What precautions do people here use when working with mains voltages?

[Psi]

I have to admit I used to look away when powering things up

i thought i'm the only one doing this. but only when i power up my "new untested" circuit.

I still do that sometimes. I always wince (with correct tongue angle, of course).

A piece of exploded TO220 in the face isn't fun

[BravoV]

When it comes to eyes or face protection, since I'm wearing glasses, safety goggles is quite annoying, and I have an acrylic board about 1 cm thickness with approx. A4 sized paper, ready every time at the bench table when I was powering unknown exposed circuit or newly assembled one for the 1st time.

The disadvantage is I lost one hand just to hold it in front of my face, and another hand to turn the switch, its just I really like to know the exact location of the problem if something goes really wrong, like a flying capacitor's cap when installed wrongly. 

This was inspired after watching the Mythbusters series when Adam & Jaime were hiding behind the two big acrylic walls when blowing things. 

[alm]

You can get prescription safety glasses, I don't think they're that expensive. The advantage of safety glasses is that you'll also be wearing them when you don't expect problems, like when taking a peek to double check if that cap is really installed backwards at the moment it confirms your suspicion by blowing up. It does sound like a reasonable workaround, though.

[Simon]

You can get prescription safety glasses, I don't think they're that expensive. The advantage of safety glasses is that you'll also be wearing them when you don't expect problems, like when taking a peek to double check if that cap is really installed backwards at the moment it confirms your suspicion by blowing up. It does sound like a reasonable workaround, though.

ah yes, that jogs my memory ! I did just that when replacing a cap on a power supply (5V 1 A only), it was something like 2200uF, by some miracle it missed my eye, that is what made me cautious, see even low voltage/power stuff can be dangerous

[Mint.]

You can get prescription safety glasses, I don't think they're that expensive. The advantage of safety glasses is that you'll also be wearing them when you don't expect problems, like when taking a peek to double check if that cap is really installed backwards at the moment it confirms your suspicion by blowing up. It does sound like a reasonable workaround, though.

Maybe a full face helmet then...

[Psi]

I would guess that most experienced people don't wear safety glasses when doing electronics, except maybe when first connecting something mains related or doing a huge amount of soldering.

But that doesn't mean new people should do the same.
Someone who is new to electronics is more likely to accidentally blow stuff up, that's just how people learn.
They also don't know what the risks are and when things are at their most dangerous.

Even soldering can be quite risky when you're starting out and haven't yet mastered how to hold/use the iron so solder doesn't splash towards you.

[hacklordsniper]

I always use a small DC-AC sine inverter when working with mains voltages and transfer the circuit to mains only when im sure its completly finished and working

[Simon]

that is a good idea

[McMonster]

I'm using safety glasses nearly all the time and gloves when drilling, I also have an isolation transformer on my wishlist. By the way are isolation transformers and DC/AC inverters doing the same thing by just isolating your circuit from mains or there are more subtle differences in how they can protect you from harm? I haven't had any electronics related accident so far and I wish it to stay this way.

What really bothers me now is the state of electrical installation in my new house. I didn't even see a grounded power outlet there when I got it, so I'll have to ask an electrician to check the whole installation, good thing I have one in family.

[hacklordsniper]

I'm using safety glasses nearly all the time and gloves when drilling, I also have an isolation transformer on my wishlist. By the way are isolation transformers and DC/AC inverters doing the same thing by just isolating your circuit from mains or there are more subtle differences in how they can protect you from harm? I haven't had any electronics related accident so far and I wish it to stay this way.

What really bothers me now is the state of electrical installation in my new house. I didn't even see a grounded power outlet there when I got it, so I'll have to ask an electrician to check the whole installation, good thing I have one in family.

I use the inverter to isolate my circuits from mains. Second benefit is that you get a short circuit protected and current limited power supply.

[Psi]

For protection I think I'd prefer mains+RCD to an inverter+battery

Which raises an interesting side question though, does an RCD actually work when plugged into an inverter running on battery?
Unless you connect the inverter earth to ground and there's a neutral -> earth link somewhere i can't see it working.

[IanB]

Which raises an interesting side question though, does an RCD actually work when plugged into an inverter running on battery?
Unless you connect the inverter earth to ground and there's a neutral -> earth link somewhere i can't see it working.

The earth/ground is always created by taking the neutral wire from the power source (generator, transformer secondary) and connecting it to the earth conductor (ground spike, cable sheathing, cable conduit, etc.).

So with the output from an inverter, you would do the same thing. Choose one wire as the neutral and connect it to the (isolated) earth wire at the output terminals of the inverter to produce three wires--L, N, E--for the sockets at the inverter outlet. Then put the RCD downstream of the grounded outlet on the inverter.

It could be that inverters and portable generators are already wired this way. I have never examined one to see.

[PetrosA]

What really bothers me now is the state of electrical installation in my new house. I didn't even see a grounded power outlet there when I got it, so I'll have to ask an electrician to check the whole installation, good thing I have one in family.

I've seen a bunch of new installations in Lublin without grounded outlets except in the bath and kitchen and I figured it was crooked inspectors. I wonder whether it could be some loophole in the code in Poland, though. Maybe with an RCD they're somehow allowed to get away without grounding the outlets in the other rooms.

[McMonster]

What really bothers me now is the state of electrical installation in my new house. I didn't even see a grounded power outlet there when I got it, so I'll have to ask an electrician to check the whole installation, good thing I have one in family.

I've seen a bunch of new installations in Lublin without grounded outlets except in the bath and kitchen and I figured it was crooked inspectors. I wonder whether it could be some loophole in the code in Poland, though. Maybe with an RCD they're somehow allowed to get away without grounding the outlets in the other rooms.

I guess there is indeed a loophole or just incopetent electricians. I'll ask someone knowledgeable about this topic and try to find some regulations.

[sonicj]

i have a 1.2kw pfc battery charger i was trying to troubleshoot but sat it aside until i understand it better.  im fairly certain the problem is on the low voltage board, but i don't think its practical to try to troubleshoot a pfc controller without the pfc attached. anywho, i set it aside for now until i understand better how to service the low voltage µC's and components without killing the charger, my scope or myself.

i may try the inverter / gfci combo for isolation and shock protection. i don't have a inverter large enough to support actual charging, but im just trying to figure out why it won't power up.
-sj

[vk6zgo]

I'm sorry,but I can't go along with all the paranoia about mains supplies.

Yeah a bit like Black snakes are generally timid and will always try to flee, just a bugger when you inadvertently corner one of the buggers. Same applies to mains terminals, a bit of respect and they are quite safe, add ignorance, stupidity or blind faith and they can bite you bad. Bad as in final, no more chances.

In the days before the prevalence of solid state equipment,built in mains supplies were the only practical way to supply power to home made Electronic equipment.

In the days I got my drivers licence, cars only had front seat belts, should we head back to that piece of memory lane too?

Hundreds of thousands of "homebrew" radios & other devices were made over tens of years,using transformer/rectifier supplies,with a vanishingly small accident rate.

Which in some cases was more good luck than good management. Are you really proposing a knot in a two core mains flex is still sufficient?

Anyone with enough common sense to not injure themselves doing any of a hundred other everyday activities
can safely create mains operated Electronic Equipment by following a few simple rules

I can only agree but some things you are best to get some help with. Sure guys have taught themselves to fly helicopters and all kinds of crazy shit, but you forget you and I have both done some form of trade and industry training. Even if it wasdone in the days of the dinosaur.

(1) The only mains connections you need to make for a transformer/rectifier supply are in the primary circuit,& these connections require the most care.

True, and the safe way of doing this is second nature to many of use. For new chums there is lots to consider. Many listed in my previous post.

(2) Apply Uncle Vernon's tips.

They are tips or rules I've learnt. Ponder most and you can see the disaster that preceded their general adoption.

I think his tips (2)& (3) require a little closer examination

Everything deserves close examination. It's the Internet people write all kinds of good and bad advice here.

UV(2)---Nice if you just happen to have a tame electrician or "Ginger Beer" on tap!
In many cases,you don't,so you may have to make do with an advanced hobbyist,or if you have to do it yourself,be like Santa,make a list of the things you have to check in the primary circuit,& check it twice,or thrice,or as many times as you need.
If you still aren't happy,apply  UV(2).

Sparkies are like about like assholes (and some behave that way), cannot be too hard to fine one, lots of them are cousins and uncles after all. I'll concede that advanced hobbyist is just as able, but they can be equally difficult to locate. The problem being advanced is subjective, anything from the guy at Jaycar who must know stuff because he has a beard through to seasoned hams. Some are not as advanced as they think they are, which is why I was cautious to suggest it.

UV(3)----Again,nice if you've got an RCD ,but if you are in an old house,you may not have one.

A plug in one can be had for around $20, an good double pole plug in one for closer to $80. A lot cheaper than, and a lot safer than, an isolation transformer suggested elsewhere.

Fear not,however,as by paying a bit above the normal price for an extension cord,you can get one with a built in RCD.

see above

We didn't have RCDs in my day,but I never connected the active line to the metal chassis---never have for that matter.
Still, I would have definitely used a RCD if theyhad been available.

More fond recollections of core balance relays and a world connected through rewireable porcelain fuseholders. Yeah nowadays I like to use an RCD by default. Beginners are likely in to be in rented homes, student slums etc. I'd recommend springing for an plug in RCD.

I reiterate,mains wiring in Electronic projects is not like Crocodile wrestling,or milking venom from Taipans,& the
application of a fair degree of commonsense makes it a simple & safe activity.

Not when you know what you are doing, Steve Irwin would have probably approached Mains with the same trepidation you or I would approach a croc.

After all,you have to learn about it sometime!
This does not mean that messing about with fixed building wiring is by any means as simple or safe,& I  believe many of the posters are addressing this from that perspective.

I hear what you are saying VK6ZGO, we don't need the fun police, or bullshit OH&S which is nothing to do with safety anyway. I don't wan to be the fun police and don't want to suggest nonsense like tradesmen only wiring.

Many more people perish from suicide or road trauma each year than by crocodile attack or electrocution, even so both still deserve a degree of respect.

Dave's suggestion of a plug pack supply is probably the best way for a beginner's first few projects,  particularly now modern switch mode ones can deliver cheap useful current.

Well,Unc,you managed to read a lot into a few comments!
What I was trying to convey was that if people could make & safely use mains powered equipment back in the days of "a knot in two
 core flex",that it should be quite safe to make one now using readily available modern hardware.

For instance,using a "Chassis male with switch & fuse" IEC inlet ,Jaycar part No.PP-4003,it is possible to reduce the mains component of a project to 3 connections-an Earth connection,& Active & Neutral connections to the power transformer primary.

Contrast this with installing a fixed power cord,with a cord clamp (or a knot ,way back when),terminating the A & N connections on a  tag strip,& the Earth (if you used one) to a daggy old 1/8" whitworth screw through the chassis,running Active & Neutral to the switch on the front,(probably a "switchpot") then back to another couple of tags on the strip,then to the transformer primary.
A lot more chances to make a mistake!

The only disadvantages of using the chassis mount IEC connector,complete with switch & fuse,are :-
(1) The switch is on the back of the equipment
(2)The fuse is an M205 type,which most of us don't have lying about in our junkbox.
(3) Uncle Vernon doesn't like IEC cables!

By the way,I think that "the connector not fitting in a kid's mouth" bit is an urban myth,as the old jug plugs were very similar in size to an IEC plug,plus the Philips type shaver cords have been around forever,& are small enough to swallow!

The people on this forum seem to be of two kinds;

Those who adopt a "Here be Dragons" approach to mains circuitry,& won't approach it,unless in full armour,& those who can't wait to hang their new Rigol across the mains & blow the S----t out of it!

VK6ZGO

PS:- If this posting is a bit rough around the edges,it is due to dear old iiNet,who are running very slow,& dropping out,so it's a matter of posting when you get a window of opportunity!

[JuKu]

Ditto inquisitive children.

VERY good advice, and applies also to hand tools. My daughter once took me from elbow and I pushed a knife deep into my thumb. The thumb still works, but it was close...

[JuKu]

There are some on this forum who are very concerned about measuring and/or testing in mains circuits,probably because that is what they do for a living.

LOL, when you work with mains, you always do it for living! (You might not get paid, but at least you live another day (hopefully).)

[Psi]

The people on this forum seem to be of two kinds;

Those who adopt a "Here be Dragons" approach to mains circuitry,& won't approach it,unless in full armour,& those who can't wait to hang their new Rigol across the mains & blow the S----t out of it!

heh,

I have no problems putting my Rigol across the mains on x10.
It's rated to 300V RMS, so i don't see any issue with doing that.

[vk6zgo]

I was more thinking about  them putting the earth lead on the Active .
Of course,you can get a good enough idea of the mains by measuring between Active & Earth.
VK6ZGO

[sonicj]

i have a 1.2kw pfc battery charger i was trying to troubleshoot but sat it aside until i understand it better.  im fairly certain the problem is on the low voltage board, but i don't think its practical to try to troubleshoot a pfc controller without the pfc attached. anywho, i set it aside for now until i understand better how to service the low voltage µC's and components without killing the charger, my scope or myself.

i may try the inverter / gfci combo for isolation and shock protection. i don't have a inverter large enough to support actual charging, but im just trying to figure out why it won't power up.
-sj

*update - i built a portable gfci. works great! my 12V to 120V inverter isn't isolated so i powered it off a battery. the result was a isolated 120V with working gfci (not sure exactly how that works), but the PFC charger didn't like the square wave power source.

so... after some research, i determined that i needed a isolation transformer.  with no isolation transformer in sight, i decided to try to hack together 2 transformers from some old APC backup power supplies i had in the garage. woohoo, it worked! i now have 120V isolated from the mains and earth. i haven't loaded it up yet, but i think it should be good for a couple hundred watts.?? 
-sj

[IanB]

You can also use a variac in place of the isolation transformer.

I had meant to comment on this earlier, but it's my recollection that variacs are usually autotranformers and so do not provide isolation from the mains?

[amspire]

You can also use a variac in place of the isolation transformer.

I had meant to comment on this earlier, but it's my recollection that variacs are usually autotranformers and so do not provide isolation from the mains?

Ian, you are right. Variacs provide no isolation.

[don.r]

You can also use a variac in place of the isolation transformer.

I had meant to comment on this earlier, but it's my recollection that variacs are usually autotranformers and so do not provide isolation from the mains?

Ian, you are right. Variacs provide no isolation.

Correct but my use of the isolation transformer was as a voltage step-down. Isolation was simply an added benefit and a good one at that.

[tbscope]

Really, all. If you build a mains powered power supply, you will get only one wire which is dangerous: the live wire.

I would still advice to disconnect the neutral wire too (it is in fact a live wire too) as it is also a dangerous wire in any circumstance. For the most simple example of all examples: inverted cables. You connect a blue "neutral" wire to a "live" socket on your circuit breaker by accident in your breaker cabinet. This is perfectly ok for most applications but a dangerous situation for someone who expects 0 volts on that wire.

One further rule I learned when working in a high voltage lab was that once you get a shock, you're out of the lab for the whole day.
I do not know the exact chemistry, but when you get a first shock, your body will change in such a manner that a second shock will be more leathal. You need a certain amount of time for your body to get to a normal state again.

The thing about working with higher voltages is that you certainly will get a shock once in your lifetime. You can take any precaution that you need, you're only human.