How dangerous is daisy chaining?

[FrodoOne]

Apparently in USA you can’t just keep daisy chaining extensions as the current capacity of the cables varies and can be less than the opd.

The USA (North America) has quite a few "regulations" which seem to be quite silly, when viewed from the perspective of others, such as we.

One of these seems to state that on any circuit where a device is permanently connected, the Circuit must be de-rated to 80% of its nominal carrying capacity.
Hence, a US 15 A circuit is only allowed to carry a permanently connected device rated at no more than 12 A.

 

[Harry Bloomfield]

One of these seems to state that on any circuit where a device is permanently connected, the Circuit must be de-rated to 80% of its nominal carrying capacity.
Hence, a US 15 A circuit is only allowed to carry a permanently connected device rated at no more than 12 A.

I'm always wary of running modern 13amp plugs/sockets flat out continuously at 13amps. They used to be better quality/more capable decades ago.

 

[JohnW2]

The USA (North America) has quite a few "regulations" which seem to be quite silly, when viewed from the perspective of others, such as we. ....

Agreed.

One of these seems to state that on any circuit where a device is permanently connected, the Circuit must be de-rated to 80% of its nominal carrying capacity.

That one might not be quite as silly as many, if it were referring to loads which were continuously (or 'fairly continuously') drawing high current - since figures used for 'current-carrying-capacity' may assume that peak loads are only intermittent. However, when it does become silly is when the load, although 'permanently connected' does not draw current anything like 'continuously' - but it would probably be impossible to draft (and certainly to enforce) a sensible regulation which distinguished between those two situation.

There are sort-of precedents. Although nothing to do with 'regulations', the manufacturers of at least some MCBs say that they should be de-rated if they are likely to be run at, or close to, their rated current 'for extended periods'.

Kind Regards, John

 

[JohnD]

Hence, a US 15 A circuit is only allowed to carry a permanently connected device rated at no more than 12 A.

So if they had a 15A immersion heater, would the MCB be 18.75A? Or does it mean the cable would have to be adequate to carry 18.75A?

 

[EFLImpudence]

Perhaps a 12A element ?

 

[FrodoOne]

North American "domestic" circuits are rated to supply 120 V (AC) at either 15 A (supplied via a AWG 14 set of conductors in a cable) or 20 A (supplied via a AWG 12 set of conductors - which are of a larger CSA [!] ).

 

[JohnD]

that's why American kettles are so slow and weedy.

 

[Diver Fred]

Not sure if this UK standards of the practise of one my previous employers - my understanding is that the UK standard plug (& socket) is rated at 10amps continuous and 13amp intermittent. In particular it applies to the plugs with shielded pins.

 

[EFLImpudence]

Not sure if this UK standards of the practise of one my previous employers - my understanding is that the UK standard plug (& socket) is rated at 10amps continuous and 13amp intermittent. In particular it applies to the plugs with shielded pins.

That wouldn't make any sense, would it?

It is true that some plugs - and sockets - are poorly made and cannot cope with a continuous 13A but others, I have encountered, have lasted 'for ever'.

 

[EFLImpudence]

Of course, the size of the pins in a UK plug are comparatively 'huge' compared with a 13A conductor.

I think the weak point is the fuse holder (plus the socket prongs) but, as has been said, they are such a brilliant design, there must be other reasons for their failure.

 

[SUNRAY]

Thanks to the brilliant design of the UK plug and socket, you can daisy-chain a million multiways if you want to.
You can plug in ... Probably about a thousand phone chargers.

That's not exactly accurate, is it?

yes.

Are you seriously trying to lead us into the totally unrealistic misapprehension that one would in any way be able to plug 334 4 way extention leads into a socket and expect it to work with reliability and safety?

 

[SUNRAY]

I have always been wary of running 13amp plugs/sockets flat out continuously in my opinion hey have never been fit for carrying 13A ad infinitum.

Some certainly were better quality/more capable but even then not fit for a constant 13A .

 

[bernardgreen]

I have thought for many years that using PolyFuse technology in the BS 1362 format could remove the overheating problem.

It is used in several type of fuse LINK

 

[JohnW2]

I have thought for many years that using PolyFuse technology in the BS 1362 format could remove the overheating problem. It is used in several type of fuse LINK

Maybe this is different, but my concern about any type of auto-resetting over-current device (some of which I have used in my time) is that, in the presence of a persisting fault (causing the over-current), the protective device will repeatedly (and potentially indefinitely) allow brief bursts of excessive current to flow, as it repeatedly tries to re-0set itself.

Clearly not appropriate or sensible for something as humble as a 'fuse', but I suppose the ideal would be a 'smart' device which would give up tryting tyo reset after, say, a couple of 'unsuccessful' attempts.

Kind Regards, John

 

[bernardgreen]

The poly fuse will remain "blown" until the supply is removed.