IEC Cable Ratings

[imroberts]

Please can someone help me out with some confusion!

I have a need for a couple of IEC - BS1363 cables which are rated to 8A.

Now I know that C13 and C14 connectors are both rated to 10A, however every spare cable I have at home is fused at 5A and is wired with 0.75mm cable which I understand is rated to 6A.

I've had a quick look online and most IEC - BS1363 cables I can find also come fused at 5A, however the few I can find with 10A fuses appear to also be wired with 0.75mm cable.

Am I wrong and 0.75mm cable is actually fine for 10A or is there another explanation why this seems to be the case?

 

[skenk]

what's an IEC - BS13613 cable?

there's 10a "kettle leads" here:
https://cpc.farnell.com/pro-elec/pe01063/lead-uk-plug-to-iec-c13-skt-10a/dp/PL13310

fitted with a 13A fuse though so you'd have to get some 10a ones!

 

[ericmark]

There are three very similar IEC 60320 connectors, the temperature they can work with varies, 70°C, 120°C and 155°C types C13 to C16A, all rated at 10A. The socket is independent to cable, and the BS1363 plug (British 13A) is also independent and the fuse has to cover all three.

Kettles tend to boil quite fast, so although it exceeds 10A in some cases, it is for such a short time it does not over heat cable or socket, but clearly 0.75 mm² cable is designed for the supply to a computer not a kettle.

 

[333rocky333]

We use them leads a lot, if you look closely on the moulded plug, some are stamped 5amp and some 13amp within a round circle
Its the ones stamped 13a that tend to be fitted with 10a fuses.
Like you say though sometimes the wire seems the same

 

[plugwash]

There are a bunch of "conventional" ratings for flexible cables, which can be found in some form in a bunch of standards.

0.5mm 3A
0.75mm 6A
1.0mm 10A
1.5mm 16A

(I forget the ratings for larger sizes, in the UK there also exists 1.25mm flex with a conventional rating of 13A, but that seems to be a british oddity)

However I have not found the original standards for these ratings or what assumptions they are calculated under.

It seems that the IEC think it's ok to sometimes exceed these ratings or at least to create situations in which users may end up exceeding them. In particular the "IT equipment" standard explicitly allows detachable power cords below a certain length (I forgot what length exactly) to use one 0.75mm for cords with 10A couplers and 1.0mm for cords with 16A couplers. In practice most IEC C13 cords on the market take advantage of this dispensation. Plug fuses can't be the reason, they are a British oddity, not something the IEC would rely on and I have seen plenty of 0.75mm Schuko to C13 leads.

The ratings also don't make much physical sense, one expects the increase in current ratings with CSA to be sublinear, but the progression of these conventional ratings for flex is superlinear. They also match up suspiciously with preferred numbers and are much lower than the "clipped direct" ratings for fixed wiring cable.

In conclusion I think a 0.75mm IEC cord is highly unlikely to overheat when used at 8A unless in really pathological conditions, but i'd still rather have the extra margin that 1.0mm gives.

 

[SUNRAY]

I had a big row with CPC recently with C19/20 connectors and due to their stupidity of not accepting that 1mm² cable is unfit for 16A they ended up refunding a lot of money for overheated leads, 3 times. and they wanted to replace for a 4th time.
The dispensation for IEC leads running way beyond the rated current of the cable was originally exclusively for kettles (in fact the original C13 was rated at only 6A) but as Plugwash indicates the rest of the industry seems to have accepted it as the standard. We had a 3KW kettle with a locking C13 and 0.75mm² flex and the cable had to be replaced 3 times under the 2 year warranty.
IIRC the official limit on the length of the overrated flex is something like 600mm which is often not enough for the domestic kitchen.