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?
