NOW I understand why forum BP goes up at the of mention Isolation Transformers - Page 1
Forum section: electronics / beginners

author: watchmaker
author_rank: Unknown
timestamp: March 15, 2025, 10:39:17 am
content: I was looking to refresh my understanding of AM radio alignment (which I did).One of the many "resources" was a youtuber who was working on a live chassis, touching an open lead to a connection with his bare hand. He stated that since he was using an isolation xformer he was completely safe and could not get hurt.How much time would it have taken to use a lead with clips, even if he refused to turn off the radio between test conditions?I am not going to feed the beast or increase his internet standing by linking to it.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 15, 2025, 11:19:36 am
content: Some old AC/DC mains radios (and televisions) did not have a mains transformer. The risk for anyone working on one is the wiring could be reversed leaving the chassis connected to mains live. Normally these radios are fitted with a bakelite case which isolates the user from touching the chassis.The problem arises when repairing these radios and the often suggested "safe" solution is to use an isolating transformer and earthing the chassis, although a basic test with a neon screwdriver, or better still a non contact Voltage tester, to ascertain whether the chassis is "live" is probably what many repairers did.The old method of keeping one hand in your pocket when probing around high Voltages is a good idea, as is completely disconnecting the supply and using a "chicken stick" (grounding wire) to short out capacitors before touching any parts in the radio.300 Volts DC across your hands is no joke!SJ

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2025, 11:29:30 am
content: Yep, dangerous idiots abound on Youtube and WWW 'social' sites.A live chassis radio in North America implies a tube radio with a series heater chain and HT from rectified 115V mains. Put that on an isolating transformer, ground the 0V rail by hooking up a scope or deliberately grounding the chassis and you've now got a ground-referenced maybe 150V relatively high current DC rail eager and waiting to bite you. The isolating transformer blocks any upstream GFCI protection, so that wont save you either.We don't get to see the consequences for the unlucky ones as they have to be alive to upload the videos and posting self-harm videos is against Youtube's 'community guidelines' TOS. Most tube era electronics can cook you like a Presto Hotdogger, so work safe, respect the high voltage hazards and *DON'T* be the hotdog!

author: pcprogrammer
author_rank: Super Contributor
timestamp: March 15, 2025, 01:21:28 pm
content: As long as you know what you are doing you don't even need an isolation transformer. You can touch the live mains wire without getting a jolt, as long as you are not grounded in any way, and the voltage is not so high that capacitive coupling or air breakdown becomes an issue.Note that this is not an incentive to go and actually do this.It is just to indicate that the person from the video mentioned by watchmaker could have done the same without the isolation transformer without being harmed.I have worked on plenty mains installations and have come in contact with the live wire more than once. I'm still here though, despite some jolts being a bit nasty. I remember one job where the owner assured me that the fuse was removed. While I was working on the socket I felt a slight tingle, on which I made sure the fuse was no longer there. Touched the neutral with the live wire and after a nice spark I was sure it was safe to continue. My luck was that I was standing on a wooden floor.Another time it was my side cutter that got the beating. The supervisor on a job told me that the power on that circuit was cut. I had to mount a socket on a pillar somewhere. The wires were sticking out of the pipe and taped together. I needed to cut them to length, which resulted in a spark and a dent in my side cutters. At least after this the supply was definitely cut.These experiences thought me to always check for myself if the power is actually cut, and never trust someones word on it.The lesson is, think twice before doing once, and always check for yourself that it is safe. Like Ian.M mentioned, don't be the hotdog.

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 15, 2025, 01:36:52 pm
content: I wonder what is the potential between either leg of the isolation transformer output to ground?

author: johansen
author_rank: Super Contributor
timestamp: March 15, 2025, 07:17:32 pm
content: Quote from: BeBuLamar on March 15, 2025, 01:36:52 pmWhatever something will make it... Which can be part of the potential shock hazard.I cut the ground on my hakko soldering iron, and put a neon lamp and resistor in series.. so i can solder on live equipment

author: J-R
author_rank: Super Contributor
timestamp: March 17, 2025, 12:42:32 am
content: Pretty much every troubleshooting guide here on the forums involves checking the DC voltages while the device is operating. If an AC input terminal is within reach, then the best solution is to tape off the potential contact points before energizing and starting work, wear gloves and eye protection, as well as cover exposed arms and use rubber-soled shoes.But an isolation transformer (in various configurations) is just another tool in the toolbox. Do you know how to use your tools or no?So 100% this isn't really an isolation transformer issue, just a knowledge and safety one.