Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Checking short!!!

Status
Not open for further replies.

Badar

New Member
sometime earlier i had a short circuit and got shocked through my air cooler.(Here air cooler is used as a good alternative of A.C which consists of a metallic box, Fan motor and a pump motor wich pumps water upwards and it passes thorugh special walls of the box and thus produces cooling.I've no idea that in other countries it is used or not so i gave this explanation). tested it with a tester and it showed the presence of short cicuit.after removing the short crcuit IN THE PUMP MOTOR the tester showed surprisingly positve result but touching it didn't give any shock while i was fully grounded.
I took it to a technician who told me that tester bulb will be on even there is no short circuit for any electrical device(i checked it with motors and it verifed the above statement.) if you have not grounded the device well.
If you have grounded a device and the tester shows the presenece of the current then it is shorted.
I wanna know what the hell is going in there.
 
That is an evaporative cooler. They work pretty well in dry conditions - low humidity.

It's kind of hard to know how to answer, as you do not say what you touched to get the shock, and how you applied the tester. I'm pretty ignorant of power distribution in Pakistan, too.
 
It's kind of hard to know how to answer, as you do not say what you touched to get the shock, and how you applied the tester

i touched the metallic cover of the motor that before removing the short gave me a terrible shock but after removing it tester even showed the light but i was not shocked.

Now the tester i used is simply a small screw driver.Just make it's contact with a conductor and touch its head.A bulb will lit up showing the presence of current if there is any.

I'm pretty ignorant of power distribution in Pakistan, too.

It is 240V AC 50-60Hz and 35-40 Amp for a normal home user.And this cooler draws 2-3 A current.
 
Just guesswork as I don't know the arrangement of components in the cooler..

If your water is "hard" - contains minerals - then thre might be a buildup of evaporated mineral deposits that bridge between a hot terminal and the fibre that the water flows into. The leakage may not be enough for a shock, but might let your tester light up. It could happen around the fan as well as the pump, or even atound the switches.
 
For the voltage test, i take it that you used a neon screwdriver test pencil.
These are only indicative and i would not rely on a true reading.
As the service technician told you as well, these can lit up even when the power switch is off and just pick up inductance to light up the internal neon.
Your finger will act as the return patch for the few µAmps required to light the neon.
Neons will generally light up at voltages above 60 to 70 Volts ( striking voltage).
In series is a high megaohm resistor to limit the current flow.
On dc application only one electrode of the neon will light up.

I would use a duspol for a course voltage measurement between phase and neutral and earth, and to check for correct polarity from phase to an independant earth.
This imposes a load of about 100 mA on the circuit under test, by means of a coil and plunger with a flag for approx volts reading.

A DMM can be used for an accurate voltage measurement. It does sometimes pick up a voltage too because of its high internal impedance.
One lead needs to be attached to the neutral or earth, the other one to test for voltage on the terminals.

It is good and safe practise to test your meter before and after your tests on a known live source to check if the meter works.

I'm not sure what system you have in your country but it is important that the polarity at your power socket is correct.
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top