Hand held safety voltage limits - Page 1
Forum section: electronics / general

author: robrenz
author_rank: Super Contributor
timestamp: November 02, 2011, 04:20:40 pm
content: Is there a universally accepted standard for safe voltages for hand held equipment? (hand held meaning accidental contact with the voltage is not preventable in use). I see Pomona listing 33 Vrms/70VDC for unshielded probe stuff that will be hand held. I see others that list 30Vrms/42VDC or 30Vrms/42V peak. I plan to print these safety limits on a hand held piece of equipment that by design will allow accidental contact with whatever voltage is supplied to it.

author: robrenz
author_rank: Super Contributor
timestamp: November 02, 2011, 06:21:37 pm
content: To clarify the question a little more. This is strictly a question of what is generally safe for the human body with dry hand contact. This has nothing to do with insulation rating. I know this question can get real complicated with body resistance and actual current across the heart etc.Here is the Pomona listing for banana patch cordModel B: Multi-stacking Banana Plug Patch Cord features a nickel plated finishAvailable in 10 colors: Black, Red, Blue, Orange, Green, Violet, Yellow, Gray, Brown, or WhiteModel 2948: Multi-Stacking Banana Plug Patch Cord features a gold-plated finishAvailable colors: Black or RedCable: 18 AWG Wire, 0.144in (3.56mm) O.D.Rating: For CE compliance and for personal safety, do not hold in hand when voltages exceed 33 Vrms / 70 Vdc. Maximum voltage for hands free use: 5000 Vdc.Here is an excerpt from a Tektronix technical brief on floating oscilloscope measurements.This warning applies to circuitsthat have voltages ofgreater than 30 VRMS (>42 Vpk).If the circuit under test hasvoltages that exceed 30 VRMS(>42 Vpk), the TDS3000 Serieschassis needs to be connectedto earth ground using thegrounding wire provided withthe instrument (Battery Pack)to prevent electrical shock tothe operator.From a fluke scopemeter pageTo avoid risk of electrical shock, use only the following accessories when a ScopeMeter COM input is connected to >42V peak (30V rms):So where did this 30V rms 42V peak come from and why is Pomona showing 33V rms 70Vdc?

author: Neilm
author_rank: Super Contributor
timestamp: November 02, 2011, 08:48:42 pm
content: Test and measurement equipment is covered by IEC61010. Hand probes and the like have there own separate part. This standard was revised last year so the differences between the two might be due to one meeting the new standard and the other meeting the old.Another possibility is that the patch cords might not be included in the scope of 61010 so the difference might be due to differences between the standards.As for the main part of your question, I don't know of anywhere there are freely available references for data on the human body model.Neil

author: Unknown
author_rank: Unknown
timestamp: November 02, 2011, 09:11:26 pm
content: It is not safe to come into contact with LV or greater, simple as that. Various definitions for the threshold of LV exist in various jurisdictions. Same as a speed limit on a public road, you can debate safety for specific instances till the cows come home. These are arbitrary lines in the sand.What would be achieved by shifting 30V to 36V or 29V, there are well worn determination of voltage and category ranges, why get hung up on the specifics?

author: robrenz
author_rank: Super Contributor
timestamp: November 03, 2011, 01:45:08 am
content: Quote from: Uncle Vernon on November 02, 2011, 09:11:26 pmI am not trying to shift what the "safe" voltage level is. I am looking for what is thegenerally accepted"safe" voltage level for accidental contact. Obviously Fluke and Tek have identified less than 30 VRMS (42 Vpk) as acceptable "safe" levels for inadvertent contact.

author: IanB
author_rank: Super Contributor
timestamp: November 03, 2011, 01:54:30 am
content: Quote from: robrenz on November 03, 2011, 01:45:08 amThis is like a "How long is a piece of string?" It doesn't really matter whether it is 30 V or 40 V, just pick one. Or pick the definition of LV used in the region where the device will be used.In other words, the intent is to protect yourself from legal action, so you need to see what the legal definition of "safe" happens to be where you are. Providing a warning is probably the most important thing to do; the exact numbers on the warning are secondary, as long as they are reasonable and defensible. (And that depends on which court you are going to get sued in.)

author: the_raptor
author_rank: Regular Contributor
timestamp: November 03, 2011, 03:24:18 pm
content: There is a verified account of a US Navy technician electrocuting himself with a 9 volt powered multi-meter so "safe" is incredibly relative. Even something like "dry hand contact" is incredibly relative.I would imagine the standards are similar to EM radiation exposure levels. Cook some animals and then set the "safe" limit to a fraction of that.

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2011, 10:08:45 pm
content: Check the regulations in your jurisdiction. Here in the UK it's anything below 25VAC or 60VDC ripple free don't need to be insulated in dry areas. Lower voltages apply for wet areas or where there are large metallic areas or in cases of permanent contact with the user.From personal experience the voltage at which I get shocked is variable, I've touched 100VDC before without even feeling anything but I've also felt a tingle off an 18VAC transformer.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 04, 2011, 12:45:38 am
content: Quote from: the_raptor on November 03, 2011, 03:24:18 pmIf you mean a battery operated meter,& the battery was the only source of current,I'd like to see the verification.Even with a perfect connection across the 9 volts,the current is ultimately limited by the internal resistance of the battery.It is extremely difficult for people with many years of experience with power supplies & batteries at voltages up to 24 volts to take these reports seriously.One thing that leads to confusion,is that the popular idea of Low Voltage & High Voltage do not agree with that of the Power Authorities.For instance,officially 120 volts AC is still classed as Low Voltage.VK6ZGO

author: the_raptor
author_rank: Regular Contributor
timestamp: November 04, 2011, 01:28:30 pm
content: Quote from: vk6zgo on November 04, 2011, 12:45:38 amI have seen it referenced in the US Navy NEETS and have read accounts from former US Navy techs who saw the actual report.The shock didn't stop his heart it just caused enough fibrillation that he died before anyone found him.Quote from: vk6zgo on November 04, 2011, 12:45:38 am'cause it is if you are an electrician. Guys around here work on 230 v AC without even wearing gloves (I think those guys are morons, but that is another story). I have been looking at mining jobs and they commonly use 11k v AC distribution around the plants, and 30k v AC for stuff like draglines.

author: Neilm
author_rank: Super Contributor
timestamp: November 04, 2011, 04:27:28 pm
content: Quote from: vk6zgo on November 04, 2011, 12:45:38 amI believe he punctured his skin on both hands, making electrical contact with his blood.Neil

author: vk6zgo
author_rank: Super Contributor
timestamp: November 04, 2011, 11:29:48 pm
content: Quote from: the_raptor on November 04, 2011, 01:28:30 pmUnless you are going to handle "hot" wiring directly,why would you need gloves?Thousands of people work safely with 230/250 volt AC wiring safely,by applying some commonsense procedures,the most basic of which is,"Turn the bloody thing off before you touch anything!"On the other hand,anyone who touches powered up 230v AC wiring with their bare hands has a death wish.VK6ZGO

author: quantumfall
author_rank: Regular Contributor
timestamp: November 05, 2011, 11:00:35 am
content: Quote from: the_raptor on November 04, 2011, 01:28:30 pmHaving worked as an electrician in the uk a while ago now I must say, and rules and regulations change, I think most electricians are cautious and not reckless, that said familiarity can breed contempt.Most electricians are doing new or additions to existing systems and work with the power off.I remember being in a large switch room (distribution system for a large bank HQ) as an apprentice and they had a glass legged teak wood topped stand you could stand on and touch 240 Volt bus bars and not feel anything.it was used to work on systems that would have been expensive to shut down I think. You work with one hand and you do not let anyone touch you as you are at 240V relative to earth, Not sure its allowed today.You could light a neon screwdriver on the head of a man when he was touching the bus bars.

author: IanB
author_rank: Super Contributor
timestamp: November 05, 2011, 05:07:06 pm
content: Quote from: quantumfall on November 05, 2011, 11:00:35 amThe key thing about voltage is it's all about potential difference between two conductive points. If there is no potential difference there is no harm, and if there is no conduction there is no harm. When you properly understand this you can be a lot safer working around electricity.One of my favorite videos related to the glass table is this one: