Electrical code Compliance - What appliance class has a plastic enclosure but also a connection to earth?

Author

What appliance class has a plastic enclosure but also a connection to earth?

fssg

2006-05-05, 4:21 am

Hello,

I want to make a device with a plastic enclosure and an earth connection.

The device needs an earth connection because it will switch mains power to
loads that have an earth, for example a metal-cased fan and a pneumatic
valve.

My question is, what device class is it?

According to the wiki for double-insulated
(http://en.wikipedia.org/wiki/Double_insulated) this would be a class 0
device, but these 'will eventually disappear... in favour of Class II
devices'.

I could make it a class I device, with a metal chassis and earth connection,
but I want to avoid this because it is heavier to ship and the enclosure is
more expensive.

I can't make a class II device, because these aren't allowed to have an
earth connection. (Why is it that a class II device *must not* have an earth
connection? What is the danger?)

I see many devices around (such as common powerboards and light timers) that
have
a) plastic enclosure
b) earth connection
but they are not labelled as class II/double insulated, and they can't be be
class 0 because the world would end if powerboards were phased out. What
class are these?

Thanks,
David

gab

2006-05-07, 8:21 am

Class I (with class II construction)!
regards

fssg

2006-05-08, 12:21 am

OK, so is it possible for a class I appliance to have exposed, ungrounded
metal parts?

"gab" <gabrio.spinelli@gmail.com> wrote in message
news:1146999463.960242.216110@i40g2000cwc.googlegroups.com...
> Class I (with class II construction)!
> regards
>

Derek Geldard

2006-05-08, 5:21 pm

On Mon, 08 May 2006 02:24:30 GMT, "fssg" <sdfsd@sdfsd.com> wrote:

>OK, so is it possible for a class I appliance to have exposed, ungrounded
>metal parts?
>

AIUI small metal parts "That cannot become live" such as nameplates
Decals, etc. are OK. But not usually the metal housing of an electric
fan, or in many cases, the pipes from a mains operated solenoid valve.

SELV (Safety Extra Low Voltage) may be a solution for you ...

I'd be a bit concerned in your original design as to what would be the
consequences of failure of the opto isolator devices (whatever they
are) I've known opto isolators fail in a "total carbonisation" mode
and allow mains to escape via their low voltage logic inputs, causing
dozens of logic gates to get fried. In your case ISTM this might
permit mains voltage to appear on the RS232 port and could "fry" a
device (computer ?) a hundred or more feet away, and the guy
investigating the fault might not expect to find mains on the
motherboard.

:-(

I've known an old British Standard for electrically energised office
equipment that specified opto isolators that were individually tested
at 2kv

Is there a Harmonised European Standard for the product you wish to
produce? Or if you are in the US a UL standard? Or elsewhere a local
standard.

Being able to show compliance with a proper standard would go a long
way to protecting you if a serious adverse event occurred.

Anyways JMHO.

DG

Ben Mack

2006-05-11, 9:21 am

In article <yZx7g.386243$hn5.353122@fe04.news.easynews.com>, fssg
<sdfsd@sdfsd.com> writes
>OK, so is it possible for a class I appliance to have exposed, ungrounded
>metal parts?

EN60950 says Class I equipment may have parts with double or reinforced
insulation. Conductive parts need protective earth if hazardous when
*basic* insulation fails, implying the earth is not needed if double or
reinforced insulation

I've certainly designed products with an earth (for EMC purposes) but
relying on double/reinforced insulation, though as gab says it is still
a Class I product

Cheers
--
Ben Mack
Watchfront Electronics - Bespoke R&D - http://www.watchfront.co.uk/
Watchfront Internet - ADSL, Colo - http://www.watchfront.net/
Are you bricking it? - Firewalls - http://www.firebrick.co.uk/

fssg

2006-05-23, 10:21 pm

Thanks for your replies.

"fssg" <sdfsd@sdfsd.com> wrote in message
news:ihC6g.311107$BL7.87139@fe09.news.easynews.com...
> Hello,
>
> I want to make a device with a plastic enclosure and an earth connection.
>
> The device needs an earth connection because it will switch mains power to
> loads that have an earth, for example a metal-cased fan and a pneumatic
> valve.
>
> My question is, what device class is it?
>
> According to the wiki for double-insulated
> (http://en.wikipedia.org/wiki/Double_insulated) this would be a class 0
> device, but these 'will eventually disappear... in favour of Class II
> devices'.
>
> I could make it a class I device, with a metal chassis and earth
> connection, but I want to avoid this because it is heavier to ship and the
> enclosure is more expensive.
>
> I can't make a class II device, because these aren't allowed to have an
> earth connection. (Why is it that a class II device *must not* have an
> earth connection? What is the danger?)
>
> I see many devices around (such as common powerboards and light timers)
> that have
> a) plastic enclosure
> b) earth connection
> but they are not labelled as class II/double insulated, and they can't be
> be class 0 because the world would end if powerboards were phased out.
> What class are these?
>
>
> Thanks,
> David
>

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