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| Do you guys use an isolation transformer for your lab/workbench? |
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| tooki:
--- Quote from: rstofer on February 02, 2023, 06:09:02 pm --- --- Quote from: tooki on February 01, 2023, 06:46:35 pm ---If you want to add safety to your bench, install a sensitive GFCI (more sensitive than the one your home may already have installed). --- End quote --- In the US, UL standard 943 covers GFCI devices and they trip at 4 to 6 mA of ground current. I don't think you will find anything more sensitive. These are used for individual branch circuits, we do not trip the panel main breaker with a GFCI nor do we use something like the UK RCD device. Typical ratings are for 125/250V up to 50A It is my understanding (from a quick read on Google) that UK RCD devices trip at 18..23 mA (30 mA max). --- End quote --- The US is a bit of an anomaly in this regard, in that it uses very low current GFCIs. Elsewhere in the world, 30mA is typical. At my previous job (vocational training center) here in Switzerland, they have 10mA GFCIs protecting each workbench, both so they trip sooner if there’s a fault, and so that it won’t take out the entire lab if there is. |
| Infraviolet:
I've heard they can be useful for some forms of high (mains) voltage work, haven't really looked in to the accuracy of such rumours or reasons behind them, but for lower voltage stuff I'd expect they could be a practical menace. Lets put it this way, the things you're designing are probably going to end up being battery powered or run from wall wart supplies, either being imperfect. If you get used to producing designs in a "perfected" environment where everything is isolated from the ground to avoid some particular sort of noise then things you design might then not work in the real world where that noise is present and the isolation isn't. That said, a lot of low voltage stuff will be isolated anyway, low voltage wall warts are floating and ungrounded relative to mains. And bench power supplies often have a phsyically grounded pin socket on them, but unless you use it the supplies will be floating relative to mains. |
| timeandfrequency:
Hi bigfoot22, tooki's first post sincerely provides you with good advice. When I have to probe into a device (DUT) with mains/live exposed parts (like boards with in situ SMPS), I do not use an isolation transformer (even if I've got one). My DUT is powered via a 10mA RCD/GFCI (trips at about 6-8 mA) and the sole allowed TE are first tier (bench) multimeters with IEC1010 compliant accessories, and a truly isolated oscilloscope (Scopemeter) with adequate fully isolated probes. You may also check out these test leads with selectable safety category and double-insulated silicon wire. Same stuff but with banana connexion. Another set from Pomona. If the DUT has a metallic enclosure, I always use a strong alligator clip to make an additional link from chassis to earth. Even if it's not practical, wearing class 00 or class 0 insulated gloves provides an additional level of safety. |
| tautech:
--- Quote from: timeandfrequency on February 03, 2023, 12:44:19 am ---Hi bigfoot22, tooki's first post sincerely provides you with good advice. When I have to probe into a device (DUT) with mains/live exposed parts (like boards with in situ SMPS), I do not use an isolation transformer (even if I've got one). My DUT is powered via a 10mA RCD/GFCI and the sole allowed TE are first tier (bench) multimeters, and a truly isolated oscilloscope (Scopemeter) with adequate fully isolated probes. If the DUT has a metallic enclosure, I always use a strong alligator clip to make an additional link from chassis to earth. Even if it's not practical, wearing /]class 00 or class 0 insulated gloves provides an additional level of safety. --- End quote --- Gloves implies 2 hands are used which for mains breaks the good old rule of keeping one hand in the back pocket when working on mains. |
| nctnico:
Has anyone mentioned not to wear jewelry? |
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