Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 14 replies
  • Subscribers 32 subscribers
  • Views 1123 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Third party modifying a Commercial Machine

AdrianWint

So, the scenario is that we have a machine shop containing 8 CNC machines.

Four are HASS CNC mills & four are MAZAK CNC turning machines.

A third party has been contracted to install an extraction and coolant mist filtering system to these machines. This system is manufactured by said third party and looks, on the surface, to be puka. These are small systems, one per CNC (it is not a large, communal system).

Said third party has taken the supply for this system from the CNC machine itself, after the main contactor such that the extraction powers on when the CNC wakes up.

 

My concerns are:

Said third party is unwilling to provide any paperwork to backup that his modifications are either approved by the original manufacturer of the CNC or that the supply he has taken/or the manner in which he has taken it, will have no adverse effect on the machine. (I do concede that these units are fractional hp 3 phase motors, so, realistically, the additional load is insignificant compared to the machine itself).

The wiring to these extraction units has been undertaken in SY flex. I'm not too bothered about the “should SY be used directly on the mains” debate. This is a modification to an “appliance” so not really BS7671 land. The environment, although a machine shop, isn't ‘heavy’ industry so I do feel that SY is appropriate - it doesn't need SWA & its better than TRS. My concern here is that he has not earthed the braid of the SY. Plastic stuffing glands have been used & the exposed end of the braid has been covered with a turn of black PVC tape. Although I feel that this isn't best practice, I'm struggling to find anything written to backup my case that he needs to return & earth the braids.

Protection for the SY is in the form of a simple, latching motor starter/overload module which is, obviously, primarily to provide overload protection to the motor. In doing so, it will provide overload protection for the SY, but what about short circuit protection? The next device back in the chain is the D32 MCB feeding the CNC sub-circuit. I'm not convinced that a D32 will provide SCP to a 1.0mm^2 SY…..

 

What are the thoughts of the learned forum?

 

 

Parents
  • 0

    mapj1: 
     

    The question is one of how ‘serious ’ the change is. If for example it involved cutting into the wiring for an E-stop it would require far more thought than this example and that would become one where maker's buy-in would be needed, or a review of the whole safety system to compare the before and after for all sensible cases.

     Here, only an LV supply is being lifted  for some ancillary - this is almost at the level of plugging in a sump pump or an extra operator light, so low risk, but even then there should be a record of how power was tapped in, and some justification that it can in no way can it impair the normal operation. Adding a load that had potential to cause RF interference for example would be a different matter.

    There ought to be a clear trail so the person who is in effect accepting the risk, knows they are and is happy with it.

    Mike.

     

    Not only the “trail of blame”.

    BS EN 60204-1 requires circuit diagrams necessary for repair. These need to be updated.

    Are the original ratings of equipment, supplies and enclosures still correct - who's updating that info?

    All based on the assumption of course that the connection won't impact any EMC measures or testing of the original manufacturer … who's checking that? And of course this could also relate to the SY cable. If one of the manufacturers recommended SY to be used, SY is used for EMC purposes, NOT mechanical protection … so the braid should be earthed, via a proper 360-degree gland … or YY (or a suitable flexible cable such H07 RN-F) should have been used instead.

    Too many open questions in my mind from an assurance point of view.

Reply
  • 0

    mapj1: 
     

    The question is one of how ‘serious ’ the change is. If for example it involved cutting into the wiring for an E-stop it would require far more thought than this example and that would become one where maker's buy-in would be needed, or a review of the whole safety system to compare the before and after for all sensible cases.

     Here, only an LV supply is being lifted  for some ancillary - this is almost at the level of plugging in a sump pump or an extra operator light, so low risk, but even then there should be a record of how power was tapped in, and some justification that it can in no way can it impair the normal operation. Adding a load that had potential to cause RF interference for example would be a different matter.

    There ought to be a clear trail so the person who is in effect accepting the risk, knows they are and is happy with it.

    Mike.

     

    Not only the “trail of blame”.

    BS EN 60204-1 requires circuit diagrams necessary for repair. These need to be updated.

    Are the original ratings of equipment, supplies and enclosures still correct - who's updating that info?

    All based on the assumption of course that the connection won't impact any EMC measures or testing of the original manufacturer … who's checking that? And of course this could also relate to the SY cable. If one of the manufacturers recommended SY to be used, SY is used for EMC purposes, NOT mechanical protection … so the braid should be earthed, via a proper 360-degree gland … or YY (or a suitable flexible cable such H07 RN-F) should have been used instead.

    Too many open questions in my mind from an assurance point of view.

Children
No Data

Community Rules & Guidelines