Rating of Flexible cable

[mattylad]

FWIW I make & fit good quality cable 1.5mm x 2m supply cords to appliances daily, ranging from 1kw-3kw and when above 2kw (especially at 3kw) the cable and the plug will be quite warm after approx 1/2 hour of testing.

Having experienced this I would never use a supply cord that has only 1.0mm cores for the same job whatever the tables say.

 

[securespark]

Just watched this:

 

[SUNRAY]

I've just received this reply to an enquiry with a well known electronic/electrical supplier:


Further to your error report for the IEC Male C20 to Female C19 Extension Lead.

After checking, the lead is certified at 16A with 1.0mm2 cable. This range of cables has 1.0mm2 cable for lengths of 2m or less, with 1.5mm2 cable for lengths above 2m.

Should I be feeling concerned about using them to supply power to a 3.6KW load?

My quick perusal of 16th came up with a 1.0mm² flexible being rated at significantly less than 16A so I replied to that effect, their response:

Morning,

I spoke with one of my colleagues in the Compliance dept. regarding this matter, they checked on the cable details and this is what they replied with:

“Unfortunately, neither we nor our suppliers benefit from any exemption – the regulations are applicable to all. It is however important to refer to the one that is appropriate to the circumstances.

I am unsure which section of BS7671 you are using. However, if you refer to Table 4D2A, which is the nearest installation category to a free flexible cable, the current specified for a 1.0mm2 cable is 17A.

However, the Wiring Regulations are for use with fixed installations, and not really appropriate for a flexible cable. These are generally covered by the standard that is applicable to the connectors used. The 16A connectors used in PL15187 are within scope of EN60320 which specifies a minimum CSA of 1.0mm2 for a cable length not exceeding 2m.”

I hope this helps you in this situation.

As a matter of course, I have always used 2.5mm² for blue 4343 connectors with ocassional specials at 1.5mm². Several times I've refused supplies to people who turn up with cables smaller than this. The only exception I make is for 13A fused ends.
It seems I've been spending too much money on cable for a long time...

 

[JohnW2]

My quick perusal of 16th came up with a 1.0mm² flexible being rated at significantly less than 16A so I replied to that effect, their response:

..... I am unsure which section of BS7671 you are using. However, if you refer to Table 4D2A, which is the nearest installation category to a free flexible cable, the current specified for a 1.0mm2 cable is 17A.

It is indeed true that Table 4D2a gives a CCC of 17A in free air for 1mm² cable. However, "which is the nearest installation category to a free flexible cable" is clearly not correct - it sounds as if you need to draw their attention to Table 4F3A!

It remains unclear as to why 4F3A gives much lower CCCs for a ('flexible') cable of a particular CSA than does 4D2A for a (non-'flexible') cable of the same CSA. The amount of energy/heat resulting from a given current flowing through a copper conductor of a certain CSA will be the same regardless of the nature of the cable - so the only way in which the temp rise with flex could be greater with flex would be if it had appreciably more (thermal) insulation - which I doubt. The lower CCCs for flex therefore presumably relate to something other than temp rise - maybe related to the stresses to which they might be exposed during use??

Kind Regards, John

 

[ban-all-sheds]

How soft does PVC get at 70°? Any chance that at that temperature a flexible, portable cable might get bent or impacted enough for the insulation to become compromised?

 

[ericmark]

The rating given for a flexible cable assumes in free air and supplying portable appliances and the appliance your supplying is not portable, it is assumed portable means intermittent use, as with a standard kettle, not prolonged use as with an immersion heater, or tumble drier or in your case large lights.

So you are limited to just over 9 meters due to volt drop, and 50% duty cycle would seem reasonable in each hour of use.

However although it seems 1 mm² is not fit for your installation, if it were not lighting you could have a longer length and if it did not supply fixed items you would likely not be using the items for so long, so to supply the flex is not really a problem it is just your use of the flex.

I see many flexes for sale at 1.5 mm² with the typical blue plug which is OK for most uses, but not for caravans where for some reason it says 2.5 mm² and 25 meters long +/- 2 meters from memory, I have never worked out why you can't use a 15 meter long cable? OK where my caravan is parked today the 25 meters allows it to be run around edge of field, but in the main 15 meters would be ample.

So if you ordered a 16A flexible cable to supply fixed lighting then supplier is wrong, but if you asked for a 16A flexible cable then they are within the limits so OK. Same as asking for a 16A outdoor cable or 16A outdoor cable to supply a caravan, it is not the same. With 25 meters it is just within volt drop with 2.5 mm which is likely why it needs to be 2.5 mm.

It would seem they supplied you with what you asked for, but not what you want. It is the old three wishes thing, wording your request is so hard.

 

[JohnW2]

The rating given for a flexible cable assumes in free air and supplying portable appliances and the appliance your supplying is not portable, it is assumed portable means intermittent use, as with a standard kettle, not prolonged use as with an immersion heater, or tumble drier or in your case large lights.

That makes some sense - particularly if the much lower CCC figures for 'flexible' cable exist because of the repeated flexing to which it might be subjected.

Are you therefore saying that you regard it as acceptable to appreciably exceed the (Table 4F3A) CCC rating of 'flexible' cable if it is being used to supply a load which you do not regard as 'portable'?

Kind Regards, John

 

[JohnW2]

How soft does PVC get at 70°? Any chance that at that temperature a flexible, portable cable might get bent or impacted enough for the insulation to become compromised?

Possibly - but the notes at the bottom of 4F3A seem to imply that the CCCs presented in that table still apply for a flexible cable 'rated at' 150°C.

 

[EFLImpudence]

I do not see why the maximum CCC for the flex is not just that - the maximum.

Derating factors could be stated for various uses - just like all other cables.

To say that the given CCC is for when it is subject to {whatever} is silly if that is not stated and it is not going to be subject to {whatever}.

 

[JohnW2]

I do not see why the maximum CCC for the flex is not just that - the maximum.

Agreed. However, I suspect that one of the issues is that, unlike the situation with non-'flexible' cables, one is not given different CCCs for different 'installation methods' - and, in reality, could not be given such figures, since there can be telling how the cable will be used.

In other words, maybe those 'maximum CCC' figures relate to the perceived "worst case scenario" (maybe 'buried under thick carpet', 'under a massive pile of laundry' etc.?).

Derating factors could be stated for various uses - just like all other cables.

Indeed - but, as above, maybe actually Uprating factors, for when the cable is used in conditions (e.g. 'in free air') more favourable than the 'worst case' ones?

Kind Regards, John

 

[ericmark]

Are you therefore saying that you regard it as acceptable to appreciably exceed the (Table 4F3A) CCC rating of 'flexible' cable if it is being used to supply a load which you do not regard as 'portable'?

Kind Regards, John

No the reverse, I am saying the rating for flexible cable is allowing for the fact that items are portable and so not being used for an extended time.

I know it is hard to work out what is reasonable, we had some concrete pumps and our boss decided they would be better wired in flex, so ordered a role of 240 mm² flex, it was simply too heavy and hard to work with, so in end went back to 150 mm² SWA which was actually easier to work with.

 

[JohnW2]

No the reverse, I am saying the rating for flexible cable is allowing for the fact that items are portable and so not being used for an extended time.

If that were the true, it would surely not make sense - because one would then expect that current ratings for such cables would be higher (not lower) than for cables supplying items that are used for extended periods of time, wouldn't one?

In any event, would you not regard things like, say, small fan heaters as being 'portable' - small and light (hence certainly 'portable' in the everyday sense), not built-in and often used 'for extended periods'?

Kind Regards, John

 

[Risteard]

I believed it to be 700mm from PAT days.

I'm certain it's 2 metres.

 

[securespark]

According to a conversation I had with Paul Cook at the IEE years ago, flexes are "under-rated" due to installation conditions being potentially rougher than fixed installs. Because flexes are manually handled by an unqualified end user, their potential for abuse is higher. Free-air does not always exist; sometimes fridge flexes are stuck behind their appliance potentially close to or touching compressors. Sometimes (despite advice) flexes are tucked under carpet. For these (and similar) reasons, flexes have lower CCC's than if used in fixed installs.

Edited for clarity.

 

[JohnW2]

According to a conversation I had with Paul Cook at the IEE years ago, flexes are "under-rated" due to installation conditions being potentially rough. Free-air does not always exist; sometimes fridge flexes are stuck behind their appliance potentially close to or touching compressors. Sometimes (despite advice) flexes are tucked under carpet. For these (and similar) reasons, flexes have lower CCC's than if used in fixed installs.

Yes, that makes sense, and is essentially what I wrote recently in this thread - that the ratting is for the 'worst possible' conditions of use - as I said, under thick carpets, under enormous piles of laundry etc. are far from impossible.

This may also be at least part of the reason why there is apparent a 'relaxation' for short cables, since it's probably unlikley that a short cable will suffer from those sorts of adverse 'installation methods'!

Kind Regards, John