Local isolator near drive, good or bad?

I have used this kind of approach in a manufacturing environment in the past to great effect. I now work in the water industry but when I suggested this approach, our VSD framework supplier was dead set against it because of the potential damage to the VSD if it output is open circuited before the VSD has time to shutdown properly. If any of your drives are supplied by VSD it might be worth checking with VSD supplier first.

I still think it is a good approach to take. Solution to the VSD issue and the heap of products on the floor issue mentioned elsewhere would be to have a procedure where there is a controlled shutdown using a cycle stop pushbutton BEFORE the isolator is switched off. The other thing to consider is the need to ensure that the isolator cannot be switched back on - i.e. a lock out tag out (LOTO) procedure needs to be in place. This then raises the question of key control... it should be one lock one key but in my experience this can get messy if the person with the key isn't available when needed to reinstate the drive. Might need some handover process if person with the key is likely to go off shift.

You might need to consider the possibility that the wrong piece of equipment is isolated (e.g. duty/standby kit - person could be injured by unexpected start up if they have isolated the duty machine but started working on the standby machine). Also need to consider proximity of other pieces of equipment... could the person working on the isolated machinery be injured by another machine... does the work require a zone of equipment to be isolated?

While I am satisfied that a local isolator provides a safe and robust solution for mechanical maintenance, I would be a little concerned if  the fitter was required to change a motor. Isolators are not infallible and supply can remain on, say, one phase. While this wouldn't be sufficient to start and run a motor, it would leave a potentially lethal hazard for an unsuspecting fitter disconnecting the motor terminals. In such cases I would recommend that fitter is issued with a two-pole tester and proving unit and is instructed on how to prove dead at the point of work - prove it, use it, prove it. Also this suggests a robust maintenance regime is required to check functionality of the isolator periodically especially in adverse environmental conditions.

Another device to consider as the point of isolation is the Marachel Decontactor. This is a plug and socket device that is rated as an isolator ... don't use a standard industrial plug and socket, it is not the same. I used this device on a mixing vessel  so that the vessel inspectors were able to isolate for themselves in full confidence that motor tails were fully disconnected and encased in a clam shell which was securely locked and under their exclusive control.

Thank you for the new name to me I have found the  marechal website  I presume it is these ones here  you used ?

I had not seen those before they seem to be quite new, and usefully unusual in a rating for 1kV AC 1k5 DC. Have you been using them for long ? I'd be interested in any  feel you may have for reliability in a real setting  - the datasheet seems to indicate a flat pogo-stick contact surface rather than the more usual pin and tube,  which would be unusual in anything for much more current than a lamp holder - have I misunderstood or is that the case ?

The profusion of pilot contacts make 'safely turn off the VFD' very practical, if as usual the pilot lines are made/broken while the main poles are already or still connected.

Not needed the earth return for a  pilot loop in the manner of the normal BS4343 / IEC 60309 is a significant improvement.

Mike

Thank you for the new name to me I have found the  marechal website  I presume it is these ones here  you used ?

I had not seen those before they seem to be quite new, and usefully unusual in a rating for 1kV AC 1k5 DC. Have you been using them for long ? I'd be interested in any  feel you may have for reliability in a real setting  - the datasheet seems to indicate a flat pogo-stick contact surface rather than the more usual pin and tube,  which would be unusual in anything for much more current than a lamp holder - have I misunderstood or is that the case ?

The profusion of pilot contacts make 'safely turn off the VFD' very practical, if as usual the pilot lines are made/broken while the main poles are already or still connected.

Not needed the earth return for a  pilot loop in the manner of the normal BS4343 / IEC 60309 is a significant improvement.

Mike

I have only used the Marechal Decontactors on two separate occasions, for two very different reasons. However, I found them to be the ideal solution on both occasions with no reliability issues. The first application was as mentioned on a group of four mixing vessels with large Ex-d rated motors. This was getting on for 15 years ago so exact size eludes me but I would say around 22kW. The decontactor was fully-rated for this application. 

The vessels were subject to a regime of regular internal inspections but the inspectors wouldn't enter the vessels unless the tails were disconnected from the motor terminals... they weren't about to take any chances with the incorrect vessel being isolated. Trouble was they might have to wait 20, 30, 40 minutes for an electrician to become available and then another 20 minutes for the isolation to be completed (and of course it was a similar story when the vessel was reinstated again afterwards). Apart from the time wasted my main concern was the potential for compromising the integrity of the flame-path and mis-connection / loose connection when reinstating the terminals. After the isolator was installed, the inspectors were able to isolate for themselves. The four plugs/sockets were keyed differently to prevent misconnections. There were no downsides I recall.

The other application was on an overhead crane with a electrical hoist conversion but manual long travel. Since the crane was originally designed for manual operations, there were no busbars and no collectors so the supply to the hoist was on an umbilical cord with plug. The bay was extremely long so a number of socket outlets were installed to allow the hoist to be plugged in at strategic points along the bay. Operators were not supposed to use the manual long travel unless the hoist was unplugged. Trouble was, there was always a chance that they might forget to unplug and the umbilical cord / sockets could be stressed or damaged. We replaced the standard industrial sockets with a Marechal decontactor with a self-ejecting mechanism of the type used by fire and rescue vehicles. If the umbilical cord was put under any strain the plug popped out of the socket before any damage was done. This was maybe 7 years ago, again no reliability issues.

Thank you - very interesting indeed. Sounds like a  name I should keep to hand.

Mike