This statement piqued my interest:
> Surely that applies only to Class I products? IF not, it would rule out
> Class II and III products entirely. Battery-operated hand-helds are
> Class III.
Class III equipment is defined as equipment that
operates from a SELV supply and does not generate
hazardous voltage.
Consider the laptop computer.
It is battery operated. Therefore it is Class III.
(However, there is an interesting discussion as to
whether a battery is a SELV supply as contemplated
by the definition of SELV.)
However, the laptop includes an inverter circuit
that generates hazardous voltage to operate the
backlight. Often, the inverter circuit is also a
limited current circuit. By definition, a limited
current circuit is NOT a hazardous voltage.
Therefore, the laptop is a Class III equipment.
Now consider a laptop whose inverter is NOT a
limited current circuit.
In this case, we have a product that does not fit
the definition of the equipment classes, I, II, or
III.
Sub-clause 1.3.3 (2nd Ed.) includes a note that
says that equipment containing hazardous voltage
is Class I or Class II. Therefore, a battery-
operated laptop computer whose inverter circuit is
not limited current is a Class II equipment
(because it does not have a protective earthing
circuit).
The 3rd edition defines equipment classes, but
has no specific statements regarding Class III
with hazardous voltage. For the 3rd edition, the
laptop with a hazardous voltage inverter is not
Class I, not Class II, and not Class III.
Unfortunately, the IEC has chosen to use these
terms, Class I, II, and III, for equipment. If
these terms had been applied to protection means
for circuits, then the battery supply to the
laptop would be Class III, and the inverter
circuit would be Class II.
Best regards,
Rich
> From [email protected] Mon Jul 30 23:53:01 PDT 2001
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> Message-ID: <[email protected]>
> Date: Tue, 31 Jul 2001 06:03:29 +0100
> To: [email protected]
> From: John Woodgate <[email protected]>
> Subject: Re: ESD Design, non-earthed products
> References: <[email protected]>
> <[email protected]>
> In-Reply-To: <[email protected]>
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>
> <[email protected]>, Doug McKean
> <[email protected]> inimitably wrote:
> >One of the requirements in 1950 is to
> >ground any exposed metal parts accessible to the end user.
>
> Surely that applies only to Class I products? IF not, it would rule out
> Class II and III products entirely. Battery-operated hand-helds are
> Class III.
> --
> Regards, John Woodgate, OOO - Own Opinions Only.
> http://www.jmwa.demon.co.uk
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