What Is An Electrical Transient?

The following is a great article we found from Alltec explaining what an electrical transient is and the effects it can have:

Transient surges are defined as momentary bursts of energy that are induced upon power, data, or communication lines. They are characterized by extremely high voltages that can drive tremendous amounts of current into an electrical circuit for a few millionths, up to a few thousandths of a second.


Surge activity is often assumed to be an outside engendered anomaly. Lightning induced electrical energy bursts, for example, typically come to mind as the primary source of surge activity. However, while lightning induced surges represent are the most formidable transient related equipment menace, most surges are originate from internal sources within a facility.

Internal transient generators range from copiers to coffee makers, from vacuum cleaners to variable speed drives, and from fluorescent light ballasts to furnace igniters. Studies have verified that approximately 80% of transient activity at a given facility is internally generated.


Copiers and laser printers, for example, are notorious transient generators – as are heating and air conditioning systems. Any time an inductive load, whether it is a vacuum cleaner or a heavy duty variable speed drive, is either powered on or off – it generates a low magnitude surge impulse that propagates back through the electrical distribution.

While internally generated transient activity can weaken equipment over time, the threat posed from lightning activity is particularly disconcerting due to its capability of delivering vast amounts of energy into unsuspecting electronic equipment loads.

According to an article on Nationwide Insurance website, ‘“The average claim for lightning-related damage is well over $10,000.” Nationwide deduces in that same article that surge suppressors, specifically, rapidly pay for themselves.*


In any event, today’s electronic equipment is particularly vulnerable to the voltage component of the transient energy.

That’s because modern computer chips are comprised of literally millions of active components, all of which are positioned upon a silicon wafer whose surface area measures no more than a square inch. For example, Intel’s Core i7 920 (D0 stepping) microprocessor employs 781 million transistors.

With that in mind, it becomes obvious that there isn’t much physical space separating the microprocessor’s individual components. It doesn’t take much of an overvoltage, lightning induced or otherwise, to cause arcing between the IC’s internal components and damaging today’s microprocessor based electronic components.

State – of – the – art surge suppressors, now more than ever, are required to protect modern day state – of – the – art electronic equipment. Transient overvoltage surges measuring as low as a few hundred volts/peak pack enough punch to damage sensitive electronic equipment beyond repair.


General Electric reported in their in-house magazine, “Current Scene”, the observation of transient “surges” of several thousand volts occurring regularly on 120 V power circuits within facilities ranging from family homes to large industrial manufacturing plants.

The voltage element of a transient surge is received like a slap in the face by modern integrated circuits (ICs), i.e. computer chips. In the same manner that we would feel a rush of facial pain should someone slap us across the cheek, the computer chip will suffer, albeit metaphorically, in a similar sense.

While a series of quickly reoccurring and repeated slaps across our face would result with our feeling intense bodily pain, multiple back to back to back transient surges occurring in quick succession will cause an otherwise healthy computer chip to fail catastrophically.


It becomes prudent to mitigate the damage causing potential that is associated with the transient threat. And, that task is accomplished with Surge Protection Devices (SPDs). The quality SPD has a very basic purpose. And, that is to protect critical electronic equipment loads by diverting intense levels of transient current away from them while limiting the corresponding voltage amplitudes to safe levels.

In other words, an SPD serves as an electronic shock absorber that attracts transient surge energy and safely soaks it up before it gets to its protected equipment loads.

With that said, SPD safety standards have been revised in recent years; calling for testing that stresses the SPD to failure while ensuring that it does so safely. The fact is SPD failures were, and still are, typically caused by temporary over voltage (TOV) events, rather than surge activity.


While most surge suppressors have always easily withstood momentary voltage bursts, they could and would fail catastrophically when subjected to a sustained overvoltage high enough to drive them into continuous conduction.

SPD safety testing, beginning in February 2007 when ANSI/UL 1449 – 2nd edition was revised to include extended abnormal overcurrent test parameters, required SPDs to be subjected to a full gamut of abnormal fault current scenarios; necessitating them to conduct various amounts of fault current until they failed in a safe and orderly fashion.

SPD products of yesteryear, without redesign or augmentation, could not meet the new enhanced safety requirements. While ANSI/UL 1449 was again revised in September 2009, with the advent of its 3rd edition, the overcurrent testing implemented in its previous iteration remains to be a key significance.

A strong argument can be made that SPDs still in service and manufactured before February 2007 – before today’s accepted safety standards adapted more robust testing requirements, are not completely safe for use. They should be replaced based solely on safety concerns.

Since most SPDs employ suppression components that wear out over time, it is not a bad idea to replace older SPDs as a preventative measure, as well.