ACA : Motor Circuit/IR

[catdog]

Hi Guys,

Got my ACA (Approved test) soon and been reading up a lot about what is involved. One thing not too hot on is the motor circuit as I don't work with motors much.

Wondering if anyone can give me any pointers on what I might need to test for the motor circuit- presume for IR, isolate motor and control circuit then test from the supply side and then also test back from Load side also?

Also for the other IR tests, will I have to test between L and N? (at present on an EICR I would link L to N and test between them to E). If this is the case, I would need to remove lamps or any other Loads on the circuits (perhaps ballasts?)

Thanks in advance,

 

[PEG]

Hi,there are prescribed test methods,in most of the decent guides (Kitcher,Scanlon,etc) but these will be for specific types of motor.

You will have to know the type of motor first,and any other factors which would affect testing,such as age,isolation of both electric and mechanical connections,and also any parts of it's design,such as centrifugal switching,capacitors,etc.

A general understanding of these variables,would be required,but dedicated testing of such items,would be a separate and detailed skill-set.

I tested a smallish AC motor yesterday,which required varied methods,to establish that the temperature cut-out,in the windings,had been disconnected and bridged out,masking a fault in said windings,causing excessive heat build up.
One set of tests,exterior to that motor,would not have revealed the full details.

Have you been informed of the possible test scenario,at this exam?

 

[westward10]

Let's hope it is a standard DOL polyhase motor without too many peripherals so a test up to the contactor then a test from the switched side.
I do the same for IR testing on EICRs but you need to see on the day the scope required, I doubt it will be a huge task to remove loads and any sensitive components.

 

[catdog]

PEG, Im hoping that it won't be quite as in depth as that or Im screwed ha!

Think its really concerned with the motor circuit rather than the windings so just need to make sure motor is disconnected. Trying to swat up as much before as I know under test conditions my logic goes out the window!

 

[PEG]

Right,so if we are talking SP and circuit only,the motor can be ignored.
The standard tests can be carried out.up to any switching or contactor,the need for disconnection assessed depending on type.
The circuit from there,can be also tested,with regard to the motor being disconnected,dependent on requirements.

Usually,any examiner will expect to see normal attention given to safe working,isolation,etc,then,just run through your standard tests,up to any "ends" of circuits,then take the next section separately.
There are situations where this may be bypassed,where the motor can be disconnected,and the contactor operated manually,to include the motor wiring.

This can have the benefit of including the contactor,in the testing procedure.

Do not build up the exam,in your mind,until it is a colossal,icy mountain....it is a simple series of events,which you can do at your normal pace,which would be ample time to carry them out correctly.

Many moons back,during my 2391 practical exam,the examiner announced that an assessor would be shadowing him,to check for conformity...
Having grown up with dealing men and travellers,expressing what is on my mind,has never been a problem...but...it is what it is

Listen politely,then satisfy yourself with what you are doing,don't try to impress anyone else.

It will be a taste of things to come,where you are trying to get to the bottom of a problem in a busy factory,and you are being coursed by the owner,his spark who could not fix the problem,and some hanger-on,who asks "have you sussed it,yet?",every 2 minutes...

 

[Wilko]

If it's a 3 phase motor - check the phase rotation is correct

 

[catdog]

thanks for comments.

I'll let you know how i get on!

 

[Pete999]

If it's a 3 phase motor - check the phase rotation is correct

If the examiner is a pedant like me don't call it phase rotation, the new buzzword is phase sequence.

 

[catdog]

ha I'll keep that in mind Pete! while you mate being a pedant.....any suggestion on testing a fluorescent fitting between line to neutral (aware I could test L/N to earth but for the ACA I think N-L is required). is it necessary to remove the starter and lamp? (although will 500v still reach the ballast?)

tia

 

[Lucien Nunes]

What happens will depend on what kind of ballast. Electronic ballasts must not be subjected to L-N IR test, you would have to disconnect in the fitting. Switch-start with choke ballast, pulling the tube will also isolate the starter but the ballast and parallel PFC capacitor will still be in circuit. If that has a bleeder resistor then it will spoil an L-N test so again would have to be disconnected or the fuse removed if fitted. Google fluorescent circuits and see how they are wired internally.

 

[Pete999]

ha I'll keep that in mind Pete! while you mate being a pedant.....any suggestion on testing a fluorescent fitting between line to neutral (aware I could test L/N to earth but for the ACA I think N-L is required). is it necessary to remove the starter and lamp? (although will 500v still reach the ballast?)

tia

As you suggest L&N to earth, diss the cable feeding the fitting use some form of connectors on the cable end, don't have any experience of ACA Are you allowed access to the trainee area, might get some more up to date help in there, ask one of the Staff members for access.
file:///C:/Users/Pete/Desktop/Trainee%20Access.htm

 

[catdog]

Pete think it depends on which examiner i get but I think if i explain to the examiner my reasons might get some hints as seems if you show you know what you're doing it's ok.. will see....

 

[Pete999]

Pete think it depends on which examiner i get but I think if i explain to the examiner my reasons might get some hints as seems if you show you know what you're doing it's ok.. will see....

OK mate good luck anyway

 

[catdog]

Just found out today passed my ACA so thanks for all the advice guys!

Would say the testing side was less complex than I thought, and although the motors were connected, was more the motor circuit and control circuit that was of interest. The examiner was a good guy and even though I made a few mistakes due to nerves, he seemed confident I knew what I was talking about. One thing would advise would be to audibly explain what you are doing for the testing-that way they know you know your stuff and also it prob will help you to remember diff things too.

 

[DPG]

Nice one!