Technical Information

Brief ‘simplified’ report, depicting the difference between other causes of electrical fire and HRC

By David W Heathcote, Electrical Engineer and innovator, 50 years – Genesis Consultancy, Oceania

Whenever one reads the disturbing news of a fire in a building or aboard ship etc being caused by electrical fault conditions, the standard phrases so often used in the accompanying descriptive article are rendered as:

“A Short Circuit” – “An Overloaded Circuit” – “Faulty Wiring” or similar

Although there is always a measure of credible content within the above expressions, they are so often employed by those who are not electrically conversant. A seemingly accurate dramatic euphemism may render a plausible sound bite, but can we be sure it is factual?

The truth is, whatever country or territory such ambiguous expressions are used, the actual facts are quite different in many cases.  Far too many cases permit innocent ignorance simply to prevail merely because it sounds good when in reality; the mistake is actually taking a heavy toll worldwide.

To be enabled to comprehend the difference between various types of fires from electrical sources, it is essential we are not beguiled by euphemisms, (notwithstanding the goodwill and innocence in which incidents are reported by whomever) as the inevitable costs can be extremely high.

Whilst attempting to retain an atmosphere of simplicity, I sense it’s also time to dispel any myths when it comes to the serious topic of fire and electrical safety.   In the interest of achieving this, I will take the three ‘reasons’ listed above and open them out a little, but firstly permit me to explain a little about electrical circuit distribution as such is essential to explain things accurately.

In the vast majority of electrical installations, there will be (or should be) a master point of distribution, these are given various different titles according to which country or territory involved.  These can either be of a master or sub circuit application; however I will not labour on this particular aspect, as it is not necessarily essential to create the primary enlightenment I wish to achieve.

I have below created a short list for English speaking countries of the names given to the above mentioned ‘points of distribution’:

In the USA and Canada such is known as a breaker panel

In the UK it is known as a consumer unit, fusebox or distribution board

In Australia and New Zealand, a switchboard

Contained within the above ‘points of distribution’ would be ,1) a mains or master switch which can isolate everything,  2) cut-out switches which handle overload for each circuit distributed to, and 3) safety switches or imbalance devices which prevent electrical shocks from happening in the circuits being served from this particular hub or ‘centralised point of distribution’.  There can be other accessories found inside the unit; however for reasons to not overcomplicate matters, I have deliberately omitted such modules from this explanation.

Returning to the three common statements referred to above as ‘reasonings’ a fire incident took place, I will take each one and expand on it with a view to achieving common enlightenment and better understanding especially for the benefit of non-electrical engineers and electricians.   I reiterate I will not be attempting to ‘Go-Overtech’ with my explanations, therefore I hope any learned ‘electro-tech-gurus’ reading my report will understand that simplicity is my prime motive to obtain certain basic arenas of comprehension for the average reader or punter.

A Short Circuit

When reading about, seeing, or hearing any news and reports of electrical fire incidents due to system faults connected via a point of distribution as indicated above whether in land buildings, maritime, mines and so forth,

it is highly likely to be the case; any ‘short circuit’ fault would have already been circumvented, thus protected by the devices located within this hub unit.    For example, a short circuit, (in lay terms) is no less than a ‘BIG’ circuit overload, where the live/active conductor in the circuit directly comes into contact with the neutral or earth/ground conductor, therefore please see the following explanation, ‘An Overloaded Circuit’

‘An Overloaded Circuit’

While this type of fault can certainly cause fires, the risks for many years have been duly accommodated.  This, similar to the above ‘short circuit’ issue, is when far too much load is placed on any one single circuit.  For instance, if a circuit is protected by a fuse or overcurrent breaker within the distribution hub, (say) with a 10 amp maximum fuse or circuit breaker fitted, then a number of heavy resistive loads are plugged in and switched on locally, the circuit will automatically isolate.      Let’s take a look at this practically:

A circuit of (say) 6 sockets protected in the ‘hub’ at 10 amps by a breaker, (or a fuse) would not be capable of remaining energised if appliances drawing 14 amps were plugged in and switched on. The fuse would blow or the circuit breaker would isolate.   For instance, if a 3 bar electric heater were to be plugged in with all bars blazing with each bar being rated at 750 watts of power @ 230 volts, the current would be 3.26 amps x 3 (bars) which would equal 9.78 amps.  This would be just below the 10 amp rating the fuse or circuit breaker would tolerate.    Now, just supposing we used another socket on the same circuit, we then plugged in and switched on yet another three bar heater, the amount of load would increase obviously to 2 x 9.8 amps ie, 19.56 amps, what would happen?  Yes, this time the fuse would blow, or if it’s a circuit breaker, it would obviously isolate the circuit and therefore reduce any fire risks to zero.

(I will return to these specific paragraphs under ‘An Overloaded Circuit’ later in my overall explanation)

‘Faulty Wiring’

Of all statements one could consider euphemistic when referencing an ‘electrical fire’, this would probably be the most fitting and without much doubt, probably the most nebulas.  Let’s face it; it could really refer to almost any fault issue pertaining to any style or type of electrical installation as everything is more or less wired together in one way or another.

From a more immediate standpoint, the above statement could actually refer to cable faults rather than faults concerning the electrical accessories connected to the wiring.  In fact in reality the statement is more likely to equate to, “There is or was something wrong with the installation”

Let’s take the wiring, (the actual cabling alone)

If the fault is perceived to be of the fire hazard type and is due to cabling alone, then it could be one or more of the following conditions:

1. Very old perished wiring could run the risk of the metal conductors coming together at one or many points throughout the cable length where probably partial conductivity between each other may be the cause of some overheating

2. Vermin, Rodents or other small creatures may nibble through a cable at one point or in a number of places which could then:

3. Create a situation as in ‘1’ above or

​4. Cause a parallel arcing fault either between conductors or

​5. In a series arcing fault between the two conductors, (now broken) where under load conditions an arc could pass across the gap left in the one single conductor directly affected.

​6. Far more commonly however, heat would be produced where the cable conductors terminate into an accessory such as a switch, socket or similar, or they mechanically connect one to another at a connecting junction point.  This then becomes HRC (or HRJ – High Resistance Joint) and although it could in some way be still classed in abstract as a ‘wiring fault’, this (wiring) fault is far better understood as a High Resistance Connection (or Joint) issue which I am currently bringing attention to.

Returning to my main theme which is being able to recognise and discern important and vital differences between factors which cause electrical fires, (or better referred to professionally as fires from an electrical origin) I will finally elaborate on those matters which interest me and my colleagues more particularly, being those which are the most common and in our studies more deadly, these being HRC or High Resistance Connections.

Any appliance connected across the mains electricity between active/live and neutral will inevitably be via cabling, and then via a switch wired directly, or a plug and socket receptacle.  The appliance would be termed technically as a load.   Depending how high or low the resistance is within the load, (or appliance) determines the size of that load.  If the load has low resistance to the flow of electricity then the current, (amps) will be high or classed as a heavy load, conversely if the resistance is high, then the current would be less and determined as a light or lighter load.

In the case of a heating element for water, air or some other medium which requires heat, the element will be the component which is deliberately and safely designed to deliver such a deliberate rise in temperature.  For instance where any medium is forced at great pressure through a restricted channel, heat will be the inevitable outcome.  I reiterate if this is designed to be so thus creating intentional functionality then it is safe.   However when the opposite is designed, such as a normal electrical connection which (say) is supposed to operate at normal air/room temperature, (known professionally as ambient)  and this happens to be an electrical connection, then it has been designed to be cold.   For example if such a connection should only match room, (or ambient) temperature when energised and under load, plus a small but safe allowance to run a little warmer, then it is imperative its thermal status should stay that way.  This would mean the integrity of each connection should remain at the lowest resistance possible.  However if that connection should become compromised by high resistance with a load is applied, then the connection would be correctly termed, a High Resistance Confection or HRC affected.

A connection can become affected by HRC through many different factors these being:

Loose due to not having been tightened to the correct torque when installed, or termination types are unsuitable

Undersized cross sectional diameter cable sizes or inferior termination clamping styles are deployed

Terminations become loose since being installed by excessive movement of the accessory or adjoining cable

When certain types of vibrations, some being of a physical nature such as being subjected to machinery or vehicles operating nearby, or electrically, which is a phenomenon known as harmonics

Ageing metal fatigue in either the clamping termination or the wire conductor adjoining

Eventual poor connectivity due to an ongoing progression of adverse atmospheric conditions such as:

Constant changes in surrounding temperature

The presence of acidity, alkalinity or other ambient chemical variations

When conductor insulation degrades causing the breakdown in metallic integrity

When there is a heavily loaded cartridge fuse connected nearby, which is ‘cooking’ yet remains in an ‘un-blown’ status.  This can create heat which damages other connections in the vicinity.  This is a classic in certain territories which can affect power intake connectivity.

None of the above will necessarily overload a circuit and consequently isolate power through the breaker or fuse.  WHY?  Because as referenced in the case already exhibited above concerning electrical heaters, unless there is either an actual overload or there is an incident which the safety switch senses as a possible electric shock taking place, things will always remain switched ON!

It is most obvious, as with the case of the electric heaters, certain appliances will quite correctly become hot and thus remain in perfect no-fault conditions.  IE, there will be no overload or any other fault observed by the safety apparatus within the distribution point.   The problems begin, (due to the very real factors and conditions highlighted above) when ‘cold’ connections begin to mimic an electric heater of which they are most certainly not designed to emulate.

In my mind one of the best and simple to understand renderings of the HRC connection was written back in the year 2000 by an engineer at the prestigious American Company PGMDI.  It is available on the following URL link:

http://www.pgmdi.com/FEUpdateSummer2000.pdf

In conclusion, I and my colleagues have more than observed over very many years of experience and research around the globe, there is most definitely a very widely spread misunderstanding which confuses the dangerous and common occurrence of HRC (or HRJ) with other types of fires emanating from electrical sources.

Even with eminent engineers whom I admire greatly, when it comes to the ‘vagaries’ which have become attached to the topic of HRC, it appears certain folk have become lost in the forest looking for trees.

We have long concurred HRC (or HRJ) should be overcome with a distinctly separate remedy in its entirety which is precisely why I innovated a resolution known as the Pre-Ignition-Protection Technology. It is exclusively different from all other fine and noble safety measures deployed and furthermore operates totally via safety imbalance devices which are probably already in situation .

Better to Learn and Not Burn!