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Safety Issue - Moulded 13A Plugs


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You will not electrocute someone with 1V. Think ohms law again. See https://en.wikipedia.org/wiki/Extra-low_voltage for what is generally considered to be a safe voltage below which a lethal current cannot be established.

 

Building sites used to use 110V power tools, but these were actually powered from a 55-0-55 V transformer so were safe as no part was ever more than 55 V above Earth potential. I seem to recall this has been relaxed to accomodate EU wrokers with 230V tools.

 

and, everything else being equal, an electric shock from 230 volts is four times more likely to be lethal than a shock from 115 volts (not twice). It's the power dissipated in a bodies cells that does the damage.

 

I did install a 230V outlet (really 115-0-115) in my shop so that I could plug in a 4kW heater or my 230V B&D drill that I brought from the UK many years ago. Shortly after that I managed to break the sheer pin in the drill and had to consign it to the bin.

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Still wildly off topic

A 110v 100W incandescent lamp is brighter than a 240v 100W of the same type. (roughley 1200lm against 1500lm)

 

Keith

 

That was a new one on me, but it's true. As 230 volt filaments are thinner they have to run at a lower temperature to achieve the same life expectancy.

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That was a new one on me, but it's true. As 230 volt filaments are thinner they have to run at a lower temperature to achieve the same life expectancy.

Does that mean that UK tungsten lightbulbs also have a spectrum tending slightly more into the red than US ones?

I see some people quote tungsten light's colour temperature at 3000K and some at 3200K but haven't tried to correlate that with the country of origin of the article.

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Why is it that when seeing this thread I'm reminded of the Four Candles sketch?

 

 

BARKER: Got any plugs?
CORBETT: Plugs. What kind of plugs?
BARKER: A rubber one, bathroom.
(Ronnie Corbett gets out a box of bath plugs, and places it on the counter)
CORBETT (pulling out two different sized plugs): What size?
BARKER: Thirteen amp!
CORBETT (muttering): It's electric bathroom plugs, we call them, in the trade. Electric bathroom plugs!
(He puts the box away, gets out another box, and places on the counter an electric plug, then puts the box away)

 

:jester: 

 

 

Jason

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Jason,

 

Now you've done it

 

 

"Bathrooms
The installation of electrical devices in bathrooms and shower rooms is regulated in Section 701 of BS 7671:2008, and Part P of the Building Regulations. For such rooms, four special zones are defined,[4] in which additional protection is required for electrical facilities:
Zone 0 is the smallest cuboid volume that contains the bath, shower basin, etc..
Zone 1 is the area above Zone 0, up to a height of 2.25 m above the floor.
Zone 2 is the area above Zone 1 up to a height of 3 m, as well as the area that is horizontally within 0.6 m from Zone 1.
Older regulations defined Zone 3 as the area above Zone 2 up to a height of 3 m, as well as the area that is horizontally within 2.4 m from Zone 2; from BS7671:2008, this is replaced by the term 'outside the zones'. This includes any space under the bath or shower that can only be accessed with a tool.{ref bs7671:2008}
Within Zone 0, no devices are allowed apart from suitable equipment and or insulated pull cords. In Zone 1, only separated extra low voltage (SELV) devices are permitted. Any AC transformer supplying such a device must be located outside Zones 0–2. The minimum required ingress protection rating in Zone 0 is IPX7 and IPX4 in Zone 1 and 2. If water jets are likely to occur, at least IPX5 is required in Zone 1–3. Otherwise, in Zone 3 and beyond, an ingress protection rating of IP20 is the minimum required. Equipment in Zones 1 and 2 must be protected by a 30 mA residual current device (RCD).
Shaving sockets (with isolating transformer) are permitted in Zone 2 if direct spray from a shower is unlikely, even if they are only IP20. Before the 2008 regulations, such shaving sockets were the only sockets permitted in a bathroom or shower room. Since BS7671:2008 normal domestic sockets are permitted, at distances greater than 3 m from the edge of the zones, providing the circuit is RCD protected. As the new regulations also require all general purpose sockets not for use by skilled or instructed persons to be RCD protected, this effectively permits normal wiring in the larger bathroom. (Earlier British wiring rules in bathrooms used to be far more restrictive, leading to British peculiarities in bathrooms such as the use of cord switches. The 2001 edition of the Wiring Regulations is more flexible now, placing restrictions on bathroom installations that are now more similar to those in other European countries. )"

 

Waiting for electricians to say that's been superseded.

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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.

Rare in hotel rooms, rare in US Army facilities, and pretty unusual in most of the private homes I’ve been in. People seem to have hob kettles more though.

 

And I have spent a lot of time in the USA.

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Does that mean that UK tungsten lightbulbs also have a spectrum tending slightly more into the red than US ones?

I see some people quote tungsten light's colour temperature at 3000K and some at 3200K but haven't tried to correlate that with the country of origin of the article.

 

I would think so, but I'm not a lighbulbologist.

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Jason,

 

Now you've done it

 

 

Waiting for electricians to say that's been superseded.

Ray

 

Errm yes I'm afraid it has, four times in fact, 3 amendments to BS7671:2008 and BS7671:2018, although most of the variations are relating to zone sizes or RCD protection of final circuits, and are not retrospective. It is worth mentioning that part P of the building regulations only apply in England and Wales, Scotland sensibly does it differently.

 

Regards

Martin

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Ray

 

Errm yes I'm afraid it has, four times in fact, 3 amendments to BS7671:2008 and BS7671:2018, although most of the variations are relating to zone sizes or RCD protection of final circuits, and are not retrospective. It is worth mentioning that part P of the building regulations only apply in England and Wales, Scotland sensibly does it differently.

 

Regards

Martin

 

I wonder how it compares with this?

 

post-25691-0-79266400-1546537731_thumb.jpg

 

All 1333 pages of it, and expensive too. I bought this obsolete version when I did the wiring in my shop.

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I wonder how it compares with this?

 

attachicon.gifDSCN4314.JPG

 

All 1333 pages of it, and expensive too. I bought this obsolete version when I did the wiring in my shop.

Andy

Thankfully nowhere near as large, only 496 pages, but still around £85 to purchase. Britain is by American standards very small and has had the benfit of a centralised electrical generation and distribution system which has resulted in a countrywide standardised approach to electrical installations. I'm not for one moment suggesting that it is inherently any better that way, just the way it developed. In my opinion the ring final circuit is an historical throwback that should be outlawed, but we seem wedded to it.

Regards

Martin

post-25528-0-31745700-1546542426_thumb.jpg

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Just  a quick pointer  back to original discussion; last year the club safety inspection turned up a moulded unfused '13A' plug as part of a mains lead to a 12V power supply for LED layout lighting. The power supply and lead came from Ebay and the S. American jungle were offering the same units.  Further inspections showed the power supply itself to be a nightmare article, but that is another issue. The first thing I noticed was a plastic sleeved earth pin, and then the total lack of a fuse compartment or means to open the plug. The attached 3 core wire was in the region of 0.5mm2 .  Overall I support factory fitted plugs, but they have to be of adequate quality and conform to the appropriate standards. There is a good pic and useful info here:  http://www.bs1363.org.uk/ The plug in question is in the third row of pics part way down the page. The lead and power supply (with it's record fourteen counterfeit safety standards logos) went in the the recycling, but what you could usefully recycle this lot into I don't know.

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Andy

Thankfully nowhere near as large, only 496 pages, but still around £85 to purchase. Britain is by American standards very small and has had the benfit of a centralised electrical generation and distribution system which has resulted in a countrywide standardised approach to electrical installations. I'm not for one moment suggesting that it is inherently any better that way, just the way it developed. In my opinion the ring final circuit is an historical throwback that should be outlawed, but we seem wedded to it.

Regards

Martin

attachicon.gifIMG_0645.JPG

 

Hi Martin,

 

Thanks for that.

 

The NEC codes are adopted pretty much as is by most states with a few exceptions, New York City being one - possibly due to the number of high-rise buildings, but I'm not sure. Most of the revisions seem to be related to solar-power, car chargers etc.

 

Having dealt a fair bit with electro-plumbing in the US and the UK I agree with you about the ring main. It's one of those things that seemed like a good idea at the time but in retrospect.....

 

Is there any discussion in UK/Europe about new standards with much lower voltage outlets? Most of the stuff that's plugged in these days doesn't need anything like 230 volts to neutral. Something along the lines of what Crosland was describing would be inherently much safer - maybe 25-0-25 would be all that's required?

 

Cheers,

Andy

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Thankfully nowhere near as large, only 496 pages, but still around £85 to purchase.

And then you have the rather larger book that provides interpretation and explanations to give you a chance of understanding it.

Rgds

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Is there any discussion in UK/Europe about new standards with much lower voltage outlets? Most of the stuff that's plugged in these days doesn't need anything like 230 volts to neutral. Something along the lines of what Crosland was describing would be inherently much safer - maybe 25-0-25 would be all that's required?

 

Cheers,

Andy

I was discussing this with a colleague before the break. We thought low voltage (eg 12V DC) lighting circuits could be a sensible move - after all, that's all you need for led lighting.

 

It would likely be more efficient to have a single larger suitable power supply next to your consumer unit powering the circuit, rather than the individual ones in each bulb as is the case with a mains circuit.

 

Part of the reason for suggesting the lighting circuit is low voltage is that it's a physically separate system to the ring mains and other spurs you get in a home typically round the walls.

 

Mark

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The lower the voltage the higher the current. While LED lighting will reduce the power consumption tenfold, reducing the voltage to 12V will double the current, and therefore require fatter cable for LED lighting, than is required for incandescent bulbs. I suspect that doubling the current will increase the potential for fire hazards to be created.

 

Reducing to 5V will further exacerbate the current problem. Perhaps -48V DC like is used in telephone exchanges might be a useful compromise between current and voltage - but I cannot see it catching on somehow.

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A resistance heating element IS a constant power device - its is fundamentally just a coil of wire and unless you introduce other electrical components to regulate it (i.e. a thermostat which alters the overall resistance and regulates current flow) or change its conductive proprieties by altering its molecular makeup (e.g. heating / cooling it) that wire will always pass a certain unchanging electrical current.

 

If the current is too large the wire gets hot and melts - it doesn't magically turn round and somehow start passing less current because its getting warm (if anything it will allow an even grater current to flow leading to thermal runaway). This is basic physics and can easily be demonstrated in in any science lab.

 

As such if it is calculated to require 10 amps at 240V then a drop in voltage WILL cause it to try and pull more Amps to re-balance Ohms law. Its basic text book physics.

 

If on the other hand you introduce extra electrical components which 'fix' the current draw at 10A then a lower voltage will naturally result in a lower power output so as to maintain the Power = Volts x Current equation in the way you quote. However should those 'fixing' components fail then the current drawn may well increase beyond the design perimeters.

 

 

Note:- I have no knowledge of RVs nor the types of heater that may or may not be fitted.

Please mate , I’m an electronics engineer , don’t embarrass yourself by this nonsense

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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?

Please stop , you have an incredibly faulty understanding and you are compounding the mistakes ,

 

In your track short example , YOU ARE CHANGING THE RESISTANCE , V=IR always applies , that’s why the current increases , the reason the voltage drops , is the source is not perfect , it has an equivalent output resistance , hence as the sources output current increase due in the change in load resistance , ie the short circuit , due to the sources output impedance , the voltage must fall

 

Whereas in the water heating element THE RESUSTANCE IS FIXED , hence if the applied voltage falls , the current will also fall

 

( take two batteries of different voltage , a multimeter and a 2 k resistor and see for yourself

 

Again ohms law always applies , you are simply engaging in faulty analysis and mis applying incorrect understanding of load and source resistances

 

 

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.

 

 

This can only happen , where constant power devices are in play , for example a switched mode battery charger , where the device can the pulse widths to effectively maintain constant power in its outputs ( for a constant load ) , hence in this case , the effect of the power supply detecting a lower input voltage is to increase the pulse width in the switcher , which in effect more current from the source , note V=IR still applies ( because in effect the input resistance of the switcher is being reduced dynamically )

 

This is an entirely different situation to say a fixed resistance heater element or a track short circuit

 

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!

 

 

All real world power sources have a finite output resistance ( which may or may not be linear ) For tha5 power source V= IR Always applies , end of story

 

On a given power supply , if you place a load which exceeds the power capability , then one of two things MUST occur , the voltage must fall or the current must fall ( due to maintenance of power requirements ) , if the load resistance is too low , ie it’s “load “ ( ie power ) is too high , then the output voltage of the real world source will AND MUST fall as it obeys ohms law hence the voltage in your example sags

 

You are mixing up source supplies and load currents and differences in active loads ( which display dynamic input resistance ) and fixed resistive loads

Edited by Junctionmad
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you are simply engaging in faulty analysis and mis applying incorrect understanding of load and source resistances

 

Agreed - which Kevin was kind enough to explain in a considerably politer / less insulting tone than you back in post number 114

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