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How to De-Energize transformer?

1 Jaw Chuck (Chuck Evans)

1 Jaw Chuck (Chuck Evans)

Cast Iron
Joined
Jun 9, 2008
Location
Burbank, CA
Just got a 240 to 480 transformer.

Going to play with the taps to see which taps
will get me to 480 but the tag and instructions
say to de-energize to prevent a shock hazard.

I don't have any 480V light bulbs around (No 240V bulbs either)
so what would be a good way to accomplish this?

Chuck
Burbank, CA
 
Ahhhh, turn off the incoming power???

If you don't have a disconnect or breaker, you can use bolt cutters; but be sure to cut all conductors at once to keep the voltage balanced.

BTW, i have a bottle of blinker fluid, if anyone needs some.

Sent from my SM-N920V using Tapatalk
18b272d20fd347765239a66c9d4a7db5.jpg
 
Chuck Evans said:
Just got a 240 to 480 transformer.

Going to play with the taps to see which taps
will get me to 480 but the tag and instructions
say to de-energize to prevent a shock hazard.

I don't have any 480V light bulbs around (No 240V bulbs either)
so what would be a good way to accomplish this?

Chuck
Burbank, CA
Click to expand...
Anyone who asks a question like this has no business messing around with 480 volt circuits. Call an electrician!!!
 
Chuck Evans said:
Just got a 240 to 480 transformer.

Going to play with the taps to see which taps
will get me to 480 but the tag and instructions
say to de-energize to prevent a shock hazard.

I don't have any 480V light bulbs around (No 240V bulbs either)
so what would be a good way to accomplish this?

Chuck
Burbank, CA
Click to expand...

Disconnect the power source. That alone will usually eliminate any voltage. Some transformers have the ability to hold some small capacitance. Just attach a wire to ground ( transformer frame or box ) and then touch to the leads in any order. Every one has to learn sometime. I worked with a guy who was told the high voltage was turned off. He touched the bus, the electricity went in his hand and came out his feet. Melted his fingers together and took a scoop out of his arm full length. He laid there on the ground with his clothes smoking. Flown to Denver burn center for 2 months. Always test with a grounded wire.
 
Well, first off, make ABOSLUTELY POSITIVELY certain the transformer is not connected to anything. I would find it unlikely that much charge remains in the transformer after sitting unconnected for a few minutes, but if you want to be sure, just touch all the inputs/outputs to a known ground and you should be good. Sequence I would take would be to touch the outputs first, then the inputs next, in pairs at a time...you are trying to shunt any pent up magnetism held in the coils so output to output shunt, then input to input shunt.
 
Transformera dont store voltage. Theoretically it could have a dc voltage stored in the capacitance of the coils (to ground) but it is pretty small and will decay quickly. A very high quality special purpose transformer with polyethylene insulation could store a charge, but transformers are usually paper. And the 480v at 1nF perhaps, you would hardly feel it.

Still, you can have lethal voltages on lines that are disconnected due to induced voltage.

The warning is just boilerplate, if its not grounded its live.
 
"If it's not grounded, it's live".

Good advice.

A transformer which does not have any sort of capacitor associated with it should not be an issue. Few do (microwave ovens are an exception).

If no input power (positive disconnection), then the thing is not live.
 
I cant even reply to this one, take off your right shoe and drop the bloody thing on your right toe that will deactivate it....twice while saying "I will never play with electricity "
 
Ok guys, very funny.

My terminology was vague. I would not have the power connected in any way while
doing this, but concerned about residual energy in the transformer, much like
the energy stored in a capacitor.


HappyWyo, drcoelho, johansen,and JST understood me just fine and I appreciate their input.

Next question, do I have to turn off the engine to change the oil in my truck?

Chuck
Burbank, CA
 
Ferrite core transformers, as found in old CRT television sets have been known to store nasty residual charges after being de-energized (A.K.A. disconnected).

Silicon steel core transformers as found in building wiring installations? No. Just do a live-dead-live test with a CAT III or CAT IV meter like you should be doing anyways. Check for DC if you're concerned about it.

Granted medium voltage systems (a' la 4160V and 13800V) can deliver nasty shocks when switched off due to capacitive coupling picking up a few hundred volts from adjacent energized systems and/or natural phenomenon. That's where ground clusters come in to play.
 
Just a Sparky said:
Ferrite core transformers, as found in old CRT television sets have been known to store nasty residual charges after being de-energized (A.K.A. disconnected).
Click to expand...

I've working on a lot of CRT TV's and never found that. What you are probably referring to is the 2nd anode connection on the side of the picture tube. The picture tube is a giant capacitor and will store a nasty charge. They can recharge themselves even after being discharged. I always left a ground lead attached for several minutes.

Tom
 
If power is removed from a small transformer like 50KW it's de-energized. If it's in you shop lock-out tag-out will not be required but if not do it!!! If your worried use your 120VAC light bulb, it will make you feel better about touching the wires. If the bulb burns out you didn't disconnect power. Better to toast the bulb than yourself! If somehow there is any residual charge stored in the transformer the bulb will remove it with out so much as a blink!
I would assume you have a diagram to make wiring changes to the transformer, connection must be correct, you just can't play with taps.
 
120v bulb

Froneck,

I like that idea. Might even try using an old heating element I have, something to dissipate residual energy.

Good to see that some in this forum see the difference between
de-energizing and disconnecting.


Chuck
Burbank, CA
 
In general, transformers cannot store sufficient energy to pose a hazard. The energy stored is in the form of a magnetic field, which requires current to continue flowing for the field to be maintained. Disconnecting the current is sufficient to destroy the field within a few cycles (a fraction of a second).

Capacitors are the primary threat, whether as part of a VFD, power supply, or power factor correction.

The prove-test-prove that you do as part of your de-energisation should prove that these energy sources are empty, or alert you to their presence.

There are additional risks when dealing with voltages >1kV (neons, CRTs, and lines) that justify extra precautions (isolating and earthing, typically). A higher risk of inadvertent contact due to one line falling on another, much better insulators that allow stronger static charges to build and stay present for much longer, and higher available fault energies.

But in general there is no purpose in discharging something unless you have first verified that it is charged and needs discharging, and then verified that the discharging was successful and there is no residual voltage remaining.
 
Ground, ground, ground.
At times there will be big sparks so be ready for that due to an oops or something upstream.
In general a transformer can not hold power but who knows what else is in that circuit up or downside, connections or if it truly dead to ground.
Have encounter some that should be dead since no input power. They were not. Why? the back end.
The green wire is your buddy.
Bob
 
I agree that small transformers have no stored charge! And that to de-energize means to disconnect from input power, I said that!! However if someone is concerned there is some residual stored energy something like a light bulb will give them peace of mind. Also if for some reason it was not disconnected the low voltage light bulb will quickly burn out and better way than shorting the wires! Another error that is posted here is to ground the output! Grounding the output of a transformer will do nothing unless it's ground referenced! Buck Boost, Auto and those that have the secondary grounded will conduct to ground. But any that remain isolated grounding a secondary terminal will do nothing even if it's not de-energized!
 
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