It’s one of those issues that are the hardest to troubleshoot. A piece of electrical equipment you supplied to a client, has failed unexpectedly. Was it a faulty unit? Will it be covered under warranty? Was it unsuitable for some reason? Will a replacement unit work reliably in the same location?

In this situation it’s often impossible to pinpoint the cause of a single failure. If you have installed several of the same device, then you can at least compare them all and look for patterns. However with a single failure on one site, there is rarely enough information to know what caused it.

Mains voltage disturbances

In fact one of the most common causes of electrical equipment failure is mains voltage disturbances – voltage surges, spikes, sags or brownouts, from the incoming mains line. These can sometimes go unnoticed by the people on site, as they come and go in an instant, and may not cause other obvious failures (such as lights). But there’s always some equipment that’s more sensitive to voltage disturbances, and these are the ones that will suddenly fail.

So what can I do about it?

Voltage waveform

Photo courtesy of Creativity103(CC Attribution)

Actually there’s an easy way to find out if the mains power is suffering from ongoing voltage disturbances. All you need is a voltage data logger that can record dips and swells, and short voltage transients (spikes). Simply set up the data logger on the site, leave it recording for a couple of weeks, and then analyse the results. Often this kind of voltage data logger is all it takes to pinpoint the cause of equipment failures. You will immediately see if there’s a pattern of over voltages, regular spikes, or dips and brownouts. If you can prove that the cause of failure was a mains voltage disturbance, you can also take steps to prevent the issue recurring, which will save you and the end user a lot of time and money. For example, installing extra mains filtering or voltage stabilisers can fix the problem for good. Alternatively if the equipment has an AC to DC power supply, you can upgrade the power supply to one that is more tolerant of input voltage variations.

What voltage range is considered normal?

In 2000 the IEC released standard 60038 which defines the standard AC voltages and ranges under normal conditions. This was aimed at bringing contries using 240V/415V (such as Australia) or 220V, back in line with the 230V/400V standard used across much of Europe. The 230V figure is for single phase (phase to neutral voltage), and 400V is for 3-phase systems (phase to phase voltage). The standard allows the voltage to vary by +/-10% in the first few years whilst transition is in progress, then it states that reduction of this range will be considered. Looking specifically at Australia as an example, Australia developed its own version of the standard called AS 60038. Australian power companies typically define their allowable voltage ranges as being +10% to -6% of the 230V/400V standard, at the point of supply. So for a single phase supply you can expect the voltage to be between 216V and 253V, for the majority of the time. This can vary though from state to state.  The standard also allows for short transients where the voltage can exceed these limits as well. For example when a load switches on or off, it takes a little time for the grid to compensate for this.

What’s a dip? A swell? A transient?

A voltage dip or sag, is a short duration drop in the supply voltage, usually caused by faults in the system or motors starting. Dips can be as short as milliseconds or as long as 10 seconds. A swell is a short duration increase in the supply voltage, usually caused by load switching in the network. A transient or “spike” is a very short duration increase or decrease in the voltage, which can be as short as a millisecond. Transients can sometimes be very high voltage, for example as a result of a lightning strike.

Which voltage data loggers will record these voltage disturbances?

CyberVisuell LDW-6095K power and voltage data logger
There are a number of data loggers on the market that can record voltage disturbances. Some data loggers are purely designed for this purpose, and they just plug into a standard single phase power outlet. This can be convenient for example if an equipment supplier wants to send a data logger to a customer site, and have them plug it into a power point for a couple of weeks, then send it back again for analysis. Larger power data loggers / analysers can be designed for not only voltage disturbance recording, but general power data logging and analysis as well. For example the CyberVisuell LDW-6095K is a 3-phase power analyser/data logger, which can be set to record voltage disturbances, and it also covers the more common power usage measurements, harmonics, unbalance etc. When you need a voltage disturbance data logger, check the specifications of the data logger in detail. Not all models are designed for detecting and recording short voltage transients – some data loggers can only record every 2 seconds or longer so they will miss short transients. If you’re in doubt about which instrument will best suit your needs, it always pays to speak to an authorised distributor of voltage data loggers, to obtain accurate advice.