CEE Newsletter: Christmas Edition
Dear Reader,  

For the December newsletter this year I would like to take a moment to reflect on how much electrical safety has improved; and also let you know what developments to expect in 2019 and beyond.  

However it’s also the start of the holiday season, so bring on the funnies! 

I’m sure that I don’t need to remind you that the methods of testing described in this post are incredibly dangerous and no attempt should be made to re-create them. As you know, “Curiosity Killed the Cat” and we at CEE are opposed to the harm of felines.  

 -The Editor 

Testing for live electrical conductors by touch.
Our story starts with an extract from the American Electricians’ Handbook (5th Edition), issued in 1942.
“158. Electricians often test circuits for the presence of voltage by touching the conductors with the fingers. This method is safe where the voltage does not exceed 250 [volts] and is often very convenient for locating a blown-out fuse or for ascertaining whether or not a circuit is live”.
Whether or not you think this method is “convenient” is open to debate. But there’s more…
“Some men can endure the electric shock that results without discomfort whereas others cannot. Therefore, this method is not feasible in some cases.”
So if you get hurt, it’s your fault! But, let it not be said that this manual was not scientific in its approach; the touch test can also be used quantitatively as well as qualitatively:
“Which are the outside wires and which is the neutral wire of a 115/230-volt, three-wire system can be determined in this way by noting the intensity of the shock that results by touching different pairs of wires with the fingers.”
The Taste Test.
The same handbook describes another method of testing for live conductors.
“159. The presence of low voltages can be determined by tasting. The method is feasible only where the pressure [voltage] is but a few volts and hence is used only in bell and signal [instrumentation] work.
Where the voltage is very low, the bared ends of the conductors constituting the [live and neutral] of the circuit are held a short distance apart on the tongue.
If voltage is present a peculiar mildly burning sensation results…”
Personally I wouldn’t call a burning sensation “peculiar”, especially if I had just licked a live circuit. But there’s more:
“…which will never be forgotten after one has experienced it.”
So the writer is talking from experience. This manual has a kind of confessional tone to it; a sort of “don’t try this at home but this is how it’s done” message. At least they’re honest about how unpleasant it is – I can only assume that this was a round-about way of trying to share the pain!
“The taste is due to the electrolytic decomposition of the liquids on the tongue which produces a salt having a taste .”
I’m sure many electricians back then would have been delighted to know that there was real science behind what they were doing. Worryingly, this extract is from the 5th edition of the handbook; the advice in this book must have been refined since the first edition. It should be pointed out that this publication is still going strong and is currently available in its 16th edition (ISBN-13: 978-0071798808). 

The point of recommending these unusual tests seems to have been for convenience rather than due to a lack of available test equipment. It would have been simple enough to test for voltage using a light bulb circuit; the brightness of the bulb could also differentiate between potentials of 115 or 230V. Cutting corners in this way seems unnecessary today. 

Would you like fries with that?
Primary Fault Tests.
Fast forward to 1976, across the Pond in the UK. Protection relays had been commonplace for several years and methods of testing them were well established. Cue A.R.Van C. Warrington’s reference book: “Protective Relays: Their Theory and Practice”, a guide for designing, installing and maintaining relay systems.

Not content with only the primary and secondary injection tests we use today, this book advocates the “primary fault test” as a means of testing protective relay systems. That is to say, deliberately initiating a phase or earth fault just to see what would happen :
“In the case of an overhead line the simplest method is to shoot an arrow over or between the conductors, the arrow being attached to a very fine length of iron wire, the other end of which is free, for phase faults, or earthed, for ground faults.”
For the faint-hearted or those who don’t believe that shooting conductive arrows at live wires is a sensible idea, the book goes on to describe an insulated pulley system that could be used as an alternative way of applying the iron wire. Why iron? Well…
“Iron wire is preferred for starting the fault arc because it breaks up into small pieces which are expelled from the arc electromagnetically and has no effect on the arc resistance; copper or fuse wire on the other hand forms a cloud of metallic vapour which creates a very low resistance arc, which is misleading for the application of impedance relays.”
Much safer to expel fragments of burning iron than to create a low-resistance (and therefore high-current) arc. Technically true, but somehow missing the point. Fetch me my bow and arrows.
Testing without test equipment.
Many of Warrington’s later recommendations for relay testing are not too different from the methods in use today; the basic principles of primary and secondary injection test sets have not changed although their accuracy and range of functions has improved a lot. However, what to do when you don’t have the correct tools?

Never fear – Mr Warrington has the answer!

In the evocatively-named section on “Improvisations” there are workarounds for the enterprising test engineer; amongst them:
“Where a suitable voltmeter is not available and the voltage is above 90 volts, a neon lamp and potentiometer can be used… the voltage can therefore be checked by connecting the potentiometer across the circuit [in parallel with the lamp] and moving the slider until the lamp lights… the voltage can be deduced from the proportion of the potentiometer connected across the lamp.”
Well, it was that or lick it.  How about this technique for improvising reactance:
“… in order to have a good waveform [during injection tests], reactance rather than resistance should be used for controlling the current because a lower ohmic value can be permitted which will allow higher test currents. If a suitable adjustable reactor is not available one can be made by taking two flat rolls of stranded wire… and varying their positions relative to each other to control their mutual coupling and hence their impedance…”
Do the Scouts have an Electrical Engineering badge?

The final few pages of the book are presumably also aimed at Scouts:
“In conclusion, the author has no hesitation in recommending protective relaying as a career for a young engineer. It offers all the essentials of a satisfying life, viz. security, interest and variety.”
At least we agree on something.
While we can’t offer any advice as to how body-parts might make useful stand-ins for electrical test equipment, we can at least predict the voltages personnel might be exposed to. PTW’s GroundMat software can be used to model substation earth grids to calculate step and touch voltages between different parts of the grid. The latest version also allows dual earth “layers” of different soil resistivities.  

Deliberately creating arcing faults, using iron wire or otherwise, is only ever performed under controlled conditions. The team behind the IEEE1584 standard uses this method to measure arc flash incident energy and refine the fault calculation methods in the standard. Therefore anybody using PTW’s Arc Flash Evaluation module can make use of the IEEE1584 calculations, backed by research. Of course, the elimination or containment of arc faults remains a key goal in industry today. The new AP900 series of arc detectors include high-speed semiconductor outputs with response times of only 2ms. For systems with potentially very high arc energies, why not link these high-speed outputs to an arc quenching device and drastically cut the amount of energy released before the arc is extinguished? 

The need for intrusive testing of protection relays and associated circuits will never be completely eliminated, but perhaps in the future some functions could be performed automatically by the relays themselves? CEE’s NP900 relays already have automatic self-diagnostic features including monitoring of internal processors, internal control voltage checks and an internal temperature probe. Could all testing be automated one day? It is already possible to automate the bench-testing of protection relays using ISA test equipment. Just ask us about customised relay test programs
Have you ever considered a career in relay protection? CEE Relays Ltd is hiring! If you are an Electrical Engineer with a few years’ experience why not contact us.
(Left): They don't make distribution boards like they used to!