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How to De-Energize transformer?

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
 

tnrcboatracer

Plastic
Joined
Aug 7, 2021
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
 

Superbowl

Cast Iron
Joined
Feb 12, 2020
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
Anyone who asks a question like this has no business messing around with 480 volt circuits. Call an electrician!!!
 

HappyWyo

Aluminum
Joined
Nov 30, 2019
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

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.
 

drcoelho

Stainless
Joined
Feb 19, 2017
Location
Los Altos
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.
 

johansen

Stainless
Joined
Aug 16, 2014
Location
bainbridge island
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.
 

thermite

Diamond
Anyone who asks a question like this has no business messing around with 480 volt circuits. Call an electrician!!!

Phht.. or maybe just a "housewife"?

A woman can de-energize the whole freakin' UNIVERSE if she takes it up as a mission.

Or simply turn OFF a switch .... for a guy who can't figure out the obvious?

:(

If you want to "turn-off" a transformer instead of "de-energizing" it?

- tell it it it acts just like its Mother, has bad breath, smelly feet and rotten crotch, farts, snores in its sleep, is lousy in bed..."etc.".
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
"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.
 

Phil in Montana

Stainless
Joined
Jul 31, 2007
Location
Missoula Mt
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 "
 

thermite

Diamond
It's not safe to de-energize a transformer without first disconnecting the Kanutin Valve for at least five minutes in order to permit the excess electrons to escape.

Don't you have to beat on pots and pans or flog the housing with a wet noodle to scare them out?

I'm leery of the universal applicability of Montana Phil's boot trick.

Not everyone has equally terrifying toe-jams and foot-munge.

:D
 

Chuck Evans

Cast Iron
Joined
Jun 9, 2008
Location
Burbank, CA
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
 

thermite

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

Chuck
Burbank, CA

Actually not. But unless downtime is horribly costly, you might not like the cost of the alternative.

:)

Major SigC telco sites where no commercial power was anywhere near, ran off a trio of Diesels.

Underfloor plumbing ran their lube oil to coolers, heaters, storage tankage annnnnd..... powered DeLaval centrifugal filters.

IOW, their oil was being "conditioned" as they ran, 24 X 7.

Eventually, old oil, cleaned but degrading, was routed out to recovery tankage whilst fresh, full-spec stable, oil was routed in.

Not that they were "never" taken off-line. One, alone, could run the critical stuff, two were mild overkill.

So "the plan" had built-in redundancy / fall-back.. but still..

Oil changes were NOT cause for downtime.

One might surmise that recip powered seagoing merchant vessels are another probable application of similar lube systems, but I wasn't tasked with writing the maintenance manuals for those, so haven't looked nor care enough to do so now.

Mind.. hard to see ANY economic upside for a "truck" vs the common oil change time budget..

Possible exception a "Belarus" mobile-mountain of a valuable ore hauler?
 

Just a Sparky

Hot Rolled
Joined
May 2, 2020
Location
Minnesota
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.
 

TDegenhart

Diamond
Joined
Mar 26, 2011
Location
Geneva Illinois USA
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).

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
 

Froneck

Titanium
Joined
Dec 4, 2010
Location
McClure, PA 17059
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.
 

Chuck Evans

Cast Iron
Joined
Jun 9, 2008
Location
Burbank, CA
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
 

SomeoneSomewhere

Hot Rolled
Joined
Dec 24, 2019
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.
 








 
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