Using a 240vac to 12vac transformer to test for shorts?

[i-didnt-start-the-fire]

Shorting devices I want to test
1. Heat Gun
2. AC Electric Motor (not sure if it is the motor so just want to test that directly)

Hi There

The two above devices trip a circuit breaker when I plug them into a wall.

I was wondering if it would be feasible to use a 240vac to 12vac transformer to power the devices to do a bit of testing etc, making it safer and to keep the circuit breaker from stopping the power getting cut off?

[eccerr0r]

Re: Using a 240vac to 12vac transformer to test for shorts?

How many watt heat gun is it? Typically they're around 1500W so they should draw 6.25A and resistance should be around 38Ω which should be easily readable with a 200.0Ω Full Scale 3½ digit DMM where in 120V land like in the USA, you'd need a 4½ digit DMM 200.00Ω FS or 3½ digit 20.00Ω FS to get reasonable data without needing to power it as resistances are less than 10Ω and the number of significant digits becomes more critical to measure precisely.

How many watt breaker is it anyway, could that breaker be bad or will the devices trip different breakers?

[petehall347]

Re: Using a 240vac to 12vac transformer to test for shorts?

not much to go wrong in either that you cant find with your dmm . if the trip is suspect try a new one or plug in to a different circuit . i dont see any need for any more than that . a regular series light bulb will let you test things safer than a transformer if you want to go that deep into it .

[budm]

Re: Using a 240vac to 12vac transformer to test for shorts?

Is the breaker tripped due to over current or due to leakage current?

[i-didnt-start-the-fire]

Re: Using a 240vac to 12vac transformer to test for shorts?

OK, Well done all.

Took the motor into the garage and it didn't trip the circuit breaker so will sort that.

Opening the heat gun further to measure resistance as I couldn't figure out the wiring. There is 5 going into to where the element is, for the different temperatures I guess. One of those had broken at the connector. That is working fine now I've reconnected it. Although 1 out of four settings is not working so will look further.

I have a 75 watt flood light bulb for a load protection device but that lights up with most things so I was to try more in series. I'm not sure if they are the right bulbs to use. I think it is incandescent.

My Transformer idea came from an isolation transformer. I connected two of the same transformers... 240v->12v to 12v->240v, to in theory make my own.
It worked from a voltage perspective but I was worried if something tried to draw too much current that something scary might happen.

So thought I might be able to test with 12v ac going through the motor and heat gun without causing too many issues????

[i-didnt-start-the-fire]

Re: Using a 240vac to 12vac transformer to test for shorts?

Is the breaker tripped due to over current or due to leakage current?

That I don't know sorry. But my new answer I just posted may answer that?
i.e. The motor works on another separate power board without tripping.
I think the heat gun had a wire shorting but I just fixed that.

[eccerr0r]

Re: Using a 240vac to 12vac transformer to test for shorts?

Isolation transformer will not help as once you connect the load, the load will be presented to the primary and you're back into step 1.

These loads appear to be fairly substantial, meaning the DBT won't work unless you had a bulb of even higher wattage than you heat gun; and the isolation transformer would need to be really hefty to deal with the wattage transferred from input to output.

If you have an RCD/GFCI breaker, yes, make sure you're not tripping due to leakage current to GND or something. Usually you won't see a huge spark if you trip GFCI - you'd probably see a large spark if you trip a breaker with a 'short' type overload.