Kettle supply

[Peter Spikings]

Hi and happy new year!

Bought a kettle at a well known supermarket (well SWMBO did). I gave it a once over and noticed the cable to the base was 1.0mm2. I thought that meant it was a lower rated kettle but no, it says 2550W-3000W and the plug fuse is 13A.

I got my power tester out and tested it carefully. It drew almost 12A and the cable didn't get hot on the outside after a few cycles.

Has the manufacturer screwed up or is there some kind of regulation that allows 1.0mm cable to carry 13A as it isn't a continuous load?

If they have screwed up, who should I tell?

Thanks,

Peter

 

[JohnW2]

I gave it a once over and noticed the cable to the base was 1.0mm2. I thought that meant it was a lower rated kettle but no, it says 2550W-3000W and the plug fuse is 13A. I got my power tester out and tested it carefully. It drew almost 12A and the cable didn't get hot on the outside after a few cycles. Has the manufacturer screwed up or is there some kind of regulation that allows 1.0mm cable to carry 13A as it isn't a continuous load?

Welcome to the forum, and Happy New Year to you, too.

I think it's common.

Since it's not part of the electrical installation, it's outside of the scope of the Wiring Regs (which would require 1.25mm² cable). However, I seem to recall that the relevant regulations for short 'portable appliance' leads do, indeed, allow the use of 1.0mm² cable protected by a 13A fuse (and carrying up to 13A).

Kind Regards, John

 

[Peter Spikings]

Ah OK... I'll leave it be then!

The kettle it replaced used 1.5 and I'm aware of the wiring regs max currents for domestic sizes hence the question

TVM,

Peter

 

[Echo the husky]

It will be fine, I had 2M of 0.75 flex here with 20A flowing through it for 25 minutes, it survived. The heat certainly made it flexible though!

 

[JohnW2]

The kettle it replaced used 1.5 and I'm aware of the wiring regs max currents for domestic sizes hence the question

You're welcome. As I said, even the Wiring Regs (BS7671) (if they applied) would only require 1.25mm² (for an unlimited length of cable). I'm sure you'll have no problem with what you've got!

Kind Regards, John

 

[EFLImpudence]

Bearing in mind that, I think it is agreed (tell me if not), the CCCs for conductors in BS7671 are on the conservative side,

is there a specific reason that BS7671 rates 1mm² flex at only 62.5% the CCC of 1mm² T&E?

and:
1.5mm² at 80%
2.5mm² at 92%
4.0mm² at 86%

 

[JohnW2]

Bearing in mind that, I think it is agreed (tell me if not), the CCCs for conductors in BS7671 are on the conservative side,

I certainly agree - very much so.

is there a specific reason that BS7671 rates 1mm² flex at only 62.5% the CCC of 1mm² T&E? ... and: 1.5mm² at 80% ... 2.5mm² at 92% ... 4.0mm² at 86%

Good questions (which I think we've discussed before).

I don't know about you, but I personally don't have a clue as to where the BS7671 CCC figures come from, or how they were determined. Given that they don't follow any precisely modellable mathematical pattern, I would suspect/presume that they were probably derived empirically (in terms of conductor temp rise, perhaps?). What we do know is that they found a way to 'revise' the figures so that 2.5mm² T+E with installation Method A could be used for ring finals (hence the small differences between Tables 4D2A and 4D5)!!

One can but speculate about possible reasons for the figures you mention. Given that most flexible cables are 'exposed and touchable' one might have expected that the CCCs for flex would relate to a lower conductor (hence cable) temperature than T+E, but Table 4F5 appears to imply that such is not the case (they give ambient temp correction figures for both 70° and 90° cables). In any event, given the relatively higher surface area, temp effects would probably be expected to affect 1mm² flex less than larger sizes.

Another possible factor is that (because the CPC is insulated), flex contains 'more insulation material' than does T+E of the same CSA, hence probably less heat loss and higher operating temp for a given CSA and current. Furthermore, that would presumably proportionately affect smaller CSA cables more than larger ones - hence conceivably going some way to explaining what you observe.

Although both flex and T+E have "PVC" insulation, the materials are clearly a bit different - so that may have some relevance.

Essentially, I haven't got a clue. Maybe this is one for RF - run various (fairly high) currents through flex and T+E of the same CSA and determine the resultant cable temps?

Kind Regards, John

 

[RF Lighting]

Remind me about this in a couple of weeks and I'll see what I can do.

 

[JohnW2]

Remind me about this in a couple of weeks and I'll see what I can do.

Many thanks - I'll try to remember to remind you! Don't you have one of these new-fangled phones (with an impossibly small on-screen keyboard ) which could be asked to remind you? - if so, that would probably be more reliable than my memory!!

Kind Regards, John