Working with mains voltage - Page 1
Forum section: electronics / general

author: DeanA
author_rank: Regular Contributor
timestamp: February 26, 2015, 11:05:17 am
content: Hi all,A question on working with mains voltage equipment and liability should someone be injured or even killed.I've designed an off line power supply (240VAC) for LED lanterns which has been in production for a few years now. I'm not concerned about the safety of the finished product which has been approved by the relevant authorities. My concern is for production staff who test the product before it's assembled in the final enclosure. There is live mains present that could be contacted during the test procedure. We've tried to make the test process as safe as possible but accidents could still happen. There is also the repair technician who works on the faulty production units who could also be at risk. Not to mention myself working on new designs and such.In Australia you are not even supposed to change a 3 pin plug unless you're a licensed electrician. So if the production staff, the technician or I get injured or killed while working on mains equipment will insurance be valid? Insurance companies may try to get out of any claim if they can. I'm an employee of the company but I hate the thought of my family being left in debt if work cover or my life insurance wouldn't pay out. I'm also worried I could be held personally liable as designer and engineering manager should anyone else be injured.I know a lot of this would be country and insurance company specific but I wanted to see what the views of the EEV community are.Thanks,Regards,Dean.

author: Kjelt
author_rank: Super Contributor
timestamp: February 26, 2015, 02:49:11 pm
content: As I see it but I am not a lawyerQuote from: DeanA on February 26, 2015, 11:05:17 amThis is the responsibility of the company they do this work for. There should be qualified, instructed personell, isolated workbenches or other safety precautions taken. All the responsibility of the company.QuoteWhat are the taken precautions? Isolated mains supply? Earth breakers? Emergency stop buttons to shut down all benches at once? Instructions never to work alone.These are just a few that were in place at my place of work when we worked on such stuff.But you are saying you are not an informed person? You are not aware of the local electrical guidelines, dangers etc?

author: German_EE
author_rank: Super Contributor
timestamp: February 26, 2015, 07:57:04 pm
content: I have seen mains powered devices under testing where they sit in an insulated enclosure with a transparent top, the mains does not switch on until the top is closed. Bonus points if your test equipment with those live connections is inside the box as well.As for the repair technician, put him in a separate area and give him a workbench that's running off an isolation transformer. I know that mains work normally means that you should not work alone but I'm more interested in keeping the 220V away from the assembly workers here.

author: katzohki
author_rank: Frequent Contributor
timestamp: February 26, 2015, 08:02:54 pm
content: Get in touch with your corporate lawyers if you can and have them work on it.Good approach is insulated box with undefeatable lockout. Product goes in, lid closes and mains gets turned on. If the box is opened mains power goes out (turns off). We work with very high voltage here and had to add discharge circuits that will drain out the HV if the box is opened. I don't have any safeties on my engineering work bench and I have felt the touch of as much as 4000V many times. Not fun.

author: calexanian
author_rank: Super Contributor
timestamp: February 26, 2015, 08:43:28 pm
content: I don't know about over there, but here in the U.S. the contract manufacturer should have their own liability insurance for their own employees. If your product is made to the acceptable standards and you are not interfering with their assembly practices for those standards then that should be their responsibility. Of course, anybody over here can sue for just about anything. They may not win, but you cant stop them from trying. All you can do is make sure you are following acceptable rules. Good contract manufacturers should have their own practices down and verified by somebody like U.L. Or an NTRL lab, or OSHA here in the states, and to a certain extent ISO.

author: David_AVD
author_rank: Super Contributor
timestamp: February 26, 2015, 09:19:38 pm
content: Repairing mains powered equipment usually means operating, probing and adjusting it while energised.I'd recommend that each work bench have it's own RCD on the power outlets. That way it's immediately obvious which bench caused the issue and who may be affected (maybe just got zapped). It also means you won't have the room lighting go out causing more safety issues. Drill into the workers that they mustunplugthe item under test/repair before soldering, touching the internals, etc. Simply switching it off on the item or the power point is not acceptable.As for the "not even supposed to change a 3 pin plug unless you're a licensed electrician", this may not apply if you are in a "prescribed workshop" (right wording?). Check with your state's electrical authority, but there obviously needs to be allowance made for assemblers. Nobody has a room full of electricians assembling and wiring up new equipment.

author: calexanian
author_rank: Super Contributor
timestamp: February 27, 2015, 03:15:59 am
content: I have been zapped countless times working of old equipment while energized. I wonder how many nerve synapses I have lost! As much as I try to expound electrical safety i myself have countless hours probing around operating tube amplifiers and mains voltage systems. 3 phase 240, 208 and 480 as well. Count my lucky stars I suppose. I do like the idea of energizing high energy equipment in some sort of clear safety enclosure. If something does go bang, such as a polarized cap or other component put in backwards, or a big transformer or wire wound resistor blowing up (I once vaporized a 250 watt resistor windings while testing a huge pulse modulator) or just a huge arc over you sure feel a lot better when all of the burning debris and toxic fumes stay on the inside of it and not on your face!

author: Someone
author_rank: Super Contributor
timestamp: February 27, 2015, 04:12:20 am
content: Quote from: David_AVD on February 26, 2015, 09:19:38 pmCan you find any references to that? Electrical work on the CAT II supply is regulated to licensed electricians, but plug in appliances can be built and used by anyone. Its when you go to sell it that you have the problems of meeting compliance (for most plug in appliances thats just the same as a normal in service "test and tag").

author: David_AVD
author_rank: Super Contributor
timestamp: February 27, 2015, 04:18:38 am
content: Quote from: Someone on February 27, 2015, 04:12:20 amYou sure about that? As far as I know (in QLD at least), to wire up or work on anything mains powered you need:To be an electricianHave a restricted electrical ticketDo the work in a prescribed electrical workshopThe last one means you can replace a plug in the workshop, but not on-site!As for references, this was from my discussions with the Electrical Workers Board some years ago.

author: Stonent
author_rank: Super Contributor
timestamp: February 27, 2015, 12:37:03 pm
content: If it's been in production for years already why the sudden concern?

author: AlfBaz
author_rank: Super Contributor
timestamp: February 27, 2015, 12:43:20 pm
content: To the OP.Start by looking at AS3000, the definition of competent person and protection by obstacle and then write them into a risk analysis. If necassary have them hook probes up before powering up

author: mswhin63
author_rank: Frequent Contributor
timestamp: February 27, 2015, 03:31:36 pm
content: Each state will be different, In Western Australia currently hold a restricted licence but there is a new system that has been devised which am looking at upgrading and it looks at my experience and qualifications and they can then determine what training program that I can go into.One of the biggest complaints that I had long time ago was our theoretical knowledge of electricity being a electronics technician is still quite good and that there was an unfortunate disparity between electronics technicians and electricians. It was soon after my apprenticeship that I realised that I should have taken the electrical apprenticeship and then transferred to electronics afterwards it would have given me a much greater experience and the ability to do more electrical work when I needed to. But I decided to follow my real ambitions in the electronics industry and got an apprenticeship radio and TV servicing later to become Communications.I think now that there is to become a greater equality in the industry understanding certain fields allowing people like myself to be able to do greater work in the Electrical industry compare to what I was able to do in the past. I only really need to be able to install mains powered smoke alarms when required or remove existing mains powered smoke alarms and replace them with a suitable one for my industry. It appears that I might be to do that now hopefully.I am not really kicking myself for that decision to pursue electrical but it would have been a distinct advantage as there was a couple of the premises that did electrical and now have become electronics technicians.

author: DeanA
author_rank: Regular Contributor
timestamp: February 27, 2015, 09:22:45 pm
content: Quote from: Stonent on February 27, 2015, 12:37:03 pmI've actually been concerned for myself since I started the design and concerned for other staff since production. We have just had a factory OHSE inspection, the inspector didn't even understand what he was looking at when he saw the test setup much less understand the dangers. In the OHSE staff meeting afterwards we were told that if we identify any safety concerns we should raise them with the safety members. So that's what I intend to do but want to do my homework first, the directors can be dismissive of safety concerns especially if it costs them money or slows down the production process.

author: DeanA
author_rank: Regular Contributor
timestamp: February 27, 2015, 09:32:04 pm
content: Quote from: Kjelt on February 26, 2015, 02:49:11 pmThanks for the suggestions.I'll suggest the emergency stop button and not to work alone, these are both good ideas.As for isolated mains, wouldn't that make things more dangerous? All the benches are protected by ELCBs, if we use isolation transformers I don't think the ELCBs would still work. BTW, the directors opinion is that the ELCBs make everything safe, my understanding is that this is not the case if you're hooked across the active-neutral with no path to ground.I need to do some more homework on the local NSW guidelines, I can start with AS3000, does anyone know where else I should be looking for NSW regulations?

author: DeanA
author_rank: Regular Contributor
timestamp: February 27, 2015, 09:45:32 pm
content: Quote from: German_EE on February 26, 2015, 07:57:04 pmThanks,We are using a "bed of nails" test jig, mains is not applied until the handle is lowered, but there is still exposed mains which could be contacted. I'll see if that can be easily insulated with some kind of cover (the directors were unhappy with the time and expense of building the current jig but when I explained the dangers to the factory foreman he insisted).

author: Kjelt
author_rank: Super Contributor
timestamp: February 28, 2015, 04:22:25 pm
content: Quote from: DeanA on February 27, 2015, 09:32:04 pmYes indeed with an isolation transformer no current can run from secondary to earth therefore the ELCB will not work.For higher voltages (3kV) you really need an isolation transformer since one pole (fase) could kill. With mains you have the ELCB switching off.Both systems however do not protect you with double exposure, eg touching both the active(fase) and neutral with two seperate hands.Even if there is a ground connection the current will pass from fase to neutral and if it goes through the heart area it can kill and the ELCB will not shut off since current just flows from active to neutral.Therefore if possible a good operating instruction would be to use one hand only for probing when mains is active