Thinking Safety with Hobby Electronics

JasonP

So as I head down the electronics rabbit hole, I've been thinking a lot about safety. For a lot of circuits a simple low amperage adjustable DC supply is good enough, but for a lot of the stuff I'm looking to do I'm going to be making my own PSUs. Not wanting to expire from a freak accident when dealing with mains voltages, I've done some research and I'm wondering what people think. Here is my plan right now:

I picked up a GFCI IEC to IEC circuit, and I'll use that to provide the mains line. Then I'll build a moderately sized board with two sets of barrier strips. One for the live mains, and one for the output of transformers on that board. Between the mains line and the incoming barrier strip I'll place a standard 5x20 fuse receptacle (likely fill it with fast blow 1A most of the time). I figure this will get me to the lower transformed voltage on the output barrier strip which I can feed to prototype/breadboard etc.

Obviously, safety is behavior first, but I figured extra steps can't hurt. Thoughts?

Tom_S

Sounds like you have a good plan. Will you be able to calculate your inrush currents? I never fused secondaries, but I was working mostly with tube gear and didn't even know that was an option when I started out. Never been bit by one of my projects, but I've always been overly cautious. They always said - one hand in your back pocket. I did learn the hard way that tiny photo flash caps in point & shoot cameras will sting you, even after being dormant for a while!

dcibel

When I was in school we used a very simple box as 120V protection device. Just a 1A fast blow fluse and a switch and a light, with banana plugs on the end. This provided a mains switch that we could locate near the project, a very visible "its live" indication, and a fuse that will trip far faster than a 15A panel breaker. For high current projects however the fuse needed to be bypassed.

For circuits that don't require an earth ground (ie unbalanced audio circuits), you can also use an isolation transformer. This will prevent any current path to eath ground if you happen to grab onto the live wire while leaning on the sink with your other arm.

Another tip is if you use an ESD mat and wrist strap when working on electronics, disconnect this when working on high potentials. The wrist strap is simply a high resistance path to ground, but its a path to ground nonetheless.

Wolf

I would also make sure the 120V primary side of the txf is accidental-touch proof. Heatsink all connections and use a covered barrier strip, or mount it upside down where connections cannot be accessed.

Wolf

Heatshrink!

Tom_S

dcibel said:

When I was in school we used a very simple box as 120V protection device. Just a 1A fast blow fluse and a switch and a light, with banana plugs on the end. This provided a mains switch that we could locate near the project, a very visible "its live" indication, and a fuse that will trip far faster than a 15A panel breaker. For high current projects however the fuse needed to be bypassed.

For circuits that don't require an earth ground (ie unbalanced audio circuits), you can also use an isolation transformer. This will prevent any current path to eath ground if you happen to grab onto the live wire while leaning on the sink with your other arm.

Another tip is if you use an ESD mat and wrist strap when working on electronics, disconnect this when working on high potentials. The wrist strap is simply a high resistance path to ground, but its a path to ground nonetheless.

That's exactly what I built for testing tube projects. Super simple and great for breadboarding circuits. I found an old variac at a garage sale few years later and ran that ahead of the switch box. I know many repair guys build dim bulb circuits into their mains boxes too.

PWRRYD

I use a variac for powering up my tube projects for the first time and a small amperage fuse.  I've never been shocked by any of my DIY projects, I respect 400+ DC.

I got hit by 480 VAC 3 phase once at work 15 years ago.  I had the panel properly locked out/tagged out but there was an externally powered circuit that was not marked per OSHA.  That hurt!  Got hit between the elbow and thumb on my left arm.  My hand and fore arm were numb for a few days.  Luckily no cardiac or kidney issues.

Wolf

I think I'll call you Sparky! J/K.

Did it throw you?

PWRRYD

Yes, it threw me back a few steps.

Wolf

That's the diff between 480 and 120. 120 won't let you let go, and 480 will make you let go.

PWRRYD

I think you are confusing AC vs DC.  AC has a zero crossing point where you are able to "let go".  DC does not so your muscles can contract and then you cannot let go.  I've had a few brushes with 120 AC around the house when I worked on stuff live.  Never had a problem other than feeling stupid for being too lazy to kill the circuit and set up a work light with an extention cord.

dcibel

On the topic of safety, I've always used a volt pick prior working near any high voltage. I've electrocuted myself zero times and am near high voltage approx once or twice per week on average. It's an inexpensive tool that take 5 seconds to use, and can save your life. In Canada we see 600V a lot more often than 480V, you want to know it's off, not assume it's off.

Wolf

I've only been nailed once by 120V through a neon-bulbed power switch, and never directly. It felt funny when I did it, and that's the only reason I knew I had. It felt like a hum, but not one I experienced aurally.

I honestly did not know 120VAC would allow you to let go. That's just what every person told me about the setup when I asked or conversed about it.

Tom_S

I remember getting zapped when I was maybe 4 or 5 years old. My dad was painting our room and took off the outlet covers. For some reason, I thought it would be fun to jam a screwdriver in the side of the outlet box. It's probably a minor miracle it didn't kill me. I don't know if this is normal for electrical shock victims, but I still remember a distinct taste when I think about it.

D1PP1N

Ive gotten zapped by 120 probably 2 or 3 times now. Once as a kid plugging in a big hard plastic light up christmas snowman . A more recent one i cant believe i didnt shock myself was i changed a ceiling fan and turned off the breaker before doing it. I changed the fan and got it back together and i pulled the chains and the fan came on. I couldn't understand why it was on. Turns out my panel was labeled wrong and my wife turned off the lightswitch i had on so i would know when the light was off i turned off the right breaker. This is when working with others can go wrong. She turned it off since we were going to work on that switch thinking it would help but didn't tell me. I came up stairs thinking the breaker shut the power off. 

The other times i shocked myself it was just a quick  jolt. No biggie.