Open neutrals have long been an annoyance for utilities resulting in many claims for damages incurred by sensitive electronic equipment. Throughout the years this problem has started to snowball.

The three examples below are some of the major causes of open neutrals. Each is further identified by conditions that contribute to the situation:

1. Connector failure
2. Transformer malfunction
3. Environmental condition equipment failures

• Salt air

• Acid rain

• Caustic chemical on the work site

1. Weather induced failure

• Hurricanes

• Tornadoes

• Rain

• Ice storms

• Flooding

• Lightning

1. Improper installation
2. Poor quality of splice
3. Improper connector for job
4. Improper drop considerations / installations
5. Accidental line contacts

Although there are other causes, they are fairly isolated and less common.

In the secondary of a properly grounded "T" wound transformer, load has little effect on the voltage other than the occasional flicker caused by switching large load, which is considered normal operation. However, if we disconnect the center tap of the secondary, which references ground, then we allow the mid point to "drift" from side to side and it becomes directly affected by load. This floating connection takes on two forms, one is high impedance (open) the other is low impedance (partial). The later example is considered the worst case, because it can vary dramatically so much from one second to another and can be difficult to locate. The first hint of a problem usually gets to the utility as a customer report (i.e. "my back bedroom lights are bright white and the living room lights are a pale orange"). To a light bulb this may do little or nothing but to a big screen TV it could mean it’s end of operational life.

Another red flag regarding open neutrals is extreme equipment failure or mis-operation. As an example of Surge Protective Device (SPD) are extremely sensitive to open neutral conditions and can fail catastrophically. SPDs are designed to deal with momentary transient surges and not extended overvoltage conditions. A transient surge is a sub cycle anomaly while swells can last for a few cycles or more. Open neutrals can theoretically last until fixed.

Sustained overvoltage conditions are usually fatal to (MOV/SAD) based SPDs. The mentioned above conditions have resulted in changes UL’s UL1449 standard, which requires thermal disconnect capabilities.

We at Meter-Treater have always provided our customers with the safest products we could take in consideration applicable standards and application scenarios. To this end we have maintained an aggressive R&D program to come up with a coordinated fusing element capable of delivering both a thermal disconnect and high current capabilities. The result of a fusing mechanism that can survive high surge current without degradation of normally associated with micro-disconnect devices. Also required a device which could provide high symmetrical fault capability yet disconnect under short circuit conditions. As a result of our R&D program all products shipped from Meter-Treater, Inc. are equipped with fuse devices fulfilling all the above requirements.

Currently the best method for locating an open neutral involves listening to your customer, and careful site inspections. There are test devices which introduce current imbalances and create one leg loading to create the voltage swings common with open neutrals. We should also comment that if an open neutral exists, and the device described above is employed, damage to SPD could result, so disconnecting the SPD is recommended.

There really isn’t a solution, but open neutrals will exist as long as people run multiple voltages in the home. All we can do to reduce the problem of open neutrals is to be alert and make proper decisions with regards to installation and application of electrical equipment in today’s electrical facilities.