how safe is 60VAC?  - Page 1
Forum section: electronics / general

author: grifftech
author_rank: Frequent Contributor
timestamp: April 10, 2018, 08:25:30 pm
content: I purchased a 240 to 120volt stepdown transformer and replaced the input cord to convert it to a 120 to 60 volt unit. How safe is this voltage? It is not isolated, also what can I use it for.

author: Monkeh
author_rank: Super Contributor
timestamp: April 10, 2018, 08:31:09 pm
content: As safe as the person using it.If you don't know what you can use it for, why did you buy it and rewire it?

author: BillB
author_rank: Unknown
timestamp: April 10, 2018, 08:34:21 pm
content: Quote from: Monkeh on April 10, 2018, 08:31:09 pmSince when does that matter?

author: grifftech
author_rank: Frequent Contributor
timestamp: April 10, 2018, 08:34:50 pm
content: Quote from: Monkeh on April 10, 2018, 08:31:09 pmmostly to run incandecent bulbs dim, with no interferance

author: helius
author_rank: Super Contributor
timestamp: April 10, 2018, 08:43:55 pm
content: As far as touch-safety, earth-referenced 60VAC is obviously safer than 120VAC, but not actually safe in situations where the user may be casually exposed.https://en.wikipedia.org/wiki/Extra-low_voltagedescribes the limit for touch-safety to be 50VAC to earth or any other circuit.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2018, 08:52:06 pm
content: Yes comes under ELV - Probably SELV depending on the quality of the transformer.Remember though that 'safe' also includes current capability, you can still start a fire with 60VAC just as easily (probably easier) than you can with mains.

author: calexanian
author_rank: Super Contributor
timestamp: April 10, 2018, 08:53:04 pm
content: The non isolated part is more of a concern. you will feel 60 volts if you are in a relatively low impedance state (Skin moisture content elevated)

author: Monkeh
author_rank: Super Contributor
timestamp: April 10, 2018, 08:53:16 pm
content: Quote from: Gyro on April 10, 2018, 08:52:06 pmErr - no, 60VAC is not ELV.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2018, 08:57:39 pm
content: QuoteDamn, yes you're right, sorry. I can't remember what happens if you have a groundable secondary center tap available - similar to building site 55-0-55V.

author: Benta
author_rank: Super Contributor
timestamp: April 10, 2018, 08:59:29 pm
content: "It is not isolated"... meaning that depending on how you plug it in, you might have 120 V (to ground) on the output. Not safe at all.

author: Monkeh
author_rank: Super Contributor
timestamp: April 10, 2018, 09:00:54 pm
content: Quote from: Gyro on April 10, 2018, 08:57:39 pmThat's RLV which is a UK specific thing. It's basically treated as LV with a reduced risk which looks good on the paperwork for building sites.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2018, 09:03:04 pm
content: Sure, I was just wondering if you could [Edit: achieve SELV] with 30-0-30. Depends on the transformer of course.

author: Monkeh
author_rank: Super Contributor
timestamp: April 10, 2018, 09:05:40 pm
content: Quote from: Gyro on April 10, 2018, 09:03:04 pmSure. But that's still LV, not ELV. Voltage between any two conductors in the circuit or any conductor and ground.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2018, 09:09:42 pm
content: Quote from: Benta on April 10, 2018, 08:59:29 pmI completely missed the "it's not isolated" in the OP- No, it's a non starter!

author: grifftech
author_rank: Frequent Contributor
timestamp: April 10, 2018, 10:57:50 pm
content: I meant that it is grounded

author: Brumby
author_rank: Unknown
timestamp: April 10, 2018, 11:01:56 pm
content: So - just clarifying - the primary and secondary are fully isolated from each other and the case/body is grounded ... right?

author: Zero999
author_rank: Super Contributor
timestamp: April 10, 2018, 11:27:30 pm
content: Quote from: helius on April 10, 2018, 08:43:55 pmThat doesn't mean that it's fine to build a device with 50VAC on live parts, uninsulated from the user.The touch voltage of 50VAC on exposed conductive surfaces, is what's acceptable under fault conditions, not normal operation.The user still needs to be insulated from 50VAC or 120VDC and below, by at least basic insulation. The voltage has to be below 25VAC (EU), 30VAC (US) or 60VDC, before the circuit no longer requires insulation from the user. This is only true for dry conditions: damp areas have even lower voltage limits, before basic insulation from the user is no longer required.

author: Yellofriend
author_rank: Regular Contributor
timestamp: April 11, 2018, 08:00:57 am
content: "Deadly" starts at 50mA and 60VAC can qualify for that.So in the ol' days in Germany they wanted to set the deadly voltage at 60V, but raised to to 62V because German Telekom (then still state owned) used 60V for their phone network and that would have meant all the wiring to the enduser would have to be up to VDE standard. That 60V only applied while ringing though. No idea how it is nowadays.

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 11, 2018, 12:55:15 pm
content: Quote from: blueskull on April 10, 2018, 11:08:23 pmFelt that many times.It's a really weird low frequency AC feel.

author: Horusaem
author_rank: Newbie
timestamp: April 11, 2018, 02:18:14 pm
content: Some ppl can withstand higher currents and voltages that would kill the "table" person , but such tables are maid to ensure that the product is safe for everyones use . To go offtopic one of my teachers that had some Soviet background ( for real he was russian ) could withstand a 220 ( back than ) Volt from the main but his hands were dry as a diamond .Transformers are always dangrous things , if you`ll be unlucky in touching those at the moment you didn`t chose the situation might be fatal. It`s not the voltage that kills but the current or more likely how it messes muscle tension around in your body . One of the things I was told a thousand times was to never grab unsealed wires and when I do I beter use my right hand only. As hear is on left if the current goes from the hand to the leg you`ll be shocked but might live with a valuable lesson if it goes from right hand to the left hand the shortest way is throygh the chest and via heart muscle and that would be end of the class for youUse CAT III or Burn BabyPS: We used to make a Legend that that teacher would drink so much vodka in his youth that the voltage is his body was higher than the mains voltage and the electric company should pay him for giving away free energy when he touched mains line( loses a little in translation but I hope you get the joke )

author: jmelson
author_rank: Super Contributor
timestamp: April 11, 2018, 10:22:57 pm
content: Quote from: blueskull on April 10, 2018, 11:08:23 pmI grabbed a PC board with through hole connectors on it once. It only had 12 V DC available. I got a pretty "shocking" shock from something that I thought couldn't possibly do that. The tail of one of the connector pins must have pierced my skin enough to contact the live layer beneath. It never bled, so must have just reached the live tissue.Jon

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 12, 2018, 01:04:10 pm
content: Quote from: Yellofriend on April 11, 2018, 08:00:57 am'Yellofriend'.... You are not quite right mate. Yes, people generally forget that it is notthe Voltage that kills you, but the Current ! Someone may have wet fingers, and be standingon a wet floor in bare feet, in circuit with say 60/80/90 Volts and receive a lethal dose! throughthe heart, resulting in uncorrected Ventricular fibrillation.Someone else way be in a relatively 'dry' environment, and have very dry skin, and not be adverselyaffected by 'brushing' their fingers or hand (hands) over 'those' voltages, or even 110-V (in the U.S.),and/or in my case even 240-V (in Australia). Yes... we feel it !!!!!........(NOTE: I've been an Industrial Electrician, and Special Class Technician for 40 years, and I know whatI am doing, and do NOT expect others to copy what is/was standard practice to me !).(BACK to CURRENT for now...)Generally these days, we have power switchboards that rely on either 'ELCBS', or 'RCDs'....(Earth Leakage Circuit Breakers, and Residual Current Devices/Detectors).VERY ROUGHLY, (and many types work in many ways!!!), they can detect an imbalance in thecurrent flow in the Active & Neutral, and 'surmise' that the 'extra' is flowing through YOU, if youtouch something 'live', and you are in some way or partially 'Earthed'.....Now USUALLY these devices are set to 'Trip', between 25mA & 30mA, and can do so in a smallfraction of a second! AT THAT current, and above, you may be killed.... However, if you havean isolating 'transformer', especially where neither output wires are 'REF'd' to Neutral/Earth, thenit may not protect you ! (This subject is too big to explain simply....... sigh....)Then we can get into 'Auto-Transformers' where there is no elect isolation from Primary to Sec.And the 'Centre-Tapped' Secondary windings which throw a whole 'nother curve ball......Basically..... 36V should never be anything to worry about.....B.T.W. Just for interest !!!!!You have a BETTER chance of surviving an 8,000V or 10,000V shock, for 1 or 2 seconds, thana 240v shock for say 3 to 5 seconds !!! Why?.....Lower voltages can leave the heart in that state I mentioned, being "Ventricular Fibrillation".This is a useless 'quivering' action by the heart, leading to death, without using a "Defibrillator" !Very HIGH voltages, although leading to physical BURNS, (and subsequent death if prolonged),initially cause the Heart to electro-muscularly clamp so tightly, that it can't get into that State !!So when the 'shock' is removed, it basically goes back to normal !!!!!(Survive but burnt)

author: Iwanushka
author_rank: Frequent Contributor
timestamp: April 12, 2018, 03:38:29 pm
content: No idea about new regulations and the other things that changed but long time ago anything above 24VAC in some conditions was asummed dangerous and in others even deadly.P.S. actuality under "right conditions" you can die from 9VDC battery that you have in your dmm, but this one is very rare only know one case of this in my country.

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 12, 2018, 06:15:15 pm
content: We have a 48v battery plant at work, 1,600a normal draw, it's capable of much more. You can touch bus bar and not have issues. The voltage still needs to be high enough to drive current through you. So voltage does play a big role.Drop a wrench across the terminals on the other hand.....Boom. Even across a single 2v cell would probably be disastrous. 4800ah per cell to give an idea of the size of these.

author: Zero999
author_rank: Super Contributor
timestamp: April 12, 2018, 07:42:08 pm
content: Quote from: Red Squirrel on April 12, 2018, 06:15:15 pm48VDC is less likely to case a shock, than the same AC voltage. The peak voltage of 48VAC is nealry 68V and the mains frequency is more likely to interfere with the nervous system and the rhythm of the heart, than a steady current.Quote from: blueskull on April 10, 2018, 11:08:23 pmYes even relatively low AC voltages heart like hell. I've had a similar experience with a transformer outputting 30VAC but with 70VDC I hardly feel anything, at worst a slight sensation when I touch and let go of the conductors, which makes sense: it's the change in current which my nerves respond to, more than when it's steady DC.

author: helius
author_rank: Super Contributor
timestamp: April 12, 2018, 08:37:33 pm
content: The human body also has some capacitance, so it blocks DC more than AC.This all seems kind of irrelevant to the original post, though, which from my reading was about powering incandescent light fixtures or luminaires. The safety of these fixtures will not be any worse when running them on 60VAC, and unless the goal is using them under water, I don't see any issue at all. This country is absolutely full of lamps with finger switches less than an inch away from exposed live terminals (the socket of the Edison Screw base) insulated with only crappy cardboard tubing, and yet shocks are extremely uncommon.By the way, there is an alternative and likely simpler way to reduce the output of incandescent bulbs: using silicon diodes in series to half-wave rectify them. There have been products packaging diodes in little ceramic discs to slide in between the bulb and its socket: for a nominal 60W bulb pulsing at 60Hz I do not see any flicker, but the perceived flicker can differ between individuals and power levels.Here's an advertisement from 1984 for a brand of slip-in rectifier for E26 bulbs:https://books.google.com/books?id=nQAAAAAAMBAJ&pg=PA47&lpg=PA47The ad copy is pretty overblown, but they do effectively reduce bulb brightness and lengthen service life. I haven't seen them for sale for a long time, though.

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 13, 2018, 01:18:50 am
content: That is true, I would imagine you'll at least feel a little tingle with 60vac. Come to think of it I connected like 10+ 9 volt batteries together once to see how many it takes to get a shock and I could not feel anything. Until my coworker told me to lick my finger... ouch!That said at 60vac I imagine the current going through you would be small even if the supply is capable of a lot. The real danger though may be short circuits. Even a 12v lead acid battery will pack a pretty nasty punch if you short it out.

author: gregariz
author_rank: Frequent Contributor
timestamp: April 13, 2018, 02:11:39 am
content: 30mA is roughly the limit for your heart. Above that it may stop.How resistive are you? Everyone is a bit different.If memory servers.... this is more than 25 years ago I was told that the record fatality was a guy trapped under piece of machinery and subjected over an extended period of time to either 24 or 48 volts (can't remember... too long(.

author: Zero999
author_rank: Super Contributor
timestamp: April 13, 2018, 08:16:15 am
content: Quote from: helius on April 12, 2018, 08:37:33 pmIt doubt it. The capacitance is negligible at 50Hz and is nothing to do with why the human body is more vulnerable to shock at powerline frequencies, than DC. It will have an effect at much higher frequencies, but they're well above the limit for shock: the risk changes to burns, which can be deep and severe. At higher voltages, the skin's insulation will breakdown, before the capacitance dominates although it can cause shock when the body isn't earthed and is only in contact with one live conductor, but the mains voltage is too low to cause a perceptible current to flow, under those conditions. It's more of a risk to those working on HV overhead cables.http://www.extremeelectronics.co.uk/capacitance-of-a-human-body/

author: grifftech
author_rank: Frequent Contributor
timestamp: April 13, 2018, 02:37:20 pm
content: The diodes cause non-sinusoidal current draw, distort mains voltage

author: Zero999
author_rank: Super Contributor
timestamp: April 14, 2018, 08:29:05 pm
content: There's a lot of misinformation on the Internet about which voltage/current and frequencies are more dangerous. After a bit of Googling I've found an in-depth study commissioned by NASA.https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730001338.pdf

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 15, 2018, 01:43:36 pm
content: Red Squirrel ..... Please do not take offense my friend, but that is not what the issue is......A 'Spot Welder' may have '2v' at the probes, but due to the low resistance, (AND the powersupply's ability to provide it...) a current flow of 2000-A !!!!... but you could put your TONGUEacross both those 'probes' and feel NOTHING......YES... more volts means more current, but the human body has RESISTANCE, such that it needsenough voltage to RESULT in the current flow through the body, for it to be a problem.I'm hesitant to explain it further, as it requires a level of understanding beyond this scope here.....Please do not be offended !

author: Monkeh
author_rank: Super Contributor
timestamp: April 15, 2018, 04:14:19 pm
content: Quote from: GlennSprigg on April 15, 2018, 01:43:36 pmI think you missed his point entirely. I'm hesitant to explain further because you'll just rant at me.

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2018, 08:56:08 pm
content: Many years ago (around 1965) when I was in the school lab I got a belt from a single cell lead acid battery, two and a half volts and it gave me a wallop, not sure if there was something that penetrated my skin or or I had a scratch but my hands were dry the cell was not on charge, at the time I assumed it had to be some sort of capacitive effect but it was a wet cell so surely internal leakage would ensure that cannot be the case.

author: SG-1
author_rank: Regular Contributor
timestamp: April 15, 2018, 09:40:54 pm
content: Here is an interesting article on the subject:http://www.ecmweb.com/shock-amp-electrocution/small-contact-voltage-exposures-not-lethal-humanOne thing to keep in mind is that not a single electron leaves the conductor & flows through the human body. Electrons cannot move in fluid.People need to learn the difference between conduction, drift, & displacement current.It's the joules that kill, 13.5 joules in < 3 seconds. Just like any componet the body has a I^2R limit.I meet a man once years ago that was hit by 4160L-L bus, 2400V L-G 60HZ. It removed his arm from the elbow down. The points of contact were his elbow against the frame & hand to a bus bar. Had his elbow not been on the frame we would have never met. The hand may not have actually touched it, it may have reached out & touched him.

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 18, 2018, 01:27:21 pm
content: Monkeh You said......"I think you missed his point entirely. I'm hesitant to explain further because you'll just rant at me."I'm sorry mate.... I don't "rant(?)" at anyone, and I welcome corrections to what I say that is wrong.Please feel free to voice your opinion mate.... I will NOT take offenseI only speak as an electrician/technician for over 40 years in the business, and as such I guess I dohave opinions on the subject. Obviously personal experiences can be complex & varied.Please have a great day/night my friend, and be at peace

author: Monkeh
author_rank: Super Contributor
timestamp: April 18, 2018, 01:28:53 pm
content: Quote from: GlennSprigg on April 18, 2018, 01:27:21 pmOh, but you do.Anyway, I believe his point was that the risk with lower voltage supplies may be more of fire from short circuits than shock.

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 20, 2018, 01:30:13 pm
content: Ok.... I hear all you are saying 'Monkeh'and am not trying to detract from that, mate.I mention my 'expertise' only to highlight that I am not like SOME 'Keyboard Jocky's',(and I certainly do not suggest you are!), though I've been around the block a few times!We/(others?) seem to agree that different people 'FEEL' different results, although it alsodepends on the "path through the body". All those 'variances' (and experience!) aside....It is the "MIlliamps" that kills.... and obviously the less of that... the better !!!!