Class I or class II appliance?

[RWJ]

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

No Worries..... Tell him if he's man enough... Come on here and he can argue the "for" case!!

 

[Des 56]

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

I'm not sure that it wouldn't make sense nowadays Tel,the price of scrap metal being what it is

The Iee may want to include those tables in their ammaendments

Metal tables bonded to the floor using approved rawl bolts for protection from thieving scumbags

 

[telectrix]

and with croc clips from 2 phases. last man out at closing time with rubber gloves. give the pikeys a wake up call.

 

[Adam W]

Basically everything you said is correct - the enclosure (or 'cassette') would need earthing unless there is adequate double or reinforced insulation between the exposed metalwork and any live parts.

The question being what constitutes adequate insulation. TBH it might be easier and safer just to earth the metal cassette.
I don't want to get caught up in this witch hunt deciding if this maintenance electrician is right or wrong and calling him a jobsworth, but he has got a point.

 

[Deleted member 26818]

I'd suggest contacting the motor manufacture.

 

[davelerave]

Basically everything you said is correct - the enclosure (or 'cassette') would need earthing unless there is adequate double or reinforced insulation between the exposed metalwork and any live parts.

The question being what constitutes adequate insulation. TBH it might be easier and safer just to earth the metal cassette.
I don't want to get caught up in this witch hunt deciding if this maintenance electrician is right or wrong and calling him a jobsworth, but he has got a point.

it's not safer to earth metal on class2 equipment

 

[RWJ]

Basically everything you said is correct - the enclosure (or 'cassette') would need earthing unless there is adequate double or reinforced insulation between the exposed metalwork and any live parts.

The question being what constitutes adequate insulation. TBH it might be easier and safer just to earth the metal cassette.
I don't want to get caught up in this witch hunt deciding if this maintenance electrician is right or wrong and calling him a jobsworth, but he has got a point.

Stick a 951 clamp on it with 10mm back to the board just to be safe!!!!

Sorry still can't see how a purpose designed class II blind motor could introduce a fault...

The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having two layers of insulating material surrounding live parts or by using reinforced insulation.

 

[Adam W]

It's not about the motor though, it's about the cable going to it and going through a metallic casing - if the cable were to get damaged in some way on it's way to the motor then the metal casing could become live. Fine if there is adequate double or reinforced insulation, but who can say what is 'adequate' and then guarantee that if something were to go wrong?

A bit like putting a plastic light switch on metal trunking - you'd still bond the trunking even though the switch is class 2.

 

[RWJ]

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

I see what your saying NovusSparkus.
It's not clear where to "wire" is located. I assumed he was talking about the internals of the motor and the wire would be no where near the metal cassette?
If the wire is in the metal cassette then it's IMHO a different story

 

[Deleted member 9648]

It's not about the motor though, it's about the cable going to it and going through a metallic casing - if the cable were to get damaged in some way on it's way to the motor then the metal casing could become live. Fine if there is adequate double or reinforced insulation, but who can say what is 'adequate' and then guarantee that if something were to go wrong?

A bit like putting a plastic light switch on metal trunking - you'd still bond the trunking even though the switch is class 2.

I agree......I dont think from the info provided it is possible to be certain that the casing does not require earthing.....a photo would be useful.

 

[Adam W]

I had assumed the cable goes into the metal cassette and to the motor, the only insulation between live parts and the metal of the cassette being the insulation and sheath of the cable (probably flex). This might be fine if it's pulled tight across the enclosure using air as supplementary insulation and unlikely to flap around due to vibrations from the motor and wear away, and that there is a suitable gland around the cable entry point preventing the cable sheath from chafing against the cassette.

These are a lot of assumptions to make considering the maintenance electrician has seen the particular situation with his own eyes.

On the other hand the flex could be replaced for 3 core, a ring crimp put on the end of the earth wire and secured to the cassette, which certainly seems easier to describe.

 

[Des 56]

I had assumed the cable goes into the metal cassette and to the motor, the only insulation between live parts and the metal of the cassette being the insulation and sheath of the cable (probably flex). This might be fine if it's pulled tight across the enclosure using air as supplementary insulation and unlikely to flap around due to vibrations from the motor and wear away, and that there is a suitable gland around the cable entry point preventing the cable sheath from chafing against the cassette.

These are a lot of assumptions to make considering the maintenance electrician has seen the particular situation with his own eyes.

.

quote original question

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??


I dont agree that assumptions have been made,the question was precise and assumptions may be being made to the posts description of the setup

 

[Adam W]

quote original question

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??

I dont agree that assumptions have been made,the question was precise and assumptions may be being made to the posts description of the setup

I don't know if I understand what you're saying, but I was talking about assuming the measures of protection are "adequate", which is an undefined quantity.

 

[telectrix]

right by the side of me is a floor standing lamp. class II, metal casing. where the 2 core cable enters the metal casing, it goes through a rubber grommet. obviously, this lamp has been manufactured to current regs. and standards. the situation as in the op is exactly the same. albeit a different type of equipment.

 

[Adam W]

Yes, I've got some table lamps similar to that and yes I understand their construction, but they would have been type tested in the factory, and at the very least flash tested to prove the insulation.
What I'm saying is that instead of trying to argue that the insulation is up to the job would it not be easier just to earth an external conductive part? That would also give some kind of recourse if something went wrong and you had to stand up in court and explain that 'some manufacturers make class 2 appliances with exposed metalwork so why can't everyone?'