safe isolation procedure

[andy]

college lecturers no nothin... again.

basically, i say:

test circuit is live
switch off
check dead
test tester on known supply/proving unit
lock supply off/keep key

they say this is wrong and it must be:

switch off
test tester on known supply
check circuit is dead
test tester on known supply
lock off

for some reason, they think its wrong to test the circuit to be isolated before starting saying you must not. now, what happens if its fed from DB 1 and has tripped. you 'think' its fed form DB 2 and switch something at the other side of building off and lock off. someone notices something off and investigates. they go to DB1 and notice something off, so switch on. you then get a shock, since you locked off DB 2. apparantly, this will never happen.

so, which, if any, would you say is right?

 

[JohnD]

I see that with your method, if it doesnt work when you've finished, you knew it was able to be energised before you started.

With their method, there might be a pre-existing fault you didn't know about.

 

[plugwash]

your method certainly sounds better to me.

if you wan't to know what to put in an exam either follow your lecturers or contact the exam board. for the real world ignore thier BS

 

[scousespark]

It is recommended to initially test on a separate circuit, as this will not be affected by what you are doing.

The sequence is
1 Test on a live circuit
2 Identify and locate the circuit to be worked on.
If this is dead investigate why.
3 Switch off and test. If still live investigate.
If it is now dead retest the original circuit.

Then attach labels and lock off the protective device.

 

[JohnD]

ideal, Paul.

 

[andy]

thx for the help/suggestions

i know the only thing with my way is it wont work if circuit to be worked on is already dead, but what was being isolated was already live.

id rather flick the breaker on/off a few times to make sure its definatly that breaker than follow whatever the college says, which is fine in the workshop, since they know where its fed from. but were all well aware its harder in real life, and can be worse where there are multiple boards.

colleges/exam boards dont know what there doin these days, last exam i had, i got a question and the answer wasnt even there! (was multiple choice)

 

[scousespark]

Apparently the confusion comes from Brian Scaddan retiring and the exams now being written by a group of people. Lads on site have come back ater exams having seen multiple-choice questions where there are more 1 correct answer. Of course only 1 is acceptable.

Isolation is not something that has changed and my answer comes straight from the texts used for 2991 (old style but still relevant I believe).

 

[andy]

Apparently the confusion comes from Brian Scaddan retiring and the exams now being written by a group of people. Lads on site have come back ater exams having seen multiple-choice questions where there are more 1 correct answer. Of course only 1 is acceptable.

Isolation is not something that has changed and my answer comes straight from the texts used for 2991 (old style but still relevant I believe).

yea, popular one is what should be used for 3 phase isolation. always have TP-N isolator and 4 pole isolator and 2 others for answers. some lecturers say go for 4 pole isolator and some say TP-N...

 

[Spark123]

The reason for testing the instrument before and after checking for voltage is to prove the intrument has not developed a fault and failed in a dangerous condition. I have sent you some additional info to your email address andy.

 

[andy]

The reason for testing the instrument before and after checking for voltage is to prove the intrument has not developed a fault and failed in a dangerous condition. I have sent you some additional info to your email address andy.

im aware of why its tested before/after etc (after all, it could fail just after your first test and could leave a circuit 'dead' when it is infact live). which is what my way of testing does, and so does the way the college says. its mainly the testing live of circuit to be isolated that they say it wrong and should not be done

and thanx for the email