Safe isolation of rotary isolator when no incoming voltage present.

[tomodo]

Hi all, trying to work out the best way for proving safe isolation of a motor.

Motor is fed from a contactor inside control panel, it then passes through a local isolator and then to the motor, the isolator has auxillary contacts so that when it is in the off position the contactor will not pull in and supply power.

How can i prove that no voltage will flow through the isolator that is locked off when there is none incoming into it?

Thanks

 

[westward10]

If the isolator is off and you have proved the outgoing conductors are dead how will voltage pass through it?

 

[mainline]

If the isolator is off and you have proved the outgoing conductors are dead how will voltage pass through it?

I think he’s saying that he needs to ensure that the isolation switch is actually working as the supply could be energised.

If that’s the case then some resistive measurements across the isolation switch may help.

 

[tomodo]

Thats all i could think of, it would mean checking across each pole for a minimum of 1Mega ohm resistance when it is in the off position? Is that the only real option?

 

[mainline]

Thats all i could think of, it would mean checking across each pole for a minimum of 1Mega ohm resistance when it is in the off position? Is that the only real option?

You could link out the aux forcing the contactor on then check the supply in and out of the isolation switch.

 

[Rockingit]

You isolate and test no volts, re-energise and test +ve volts, isolate and prove no volts again. Lock-off prior to working on the motor.

 

[James]

If you have concerns that the isolator may be faulty, take the outgoing wires out of it and leave them in wago's until the work is complete.

 

[mainline]

You isolate and test no volts, re-energise and test +ve volts, isolate and prove no volts again. Lock-off prior to working on the motor.

That still wouldn't prove that the isolator switch actually works, it only proves that the aux one is disconnecting the contactor.

 

[Rockingit]

That still wouldn't prove that the isolator switch actually works, it only proves that the aux one is disconnecting the contactor.

That wasn't the question, though. The question was how to prove safe isolation of the cct.

 

[mainline]

That wasn't the question, though. The question was how to prove safe isolation of the cct.

Yes, safe isolation of a contactor controlled isolator.

I doubt that the contactor used complies with Safe isolation, so the isolator switch itself has to be proved to work.

This was clarified by the OP #4

 

[mickegh]

You isolate and test no volts, re-energise and test +ve volts, isolate and prove no volts again. Lock-off prior to working on the motor.

Proving no volts is a question .

In theory you can't with a 2-wire tester

 

[mainline]

If you have concerns that the isolator may be faulty, take the outgoing wires out of it and leave them in wago's until the work is complete.

I am playing devil's advocate a bit as in reality you would as said already by @rocket check supply in supply out and lock it off as the OP doesn’t need to have Safe isolation just isolation for maintenance.

But in theory, you could leave it unsafe for someone else.

 

[mainline]

Proving no volts is a question .

In theory you can't with a 2-wire tester

I can’t see why not using a decent one, along with some form of stable reference.

 

[mickegh]

I can’t see why not using a decent one, along with some form of stable reference.

Fair point

You could then argue you need to prove the reference

 

[mainline]

Fair point

You could then argue you need to prove the reference

The reference would be the checkbox.

 

[Avo Mk8]

Fair point

You could then argue you need to prove the reference

Which you do by having the proving unit/equipment 'calibrated' (ie checked against its spec.) every so often, (generally by a calibration laboratory), the period being determined from an assessment that considers service conditions, usage, previous pre-cal results, and manufacturers recommendations.
This is standard procedure in industry, particularly for companies certified to quality standards, and they get independently audited to check they are doing it satisfactorily!

As per mainline - must cut down on my words

 

[mickegh]

Which you do by having the proving unit/equipment 'calibrated' (ie checked against its spec.) every so often, (generally by a calibration laboratory), the period being determined from an assessment that considers service conditions, usage, previous pre-cal results, and manufacturers recommendations.
This is standard procedure in industry, particularly for companies certified to quality standards, and they get independently audited to check they are doing it satisfactorily!

As per mainline - must cut down on my words

I was referring to the 2-wire testing which assumes there would be a valid reference point if testing between an energized line conductor and some other point

 

[Avo Mk8]

I was referring to the 2-wire testing which assumes there would be a valid reference point if testing between an energized line conductor and some other point

For this particular question of safe isolation in a working environment, is there philosophical difficulty in assuming the installation PE would be a valid reference?

 

[UNG]

I suppose there is an argument here for having the holy grail for some in your toolbox which is the neon screwdriver alternatively there is one of these Socket & See EPF-PRO single point testers which I have found to be very useful over the few years I've owned it

 

[James]

I suppose there is an argument here for having the holy grail for some in your toolbox which is the neon screwdriver alternatively there is one of these Socket & See EPF-PRO single point testers which I have found to be very useful over the few years I've owned it

I do keep in my work trouser pocket one of the much loved/hated “volt stick”
Devices.
As said before, NOT to be used to prove anything is live or dead, but a quick wave over a bunch of cables sometimes will make you recheck all possible sources of supply before cutting or disconnecting anything.

 

[mickegh]

Ya I looked at those Socket and See onetime . I think the threshold was 50V AC

My martindale single-point test is > 100V AC on the 2-wire voltage tester

 

[mainline]

View: https://www.youtube.com/watch?v=glsg2HpWyok