Safety Issue - Moulded 13A Plugs

[jjb1970]

This thread reminds me of a comment I once heard from some new age lunatic I once heard trying to sell some snake oil - it's like electricity, nobody knows how it works, it just does.

[melmerby]

Re moulded plugs.

Where I worked (admittedly now more than 20 years ago) moulded plugs were outlawed as the local safety regulations deemed them dangerous, so immediately any equipment arrived with a moulded plug it was cut off and replaced by a Crabtree, MK or other quality wire-on plug.

(There had been instances of a moulded plug leaving the live pin in the socket when it was withdrawn, even though they were supposed to be to BS1363)

 

N.B. we had tighter mains regs than the BS.

As an example the trip currrent for RCDs was half that of the BS standard of 30mA.

 

Keith

[AndyID]

In America, electric kettles are rare. So is decent tea. I always take a Tesco Value (£4.95) kettle and Yorkshire Tea when I go for work. Normally, with 110V, the kettle takes 4 times as long to boil as it does here.

 

Using Ohm’s law, we can deduce that as a 2200W (10 Amps x 220 volts) device on 220V, it has a resistance of 22 ohms. This means that at 110V it will only draw 5 Amps. It therefore becomes a very slow 550W kettle.

 

Despite this, my American friends are usually so impressed with a device that actually boils water, that they are delighted to accept it as a parting gift, giving me more room in my bag for all the stuff I have ended up buying.

 

Paul

 

No, they're not rare here at all. We've had plenty of electric kettles and they usually have 1500 watt elements rather than the typical 3000 watt element in the UK. They take twice as long to boil a given amount of water.

[phil-b259]

Phil

 

"...... if the power figure is to be maintained when voltage lowers then the current must increase."

 

True.

 

But, I think that the root of the confusion here is an assumption that in most loads the power figure will be maintained when the voltage varies, when in fact it won't.

 

In order for a load to maintain constant power dissipation, it must incorporate the capabilities to measure voltage and current, then self-adjust its effective resistance, so that the product of the two remains constant ........ and most loads simply don't incorporate those capabilities, and even those that do can only maintain constant power across a stated range of conditions.

 

For most loads, the rated "power" is not what it will dissipate under all (or even a range) of conditions, but one of two things:

 

- the maximum power that it can dissipate without doing harm by overheating; or,

 

- the power that it will dissipate when supplied with a stated voltage.

 

Does that make sense?

 

Kevin

 

It does make sense in a way, but perhaps it might be more useful to illustrate my though process from the very beginning. You can then tell me where the flaws are.

 

If I return to my example of a track circuit, under typical situations the circuit will have a resistance of X and a power consumption of Y. Put a short circuit condition on it (be that a train or a fault) and the power consumption will go up, the current will go up but the voltage will go down as the circuit tries to pull as much current as possible from the transformer or battery.

 

I believe this all matches the relevant equations in physics  - there is a maximum limit the transformer / battery can provide given as a VA rating which governs the overall power available to the circuit and resistance change in this circumstance will thus drive the voltage and current values in opposite directions - not in the same way as the P=IV equation suggests.

 

Now that doesn't mean the P=IV equation is wrong, the power consumed by the track circuit is still the result of Current multiplied by Voltage at any given time - but at the same time using the basic P=IV formula is no the holy grail some are trying to make out and it cannot be used to prove that current will always fall if voltage falls - because practical testing shows that to be false.

 

For avoidance of doubt the track circuit test can be repeated in a laboratory - and at 1000s of volts or 1000s Amps and you will still see the same effect - namely if the demand is grater than the supply can provide then the current will increase and the voltage will fall.

 

Now obviously manufacturers don't normally intend devices to consume more power than they can be supplied with so in ordinary situations the basic P=IV formula works fine to describe the current flowing through a power chord. However its not always so simple

 

At Horsted Keynes station for example having all the Christmas lights and Santa gubbins plugged in was too much for the mains supply point and the 240V ended up being nearer 190V (with a knock on effect to the signalling supplies - although the use of battery back ups made sure it wasn't low enough to cause signalling problems). Had anyone measured the current being drawn from he mains supply they would have found it to be grater than the VA rating of the supply and as such the voltage started dropping. Turn off the lights, the current draw drops and up goes the voltage Simples!

 

It doesn't matter what some folk on here say, that is another practical demonstration that P=IV is not the sole arbiter of Current / Voltage relationships

 

The National Grid is not a limitless supply - each connection point will have a limit to what may be attached to it.

 

So if you replace Horsted Keynes station with a campsite full of RVs running heaters full blast then the situation will not magically alter - hence the comment that its quite possible for an RV to draw more current than it ideally should do if the site voltage is low.

 

Its all sound electrical theory and can be proved to be correct by the relevant formula (not necessarily P=IV).

 

Finally it doesn't take a genius to work out that plus / sockets are a week point in any electrical circuit. If there are any defects or the mating surfaces are not perfect then arcing may occur. The greater the current the grater the arc (its why the ones produced by 3rd rail trains pulling hundreds or thousands of Amps thanks to the low 750 Volts present are so dramatic?) and the grater the heat generated. It therefore follows that prolonged exposure to higher currents than the connection is designed to (or can accommodate due to a manufacturing / coupling defect) will in turn generate more heat and melt the plug.

 

Logical?

Edited January 2, 2019 by phil-b259

[sharris]

It's not always as simple as that as the hot resistance on 110v is different to 220v and therefore will have a different power.

We used to have a small "Travel" kettle which was suitable for 100-220v but the quoted power at 110v wasn't 25% of the power at 220v (I can't remember what it actually quoted

 

Keith

Looking at some dual voltage kettles on Amazon I see they have a voltage switch. I would imagine that the element is split into two and for the 110V setting the two halves are connected by the voltage switch in parallel and for 230V they are connected in series - that way you should get more-or-less full power at either voltage.

 

I would hope they have an over-current trip to cut out if you leave it on the 110V setting in a 230V country.

Edited January 2, 2019 by sharris

[Martin Shaw]

47 years in the industry may well taught you Ohms law - but it doesn’t seem to have taught you respect when dealing with mistaken folk or the ability to recognise that when someone may be 100% correct with the equations / relationships but have given them the wrong name.

Your quite right, it hasn't taught me any respect for someone who despite many posts that they are wrong, continues to argue to the contrary. I have read your last post, I would suggest you speak with Charles Hudson MBE who can possibly elucidate you. In respect of your use of a track circuit example, of course when a train occupies it, the voltage drops and the current rises, because quite simply the resistance has fallen, it's no more magical than that, if you can't grasp this basic principle then there really isn't any point. Stop fighting it.

Best wishes

Martin

[AndyID]

Looking at some dual voltage kettles on Amazon I see they have a voltage switch. I would imagine that the element is split into two and for the 110V setting the two halves are connected by the voltage switch in parallel and for 230V they are connected in series - that way you should get more-or-less full power at either voltage.

 

I would hope they have an over-current trip to cut out if you leave it on the 110V setting in a 230V country.

 

My wife had a really neat little dual-voltage hair dryer. It worked really well on 120 in Spain. Didn't work so well when we got back to the UK. She forgot to switch it back to 240

[sharris]

It does make sense in a way, but perhaps it might be more useful to illustrate my though process from the very beginning. You can then tell me where the flaws are.

 

If I return to my example of a track circuit, under typical situations the circuit will have a resistance of X and a power consumption of Y. Put a short circuit condition on it (be that a train or a fault) and the power consumption will go up, the current will go up but the voltage will go down as the circuit tries to pull as much current as possible from the transformer or battery.

 

I believe all matches the relevant equations in physics - there is a maximum limit the transformer / battery can provide given as a VA rating which governs the overall power available to the circuit and resistance change in this circumstance will thus drive the voltage and current values in opposite directions - not in the same way as the P=IV equation suggests.

 

Now that doesn't mean the P=IV equation is wrong, the power consumed by the track circuit is still the result of Current multiplied by Voltage at any given time - but at the same time using the basic P=IV formula is no the holy grail some are trying to make out and it cannot be used to prove that current will always fall if voltage falls - because practical testing shows that to be false.

 

For avoidance of doubt the track circuit test can be repeated in a laboratory - and at 1000s of volts or 1000s Amps and you will still see the same effect - namely if the demand is grater than the supply can provide then the current will increase and the voltage will fall.

 

Now obviously manufacturers don't normally intend devices to consume more power than they can be supplied with so in ordinary situations the basic P=IV formula works fine to describe the current flowing through a power chord. However its not always so simple

 

At Horsted Keynes station for example having all the Christmas lights and Santa gubbins plugged in was too much for the mains supply point and the 240V ended up being nearer 190V (with a knock on effect to the signalling supplies - although the use of battery back ups made sure it wasn't low enough to cause signalling problems). Had anyone measured the current being drawn from he mains supply they would have found it to be grater than the VA rating of the supply and as such the voltage started dropping. Turn off the lights, the current draw drops and up goes the voltage Simples!

 

It doesn't matter what some folk on here say, that is another practical demonstration that P=IV is not the sole arbiter of Current / Voltage relationships

 

The National Grid is not a limitless supply - each connection point will have a limit to what may be attached to it.

 

So if you replace Horsted Keynes station with a campsite full of RVs running heaters full blast then the situation will not magically alter - hence the comment that its quite possible for an RV to draw more current than it ideally should do if the site voltage is low.

 

Logical?

I think the situations you describe can all be explained in terms of a potential divider.

Line resistance.    SocketMains.    ----[=====]-------(A)---o <-----------                                      Ammeter   |                       |                                                      Z.                      |                                                      Z load.            (V) voltmeter                                                      Z resistance     |                                                       |                       |Source.   ----------------------------o <-----------

In all the cases you describe the line resistance will be constant, small but non-zero (I've simplified things by lumping all the line resistance on one side here, in reality it will be shared between the out and return (live/neutral) wires. What you see at the volt meter will be Source voltage x ( load resistance / ( line resistance + load resistance).

 

For an open circuit you'll see exactly the source voltage, but as you add more loads (RVs with their heaters blazing away, Christmas lights, etc) you are decreasing the load resistance with each thing you add, so the measured voltage will drop. With a short circuit your load resistance is very small so your measured voltage will be very low.

 

As you keep adding more things into the circuit the current which is Supply voltage / (line resistance + load resistance) will increase, limited in the end by the line resistance, so a short circuit will have almost no volts but a high current.

 

In the case of the RVs, if the campsite is full of them with their heaters going the voltage at the socket will drop because the supply is heavily loaded, and the total current to supply them all is high, however if you look at a single RV, the voltage will be low but there will be no magical compensation to boost the current to make up the power as the load resistance for an individual RV heater will be constant.

 

The only way you would up the current would be if you said 'that heater's not working so well, I'd better switch on a second one too"

 

Edit: well that was a bit of a disaster trying to ASCII art a circuit diagram from my phone!

Edited January 2, 2019 by sharris

[phil-b259]

I think the situations you describe can all be explained in terms of a potential divider.

Line resistance.    SocketMains.    ----[=====]-------(A)---o <-----------                                      Ammeter   |                       |                                                      Z.                      |                                                      Z load.            (V) voltmeter                                                      Z resistance     |                                                       |                       |Source.   ----------------------------o <-----------

In all the cases you describe the line resistance will be constant, small but non-zero (I've simplified things by lumping all the line resistance on one side here, in reality it will be shared between the out and return (live/neutral) wires. What you see at the volt meter will be Source voltage x ( load resistance / ( line resistance + load resistance).

 

For an open circuit you'll see exactly the source voltage, but as you add more loads (RVs with their heaters blazing away, Christmas lights, etc) you are decreasing the load resistance with each thing you add, so the measured voltage will drop. With a short circuit your load resistance is very small so your measured voltage will be very low.

 

As you keep adding more things into the circuit the current which is Supply voltage / (line resistance + load resistance) will increase, limited in the end by the line resistance, so a short circuit will have almost no volts but a high current.

 

In the case of the RVs, if the campsite is full of them with their heaters going the voltage at the socket will drop because the supply is heavily loaded, and the total current to supply them all is high, however if you look at a single RV, the voltage will be low but there will be no magical compensation to boost the current to make up the power as the load resistance for an individual RV heater will be constant.

 

The only way you would up the current would be if you said 'that heater's not working so well, I'd better switch on a second one too"

 

Edit: well that was a bit of a disaster trying to ASCII art a circuit diagram from my phone!

 

 

Hmm, I sort of see what you are saying but it would be even more helpful if you could try and sketch it out on paper and attach it as a picture at some stage. As you say ASCII is a little hard to interpret.

 

I get the idea that multiple devices added to a single supply point (i.e. in a parallel configuration)  lowers the overall load resistance 'seen' by the power supply (and thus increases the current as a result) - but IIRC in parallel circuits the voltage drooped across each 'branch' as it were remains the same - it being series circuits where you get the voltage altering across each resistive element.

 

True if you work out the effective resistance of all those RVs in parallel then I guess you could substitute them for a single resistive load across the powers supply nut that still woldn't lower the voltage across it (a 240V supply will in theory still kick out 240V regardless of load until it reaches its max VA rating)

 

Therefore in the campsite scenario surely increasing the number of RVs will merely increase the current and not lower the voltage seen by any RV due to them all being in parallel with each other.

 

As such it doesn't seem to account for the real world situations I have outlined where the voltage does indeed drop with increased current.

 

I therefore deduce that different equations must come into play when the power demanded exceeds that available to explain the different outcomes with respect to voltage.

Edited January 2, 2019 by phil-b259

[AndyID]

True if you work out the effective resistance of all those RVs in parallel then I guess you could substitute them for a single resistive load across the powers supply nut that still woldn't lower the voltage across it (a 240V supply will in theory still kick out 240V regardless of load until it reaches its max VA rating

 

Unless the cables feeding the RV power outlets are superconductors the voltage at each RV will droop as the load increases. All power distribution cables are resistors. In fact it's a big problem for utility companies because a lot of the energy they put into the distribution network never makes it to the consumers. It's dissipated as heat from the cables. It's also the reason we have cheap hydroelectric energy here. If the producers could export it to California, they would, but it's not cost effective because of the energy loss in long transmission lines.

[kevinlms]

My wife had a really neat little dual-voltage hair dryer. It worked really well on 120 in Spain. Didn't work so well when we got back to the UK. She forgot to switch it back to 240

A friends then young son did something similar. He was fiddling with his computer one day and found a switch on the back, marked 230, so he flicked it to see what it did! So that was the end of the power supply & motherboard.

At least he learnt what it did!

[AndyID]

A friends then young son did something similar. He was fiddling with his computer one day and found a switch on the back, marked 230, so he flicked it to see what it did! So that was the end of the power supply & motherboard.

At least he learnt what it did!

 

At the risk of veering even further off topic  our mother was probably addicted to tea. We used to go for holidays in France (they can't make tea there either) in the car and our dad was quite inventive, so he bought a 12 volt kettle. It had big croc-clips that clamped on to car battery posts. He rigged up a holder for the kettle under the bonnet of the Vauxhall. When mum was in need of refreshment he'd stop, fill the kettle, attach it to the battery and set off. When steam emerged from under the bonnet we'd stop in a lay-by and have a cup of tea.

[Pannier Tank]

Ok - if it satisfy your macho streak then yes I admit Ohms law only talks about the Voltage, Resistance and Current relationship - and therefore should not have been cited when talking about Power.

 

However according to Wikipedia (other references sources are available)

 

”In the case of resistive (Ohmic, or linear) loads, Joule's law can be combined with Ohm's law (V = I·R) to produce alternative expressions for the amount of power that is dissipated: P=IV”

 

This equation quite clearly sates power is a function of voltage multiplied by current, and that if the power figure is to be maintained when voltage lowers then the current must increase.

 

It has got nothing to do with having a "macho streak", several other people have tried to help you understand the Basic principles of Ohms Law. I quoted an example showing what happens to the Current Drawn when the applied Voltage is changed. You stated "Ohms law states that if the voltage goes down then the current must go up if the resistance stays the same." when in fact it is the opposite.

 

Ohm's law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance ( R ). Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit remains the same.

Edited January 2, 2019 by Pannier Tank

[Nearholmer]

Phil

 

See circuit diagram below .......

 

V is the fixed source voltage

Rs is the source impedance

Vo is the source output voltage (battery terminals, for instance)

Rc is cable/line resistance

VL is the voltage across the load

RL is load resistance.

 

In your track circuit case, Rs is a high value, and when a train occupies the circuit, RL falls suddenly from a (hopefully) very high level, a high resistance relay coil in parallel with a vanishingly small leakage current flowing through the ballast, to effectively zero.

 

Because RL is now zero, however much current is flowing through it, no voltage is dropped across it, VL= 0. In fact, even a train on line isn’t a pure short circuit, so you will be able to detect a minute voltage. At the supply end, you have a source with very high internal impedance, and the line itself has relatively very low impedance, so, with the short circuit in place and current flowing, nearly all of the voltage is dropped across the source impedance ....... Vo, the voltage measured at the output terminals, has collapsed to be close to zero.

 

A track circuit has to have a high source impedance, because it is a very rare sort of circuit, one designed to operate safely for long periods with a short-circuit in place.

 

The circuit in the caravan park will behave in exactly the same ways, but the source impedance will be comparatively lower, and the cable/line impedance probably higher, so the proportional distribution of voltages slightly different.

 

And, the concept of a supply having a fixed limit in terms of VA capacity is sort-of false. It has a limit as to what can be supplied while still maintaining output voltage within specified tolerance, but unless it is fitted with some ‘artificial’ limiter, such as fuses and/or undervoltage protection, it will go on supplying power as demand increases, getting rather hot due to its internal resistance, the output voltage dropping. The VA supplied will increase, at a decreasing rate, then level out, then cease altogether as it burns out!m

 

Again, does all this make sense?

 

Kevin

Edited January 2, 2019 by Nearholmer

[sharris]

Cheers Kevin - that's saved me from having to fix my ASCII art version!

[chris p bacon]

Am I the only one reading this thread about a hot plug, who hasn't the foggiest idea what's being discussed.....

Edited January 2, 2019 by chris p bacon

[melmerby]

Looking at some dual voltage kettles on Amazon I see they have a voltage switch. I would imagine that the element is split into two and for the 110V setting the two halves are connected by the voltage switch in parallel and for 230V they are connected in series - that way you should get more-or-less full power at either voltage.

 

I would hope they have an over-current trip to cut out if you leave it on the 110V setting in a 230V country.

I think you will find most just run at lower power on 110v. no switching involved. Especially the cheaper ones.

 

Keith

[melmerby]

My wife had a really neat little dual-voltage hair dryer. It worked really well on 120 in Spain. Didn't work so well when we got back to the UK. She forgot to switch it back to 240

Where did you find 120v in Spain?

I first went in the '60s and it's always been 220v.

 

Keith

[kevinlms]

Where did you find 120v in Spain?

I first went in the '60s and it's always been 220v.

 

Keith

A late friend of mine used to live in Paris pre-WW2 and he 'learnt' about electricity from the 100? Volts DC circuits back then.

 

He maintained that the problem people have, is that they are 'afraid' of electricity. 

 

He never did understand that 230 Volts is significantly more dangerous than 100 Volts. Tried to explain to him that electricity needs treating with respect, which is completely different to fear.

[Free At Last]

I have two bulkhead light fittings on my garage at the back of the house. I was forever replacing the 60w bulbs so I wired the two fittings in series and put a 100w bulb in one and a 60w bulb in the other as one shone on the back bedroom and I didn't want it to be too bright. When I retired that night, as I was closing the curtains I noticed the different brightness of the bulbs and thought 'dammit, I've put the bulbs the wrong way around' as the one shining on the bedroom was the brightest. 

Next day I went to change them and as I took the dim one out first I noticed it was the 100w bulb and thought I must have somehow put a 150w bulb in the other fitting. On taking that out I was confused that it was only 60w. Then the theory kicked in about volt drop.

Changing them around did the trick, the 60w bulb being brighter than the 100w one when wired in series.

I never had to replace the bulbs again, they lasted many years, coming on every night on a time clock. I eventually changed them for low energy lamps and had to rewire the circuit back to parallel.

Edited January 2, 2019 by Free At Last

[Pacific231G]

Going back to moulded plugs, the problem seems to be that wired plugs may be safer IF they're competently wired (a competent person wiring one should spot any faults) but extemely dangerous if they're miswired. Moulded plugs are very rarely (if ever?) miswired but may be more subject to manufacturing defects that are harder to spot and, because consumer electrical equipment must be supplied with a plug fitted, it's cheaper and possibly safer for manufacturers to supply moulded plugs. 

 

I assume that real world experience has been that electrocutions from miswiring of separate plugs presented a greater danger than fires caused by overheating of badly manufactured moulded plugs, simply because a lot of them end up getting wired or rewired by people who don't actually know what they were doing (as I'm sure any professional electricians here will confirm though even professionals can make mistakes)

 

Our hobby involves a more sophisticated use of electricity than most so we do need to be properly aware of its dangers. I remember being quite shocked to discover from those refurbishing their layouts that both Peter Denny and Frank Dyer had mains voltage wiring mixed freely with the low voltage wiring under their respective layouts. I believe Frank Dyer was a professional electrician/electrical engineer but it's often the strongest swimmers who drown. I've seen similar things on exhibition layouts with integral 240V lighting.

Edited January 2, 2019 by Pacific231G

[Fat Controller]

A late friend of mine used to live in Paris pre-WW2 and he 'learnt' about electricity from the 100? Volts DC circuits back then.

 

He maintained that the problem people have, is that they are 'afraid' of electricity. 

 

He never did understand that 230 Volts is significantly more dangerous than 100 Volts. Tried to explain to him that electricity needs treating with respect, which is completely different to fear.

The French attitude to domestic wiring has always struck me as rather cavalier. A common feature of early domestic installations was a light switch, with an unswitched socket below. Possibly not that unsafe in itself, provided either the socket wasn't being used, or any plug was pushed firmly home. However, the socket often resisted the plug been pushed in, so that there were two bare, live, conductors immediately below the light switch. My French friends couldn't understand why this worried me.

110V dc was still in use in parts of France in the late 1970s; I remember reading the notices about the forthcoming switch-over on our village noticeboard.

[melmerby]

 

Our hobby involves a more sophisticated use of electricity than most so we do need to be properly aware of its dangers. I remember being quite shocked to discover from those refurbishing their layouts that both Peter Denny and Frank Dyer had mains voltage wiring mixed freely with the low voltage wiring under their respective layouts. I believe Frank Dyer was a professional electrician/electrical engineer but it's often the strongest swimmers who drown. I've seen similar things on exhibition layouts with integral 240V lighting.

I could have be included in the "professional electrical engineers" category due to my line of work.

However I would never dream of including 240v AC supplies actually on the layout. It beggars belief.

 

Keith

[phil-b259]

Phil

 

See circuit diagram below .......

 

V is the fixed source voltage

Rs is the source impedance

Vo is the source output voltage (battery terminals, for instance)

Rc is cable/line resistance

VL is the voltage across the load

RL is load resistance.

 

In your track circuit case, Rs is a high value, and when a train occupies the circuit, RL falls suddenly from a (hopefully) very high level, a high resistance relay coil in parallel with a vanishingly small leakage current flowing through the ballast, to effectively zero.

 

Because RL is now zero, however much current is flowing through it, no voltage is dropped across it, VL= 0. In fact, even a train on line isn’t a pure short circuit, so you will be able to detect a minute voltage. At the supply end, you have a source with very high internal impedance, and the line itself has relatively very low impedance, so, with the short circuit in place and current flowing, nearly all of the voltage is dropped across the source impedance ....... Vo, the voltage measured at the output terminals, has collapsed to be close to zero.

 

A track circuit has to have a high source impedance, because it is a very rare sort of circuit, one designed to operate safely for long periods with a short-circuit in place.

 

The circuit in the caravan park will behave in exactly the same ways, but the source impedance will be comparatively lower, and the cable/line impedance probably higher, so the proportional distribution of voltages slightly different.

 

And, the concept of a supply having a fixed limit in terms of VA capacity is sort-of false. It has a limit as to what can be supplied while still maintaining output voltage within specified tolerance, but unless it is fitted with some ‘artificial’ limiter, such as fuses and/or undervoltage protection, it will go on supplying power as demand increases, getting rather hot due to its internal resistance, the output voltage dropping. The VA supplied will increase, at a decreasing rate, then level out, then cease altogether as it burns out!m

 

Again, does all this make sense?

 

Kevin

 

Thank you for that Kevin, it does make sense.

 

So I take it that the situation which occurred at Horsted Keynes (and for the Benefit of Martin, which was explained to me personally by a Certain Mr Charles Hudson MBE in the terms I used), the mains transformer would have been getting rather warm as the missing 40 odd volts was actually being dropped across the internal windings?

 

I had not appreciated the true nature of VA ratings ether - I've never had a transformer become damaged through short circuit / low power conditions although I note what you say about those used in certain situations to be designed to cope in certain applications.

[Pacific231G]

A late friend of mine used to live in Paris pre-WW2 and he 'learnt' about electricity from the 100? Volts DC circuits back then.

 

He maintained that the problem people have, is that they are 'afraid' of electricity. 

 

He never did understand that 230 Volts is significantly more dangerous than 100 Volts. Tried to explain to him that electricity needs treating with respect, which is completely different to fear.

I've noticed the rather casual attitude with which the French regard electricity.

I've stayed in more than one hotel room with bare wires present and it used to be quite common to lean out of a window and find yourself in alarmingly close proximity to 440V 3-phase wiring strung along the side of the building. 

Until 1973 the canals in NE France had an extensive system of metre and 60cm gauge electric towing railways occupying their towpaths (about 1200kms roughly from Dunkerque to Mulhouse with various branches) and the 600V DC conductor that a trolley ran along often ran under low overbridges. Some short stretches of the system continued until comparatively recently around certain long tunnels and though the overhead cable was removed fairly quickly  (the track often remained far longer), there are places where you can still see the insulators bolted to bridge and retaining walls often no more than six feet off the ground though where they were on poles  they were at a somewhat safer height. 

Edited January 2, 2019 by Pacific231G