Myths

[JohnW2]

Why not? The former being a fault and the latter an overload seems quite logical even if the result is the same.

You're obviously free to make up your own terminology if you so wish but, by convention (and, for example, BS7671 definition), a 'fault' results in 'fault current' (of any magnitude, possibly very small) flowing through an 'unintended path' (virtually always from L to E), whereas an 'overload current' is an 'excessive current flowing through the 'intended' path (i.e. equally in L & N, with none flowing to earth or anywhere else) in a circuit which is 'electrically sound'.

By those conventional definitions, an excessive current due to a jammed washing machine motor (supplied by a circuit which was 'electrically sound') would qualify as an 'overload', not a 'fault' current.

Kind Regards, John

 

[EFLImpudence]

I said logical.

 

[JohnW2]

I said logical.

You did.

We have the same problem here as in other situations (e.g. "Low Voltage") in which some clever clogs has decided to produce a 'technical definition' of a word or phrase which differs from the meaning of that word/phrase in 'everyday English'.

In this case, I totally agree that 'fault' simply means (in everyday English) something along the lines of 'something wrong', but we are stuck with the situation in which an 'electrical fault' has been defined as having a far more restricted and specific meaning than that.

... and that I would personally not regard that as particularly 'logical' - but it's 'how is'.

Kind Regards, John

 

[ebee]

No John,
Overload is overcurrent in a sound circuit - too many sockets drawing to overload, but the circuit is sound.
A short circuit is a fault.
Both situations are over current and may well be protected against by the same device but one is a fault and (fault current in a short circuit) but the other is not.
An earth fault is not a short circuit or an overload as such.
However you might use the same device to protect against 1, 2 or all three of those situations though or you might use other devices or other means.
We keep them as three seperate problems and protect against them if needed.

Low voltage depends what you are comparing it too.
We class hills and mountains as varying by height, we might also class this variance according to country too, each having slightly differing definitions.
Fast or slow is another relative classification depending to how you are comparing it.
In Electrics the Europe and a lot of the world class voltages as high or low mainly, Low is further classified at the lower end of low .
Basically we tend to utilise low voltages but only use high voltages for transmition/distribution.
240V might be somewhere in the low voltage range around which a lot of folk utilise it as mains voltage.
A 1.5V battery is low voltage too but is also in one of the Extra Low range too.
Likewise Reduced Low Voltage (a pretty much British/UK thing) is still a low voltage.

I remember some years back at senior school I was doing a Geography test and a place was marked with a dot on a map.
I had to state the "Town" I was trying to think of a Town near Paris because I recognised where it was but could not think of the answer.
It turned out the "Town" was Paris. I protested that Paris is not a Town it is a City.
Turned out that as far as the school was concerned all were Towns but some of those Towns were Cities and some were villages but some were just towns and only towns.
I never scored well in Geography but this did not help me either.
I suppose a mountain might be a hill and a mountain but some hills are only hills and not moutains.

Some months ago, this year, I broke my shoulder.

It was just immediately just below the groove that runs diagonally below the ball on the end of the humerous ball and someone quite medically qualified declared it`s not your shoulder its your arm. Apparently a break on the joint or somewhere very near it counts as a broken shoulder and the further it gets down your arm starts to count as your arm and not your shoulder. I`m not exactly sure where that demarkation line is, if it actually exists at all, it might be near the elbow i.e most of your upper arm.
Anyway it hurt, more than a bit!

 

[JohnW2]

No John, Overload is overcurrent in a sound circuit - too many sockets drawing to overload, but the circuit is sound.

Indeed

A short circuit is a fault.

As I said, BS7671 says that a fault is something that results in current flowing through an 'unintended path' and, as far as I am aware, the only context in which it ever uses the word is when the 'unintended path' is from L to E.

Conversely ... as you say, an 'overload current' is an excessive current in a "circuit which is sound". So, as far as I can see, in addition to the example you give, that would also apply when the excessive current were due to 'something wrong' in equipment connected to that ('sound' circuit - and that 'something wrong could go all the way down (or up ) to an L-N 'short circuity' within the connected equipment, couldn't it?

Do you still disagree?

Kind Regards, John

 

[ebee]

No I would say the "circuit" describes the circuit itself that we have created not what is plugged into it. Example if the TV short circuits inside the TV set then that is the job of the manufacturers equipment to have some protection and not our job as protectors of that circuit up to and including the plug used to plug the TV into the mains.
If we plug too many TV sets into our plug circuit then we have allowed to to overload by our design.
Limiting the number of sockets on this circuit could be one way of achieving this - although impractical.
The other way is to add overload protection to the circuit for the circuit.

 

[JohnW2]

No I would say the "circuit" describes the circuit itself that we have created not what is plugged into it. Example if the TV short circuits inside the TV set then that is the job of the manufacturers equipment to have some protection and not our job as protectors of that circuit up to and including the plug used to plug the TV into the mains.

So does that mean that you are agreeing with me.

If we plug too many TV sets into our plug circuit then we have allowed to to overload by our design.

Well, sort of, but as you go on to say ...

Limiting the number of sockets on this circuit could be one way of achieving this - although impractical.

... since that would presumably mean, for example, limiting a 20A radial to one single socket (possibly one double socket, but there could well be argument about that!) ?

'Time for Christmas', I think

Kind Regards, John

 

[ebee]

Go on the John, Merry Christmas then LOL (don`t drink too little though)

 

[JohnW2]

Go on the John, Merry Christmas then LOL (don`t drink too little though)

Thanks - and the same to you and everyone else - and 'drinking too liuttle' is not usually one of my vices

Kindest Regards, John

 

[SimonH2]

Getting back to the original discussion of where some myths come from ...
I'm sure some it comes from misunderstanding.

(cough) years ago when I was adding an IMC rating to my pilot's licence, I had a 'bit od a disagreement' with my instructor. It concerned limitations of DME (distance measuring equipment).
The DME in an aircraft sends out a pulse on a specific frequency, ground equipment picks it up and replies with anither pulse, by timing the delay the aircraft unit can determine the (slant) distance to the ground station - this was (apart from augmented GPS which wasn't really a thing back then) the most accurate navigation tool available in a light aircraft. It can also do the basic time/distance calculations to indicate speed to/from the station.

So what was the 'disagreement' about ?
My instructor was adamant that the DME was only accurate when flying directly towards/away from the ground station - if you were flying at an angle, then it wasn't accurate.
When I tried to get him to explain what I thought was wrong, it came down to "that's what my instructor taught me".

Digging a bit deeper, what became apparent is that he'd misunderstood what he was being taught - and then went on to teach that misunderstanding to his students. At this point I'll add that it's common for would be comnercial pilots to do a spell instructing as a way of building up flying hours while someone else is paying
So those paying attention will have noted the 'calculate speed to/from the ground station' bit. That is only accurate when on a ground track directly to/from the station - and a reasonable distance from it.
If close to the station, the slant distance is longer than the ground distance - e.g. if you were flying a mile up and directly towards the station, you'd see the distance count down to 1 mile then count up again after you'd flown over it. Similarly, the speed calculation would reduce, get to zero when overhead, then increase again. If several miles away, the difference between ground distance and slant distance is not large.
Also, if you are flying past, not over, then the same thing happens - when the ground station at 90deg to your track, then the speed indication will be zero.
But the distance indication is always accurate.
There are some navigation procedures involving a "DME arc" - flying a circular arc a set distance by DME from an airfield. DME distance is accurate, but DME speed will be zero (if you get it right !)

So my instructor had heard "only accurate flying to/from the ground station" and missed that it only applies to to speed calculation. So he then went on to teach his students a "myth" - which many will fail to recognise as incorrect (sounds like something anyone should spot, but your head is turning to mush with the learning pace) and so it gets passed on.


In a similar vein, I once had an argument with an examiner when he insisted on deducting a day when signing my licence for bi-annual renewal.
He insisted the CAA had said he needed to deduct a day - again missing the "when ..." bit.
On initial issue (e.g. when passing a test) that does apply - so if passing on (say) 10th Jan, expiry date is 9th Jan. But on renewal, valudity is 10th to 9th again. He insisted it had to be 9th to 8th. Not only that, but this was second renewal, so he "corrected" the previous entry and applied 8th to 7th.

It's easy to see how true facts, when misunderstood, can turn into untrue myths. And I have to admit, I've fallen into this trap myself ... more than once