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SparkyChick

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I believe most, if they comply to the standard 2G sockets are rated at 20A total. And the issue depicted would occur because that one socket is overloaded or is suffering the effect of a bad connection, either the pin/contact interface, the fuse/terminal/pin interface.
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Should have included... with each socket being rated at 13A maximum.

To comment on the statement they made... I tend to use 2 single socket outlets if there are going to be two hungry appliances supplied by them.
 

Lucien Nunes

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BS1363:1995 requires a double-socket to handle 20A total load; the test conditions are 14A on one and 6A on the other. From P=I²R we note that the total heat dissipated under these test conditions (with the abnormal 14A load) is greater than with 10A load per socket. Therefore, continuous satisfactory operation would be expected with two 2kW heaters plugged in. In a 120V equivalent power context, that is like being able to take 38A total from any ordinary duplex receptacle, an unusual requirement I think you would agree.

Note that the total load limit of the two sockets is a different parameter to the maximum circuit cable through-current. There is an important difference between UK and US sockets here, in that UK sockets only ever have one terminal for line and neutral, so the incoming and outgoing cables are always in intimate contact when correctly installed. There is no snap-out link or side wire/back wire/back stab interconnection to take into account. A normal BS1363 socket will take 32A passing through the terminal, as necessary on a 4mm² 32A radial.

The damage shown in your picture is specifically caused by a defective fuse clip in a moulded plug where the fuse lies crossways above the L & N pins. That was not caused by any defect in the socket or general overload.
 
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  • #7
Not unusual if you wanted to run two heavy devices (like resturant equipment) from a single duplex which is typical in diners and cafes. My understanding is that you could pull 40 amps (20+20) through a NEMA receptacle if you broke the tabs and ran two circuits. In a single circuit application you are limited to a 20 amp breaker. In the two circuit application each half of the receptacle is still rated 20 amps.
 

Lucien Nunes

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In order to make the 40A / 4.8kW available at one duplex, as you say it would be necessary to run two circuits or one multi-wire circuit for just that one outlet, which would not be done generally throughout an installation. High loads would then be concentrated at the outlet known to be equipped for them, making its heavy usage a self-fulfilling prophecy. In contrast, every double socket in a normal home wired with BS1363 sockets on 32A circuits is capable of supplying 4.6kW, therefore there is no inclination to concentrate load at a single 'special' socket. Whilst there is nothing to prevent 26A total being used, the effects of such usage persisting long enough to cause damage would be buried in the noise of random differences between different brands of socket, plug and operating environment. I have studied many damaged sockets and have never seen any where excessive combined current was definitely responsible for damage, absent other problems like improper cable termination.
 
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  • #9
In order to make the 40A / 4.8kW available at one duplex, as you say it would be necessary to run two circuits or one multi-wire circuit for just that one outlet, which would not be done generally throughout an installation.
Right, the rest of the installation would place the duplex receptacle on a 15 or 20 amp breaker which would trip if the duplex was subjected to more than 15 or 20amps well before it overheated.

High loads would then be concentrated at the outlet known to be equipped for them, making its heavy usage a self-fulfilling prophecy. In contrast, every double socket in a normal home wired with BS1363 sockets on 32A circuits is capable of supplying 4.6kW, therefore there is no inclination to concentrate load at a single 'special' socket. Whilst there is nothing to prevent 26A total being used, the effects of such usage persisting long enough to cause damage would be buried in the noise of random differences between different brands of socket, plug and operating environment. I have studied many damaged sockets and have never seen any where excessive combined current was definitely responsible for damage, absent other problems like improper cable termination.
Right- you know said receptacle being used for two 16-20 amp loads each with a NEMA 5-20r cord cap. What stops me from taking a single duplex, breaking both hot tabs, then running two circuits and a shared neutral? 32 amps continuous or 40 amps intermittently? The receptacle would not over heat.

Both scenarios are covered- but not with a BS1363 socket.
 

Lucien Nunes

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In dealing with out-of-specification occurrences that are not protected against, it's important to consider the severity of the consequences. Typically, a double 13A socket subjected to 26A total load for a typical duty cycle will not 'overheat' in the sense of melting or catching fire. Its service life might be shortened, or the plastic might discolour sooner, or some such progressive deterioration caused by the additional temperature rise. Manufacturers can and do make accessories that exceed the BS specification, either explicitly in their ratings or through proven reliability despite the rating being exceeded.

From personal / anecdotal experience I would rank the root causes of thermal damage to BS1363 socket outlets in the following order, most common first:

Faulty fuse contact in plug (heat conducts through line pin and damages socket contact and faceplate)
Loose terminations in plug.
High-resistance contact between plug pin and socket contact, through user-inflicted damage, thermal fatigue, corrosion or poor design.
Loose terminations in socket.
Usage for high, continuous load (per 13A socket, ignoring total) without occasional mating cycles to remove oxide buildup at contact interface.
All other factors (including switch resistance, excess total load, high ambient temp)
 

davesparks

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What stops me from taking a single duplex, breaking both hot tabs, then running two circuits and a shared neutral? 32 amps continuous or 40 amps intermittently? The receptacle would not over heat.

Both scenarios are covered- but not with a BS1363 socket.
Can you explain what breaking the hot tabs means? Is this some way of seperating a twin USA type socket so that you can wire to each of the individual outlets separately?

BS1363 sockets only have one set of terminals and you cannot feed each side seperately.
 

Lucien Nunes

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Yes, most NEMA duplex receptacles have two sets of terminals linked by the flat pieces of metal that you can see projecting at the side between the screws. These can be broken off to separate the two halves. Traditional side-wiring using the binding-screws only accommodates one wire per screw, so the circuit through-current would pass through the tab. Some products have a rising clamp back-wire terminal incorporated, that will allow for two cables per terminal with the tabs out.
 

freddo

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Is this some way of seperating a twin USA type socket so that you can wire to each of the individual outlets separately?
Commonly used to have one outlet permanently fed and the second switched by the door for example for plugging in lamps.
 

pc1966

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Commonly used to have one outlet permanently fed and the second switched by the door for example for plugging in lamps.
In the UK I have only seen that in hotels, etc, and normally via a 5A round-pin plug so not used for anything else.
 
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  • #15
Can you explain what breaking the hot tabs means? Is this some way of seperating a twin USA type socket so that you can wire to each of the individual outlets separately?

BS1363 sockets only have one set of terminals and you cannot feed each side seperately.

Yes, each half of the receptacle can be separated electrically and fed by its own circuit. There is a metal "bridge" that can be removed on each side of the screw terminals.
 

Lucien Nunes

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We do think about them, and they seldom occur, and if they do occur, nothing terrible happens. I bet if we took a bunch of average duplex 5-15's off people's walls and loaded them up to 2x15A, and the same for a bunch of double 13's loaded to 2x13A, we would see as much excess heat from the 5-15's as from the 13's.

About the only time I have ever seen two 13A loads regularly plugged into one double socket was back in the 1970s in my dad's shop. There was a ducted warm air heating system but it wasn't really powerful enough for a cold winter and the vents were in the wrong places, so they tended to supplement it with some portable heaters. I remember two 3kW fanheaters used to sit side by side plugged into a double socket in the main sales floor. It lasted all the years I knew the shop, and that is about as exciting as 26A on a double 13A usually gets.

I suppose my main point, as I tried to convey with my priority list of heat sources, is that BS1363 is a safe and reliable connector, although it does tend to heat more that some others due to the presence of the fuse and its contacts mainly if they are of cheap manufacture. Thermal failures due to total loads on doubles in the 20-26A range are utterly insignificant compared to thermal failures due to loads in the 10-13A range on one plug, which are not exactly common either.
 
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  • #23
But the thing is a NEMA 5-15s are made with 20 amp internals and limited to a 20 amp circuit. Its impossible to overload such a receptacle when wired to code.
 
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  • #25
OK, great, that's an extra box you can tick in favour of the NEMA configuation. Now, about those unsleeved prongs...

Relax, they come in extra large ;)

1596161553884.png

Its ok if you are jealous of NEMA design. I think we can all admit its just so much more superior in every way including human safety :p
 

DPG

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Relax, they come in extra large ;)

View attachment 59827

Its ok if you are jealous of NEMA design. I think we can all admit its just so much more superior in every way including human safety :p
Unfortunately, the unsleeved pins negate much of the safety aspects. It's a basic onefor me - stop people accidentally touching electrical contacts where possible.
 

Lucien Nunes

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Every system has its pros and cons. The NEMA coding of different supply configurations and specific compatibilities is good, some of the constructional features of the better-quality brands are admirable, etc. But I agree with DPG that the inferior protection against direct contact somewhat overshadows everything else. The Australian solution of sleeving the prongs leaving a wafer-thin metal core has its own drawbacks, so unfortunately that particular issue (flat prongs + compact plug body + non-recessed outlet face) is rather heavily designed-in. We had the advantage in BS546 and BS1363 of a large enough cross-section that adding insulating sleeves did not noticeably compromise the strength of the pins.
 

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