meter but only in one place and at the "source".

In a properly functioning system the ground (earth) will dissipate stray voltages that can creep into a complex wiring system. So, in essence, the neutral is forced to ground by bonding it to ground in the panel.

But beware of white wires anywhere else as there is lots of opportunities for a white wire to be hot! Remember white (neutral) wires are connected to black (hot) wires by the appliance itself and can be at 110 volts in household wiring or even 220 or 460 volts in these higher voltage circuits.

LugsDirect.com can help you with your Neutral Bar needs whether you need one or thousands!