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| Do you guys use an isolation transformer for your lab/workbench? |
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| nightfire:
I have some diff probes on my shopping list, but even micsig are 200+ Euros here in germany- do you have any hints where to buy used gear that is not worn down? Regarding RCD: Yes, they are very useful, so they should be included in every setup on a work bench, but in case you really need then and they do the things they are intended to do, you also get zapped- at least a little bit. Therefore I would regard them as one of the multiple pieces you (or the one setting up a bench) should consider as part of safety measures. Which means, that the person doing the setup is responsible for this, and has to think beforehand if a safety/isolation transformer in front of the DUT will and can improve the safety, or simply be a cause of different issues. In the same league I would sort: - gloves - isolated bench - isolated tools - diff probes - lightbulb inrush current limiter - RCDs (including type B for pulsed or DC currents) |
| Electro Detective:
Whatever 'isolation' strategy used, don't forget protective eyewear, it's one - oops! arghhh!!! ****! - :o you can't easily walk away from How many times do people stick their face into a project or repair :-/O filled with with pop-able capacitive parts and solder fumes etc FWIW, there is NO way I would rely on one 'worked fine yesterday..' RCD or GFCI to bail me out of a situation involving voltage surfing especially if not externally trip tested immediately beforehand rather than the onboard TEST switch Have come across a few faulty mains switchboard units that tripped fine with the onboard TEST monthly 'good luck' switch, that NO ONE on this Earth ever tests, remembers, or even knows about.. but same RCD big fail when pumped externally or at the domestic power point receptacle with 30ma and beyond. Another factor many may have not considered is using smaller, fast fuse input and delayed fuse output, isolation transformers, that just meet the current draw requirements of the DUT This way you at least are not copping the full output of the street transformer through the shorted gear or shorted YOU! i.e. if most of the powered DUTs you work with only pull in under 1 amp, why have that 10 or 20 amp isolation transformer monster powering it, unless there is DUT inrush surges to consider? Plus the junior sized one hums and buzzes less, easy to move about and find parking space, and may be all you can afford at this time. or if you can afford or have both, bring out the big one when needed Either way any of the above may be 50/50 coin toss 'luck' unless you read up and understand 'isolation' in all it's forms and RCD/GFCI pros, cons etc You only have to spend that time learning and testing ONCE, verifying what you think you now know safely, and get on with it, or toss coins for the rest of your long (or cut short) electo-life using and surfing suspect voltages Personally I'd rather swap out fuses, reset breakers and RCDs, and work from a a tested working isolation transformer, and avoid the local street power transformer :box: trying to supply all it's current into the gear or me :phew: |
| nightfire:
To alleviate the fear of grilled by the street transformer: It only can do 230V in case of a short circuit in the DUT. Voltage in case of a real low impedance short also tends to drop a little, so basically the most annoying part of it would be particles moving away from the DUT with high velocity and/or temperature. This is also limited a bit by the impedance of the cable from the DUT to mains, which limits the short circuit current a bit. Rule of thumb: After 3 meter of 1.5mm², there can be onyl around 2000A- in reality, a standard outlet brings between 200A and 400A short circuit current- here the type of fuse you use would be important, as those clear glass fuses can break under this stress. So ceramic fuses are strongly recommended if you want to protect against shorts like this. Also a reasonable fuse limits the short circuit current a bit, so that part of the (prospective) energy goes into melting the metal inside of the fuse. Depending on the isolation transformer, you can change the fuse, so exchanging the mostly slow-blow fuses to faster ones or with lower rated current is also a way of getting them a bit more sensitive. |
| tautech:
--- Quote from: bigfoot22 on February 05, 2023, 03:45:39 am ---Think what I might do is build a lamp socket with a bypass switch and mount it up on the wall and keep a few incandescent bulbs laying around for current limiting, 40w, 60w, 100w, 150w flood. Use that for powering DUTs when needed otherwise use the bypass switch normally. --- End quote --- Too complex, just KISS. That was a similar plan to what I had with an always ON DBT through the bulb and flick the switch the other way to bypass the DBT and supply full power to the DUT. I just used that ^ setup for a very short time then became properly aware of the hazzard it was and changed the switching to just a series power switch to properly kill the power and not the user ! That's not to say you can't build something lots lots safer with dual switches or a 3 position switch but unless you're using it all day IMHO it's better to KISS. Below is the DBT I knocked together with scrap from around the bench all those years ago and it's remained unchanged since the mods to make it safer. |
| nctnico:
--- Quote from: AVGresponding on February 03, 2023, 02:19:15 pm --- --- Quote from: Electro Detective on February 03, 2023, 10:35:35 am --- --- Quote from: tautech on February 03, 2023, 01:58:10 am --- --- Quote from: timeandfrequency on February 03, 2023, 01:45:11 am ---I couldn't find any seller that only sells one glove. --- End quote --- :-DD --- End quote --- Bob has you covered: :-+ www.bobthewelder.com.au/products/xt-left-handed-welding-gloves-green-long --------------------- FWIW folks: 30ma RCDs rarely trip at 30ma Anywhere from 15 to 28ma is what usually happens, and a good unit will have about 2 to 3ma repeatability i.e. test the suckers properly before trusting your life and gear with them, better still, use two RCDs piggy backed. One of the two 'may' trip 'faster', or both will work if the trip current approaches zap city. But they won't do you much good with an electrical fault or short in the chain, so..FUSE UP, just past the DUTs current rating, and you won't need an imitation rabbits foot or garlic necklace :phew: --- End quote --- Yes, unlike fuse or circuit breaker ratings, the RCD trip current is the maximum allowable for it to meet its standards. --- End quote --- Did'nt read the Eaton article but fully I doubt this statement is entirely true. There has to be a minimum as well so you have a defined amount of allowed leakage current. Otherwise it wouldn't make sense to sell unsensitive (300mA) and super sensitive (5mA) GFIs / RCDs |
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