And insulated & sheathed ≡ ?
New House, Service Head
- Thread starter wcavanagh
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The sheath may or may not be considered as a second layer of insulation, often not regarded as insulation as it's mechanical construction is so similar to the first layer of insulation and it is applied to the wire and not to the case of the appliance.
My "education" was that double insulation meant the wire was insulated (1st layer) and the metal housing was insulated (2nd layer) on the inside to prevent any wires whose insulation had failed from making electrically conductive contact with that metal. In effect this could often mean triple insulation when there an air gap providing a third layer of insulation.
Conductor~~insulation~~air gap~~insulation~~metal case
You need to look inside some Class II items.
I struggle to understand the logic of that. At first sight, what you say would seem to be an argument for, rather than against, regarding it as insulation.
Kind Regards, John
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Having two layers of tightly layered insulation on a conductor is different from having one layer of insulation on the wire and a loosely fitted ( * ) second layer of insulation. ( * ) loosely relative to the layer of insulation on the conductor.
Obviously 'different' - but I'm still not clear as to why you feel that what you describe as a "second layer of insulation" should not be regarded as insulation!
Kind Regards, John
Double insulation, = individual insulation of two items that must not come into contact.
So bellwire is a DI cable?
An interesting proposal - but where (other than your personal view) does that come from? As BAS has pointed out, that definition would seem to encompass any two (separate) conductors which each had 'single insulation'.
In terms of Class II items, this all becomes a little silly when one realises that a single layer of 'reinforced insulation' (whatever that may be) is an acceptable alternative to 'double insulation'. ... and what about a single layer of insulation which is twice as thick as qould be required to provide 'single insulation'?
Kind Regards, John
If each meets the requirements of basic insulation then that is double insulated, if only one piece meets the requirement its still basic insulation. If the insulation alone is twice what is required for basic insulation the its reinforced insulation and ths may be used in place of double insulation. Obviously thats from a product design point of view, it may well be different in other situations.
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A single piece of insulation at twice the thickness of that required for basic insulation is reinforced insulation which may be used in place of double insulation.
For equipment as defined by BS EN 60950:
Class I
Equipment where protection against electric shock is achieved by:
a) using basic insulation, and also
b) providing a means of connecting to the protective earthing conductor in the building wiring those conductive parts that are otherwise capable of assuming hazardous voltages if the Basic Insulation fails.
Class II
Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation, are provided, there being no reliance on either protective earthing or installation conditions.
You can buy en60950 cheaply if you are interested in the definitions. Just search for "estonian standards" they are a fraction of the cost of bsi...
You could also speak to someone like York EMC in Bristol or TUV in Fareham etc if you had money to throw away and wanted clarification
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... that seems to imply that one cannot have Class I equipment which is used other than "in a building"!
Kind Regards, John
I realise that, but what if one is distant from any building and using a generator supply? The definition implies that Class I equipment cannot be used in that situation.
Kind Regards, John
You have to get into the compliamce mindset.... as far as en60950 is concerned there are only different installation (overvoltge) categories defined.
If your building fixed equipment it has to be tied to something and they use the term building for that. They couldnt give a monkeys if its a generator, UPS or any other supply. Look up the over voltage categories and have a read...
If your building fixed equipment it has to be tied to something and they use the term building for that. They couldnt give a monkeys if its a generator, UPS or any other supply. Look up the over voltage categories and have a read...
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