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BobLfoot

Shock Hazard Prevention

36 posts in this topic

In the US we have a device called a GFCI {Ground Fault Circuit Interrupter} OSHA defines it as follows: A ground-fault occurs when there is a break in the low-resistance grounding path from a tool or electrical system. The electrical current may then take an alternative path to the ground through the user, resulting in serious injuries or death. The ground-fault circuit interrupter, or GFCI, is a fast-acting circuit breaker designed to shut off electric power in the event of a ground-fault within as little as 1/40 of a second. It works by comparing the amount of current going to and returning from equipment along the circuit conductors. When the amount going differs from the amount returning by approximately 5 milliamperes, the GFCI interrupts the current. The GFCI is rated to trip quickly enough to prevent an electrical incident. If it is properly installed and maintained, this will happen as soon as the faulty tool is plugged in. If the grounding conductor is not intact or of low-impedance, the GFCI may not trip until a person provides a path. In this case, the person will receive a shock, but the GFCI should trip so quickly that the shock will not be harmful. Right now from my understanding GFCI is required by Construction Trades. Is anyone else using these devices and if so with what results?

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There was an article passed around the chemcial industry a few years ago about a welder who was grinding inside a stainless steel tank, some how he ground through the power cord and electrocuted himself. Since then we require ALL hand tools to be feed through a GFCI. We didn't have the time or money to replace all the outlets in the plant, so we purchased a bunch of portable ones. They plug into any outlet, has about a 6 inch pigtail, with the GFCI built in. Now any maint. worker or contractor must have one at the work site, before a work permit will be issued. If anyone if found using a tool without a GFCI, there are severe consequences, depending on the record of the person involved, it could be termination or if a contractor, ejection from the site, and no future work. For employees we have periodic training, and for contractors we have a safety training course that must be completed before allowing any work to be preformed. So far, (knock on wood) we have not had any cases of electrical shock.

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I design circuits on an ungrounded power system. On most of our outlets we don't use GFCIs, we just float the ground at the receptacle and put a small fuse inline. This way you can short to ground, but never lose service. $

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Same here. Be careful with the ungrounded systems. The first acidental ground is free, the second could get you in trouble. If that is the case then use a ground detection monitor.

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This does absolutely nothing to protect the operators from electrical shock.

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Sounds like there are two opposing views developing. 1. Those who place the prioriity on the machine continuing to function when a hot is grounded and therfore 'float" the receptacle ground like M4N and GerryM. 2. Those who place end user safety as priority 31 and want any ground and /or shock potential no matter how small to shut off the tool and protect the operator. Ken moore and Alaric would seem to fall in this group. Obviously the above is a generalization. Each case needs to be considered individually. Hopefully others will continue to add their thoughts.

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You misunderstood me, or i wasn't very clear. I'm with number 2. I agree with using GFCI's on the extension cords. My earlier comment was regarding the use of ungrounded systems in general. I didn't think M4N's implementation of an ungrounded system, in his case, was quite correct. There are instances where they are safer than a grounded system when implemented correctly. For example, many Hospitals use ungrounded systems. Edited by GerryM

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Apologies Gerry as I said my post was a generalization. The only ungrounded systems I've worked with were 24vdc control never 120 ac.

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Hi, In the U.K. we call them R.C.D.s - Residual Current Device. They are available in trip currents of 10mA or 30mA. What one often finds over here is that most portable tools in factories and construction sites are supplied via a 240/110v isolating transformer. These were originally intended to protect construction site workers from shocks. 'Unfortunately' they are widely used in factories (maintenance depts.) so we technicians have to lug heavy transformers around whenever we wish to use a drill/grinder etc. I guess RCDs (robust portable ones) have only relatively recently become available. Hopefully the 'legacy' transformers wiil die out.

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So USA = GFCI and UK = RCD and I know Austraila calles them something else. others care to educatee us all.

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I think Australia uses RCD also. HERE is Sleepy Wombat's thread asking about the RCD symbol

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Hi gents, In South Africa we call them Earth Leakage Circuit Breakers. As mentioned, if there is a differential larger than x mA, the supply will be tripped. This is standard throughout all houses in South Africa.

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Oh, to educate you all, in Sweden we call them "jordfelsbrytare" - "earth fault breaker". And in German "Fehlerstromschutzschalter" - "error current protective switch" or "FI-Schalter" (error current switch). And in Spanish "Interruptor diferencial" - "differencial breaker". :) http://en.wikipedia.org/wiki/Residual-current_device

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Thanks Tedron, we can now add tose to our list compiled by Sanif RCDs (Residual Current Devices), common usage in Australia RCCBs (Residual Current Circuit Breakers), common usage in Australia ELCBs (Earth Leakage Circuit-Breakers), common usage in Singapore, Malaysia CBRs (Core Balance Relays), I don't really know where it is commonly used GFIs (Ground Fault Interrupts), common usage in USA GFCI ( Ground Fault Circuit Interrupter), common usage in USA And now Sweedish - "jordfelsbrytare" - "earth fault breaker" German "Fehlerstromschutzschalter" - "error current protective switch" or "FI-Schalter" And in Spanish "Interruptor diferencial" - "differencial breaker"

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I recognize the Core Balance Relay. Can't swear it is common or even origionates from the US but have heard people call them that when you ask what a GFI is. Also refered to in some AB motor protection part numbers

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In emails with people in Asia, I have seen the term "earth leakage relay" used instead of "core balance relay".

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I might as well complete the list with the rest of the languages from Wikipedia as well. Where I understand anything of it, I have written a literal translation. :) Czech: Proudový chráni? Danish: Fejlstrømsafbryder (fault current breaker) Italian: Interruttore differenziale (differential breaker, don't really know Italian but it's almost identical to the Spanish term.) Hebrew: ???? ??? (I can't even tell you the names of those letters!) Dutch: Aardlekschakelaar (Unsure, but my knowledge and German makes me guess it's "ground leak breaker") Polish: Bezpiecznik ró?nicowo-pr?dowy

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Translate to earth leakage switch....

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Opening the circuit breaker off while working with outlets will protect from shock. It seems to me that if the 120VAC shorts to floating "ground", nothing will change, because there is no conducting path to the neutral through ground. The current must still travel on the neutral conductor to get back to the transformer. $ Edited by Money4Nothing

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Yes and no. Legally in the USA a 50-250 volts are considered the same shock hazard. But...

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With all respect my friend, there's nothing legal about it (the voltage that is). If your neutral is ungrounded at the source, and you short the hot to ground, no matter what the voltage is (within 250V or so ), you won't cause a shock hazard because there is no conducting path from ground to the voltage source (in my case, a Delta-Wye 480/208 transformer). This is a well-established technology, its used in many hospitals and other facilities throughout the USA and the world, and is accepted by many governing bodies throughout the world. Cheers! $ Edited by Money4Nothing

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Hey I'm just reading straight out of the NFPA 70E. Grounded or not it's not legal according to the book

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I think we are dealing with Apples and Oranges here.in this post and I'll be the first to admit the portion I understand is less than the portion I don't understand. Perhaps after this post M4N and TW can claify the Apple and Orange systems as I'll call them. Please forgive any assumptions or over simplifications. I am learning a lot from this discussion and hope it continues. Apple System {no relationship to MAC}- Used primarily for Industry and goverend by NFPA70. A normal 120 volt outlet in this system had a ground which can be traced back to earth ground. It also has a neutral which can be traced back to a common point at the power source and at this common point it bridges to ground. A GFCI used in this system will trip on the following conditions. Condition 1 a current flow detedted in the ground will trip the breker. Condition 2 a current flow inbalance between Hot and Neutral will trip the breaker. The assumption is that an alternate path to source exists and that path could be the operator. Primary concern with GFCI in this system is operator safety. A short between an easrth ground source {Water Pipe} and a Hot through the operators body would trip the GFCI and result in minimal injury. Orange System - Used primarily for Institutional and Medical applications and is goverend by ???. A normal 120 volt outlet in this system has a ground which does not connect to earth ground. This is what I believe is called a "floated ground". The neutral in this system does return to source. The GFCI breaker will not function in this environment. An operator touching "Floating Ground" and Hot in this system would not receive a shock and operation of the device would continue. A short between an earth ground source {Water Pipe or Sink Faucet} and a Hot through the operators body would continue to shock the operator until the overcurrent limit device was tripped and would result in significant potential danger to the operator. Ok guru's and experts from all over poke holes and let's all learn to do better.

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I'm positive that the hospital is not exempt from the shock hazard but there is an additional section for hospitals that may have additional stipulations. Finally home so will have read it tomorrow. Floating ground, hooked to neutral, not connected, or hooked to a radio antenna for better reception: The shock hazard guidelines still apply

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OK I'll go a little bit more in depth on this issue. First of all, the NFPA 70E is a standard addressing electrically safe work practices, while the NFPA70 is an electrical installation document and protects employees under normal circumstances. NFPA 70 (aka the National Electric Code) Article 517 contains regulations for grounding in health care facilities. 517.19 Critical Care Areas (F) Isolated Power System Grounding. Where an isolated ungrounded power source is used and limits the first-fault current to a low magnitude, the grounding conductor associated with the secondary circuit shall be permitted to be run outside of the enclosure of the power conductors in the same circuit. 517.20 Wet Locations (A) Receptacles and Fixed Equipment. All receptacles and fixed equipment within the area of the wet location shall have ground-fault circuit-interrupter protection for personnel if interruption of power under fault conditions can be tolerated, or be served by an isolated power system if such interruption cannot be tolerated. (B) Isolated Power Systems. Where an isolated power system is utilized, the equipment shall be listed for the purpose and installed so that it meets the provisions of and is in accordance with 517.160. 517.21 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interrupter protection for personnel shall not be required for receptacles installed in those critical care areas where the toilet and basin are installed within the patient room. 517.160 Isolated Power Systems (A) Installations. (1) Isolated Power Circuits. Each isolated power circuit shall be controlled by a switch that has a disconnecting pole in each isolated circuit conductor to simultaneously disconnect all power. Such isolation shall be accomplished by means of one or more transformers haveing no electrical connection between primary and secondary windings, by means of motor generator sets, or by means of suitably isolated batteries. etc, etc...... Interstingly enough, (and humorously enough) you don't need ground fault protection if you classify your receptacle as a "shaver". 422-40 Polarity in Cord- and Plug-Connected Appliances. If the appliance is provided with a manually operated, line-connected, single-pole switch for appliance on-off operations, an Edison-base lampholder, or a 15- or 20-ampere receptacle, the attchment plug shall be of the polarized or grounding type. A 2-wire, nonpolarized attachment plug shall be permitted to be used on a listed double-insulated shaver. In my case, several of my installations use isolating transformers, and meet the isolation protection described in 517.160. The surveyor having authority over my installation is the American Bureau of Shipping. They require a method for grounding and ground fault protection that is defined in NFPA70. It doesn't matter to ABS that the scope of the article is Health Care Facilities, just as long as it is a method that's defined in the NFPA70. Now of course my first consideration is whether or not the installation is actually safe, regardless of what the regulations say. I am convinced that it is, from an electrical design standpoint. Its impossible to receive an electric shock due to a ground fault, because no potential exists between ground and hot (not even 50-250V, ). Anyway, I only use this method in a couple of places where it's convenient. The majority of my installations use GFCIs. For some of you, keep in mind that NFPA70E is not Incorporated by Reference in 29 CFR 1910.6 (Therefore, OSHA does not enforce it). However, OSHA has several comparable requirements that are enforceable, but these have to do with the use of protective equipment. But OSHA is not my regulatory agency, ABS and IMO are, so I don't have to worry about them. I hope this helps! Cheers! $ Edited by Money4Nothing

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