How I "safely" use 2-prong amps until I change to 3-prong!

[clydey]

your electrician was a fool
we have 230 volts uk
110 volts on site with a centretap transformer giving 55v to centretap
we have 30 milliamp rcd why
because 50 ma will stop your heart
try to understand its the current that kills you
i am a napit certified electrician inspector and tester and live working is always avoided unless absolutely necessary
and as an electrical inspector i feel that in the interest of safety your post should be deleted

[ParthaD]

A mathematical analysis...

your electrician was a fool
we have 230 volts uk
110 volts on site with a centretap transformer giving 55v to centretap
we have 30 milliamp rcd why
because 50 ma will stop your heart
try to understand its the current that kills you
i am a napit certified electrician inspector and tester and live working is always avoided unless absolutely necessary
and as an electrical inspector i feel that in the interest of safety your post should be deleted

Those are strong words Sir, so I will have to go the full length to explain things here. First of all that (fool) electrician has several decades of experience and secondly you are right, its the CURRENT that kills not the voltage. We were both wearing rubber soled shoes, not barefeet on a wet cement floor and he made sure to explain the difference before letting me "try" it! So the possibility of any significant current was non-existent. You can of course call him anything you like!

Secondly before I get into the amps discussion, let me present my credentials a bit here... I have 2 advanced engineering degrees from a top US school, an MS and PhD in Chemical Engg. It normally takes 2 years to do an MS and 5 to do a PhD. I did BOTH in 4 years. I have written books on Air Pollution that one can buy right now on Amazon.com. 4 months ago I had never read an amp schematic.... and now I am writing a book on the evolution of guitar amps, circuits, and sounds from the 40s to date for McGraw-Hill (and a huge amount of the research for that comes from MEF). So I would dare guess that my engineering ability and intelligence are just maybe 1 notch over utter imbecile!

During the course of my professional career I have participated in numerous court investigations and provided expert testimony on several risk related issues. So, while I am by no means an expert on Guitar Amps, I am considered an expert on risk issues, by the US courts anyway!

A risk of something happening such as a car wreck, a divorce, falling and breaking your bones, getting cancer, and YES.. death by electrocution because you stubbornly refused to change your vintage amp power cord to a 3-prong can all be mathematically expressed and if that number exceeds a certain value then the legal system and insurance companies consider it as something that needs to be looked into.

If you are tossing a coin there are 2 possible outcomes and if your life and death depended on that outcome then you have a 50% probability of living, i.e. a probability of 1 in 2.

There are 250,844,644 registered passenger vehicles in the US per Wikipedia. There were an average of 6.3 million accidents and an average of 42000 deaths in the 2002-2005 timeframe per year in the US. Hence the odds of having a car wreck for any one car in a given year is first of all 1 in 6.3 million/250 million or approx 1 in 40. Next if you are in 1 of those accidents, the odds of dying is 42000/6.3 million or 1 in 150 . Hence the odds of BOTH happening together, i.e. being in a car wreck and dying , are 1/40 (1st event) x 1/150 (2nd event) = 1 in 6000. So your chances of dying in a car wreck is 150 times LESS than of simply having a wreck.

Compare this to your odds of dying by homicide in New York city. The population is 8.3 million approx and the number of homicides was 516 in 2008. Hence the odds there are 1 in 516/8.3 million or 1 in 16,000. Hardly a reason to carry around a sword to protect yourself!

Now lets translate that to getting electrocuted by a guitar amp. In all my searches I have come across maybe the names of a 3-4 musicians who are SUSPECTED to have been killed in this manner. There was no conclusive evidence. However, thousands of musicians and I'd dare guess that EVERY amp tech on this forum has at some point received an electric shock. Yet how many deaths do we have? Also note that an amp techs exposure is totally independent of the power cord since they have the amp open and are in direct and close proximity with voltages several times greater than AC mains for tube amps at least!

I've researched the number of deaths by electrocution:

http://www.cpsc.gov/library/shock95.pdf

Check out this document. I'll save you the time and quote the relevant section here:

"According to data from the National Center for Health Statistics (NCHS), total
electrocutions in the U.S. have decreased from 810 deaths in 1985 to 560 in 1995 (the most
recent year for which data are available), a reduction of 31 percent. Table 1 shows that during
this period, the estimated electrocutions related to consumer products decreased from 340 to
230, a reduction of 32 percent. A regression analysis of the total and consumer productrelated
electrocutions from 1985 to 1995 showed a significant downward trend in both total
electrocution deaths and consumer product-related deaths for this period1 (see Figure 1).
Also, the per capita electrocution death rate has declined. In 1985, estimated consumer
product-related electrocutions occurred at a rate of 1.4 per million U.S. population. In 1995,
that rate had been reduced to 0.9 per million, a reduction of 36 percent.
Table 2 shows that installed home wiring was the most frequently reported product
(23%) involved in electrocutions for 1995. Small appliances including fans, microwaves, radios,
televisions, and stereos were the second most frequently reported group of products (17%)
involved in electrocutions. Large appliances such as air conditioners, refrigerators, freezers,
pumps, and generators were the third most frequently reported group of products (14%)
involved in electrocutions. Antennas that came in contact with power lines accounted for 10
percent of the deaths; lighting equipment, mainly lamps and light fixtures, accounted for 9
percent; ladders that came in contact with overhead power lines accounted for 7 percent;
power tools, such as drills and saws, accounted for 6 percent of electrocutions; and garden
and farm equipment accounted for 6 percent of the electrocutions. Other products including
pipes, poles, fences, boat hoists, and amusement rides accounted for the remaining 8 percent
of the deaths.

As you can see in the consumer devices listed as causing deaths by electrocution, Fans, Microwave ovens, stereos - YES all 3 prong devices - have been listed. Also it said that the rate in '85 was about 1 in 1.4 million. Based on the class of devices I doubt very much if the 60s and 70s were signifcantly higher. Based on my own experience with buying vintage amps, right around the 68 I am still seeing 2 prong devices. I have some 71-72 amps where I start seeing 3 prongs so I bet the switch to 3-prong happened right around then. Yet based on the lack of even REPORTED fatalities from guitar amps which were presumably all 2 prong at this time, the mathematical odds of getting fatally electrocuted by a guitar amp are close to ZERO!!!

If I'm not worried about the car fatality stat and still drive then I will surely not be worried by getting electrocuted by a power cord which is AT LEAST 1.4million/6000 = 233 times LESS! The actual odds are probably thosands of times lower since that 1.4 million number is for ALL electrocution deaths.

So while it may feel good thinking that you're saving lives by converting a 2 prong to 3 prong, the mathematics of reality shows no effect. Your odds of getting divorced or mugged or falling and breaking your bones or having a car wreck are all ASTRONOMICALLY higher!

And the DEATH CAP... yes... lets not forget that... I'll refer you to your very own Bruce of Mission amps who said this in a post recently:

http://music-electronics-forum.com/t17440/

Does anyone actually know anyone that has been killed, seriously or mildly injured by this much maligned capacitor?

Seriously... in my opinion, this death cap term is, wanna be amp guru, NET driven hysteria with virtually very little real world data to back it up.
Most of these caps across a 120v-240v line are rated at 400v to +600v, plastic film, poly something or another caps and not cheap junk.

To be honest, I think I have only seen one or two of these caps gone bad since I built my first vacuum tube radio in 1963-1964.
By comparison, I've seen a hundred or more frayed power cords dangling from a sharp hole in a chassis where I was afraid to touch it and the goof ass is still using the damn thing!

I do agree, replacing any two wire power cord with a three wire cord, (one that has a separate chassis ground wire), is a real important improvement and I recommend it be done to all your two wire power corded vintage equipment... but that has nothing to do with this so called Death Cap.

There are so many other real dangerous things with 120vac-240vac power line devices that I really have to laugh at the notion of this cap being the almighty,
Death Cap.
__________________
Bruce

Mission Amps
Denver, CO. 80022
Mission Amps Your Tube-Amp Specialist
303-955-2412

He recommends changing to 3 prong of course but note what he said about the death cap.

One last note for guitar techs. If someone comes to you with a very expensive 40s to 60s amp you better get his written approval to change that power cord because, based on my experience with the US legal system, you are COMPLETELY vulnerable to an expensive lawsuit if he did not want that done and claims damages resulting from a real or perceived loss in antique value of that amp because of that change. The courts will not recognize you saying that it was good faith safety enhancement unless of course you can prove that using actual fatality stats.

I rest my case!

[Steve Conner]

I have 2 advanced engineering degrees from a top US school, an MS and PhD in Chemical Engg.

Well, I think we figured out it wasn't electrical engineering already.

4 months ago I had never read an amp schematic.... and now I am writing a book on the evolution of guitar amps, circuits, and sounds from the 40s to date for McGraw-Hill (and a huge amount of the research for that comes from MEF). So I would dare guess that my engineering ability and intelligence are just maybe 1 notch over utter imbecile!

I SO believe that McGraw-Hill, international science publishers, are paying some guy who only has 4 months experience of music electronics to write them a book about some stuff he read on the internet. They must be one notch under utter imbeciles. Sample chapter or it didn't happen!

Now, you can use an amp with a 2-prong power cord, if you're confident that it's in good working order. You can replace the "death cap" with a modern Class-Y one covered in safety approval logos. But how good is the insulation in that 50 year old transformer?

Ironically, most switchmode "wall wart" power supplies nowadays have no ground pin, and a capacitor between primary and secondary sides exactly analogous to the death cap, mandated by EMC regulations. And you can get little tingles off apparatus powered by them. The only difference between this and an old guitar amp is that the insulation in the wall wart is better, because it's mandated by safety codes, and of course the Chinese never, ever cut corners to save money. Rod Elliott has written about this on his site.

[clydey]

firstly most electrocutions take place across the heart ie hand to hand
rubber sold footwear and one hand in your pocket equals no current flow
therefore whats the point
i am at 57 years old not far short of experience in ELECTRICAL inspection and TESTING
our job is to stop people from being electrocuted by doing our job properly and safely
I fail to see what your credentials have to do with it
do you have any electrical credentials
if you want to back up your post with statistics that you have read then more fool you
check out this site for clyde electrical
Part P | Electricians | Building Regulations - NAPIT UK
we go through a lot of credentation to be an inspector / far above reading about it
i still hope a moderator pulls this post it may stop another electrocution

[ParthaD]

Hey guys, dispute my facts with your facts.. why stoop to personal attacks and name-calling??!

[Fragger]

ParthaD +1

[Steve Conner]

Well, I am a moderator and could delete the whole lot if I wanted, but that isn't really the MEF style. We don't do the censorship thing.

Like most other things in electronics, the 2 prong issue is more subtle than it looks. Those old amps wouldn't pass code if they were brought onto the market now, but because they were made 50 years ago, they get grandfathered in. You can use them at your own risk.

And of course the increased risk is due to the following:

The transformer is old. That means its internal insulation is aging, and probably wouldn't have passed modern electrical codes even when it was new.

The same applies doubly to the death cap. Not only is it old, it's of a kind not legal for direct connection between the AC line and metalwork that can be touched. Modern codes require a special Class Y capacitor here. Again, though, grandfathered in.

If the insulation in transformer or death cap gives out, then the chassis, and hence your guitar strings, may end up connected to live mains. Normally the ground wire would cause the fuse to blow at this point, but you don't have a ground wire! So you won't even notice anything's wrong until you get shocked by the thing.

These are the facts. Of course nothing in electronics is simple. I know of a friend of a friend of a friend who was killed by bad wiring at a gig, causing the ground connections of some outlets on the stage to be live with 240V. If he had had an old 2-prong amp with no ground, he'd be alive!

But our party line is that all amps should be equipped with a 3-prong cord and have their death caps removed. This brings them into compliance with modern electrical codes, and overall probably prevents more accidents than it causes.

[Gibsonman63]

Outrage?

"Posting this here because there is a very evil streak in me which gets tickled when I break rules and do what I am not supposed to do, and even more when there is a possibility that others may get outraged that I do so!!!"

It seems to me that you are now sharing in the outrage you hoped to initiate. This forum has some great members who openly share the benefit of their experience to help others. It is rather pointless to post if you have already made up your mind you prefer to debate than take the sage advise of some very experienced gentlemen, particularly when they are the target market for your upcoming book.

Hopefully this thread will keep others from such an easily avoidable safety hazard.

[Steve Conner]

particularly when they are the target market for your upcoming book.

I've preordered! I'm looking forward to some top vintage tone tips, like

To summon Hendrix's mojo, simply stand in the bath while playing, and stick your tongue in the lamp socket. If it doesn't work, at least you'll have his hairstyle and an authentic burning guitar.

[clydey]

hi steve just noticed urefrom glasgow
i came from springburn moving to knightswood before coming to london
appreciate the witty comments
on a more serious note these threads are viewed by young and old clued up and otherwise and dangerous advice is bad advice
on a more witty note my local wellington boot maker is testing the electrical insulation of their footwear and waterproofing qualiity at the same time any takers

[ParthaD]

Gibsonman, that first line that you quoted was just intended as a joke nothing more nothing less so please don't read anything more into it!

Also in response to the credentials thing that people have questioned, my reason to mention those was because we were talking about risk, and I wanted to explain that I was qualified to talk about RISK! It was also to establish that I was not just a high school student who'd played on a couple of gigs!

No one's denying there IS a risk, but I have attempted to quantify the risk and explain that it is miniscule in comparison to other daily risks which we all take! And lastly I would seek the advice of knowledgeable members of the forum on amp troubleshooting issues not on RISK issues. This post was not about seeking advice but to bring about this very discussion (and I have stepped on several toes here - but I don't think anyone can accuse me of being disrespectful or impolite which is more than can be said of some of the responses!!!), to illustrate that fatality facts indicate that the risks don't warrant this kind of hysteria!

Also, no sense in giving you ALL the history but in my career I have also been a start-up engineer involved in several large chemical processing plants including large refineries and am familiar with working with as much as 24kV and 50kv lines not just your home AC mains. Chemical engineers worldwide undergo some of the toughest training regimens of any engineering stream, not just chemistry, but also electrical engineering, mechanical engineering, metallurgy, statistics, economics, industrial engineering aspects, because our work involves that entire spectrum. And one would be grossly underestimating the capability of US higher education institutions in thinking that one could get graduate degrees by simply "reading something off the internet"!!!

As I said, it's not the POTENTIAL for something to happen, but the odds of something happening that governs everything from precautionary measures to our insurance premiums.

[BackwardsBoB]

... Posting this here because there is a very evil streak in me which gets tickled when I break rules and do what I am not supposed to do, and even more when there is a possibility that others may get outraged that I do so!!!

Regards!

You shouldn't get all twisted when we help tickle your fancy...

[ParthaD]

You shouldn't get all twisted when we help tickle your fancy...

Not getting twisted at all... I can handle ribbing, ridiculing, name calling, and insults just fine.... but I am still waiting for some solid numbers that challenge my hypothesis that the facts don't warrant the hysteria! And if one digs around, there are PLENTY of others who think the same, just not on this forum looks like!

[clydey]

parthad you opened a discussion about a dangerous subject.
i am not name calling and i stopped the electrical game for four years and went to goldsmiths university london to receive bmus(hons) but just because i have a degree does not make me more cleverer than anyone else
but when it comes to electrical safety i 100 per cent know what i am talking about and you do not
my only concern is for the people with a two pronged plug thinking that it is safe when it is downright dangerous.

[Steve Conner]

Yep, I'm currently working at Glasgow Caledonian uni, and oddly enough, researching the causes of breakdowns in high-voltage electrical plant. We don't really get out of bed for anything less than 11kV.

I agree that ParthaD's method is somewhat risky. He'll be OK if his death cap shorts out, because his method ensured that it was hooked up to neutral. But if the transformer shorts out, it could go either way.

This is my technical analysis of the situation as an engineer. I offer it for reference to anyone interested, but I don't want to endorse the method. I concede that the risk of getting electrocuted by ungrounded equipment is small, but there's simply no point in taking it, because it's so easy to make it go away by fixing up a ground! Like a previous poster said, 6 dollars and half an hour to fit it: that's cheap insurance.

And from the point of view of education and the like, grounding is the "right" thing to do. We all probably do nasty things in the workshop (removing the ground wire from your oscilloscope is a classic) but you're not supposed to go about telling everyone else how much fun it is! Joe Public isn't expected to know enough about electricity to take calculated risks with it, so we make it as safe for him as reasonably possible. This is the viewpoint clydey puts forward, and I respect it. Heck, I offer up all my workshop gear for PAT testing once a year.

Note for the hardcore:
Appliance classes - Wikipedia, the free encyclopedia
The old 2-prong amps are IEC Class 0, and by fitting the 3-prong cord you upgrade them to Class I. Modern 2-prong equipment is Class II.