Local isolator

MrJack96:

Hi guys I’ve come across a local isolator that has been linked out for a motor but still can be isolated upstream. Trying to get my head around emergency switching and if a local isolator is the means of it. I always thought it was just e-stops where used for emergency switching. Guess my question is is it a big no no that’s this has been done? The isolator is getting replaced when the parts are in. 


cheers guys

Emergency switching for such things as motors and machines where a danger is to be prevented or removed, used to need a single simple action, such as bashing a red coloured emergency stop button which would latch in the OFF position. This could be easily done with a hand.


I have noticed that Reg. 537.3.3.5 under the heading of DEVICES FOR EMERGENCY SWITCHING OFF, mentions handles and push buttons, coloured RED with a YELLOW background. So things appear to have changed, but not for the better I say.


Years ago if somebody's clothing was caught in a moving part and they were being dragged into the gears of a machine you could run up to a red mushroom head push button bash it and it would stop the machine. Now with a handle you have to undertake TWO actions. 1. Grab the handle and work out which way to rotate it, then 2. Rotate it to turn off the supply.

This may introduce a delay in stopping the machine or removing the danger in  a panic.


Edit. I have just found Reg. 465.3 which does require ONE SINGLE ACTION  ONLY  FOR EMERGENCY SWITCHING TO REMOVE AN UNEXPECTED DANGER.


537.3.3.3 prohibits the use of plugs and sockets for emergency switching off, so the spirit of "one simple single action" lives on.


Table 537.4 lists things that can be used as emergency switches.


Z.


 

MrJack96:

So an isolator isn’t for emergency switching as it requires two steps? 

B.S. 7671 has two different definitions for "Emergency stopping" and "Emergency switching".


The first is to stop an operation, the second is to to remove a danger as quickly as possible,  which may have occurred unexpectedly.


Z.

MrJack96:

So an isolator isn’t for emergency switching as it requires two steps? 

Table 537.4 allows a BS EN 60947-3 switch for emergency switching, but it is the normal 100 D.P. switch as found in many consumer units. I would not choose it as a first choice for an emergency stop switch for an industrial machine application. I would use the red mushroom head with a yellow background that once activated locks off as my first choice connected through suitable circuitry.


Z.

Commissioning a control system for a customer installed rig that had lots of 9" and 6" pipework with various valves and a massive pump fed by a large water  tank with a 20ft head when one of the stop ends blew off. A large fountain started driven by the pump. In a panic I pressed the emergency stop. A big mistake as it also cut power to the control system and while the pump stopped the head of water coming through a 9" pipe fed an only slightly smaller fountain. With the power off I could not operate the valves which could be operated manually but the only manual control leaver was on a valve under the fountain. So I got wet!


Shortly after the customer returned, he was not concerned and went away to get a three phase wet vacuum cleaner with a large 4ft high tank on it. I left him to sort out the pipework and drove home wet and wiser.

MrJack96:

So what is the key differences between emergency switching and emergency stoping?  

537.3.3


Devices for Emergency Switching Off


"Emergency switching off is an emergency operation intended to switch off the supply of electrical energy to all or part of an installation where the risk of electric shock or another risk of electrical origin is involved. "


Emergency Stopping is defined as "emergency switching designed to stop an operation." This would involve stopping a working machine or mechanical system such as a conveyor belt in a factory.


Z.