Equiotential bonding of machines according to IEC 60204

I think the answer to this question lies in understanding three separate points in relation to BS EN 60204-1:

(a) What needs to be connected to the protective bonding circuit (Clause 8.2.2)

(b) When can a metal enclosure or frame be used as a bonding conductor (Clause 8.2.2)

(c) The requirement in the 1st para of Clause 8.2.3 which states "Where a part is removed for any reason (for example routine maintenance), the protective bonding circuit to remaining parts shall not be interrupted."

So, for example, if the motor is removed, is there a connection to other components?

This is really difficult to fully analyse without seeing the particular product ... for example,separate to the motor, are there any other monitoring, control, or interlock devices in the rest of the machine - but I hope that it will help you find what you are looking for in the standard itself.

Thanks for your reply gkenyon,

For purposes of clarity I found another picture from another system with similar conditions except that the 4x2,5mm2 motor cable runs along side the screw conveyor it self. Does this help in order to point out which parts need to be connected to the protective bonding circuit ? in my mind the screw conveyor it self is a "conductive structural part of the machine" as pointed out in 8.2.2. and also the lid but it has no electrical parts so does it need to be connected to the protective bonding circuit ? how about the motor casing, should an additional protective conductor be connected to the outside of the motor casing ?

Best regards,

Steinar R

Steinar Runarsson said:

in my mind the screw conveyor it self is a "conductive structural part of the machine" as pointed out in 8.2.2. and also the lid but it has no electrical parts so does it need to be connected to the protective bonding circuit ?

Yes, all structural parts require connecting to the protective bonding circuit as defined in the standard ... either directly, or through another part of the machine.

That could be through the motor itself (via the casing, if that is bonded through the protective conductor to the motor) ... BUT, if the motor is removed during maintenance, the cable still runs alongside the screw conveyor body, and therefore if it's only earthed through the motor, there is still a risk. I guess all of this depends on the containment for the cable - that ought to be earthed, but how is that achieved? If it's from the conveyor, then that would need to be earthed separately to the motor.

Steinar Runarsson said:

how about the motor casing, should an additional protective conductor be connected to the outside of the motor casing ?

Well, if the motor casing is earthed via the protective conductor in the cable feeding the motor, and all electrical parts of the motor are removed together, I could see that not needing a separate connection.

But it's not clear to me whether the motor and gearbox are all one unit, and I can see cable containment attached to the gearbox ... and it's not clear whether the containment is metal or plastic ...

I'm afraid it's really not easy to decide from pictures like this, and the manufacturer or importer of the machinery will need to undertake a suitable risk assessment and make that decision ... and then document the wiring required to let the installer and maintainer know as part of the required documentation to the standard. (In the EU or UK, that would be necessary to comply with the relevant legislation.)

Since the motor is the only electrical consumer on the screw conveyor it is highly unlikely or even impossible for the screw conveyor to become a live part since the cable does not run along side the screw conveyor, with that in mind can we do without connecting the screw conveyor body and lid to the protective bonding circuit ?

60204 isn't my area at all, but if they're using the term "bonding" as distinct from "earthing" there may be more thinking going on behind the scenes than simply providing ADS.  There may be EMI considerations or providing some attempt at equipotentiality between other voltage sources  (e.g. potentials imported from neighbouring machines it might be in fortuitous contact with or just from true earth potentials (e.g. the concrete floor).

   - Andy.