Spikes damage standard
household appliances

Lets first define a household appliance. There are two categories, 'hi-tech' and 'non hi-tech'. Hi-tech will include the usual TV, Video, Hi-Fi, PC, and at a stretch a computerised washing machine (ok, I'll even stretch to the microwave oven). Such damage has been covered in the section on "equipment failure" and is recognised as highly possible to fail during a "power wielding" transient. Low voltage lighting systems are a rather grey area as they can be coupled to a dimmer circuit which in itself is a transient creator (so let's just leave this as a grey area).

Non hi-tech will be the electric cooker, the immersion (hot water) heater, fridge / freezer (and combos), non-computerised washing machines, and mains powered light bulbs. These are the items under discussion here.

What becomes interesting is hearing Power Quality Investigators tell their tales of woe of customers claiming for damage to a fridge owing to a "spike on the mains". Similar stories are told of electric cookers and kettles. The classic is light bulbs blowing, although there are issues surrounding these it's generally not 'spikes'.

When analysing a complaint like this the question that should be foremost in one's mind is: Does the appliance allegedly damaged by such a transient contain passive components (as opposed to 'active' semiconductor riddled appliances)? To substantiate our belief that the damage in question is a myth we need to investigate the way passive components react during a transient.


Heater Elements:
When such elements are first turned on they have a lower resistance than when fully heated. This means they draw more current until warm with ratios of cold to warm current reaching as high as 2:1. Being able to conduct twice the current it usually runs on means it should be able to handle transients of up to twice the mains voltage. In reality one must remember that power is related to V2 meaning our device would be able to handle short bursts of 1.414 times mains voltage. This is still a large transient!

Motor Elements:
There is another name for motor elements - inductors. One feature of inductors is they are 'frequency dependent resistors' with the 'resistance' (impedance) increasing proportionately with frequency (which, by the way, is why transformers are such handy "transient stoppers"). As transients are high frequency overlays on the fundamental the inductive component will simply present a high impedance to the transient and continue its work unhindered.


The reason 'spikes' are interpreted as the cause of damage is the 'mechanics' taking place during a fault. Heat plays the major part in both a typical appliance fault and one caused by a genuine transient. The difference between a typical appliance fault and a genuine transient is the latter will most likely damage more than one appliance at the same time. It is the characteristics of the heat damage that determines whether this was instantaneous (transient) or long term.

Long Term Heat Damage:
Such damage is usually a result of 'under designing' and will more often than not involve switches, relays, and connection points (places where 'hot spots' are most likely to develop). Included in connection points are printed circuit boards whose primary function is interconnecting the various devices of an appliance (and often hold components such as relays etc.).

Heat damage from a hot spot is easily recognised. The damage is relatively wide spread and will 'distort' heat sensitive components (e.g. plastic). Hot spots on PC boards will show up as a dark area that gradually lightens to the original colour of the board the further you move away from the hot spot.

Transient Damage:
This is recognised by two distinct features. The heat damage is very localised and usually does not result in much (if any) distortion of any heat sensitive components. Transient generated heat on PC boards will have an almost distinct border where the heat damage 'stopped' as the heat is intense but short-lived.

The second feature is 'flash marks' (a silvery-bluey tinged area). Destructive transients usually exceed the breakdown voltages or current carrying capabilities of the damage components. These flash marks are created by the metal parts, with the high current involved, vaporising and the metal depositing on the surrounding surfaces.

So how are mistakes made ?
What often happens during a heat induced fault is a wire or contact may break creating a hefty spark, enough to vaporise sufficient metal to create the tell-tale flash mark. Instead of going beyond the flash mark and investigating the heat damage, the inexperienced individual will stop at the flash mark and incorrectly claim "mains transient".

'Dry joints' (where a soldered connection has hairline cracks which have high resistance) are renowned for 'exploding' and vaporising rather spectacularly leaving a very unmistakable flash mark. What will also be seen is the heat damage is very contained. Again, the inexperienced individual will take this to be transient damage. What is not known to this individual is that such damage, at a soldered joint, was as a result of a bad joint.... not a transient. The transient would melt the surrounding printed circuit before melting the soldered joint, purely because of the physics involved - it takes more energy to melt a larger mass.

And finally:- The picture alongside has all the apparent tell-tale signs of transient damage. The heat damage is localised, and flash marks appear on nearby components yet nothing is distorted.

However, this was a design fault. The inexperienced individual would overlook the fact that the component around where the fault took place was a gas discharge tube. This should have absorbed such a transient.

The actual fault was the design brought the two sides of the incoming mains within an unsafe distance of each other through the placing of a track on the board and one leg of the gas discharge tube. The only insulation was the solder-mask which then finally broke down allowing the full potential of the mains to arc over and cause the destruction.


We are not claiming that destructive transients do not exist and that damage to standard household appliances does not occur because of them (having lived in the highest lightning occurrence area in the world, I should know!).

We are, however, claiming that there are individuals out there that cannot make the distinction between what was a genuine case of transient damage and what was not (especially if the electricity supplier or insurance company is footing the bill). If you are involved in power quality claims issues, it would be extremely prudent to learn the difference for yourself.

Myths (index)  >>

| | Ask a Question |

© 05.09.01