AC power line safety: Why no one can tell you what's safe

[R.G.]

I'm certain that I've irritated a number of people over time by my stock advice not to do AC power wiring unless you ALREADY KNOW how to do it safely. I think I ought to explain that.

In today's litigation-mad world, ... no one ... can tell you how to do it safely. YOU have to research and decide what is safe, make your own decisions based on your learning and observation, possibly by observing others and reading the safety literature. That is, YOU have to figure out what is safe, and do it the way YOU think is safe.

Let me explain why this is so complicated.

"Safely" means "even under the full range of reasonably-foreseeable failures of any one component, no significant injury to people, animals, buildings or property other than the failure's damage to the unit itself." It says something like that in the safety standards that UL and the EU's safety laboratories put out, and in the safety standards for most nations.

So it seems reasonable to think that if you got that standard and followed it, your whatever-it-is would be safe, right?

Wrong-o.

The standard is not a description of what's safe. It's a description of if-you-don't-do-at-least-this-it's-NOT-safe. The difference is this: at one time, in Europe, if you passed the national laboratory's safety inspection, meeting the letter of the national safey standards (and there were many of them, slightly different), then your equipment was deemed safe and you could not be sued (in that jurisdiction anyway) for non-compliance; looked at another way, if you met the letter of the law, as inspected by the government lab, you were presumptively safe.

No more. The national standards have been smashed into an EU-wide standard, and the presumption of safety is removed. So if you do not comply with the safety standard, you ARE NOT safe. But if you comply, you only MAY BE safe. There is no presumption of safety based on following the standard. So following the advice and written standards of the wizest safety gurus is not enough to be safe.

In the USA, this is even easier. There is no national law on safety standards. Underwriter's Laboratory issues statements to the effect that you comply (or not) with their safety standards, which are a private thing. However, insurance companies rely on UL certification for what they will insure - and pay for damage on - among other things. And in the USA, you can sue anyone for anything, any time. If you make a device but do not get it UL certified and then it causes someone, anyone, real or emotional damage in any way, you will in addition for damages also be sued for reckless and wanton disregard for safety because you did not follow the existing standards at a minimum. That is, you're on the hook for damages in any case; ignoring the private, non-legislated standards adds willful disregard for safety. I believe the EU allows this angle in some jurisdictions these days as well since the presumption of safety upon tested conformity is now gone.

So - if you wire up an AC power line device, YOU must decide what is safe for (a) you and (b) anyone else who ever comes into contact with the device. Killing yourself is one thing. You should read the Darwin awards for one possible view of that state of affairs. But injuring or killing someone else makes all of your personal possessions ... now and in the future... up for grabs in a court of law. Notice that courts have held the original maker responsible for damages for machines which were decades old, being used improperly, having been modified and operated without guards, etc. If your best friend's grandchild finds a box you made in the attic and gets electrocuted or it starts a fire while he's playing with it, you're on the hook. If you happen to be dead at the time, your estate is liable for your wanton disregard of the safety standards that tell you what is not safe to do, but do not tell you what IS safe to do.

If you mess around with AC power line stuff, you really, really, really need to be sure that the risk you're accepting for yourself and your estate (i.e. they take the house you left to your wife and children) is a reasonable one. Better either (a) get educated (b) leave that stuff alone (c ) get a big potful of insurance or all of the above.

If you insist on messing with this stuff, find a copy of IEC 600650 or UL600650 and read it. And follow it, documenting that you did. That will remove the presumption of recklessness at least.

Oh, the safety standards are issued by private agencies. They are not governmental publications, and as such are copyrighted and sold, not freely available. A copy of one of these will cost you about $200-$400. I turned purple in the face for a while when I found out about that one. 

So - my word is not good enough. I cannot tell you what IS safe. I can only tell you what is not when I, as a lay observer with no official standing or oversight happen to notice you talking about doing something that might be dangerous. I will try to do that when I can, but I cannot possibly catch them all. You must take full responsibility for learning what is not safe, and also for contriving what you personally think IS safe. And ignorance of safety standards is no excuse. 

[Rob Strand]

Even the standards people don't have all the answers.  Standards dictate a baseline level of safety which prevents injury in most cases.  Than can prevent injury from ignorance and naivety.  Some safety standards now incorporate risk management where you present your case that you have considered all the variables.  The idea is you have to put warnings in the manual...which no one reads, and it could go on forever with the disclaimers....

You can't stop people killing themselves by trying to swim with their hairdryers, or swinging an iron around that hits someone in the head.

[Sir_Ian]

Kinda confused.

I think you are referring to making homemade transformers for powering guitar stompboxes.....is this rite? Or are you talking about things even as simply as sticking in an AC adapter jack to a pedal. (I don't think its the latter).

[ClinchFX]

Thanks R.G., you've made some very important points.

Here in Australia, standards are also distributed by a private company, but it appears that they are less expensive than in the US, however ------ if I manufacture a product that requires compliance and I don't obtain compliance, I can be penalised by a government agency.

To me it is the same situation as complying with any other law, for instance obeying the road rules.  We don't have to buy a copy of the road rules because the documents are freely available, so why should we have to pay for a copy of any other set of rules.

The compliance issue has spawned a whole new parasitic industry that produces nothing but costs both the manufacturer and industry.

Peter.

[darron]

Kinda confused.

I think you are referring to making homemade transformers for powering guitar stompboxes.....is this rite? Or are you talking about things even as simply as sticking in an AC adapter jack to a pedal. (I don't think its the latter).

Yes, I'd say R.G. is talking about making the actual power supplies for your pedals, but also making high voltage mains-supplied devices like mini tube amps etc. Plugging a low (9-24)V AC into a DIY or bought pedal isn't of concern.

[R.G.]

I think you are referring to making homemade transformers for powering guitar stompboxes.....is this rite? Or are you talking about things even as simply as sticking in an AC adapter jack to a pedal. (I don't think its the latter).

Darron is correct, and you are as well. If you are using a wall-wart, the dangerous stuff is encased inside the wall wart; so if you don't open the wall wart, the output is low voltage, limited current, and you can sue the makers of the wall wart if it hurts you. The wall wart makers have taken the responsibility for being safe in return for your buying their product.

However, if you ever connect, disconnect, or reconnect anything which has AC line voltage on the wires, or the connection of the AC safety ground to the metal chassis, or any voltage over 42V, or put in a jack which allows more than 200ma to come out of it, you are liable for following the safety standards, as all of those happen to be things specifically mentioned in the standards as being not safe.

This is one reason I recommend a wall wart in the Neovibe, not an internal transformer like the original.

[JOHNO]

The moral of the story is dont muck with mains power unless you know what you are doing.PS.Thanks for the tip on the uni-vibe R.G. Im going to start my build right now.The power supply was the thing that was holding me back.

[petemoore]

  Stupid wiring.
  Available at your local hardware store. AC wires not crimped..at all [~two strands dangling on the crimp]..one teeny tug or twist [and I mean you have to plug the wire in the plastic so it touches the crimp]...yupp...I called and told the hardware store...they're like what, no if you want to return something, take it to the returns desk...
  So not even Lowes seems to be able to become 'aware' enough to care about their own risk [at least not the desk-dummies]...they're so big, that when the danger-junk comes off the ship and gets spread all over their shelves...so what !
  I'm talking about AC wires, voted most likely to short circuit before ever supplying power to anything.
  I unplug my stuff when I'm not watching it...I figure the wiring is likely to be shit.
  We had a house fire here recently, the fire marshall said "It looks like the bedside lamp cord shorted, and cause the fire."....go figure...
   don't assume anything you buy that a Mfr. is taking responsibility for was responsibly constructed, the opposite is true, I can take you to the hardware store and show you the destined to short circuit wirings...I decided to wire it 'right' myself instead of messing about with taking it back [plus I liked the overall design of the lighting]..and to call them and tell them they're selling stuff that not only doesn't work, is totally as unsafe [as in: almost guaranteed to short out] as I've ever seen when unpackaged...talking to the store about it...it's like...could you put someone with a brain on the phone, or get in touch with them and have them give me a call ?
  The Mfr., Seller, and end user [consumer] have all been successfully separated, the 'safety feedback' lines are all hacked up...try to tell 'em about the 'danger junk' they're sellin' and you get 'huh?'...'returns desk, sir'.

[Minion]

Here are a few tips that I use when wireing any Mains powered equipment like wireing the mains to a Transformer....

1) Allways put a Light bulb in series with the mains voltage and your Transformer and use a suitable sized fuse...If there is a short in the Transformer or the curcuit the light bulb will light up and absorb the current.....

2 ) Allways cover exposed wires with shrink tubeing or Tape so there aren"t any accidental shorts on the mains side of the transformer....

3 ) Make sure you aren"t touching your Curcuit/Transformer or any wires when you turn the AC Power on, and allways have a safe way to turning off the AC without comeing in contact with with the Wires,Transformer or Curcuit, Like useing an isolated switch or a Power bar with a switch....

4 ) Whenever possible connect safety earth to the 0V point of your transformer....

5 ) Tripple check and recheck that you have your mains wireing done correctly ,If there is any doubt do not procede and get clarification on the proper wireing scheme...

Usually if you follow these basic rules you should be safe, I"m sure there are other precautions that should be taken but these were the biggest concerns that i could come up with....


Cheers

[R.G.]

Here are a few tips ...
1) Allways put a Light bulb ...
2 ) Allways cover exposed wires ...
3 ) Make sure you aren"t touching your Curcuit/Transformer ...
4 ) Whenever possible connect safety earth ...
5 ) Tripple check and recheck ...

Those are good bits of advice, all right. However it misses my point. Specifically when you say:

Usually if you follow these basic rules you should be safe...

If someone relies on your advice, and does exactly that, and nothing else, they could easily still get hurt.

For instance, one section of the safety standards talks about temperature rise under both normal operation and in the case of the most unfavorable component being open or shorted, which ever is worst. So they could get burns. You don't mention fuses at all; so someone following exactly that set of tips could burn down an apartment building by not putting a fuse. The standards include tests for whether live wires or hot surfaces can be touched by, for instance, small children; and the one that got me - speaker cones don't count for keeping children out. Another section is flammability ratings. If your wire is PVC insulated but it is not flame-retardant PVC, a short may melt the wire insulation, set it afire and drip burning plastic out of the box.

IEC600650 is over 200 pages of ways you can be not safe if you don't do at least this much. Even then, you may not be safe, only not reckless. Worse yet, it references other standards for a number of points. 600650 is not the only one.

It is really very sobering to think of the possibilities of what your AC power wiring might happen to do. Even more so to think of what someone might do upon your advice, because you can't tell them everything, and probably don't want to be liable for it if you do.

[The Tone God]

A few years ago someone was telling me that they built a mini low wattage tube amp head. For the high voltage they used a transformer off the line AC. A bunch of people they knew wanted one so they were going to build a batch and sell them. They had the parts and were ready to go. In passing conversation I mentioned the liability issues with line AC. Never heard from them again and never saw anything sold from that person/company.

I guess I busted their bubble.

Andrew

[R.G.]

Or provided them some education cheaply and efficiently that would otherwise have been painful and expensive.