5A BS 1363 plug?

[ban-all-sheds]

If the insulation and sheathing become too soft to resist damage if the conductor temperature is raised to 70 degC then that cable is not suitable for such use. That is not directly related to the CCC.

Of course it is.

CCC limits for cables are not bounded by the melting point of copper, but by the behaviour of the plastics used in them (and the accessories they connect to).

That's why the It of XLPE cables is higher than that of PVC - the former can run at 90°C and can therefore carry more current.

If an XLPE cable is used in an application where it may not run at 90°C, then its CCC is reduced.

It's not a question of "if insulation & sheathing become too soft" - at too high a temperature they will , and they will, at a certain point, become so soft that the conductors will migrate through them if the cable is bent, or compressed. Keep going, and the point will come where they start to melt. Go further and they will catch fire.

But you'd still be nowhere near any CCC limit which was due to the physical properties of copper.

It's not some magic copper which gives bare 1mm² MICC an It of 26A, it's the fact that the lack of any PVC to go soft means it can run hotter than 1mm² T+E.

So yes - if a PVC cable, which uses PVC for all sorts of good reasons, which gives the cable the properties which are desirable for a flexible cable, gets too hot it becomes insufficiently able to resist the mechanical stresses to which it is subject, or at risk from, because it's a flexible cable used for portable applications. The answer to that is not to say "well if PVC becomes too soft at 70°C then it's the wrong material, and the cable isn't suitable", the answer is to limit the CCC so that it does not get to 70°C.

 

[ban-all-sheds]

If I know nothing about, and have no control over, what load may be supplied by the lead (hence cable), I surely cannot be satisfied that the cable is "not likely to carry overload current", can I??

Of course you can.

You've made it, rated it, marked it and sold it as an assembly with a rating of 6A, therefore when used as directed it is not likely to carry an overload current.

If your customer buys it for an application where it is likely to carry an overload current which will damage it then it's not that you have made the wrong thing - he has bought the wrong thing.

 

[JohnW2]

If I know nothing about, and have no control over, what load may be supplied by the lead (hence cable), I surely cannot be satisfied that the cable is "not likely to carry overload current", can I??

Of course you can. ... You've made it, rated it, marked it and sold it as an assembly with a rating of 6A, therefore when used as directed it is not likely to carry an overload current. ... If your customer buys it for an application where it is likely to carry an overload current which will damage it then it's not that you have made the wrong thing - he has bought the wrong thing.

That would only be true if it were possible to (and I could be bothered to!) create an exhaustive list of all the ≤6A (under normal conditions) loads which, under certain abnormal ('fault' in the everyday sense) conditions might result in a a current 'moderately above' 6A. Unless I could do that, and included it in the instructions provided with the product, I would have to assume that it might be used to supply such a load - and therefore would have to provide the cable with adequate overload, as well as fault, protection.

Have you ever seen anything approaching such a list of 'unsuitable types of loads' provided with a made-up lead such as we are discussing?

Kind Regards, John

 

[stillp]

John, that's nonsense! There is no need to list all the unsuitable loads; the rating is sufficient. BAS is correct.

 

[stillp]

If the insulation and sheathing become too soft to resist damage if the conductor temperature is raised to 70 degC then that cable is not suitable for such use. That is not directly related to the CCC.

Of course it is.

CCC limits for cables are not bounded by the melting point of copper, but by the behaviour of the plastics used in them (and the accessories they connect to).

That's why the It of XLPE cables is higher than that of PVC - the former can run at 90°C and can therefore carry more current.

If an XLPE cable is used in an application where it may not run at 90°C, then its CCC is reduced.

It's not a question of "if insulation & sheathing become too soft" - at too high a temperature they will , and they will, at a certain point, become so soft that the conductors will migrate through them if the cable is bent, or compressed. Keep going, and the point will come where they start to melt. Go further and they will catch fire.

But you'd still be nowhere near any CCC limit which was due to the physical properties of copper.

It's not some magic copper which gives bare 1mm² MICC an It of 26A, it's the fact that the lack of any PVC to go soft means it can run hotter than 1mm² T+E.

So yes - if a PVC cable, which uses PVC for all sorts of good reasons, which gives the cable the properties which are desirable for a flexible cable, gets too hot it becomes insufficiently able to resist the mechanical stresses to which it is subject, or at risk from, because it's a flexible cable used for portable applications. The answer to that is not to say "well if PVC becomes too soft at 70°C then it's the wrong material, and the cable isn't suitable", the answer is to limit the CCC so that it does not get to 70°C.

Yes BAS, that's correct of course, but BS 1363 does not specify the insulation material (at least not in conjunction with Table 2). Hence my statement that if the cable's insulation becomes too soft at 70 C then it is unsuitable. The alternatives are to reduce the temperature, which might involve reducing the current, to use a cable having a higher-temperature-resisting insulation, or to reduce the mechanical stress on the cable.

 

[JohnW2]

John, that's nonsense! There is no need to list all the unsuitable loads; the rating is sufficient. BAS is correct.

I don't believe that is the case, and I doubt that even BAS would say that it was acceptable to omit overload protection of a cable unless (per BS7671 regs) the designer/manufacture was satisfied that the nature of the load (drawing less that the rated current of the item under normal circumstances) was such that an overload current was unlikely. He suggested that such would be the case unless a consumer had "bought the wrong thing" (which would then be 'their problem') - but, as I said, a consumer could only know that they had "bought the wrong thing" if they were made aware by the manufacturer of the type of loads for which it was unsuitable.

Kind Regards, John

 

[stillp]

if they were made aware by the manufacturer of the type of loads for which it was unsuitable.

That would be loads for which a 6A rating is inappropriate then.

 

[stillp]

... (per BS7671 regs) ...

What has BS7671 to do with a non-rewireable plug in accordance with BS 1363?

 

[JohnW2]

if they were made aware by the manufacturer of the type of loads for which it was unsuitable. ...

That would be loads for which a 6A rating is inappropriate then.

Not really. Don't forget that (although you will say he shouldn't), BAS was invoking 433.3.1(ii) of BS7671 to justify the cable not having overload protection. That regulation requires that the nature of the load is such that it is considered unlikely that (under abnormal circumstances) it can result in an overload current.

Kind Regards, John

 

[JohnW2]

... (per BS7671 regs) ...

What has BS7671 to do with a non-rewireable plug in accordance with BS 1363?

Well, you really should be asking BAS, since it was he who invoked a BS7671 regulation to justify the omission of overload protection of a cable attached to a BS1363 rewirable plug. However, I essentially agree with him that the BS7671 regs concerning over-current protection of cables seem reasonable rules-of-thumb in relation to the use of the same cables in cable-sets (and I don't really feel any differently when the plug is not rewirable, either!).

Kind Regards, John

 

[ban-all-sheds]

Yes BAS, that's correct of course, but BS 1363 does not specify the insulation material (at least not in conjunction with Table 2). Hence my statement that if the cable's insulation becomes too soft at 70 C then it is unsuitable.

I wasn't talking about what BS 1363 does, or does not say (and neither were you, since BS 1363 does not have a table of cable types or tabulated CCCs) - I was replying to your assertion that the performance of a given type of cable at a given temperature has nothing to do with the current it is deemed capable of carrying.

The alternatives are to reduce the temperature, which might involve reducing the current

I can't think of any other practicable way.

Q: How do you ensure reduction of the current from that which would raise the conductor temperature to 70°C?

A: You assign a CCC to the cable which if adhered to will not raise the conductor temperature to 70°C.

to use a cable having a higher-temperature-resisting insulation

Yes - it's conceivable that different materials would allow an Xmm² cable to safely carry a higher current than the same sized cable which uses PVC. But it might be that the price would be unattractive, or the physical characteristics of the cable would make it less suited for its intended use. MICC, for example, would make a pretty poor cable for a portable appliance.

or to reduce the mechanical stress on the cable.

Can't do that - flexible cables for use with portable appliances have to be able to cope with the mechanical stresses reasonably expected to occur to flexible cables for use with portable appliances.

 

[ban-all-sheds]

Well, you really should be asking BAS, since it was he who invoked a BS7671 regulation to justify the omission of overload protection of a cable attached to a BS1363 rewirable plug.

No I wasn't. I mentioned that regulation because you seemed to be struggling with the idea of a plug having a fuse in it with a rating higher than the CCC of the cable.

but, as I said, a consumer could only know that they had "bought the wrong thing" if they were made aware by the manufacturer of the type of loads for which it was unsuitable.

They have been made aware - the manufacturer has stamped the rating of his product on the bearing face of the plug, as per BS 1363. If that says '6A' then the consumer has been made aware that it is unsuitable for any load greater than 6A.

 

[JohnW2]

Well, you really should be asking BAS, since it was he who invoked a BS7671 regulation to justify the omission of overload protection of a cable attached to a BS1363 rewirable plug.

No I wasn't. I mentioned that regulation because you seemed to be struggling with the idea of a plug having a fuse in it with a rating higher than the CCC of the cable.

Whatever words one uses, you mentioned it in an attempt to help me understand how/why/when it might be acceptable (in BS7671 terms) for a cable not to have overload protection (even though I had already anticipated, and I thought 'pre-empted', your point about that regulation).

but, as I said, a consumer could only know that they had "bought the wrong thing" if they were made aware by the manufacturer of the type of loads for which it was unsuitable.

They have been made aware - the manufacturer has stamped the rating of his product on the bearing face of the plug, as per BS 1363. If that says '6A' then the consumer has been made aware that it is unsuitable for any load greater than 6A.

You seem to be missing the point. What you say is obviously correct - that if the product is 'rated' at 6A, then it should not be used for a load which (normally) draws more than 6A. However, if BS7671 were applicable, and if one wanted to invoke 433.3.1(ii) to allow overload protection of the cable to be omitted, one would have to be satisfied that it was 'unlikely' that the (normally) ≤6A load would (assuming cable CCC=6A) draw >6A under abnormal ('fault' in everyday sense) conditions. Without detailed instructions, a user cannot be expected to know whether or not his/her particular (normally) ≤6A load comes into that category.

Kind Regards, John

 

[plugwash]

What size is the flexible cable?

In my experiance it's common to see BS1363 to IEC leads with 0.75mm flex (6A rated IIRC) and 5A stamped on the BS1363 plug (and hopefully a 5A fuse fitted) but the IEC connector is always stamped as 10A regardless of the rating of other parts of the assembly.

If you have on of the (uncommon) devices that needs more than 5A and has an IEC inlet then you need to check carefully when chosing a mains lead for it.

 

[JohnW2]

What size is the flexible cable? In my experiance it's common to see BS1363 to IEC leads with 0.75mm flex (6A rated IIRC) and 5A stamped on the BS1363 plug (and hopefully a 5A fuse fitted) but the IEC connector is always stamped as 10A regardless of the rating of other parts of the assembly.

That is precisely the situation we've been discussing, per the lead described by eric. However, the real issue is that BS1363 appears to allow that lead to have a 13A fuse (despite the 0,.75mm² flex) - and stillp is strongly defending that situation. That's become the main issue being 'debated'.

Kind Regards, John