Class I or class II appliance?

[Paul1971]

Hi - I have an issue with an installation involving a motorised roller blind and would like some advice. I work for a company that supplies motorised blinds and we are being told that a system recently installed does not conform with BS7671 - by the way I'm not an electrician, hence why I need help.

The blind is powered by a Class II mains powered tubular motor and therefore does not have an earth wire (only live and neutral). The motor sits inside a metal cassette, which provides the structure for the roller blind mechanism. We are being told that because the motor has been installed inside the metal cassette, we have created a Class I electrical appliance and this needs to be earthed.... Is this correct???

I presume that it is possible for the live wire of the motor to render the metal cassette live if through a fault scenario the live conductor became exposed and touched the cassette, but if adequate measures of protection have been taken to prevent this potential issue is it still necessary to earth the cassette mechanism??

Would really appreciate some clarification on this issue - thanks.

 

[davelerave]

there's a lot of class2 equipment out there with metal enclosures

you're prob ok-assuming your equipment conforms to standards

 

[Paul1971]

Thanks - this is what I thought, but we have an on-site electrical contractor who insists that the cassette must be earthed and I'm not sure how to respond as he's quoting infinite BS7671 regulations at us.
Is he correct in his insistence that the cassette must be earthed or am I dealing with someone who likes to lay down the electrical law his way to feel more important??

 

[malcolmsanford]

Paul ask him to confirm the regs and post them here.

 

[telectrix]

think he's got a little knowledge and using it to be a jobsworth. ask him which specific reg. he is referring to.

edit. ask him if the cassette meets the criteria for being an " extraneous conductive part", and if not, why does he want to introduce an earth potential.

 

[Des 56]

Definitions
Class 2 equipment
Protection against electric shock does not rely on basic insulation only,additional safety precautions included and no provision for connection of exposed metal work of the equipment to a circuit protective conductor

Exposed conductive part (Which it appears your metal cassette is being classed as )
Exposed conductive part of equipment is equipment that can be touched and which is normally live when basic insulation fails

If basic insulation fails there would not be live metal contact,because of the presence of supplementary insulation

My veiw is the cassette is not an exposed conductive part and the class 2 insulation protective measure seems to be adequate
Because that metal enclosure forms the containment,it has not become an exposed conductive part

 

[Paul1971]

Here's what I have from an email thread:

“Exposed conductive parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in regulations 411.4 to 411.6”

 

[malcolmsanford]

Nice one Des was actually reading the definations part of the regs thinking the about the same

 

[malcolmsanford]

Here's what I have from an email thread:

“Exposed conductive parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in regulations 411.4 to 411.6”

Des as just given the answer and the relevant sections of the regulations in section 2.

 

[telectrix]

4-1 against the jobsworth.

 

[RWJ]

The blind is powered by a Class II mains powered tubular motor and therefore does not have an earth wire (only live and neutral). The motor sits inside a metal cassette, which provides the structure for the roller blind mechanism. We are being told that because the motor has been installed inside the metal cassette, we have created a Class I electrical appliance and this needs to be earthed.... Is this correct???

I presume that it is possible for the live wire of the motor to render the metal cassette live if through a fault scenario the live conductor became exposed and touched the cassette, but if adequate measures of protection have been taken to prevent this potential issue is it still necessary to earth the cassette mechanism??

Would really appreciate some clarification on this issue - thanks.

If it's Class II then there should be not chance of the metal roller becoming live since the motor would be double insulated. As has already been stated there's loads of Class II equipment with metal enclosures.

 

[RWJ]

4-1 against the jobsworth.

Make that 5 - 1

 

[telectrix]

one more and it's game, set and match.

 

[telectrix]

maybe the guy's last job was bonding all the tables in a pub kitchen

 

[Paul1971]

Thanks Des (and all who contributed) much appreciated - I'll go back with this and hopefully the jobsworth with back down - thanks again.