Electronics > Beginners

Mains Isolation Transformer

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furnacemike:
I am kind of new to electronics work, and I am looking for a suggestion for a reasonable priced mains isolation transformer that I can use to safely work on hot equipment for the purpose of troubleshooting. Basically I want peace of mind for safety. I don't need a top of the line model, just something basic for beginners. I'm located in the USA.
Thanks!
Mike

Ian.M:
Since the advent of cheap reliable GFCIs (RCDs), in almost all circumstances an isolation transformer *DECREASES* safety for a repair technician, as they prevent upstream or downstream GFCIs tripping if the technician accidentally becomes part of the circuit.

If that's not clear enough, without an isolation transformer, the GFCI in the feed to your bench* will trip if you touch a 'hot' connection.  You'll get a shock, but the GFCI cuts power quickly enough to reduce the risk of death or permanent injury to near zero.   With an isolation transformer, the GFCI cant trip, the shock continues till you die or break free and meanwhile the current is cooking you like a hotdog in a Presto Hotdogger!

Additionally, most people get careless as they *think* it provides protection, which it will do as long as you only make contact with ONE point in the D.U.T (device under test), but that protection vanishes as soon as you make any connection from the D.U.T to anything ground-referenced, (including oscilloscopes,  signal generators, outdoor antennas etc.) so it increases the risk of you getting electrocuted.

There are still uses for an isolation transformer on the test and repair bench, but providing 'SAFETY' is *NOT* one of them.

* If your bench isn't on a GFCI protected circuit, or fed through a plug-in GFCI, you are a suicidal idiot.  Even if you don't care about your own life, get one for the sake of your family or the first responders who'd otherwise have to deal with your electrocuted corpse!

bob91343:
Isolation transformers are expensive; I think they start at around $100.  However you can cobble one up with a pair of like transformers.  Just connect them back to back and you will get nearly the same output voltage as you put in.

Having said that, you didn't mention how much power you want to provide.  I do have an extra one if you want to PM me I can tell you about it.  However, these things are heavy and cost as much to ship as they are worth.  I am in Los Angeles.

golden_labels:

--- Quote from: Ian.M on May 16, 2022, 03:56:40 am ---Since the advent of cheap reliable GFCIs (RCDs), in almost all circumstances an isolation transformer *DECREASES* safety for a repair technician, as they prevent upstream or downstream GFCIs tripping if the technician accidentally becomes part of the circuit.
--- End quote ---
I am not arguing about which solution is safer, as that is a statistical statement and I have no data to support any of the three options, but above sentence looks a bit weird to me. How is a GFCI providing protection if the operator become a part of the circuit? Current on both lines remains balanced, so what is GFCI detecting in that scenario. Was that just poor wording or am I missing some risk?

fourtytwo42:

--- Quote from: Ian.M on May 16, 2022, 03:56:40 am ---Since the advent of cheap reliable GFCIs (RCDs), in almost all circumstances an isolation transformer *DECREASES* safety for a repair technician, as they prevent upstream or downstream GFCIs tripping if the technician accidentally becomes part of the circuit.

--- End quote ---

So why do we still have stringent primary to secondary circuit insulation standards for consumer equipment!

I think your statement is both misleading and dangerous particularly in a beginners section.

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