electrical.theiet.org/.../
Personally I think Rotary Isolator would be far better than 20 amp Double-pole switch shown Fig 2 as this allows for isolation and LockOff/LockOut
The cost of the Rotary Isolator is still quite low see URL below. (Other brands and other Wholesalers are available).
www.superlecdirect.com/.../
As always please be polite and respectful in this purely academic debate.
Come on everybody let’s help inspire the future
In terms of waste and sustainability, some would argue that it is poor practice to over-engineer products when in general their use causes no such problems, and products that utilize 3 kW for extended periods of time can be connected in other ways?
If an accessory with a nominal rating of 13A, which in electrical engineering typically denotes its continuous operating rating, cannot carry 13A continuously and indefinitely, safely, in normal use (as suggested in the article, recommending limitation to 11.7A for continuous operation) then far from being over-engineered, I would argue it is concerningly under-engineered.
That in many applications the load current is below 13A and the accessory operates satisfactory is irrelevant - equipment should be capable of operating safely at its rated capability. If it cannot, then the standards which specify the design and testing of that equipment need improving to ensure it can function as specified, or the ratings within those standards need correcting the reflect the actual capability of the accessory.
The 13A plug or fused connection unit, should be re-named to reflect the reality that with the current standards and manufacturing practices, it is now actually an 11.7A device.
It doesn't really matter whether you change the product standard to accommodate a higher rating, or select a connection product with a higher rating.
As we have heard in this thread, others just do the latter anyway, so what's the point?
I would argue that in engineering, specifications and ratings are very important and it is important that equipment is designed and testing so that operates safely at its rated values, so a device with a 13A rating should be capable of operating continuous and safely at 13A, without relying on introducing de-rating factors or other obscure caveats, whereby 13A actually means 13A for 30 mins and 11.7A continuously.
In this case, the better and safer approach should be to have the nominal rating changed to 11.7A with an overload rating of 13A for 30 mins.
The 13A plug or fused connection unit, should be re-named to reflect the reality that with the current standards and manufacturing practices, it is now actually an 11.7A device.
I disagree ... we are looking at currents likely to exceed 13 A for the most part with a 3 kW immersion heater, but also environmental conditions outside those in the product standard.
In addition, there's no problem with an appliance that intermittently uses 2990 W.
I would argue that in engineering, specifications and ratings are very important and it is important that equipment is designed and testing so that operates safely at its rated values, so a device with a 13A rating should be capable of operating continuous and safely at 13A, without relying on introducing de-rating factors or other obscure caveats,
That's interesting, when we accept OCPDs that don't operate until at least 1.4×In.
In reality, we are looking at definitions ... the fuse rating means it is rated to carry the current under specified conditions (not operate at that current), and similarly a BS 1363-4 FCU is rated to carry 13 A under specified conditions (and perhaps with a tolerance).
The mis-match is that there's the tolerance permitted by BS EN 60335-1, applied in addition to a tolerance that relates to utilization voltage range.
So, I agree that we need to be sure about what tolerances we are working with, in the same way that we know we are happy saying that protection against overload is generally provided by Iz≥In even though we know the OCPD won't operate until at least 1.4×In, AND knowing it's still necessary for the BS 7671 requirement that circuits shall be arranged so that small overloads for long duration do not occur ...
However, these points are really points for product standard committees to decide on ... noting that the general public won't get anywhere near the information we are looking at in this thread.
I disagree ... we are looking at currents likely to exceed 13 A for the most part with a 3 kW immersion heater, but also environmental conditions outside those in the product standard.
That is not what the article concludes, it refers to all domestic appliances, not just immersion heaters:
"In general, the maximum domestic appliance loads that use full power for periods above 30 minutes, connected to BS 1363 plugs and fused connection units, is limited to 2.7 kW (11.7 A)."
The implication of this statement is that the continuous current rating for safe operation of BS1363 plugs and fused connection units is only 11.7A, it is not 13A.
In addition, there's no problem with an appliance that intermittently uses 2990 W.
A higher, limited-duration rating for a piece of electrical equipment is an overload rating, the article is in-effect proposing that BS1363 plugs and fused connection units have a continuous rating of 11.7A and a 30 minute over-load rating of 13A.
The nominal ratings used to describe electrical equipment are normally the continuous ratings, we shouldn't be using the 13A overload rating as the nominal rating, if this should be limited to only 30 minutes for safe operation.
That's interesting, when we accept OCPDs that don't operate until at least 1.4×In.
In reality, we are looking at definitions ... the fuse rating means it is rated to carry the current under specified conditions (not operate at that current), and similarly a BS 1363-4 FCU is rated to carry 13 A under specified conditions (and perhaps with a tolerance).
Yes, for OCPDs and fuses we use the continuous rating of the device, we expect it to be able to operate continuously for an indefinite period at that nominal rating, we do not use a short-term overload rating for the fuse to describe its nominal capability.
If the 'specified conditions' for BS1363-4 FCU is that it can only carry 13A safely for a maximum of 30 minutes, then it should correctly be described as an FCU rated for 11.7A continuous and suitable for overload at 13A for upto 30 minutes.
An interesting debate between TurboGen and GK, but I am leaning towards the former.
Suppose that your car tyres are rated at 70 mph (in reality, perhaps 130 mph, or more). Would you assume that you can travel for hours at that speed (e.g. from the Channel coast to Côté d'Azure), or could you do it only intermittently?
The Americans seem to have a sensible rule that plugs and sockets have to be derated to 80% when used for appliances that will run at full power for long periods.
The "granny lead" EV chargers that use a 13A plug are normally limited to 10A (2.3kW), and even then it's common for them to have a thermistor built into the plug to detect overheating. I don't know of any other appliances that do that.
all generally increasing the safety margin
Beware the fallacy that improving component safety improves system safety. All we do is move the failure somewhere else.
Major fires, it would appear, are roughly every 10 years before the next major 'headline' event, followed by awareness, crackdown, slow fade (regression to the mean;-), focus elsewhere; Oops another fire.
We should know where our 'bottle necks' are and manage them. Slowly burnt out plugs (observable) maybe a good place to see degradations that are then captured by either humans (or remote circuit disconnections).
That is not what the article concludes, it refers to all domestic appliances, not just immersion heaters:
"In general, the maximum domestic appliance loads that use full power for periods above 30 minutes, connected to BS 1363 plugs and fused connection units, is limited to 2.7 kW (11.7 A)."
I fear this has been misunderstood. The 2.7 kW is merely a roughly rounded figure to reflect the additional 10 % "tolerance" permitted by BS EN 60335-1:
2700 W + 10 % = 2970 W ... 13 A at 230 V is equivalent to 2990 W.
This, I fully agree, is wholly unexpected, and one might expect a requirement that at the nominal voltage, the current (or power) should not exceed the rating plate value. More importantly, how will the public know?
It has nothing to do with the capability of accessories to BS 1363 series, which, as everyone has seen, could (at the stated range of ambient temperatures) cope with 13 A nominal current, that increases if the supply voltage increases perhaps up to 10 %.
The big issues are:
Simples.
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