Difference Between a 220V & a 277V shock...

[icefalkon]

Hi fella's, hope everyone's doing well. I have been put to task to explain the difference between a 220V shock and a 277V shock. Now both have happened to me in the past and without much soapboxing I can say the 277V shock hurt a HELL of a lot more. My question is...how do I explain the WHY of it?

I remember long ago being told but can't remember and can't seem to find any of my books from my apprenticeship...

Can anyone give me a hand with this?

Steve from NY

 

[joe tedesco]

Hi fella's, hope everyone's doing well. I have been put to task to explain the difference between a 220V shock and a 277V shock. Now both have happened to me in the past and without much soapboxing I can say the 277V shock hurt a HELL of a lot more. My question is...how do I explain the WHY of it?

I remember long ago being told but can't remember and can't seem to find any of my books from my apprenticeship...

Can anyone give me a hand with this?

Steve from NY

Look here for some answers

 

[icefalkon]

Hi Joe,

Thanks for the link! What I was looking for though was something like the descriptions of the differences between the line voltage and the high voltage and what exactly about the 277V causes the more severe shock. Is it demonstrated in the sine wave?

Steve from NY

 

[iwire]

Steve it is very unlikely you got a '220 volt shock'.

By '220' I must assume you mean 240 and that is a line to line voltage.

240 line to ground is 120 volts.

In order to receive a 240 shock you would have to touch both lines at the same time. That would be unlikely.

It is much more likely that you touched one line and ground which gives you a 120 volt shock.

However 277 volts is line to ground so if you touch a 277 line and ground you get a 277 volt shock and yes they hurt badly.

Now all that aside you had better change your work habits before you wind up dead.

 

[Jim W in Tampa]

As Bob said ,you most likely got 120 not 240.Either one can kill you.277 is nothing to toy with.I been hit 2 times.All it takes is one loose strand of wire or a nut that falls off.Do not work 277 live.

 

[joe tedesco]

See the following for electrical safety:

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70E

NEC 410.73 has added a new rule to become effective 01/2008 concerning disconnects for fixtures that was added to the NEC because of the dead electricians who encountered 277 volts in ceiling spaces in the field!

Researching www.osha.gov for additional information is also suggested.

http://www.osha.gov/SLTC/electrical/index.html

Some major changes in the 2008 NEC are being consideered too related to energized circuits. Se the ROP at www.nfpa.org

 

[icefalkon]

Thanks for the info guys.

The first time I was hit with 277V was in a hospital here in NYC. We were working on the emergency lighting circuit and had properly shut the circuit down and locked/tagged out the breaker. We made our run into the 1900 box and I was splicing the neutral (first) when the outer pad of my hand made contact with the box. BAMMMMMMMMMM

After recovering, much swearing, finding my linesmans from where I threw them....we found out that Building Maintenance TAPPED the neutral and added another 277V line to supply the lights in a shanty they built. Instead of pulling another pair of wires to the panel, they found a spare where they were working but apparently couldn't "fit" another neutral into the splice in their box. So they ran a line into the closest 1900 box they could find to pick up another neutral...right outside the door of the shanty.

The other time was when changing a 277V ballast in a manufacturing plant. While it's difficult to differentiate the difference in pain...I'll go with the ballast hit was worse. Here in NYC there are locations that simply cannot be worked on dead. While the Union has made it the rule to ALWAYS work on de-energized circuits, there is no rule for such according to OSHA. Certain manufacturing plants, printing presses and hospitals require certain circuits to have their maintenance performed on them "live". Only recently with the NFPA-70 have institutions like these been purchasing the proper safety equiptment for live work.

The 220V was actually 240V and was my own fault. 100%

About 10 years ago I was working in a control panel for some machinery and talking to someone. I had the schematic on the bottom lip of the panel and while talking to the person...like an ass I reached in for the print. My hand went right onto the end of the terminal strip where the two phases were landed. Haven't repeated THAT one thank God...it was an eye opener and makes one pay closer attention.

While it's good practice and gospel to say that all electricians should NEVER work on live circuits...the truth of the matter is that we ALL have at one point or another. Whether it's getting buzzed from a splice or getting hung up on a Federal breaker that never popped...it happens. We can only try our best to make our work habit safer.

I brought this thread up because a kid on the job got blasted while changing a ballast. While it's easy to say that 277V hurts more than a 120V shock...he asked about the "why's" of it. How come 277V will hold you up more often than 120V will....what about 220 (240V)? Doesn't that have an equal chance of holding as 277/480V? I remembered something about the differences in the sine waves between Line and High Voltages but couldn't remember exactly.

Again,

Thanks for all your input guys.

Steve from NY

 

[bphgravity]

I agree that contact with 240V is not likely. In general, the higher the voltage, the less time duration you have to survive the shock.

 

[iwire]

Here in NYC there are locations that simply cannot be worked on dead. While the Union has made it the rule to ALWAYS work on de-energized circuits, there is no rule for such according to OSHA. Certain manufacturing plants, printing presses and hospitals require certain circuits to have their maintenance performed on them "live".

That is not really the case.

OSHA does not allow working hot except for very few instances and if it is a situation that must be worked hot you have to suit up.

Yes your right we have all done it.....but nothing will change until we change our own attitudes about it.

Why should we put our selfs at risk just so a factory can keep on making what ever it is they make?

As far as hospitals you don't want to be working critical circuits hot as if you do mess up and the circuit drops you have a much bigger problem than a scheduled shut down would have caused.

JMO, Bob

 

[icefalkon]

I've been looking for where OSHA says you cannot work live and where it's mandated for two men to be working on a live circuit and am coming up with nothing. The most I've gotten is that...if a circuit must be worked on live...wear PPE. There's not a hospital I've ever worked in (quite a few) that has a rule for turning their emergency lighting circuit off for ANY reason whatsoever. It's either work live or don't work. Only recently has PPE become the way to go and that's a damn good thing. Prior to that it was wear gloves and goggles if you're worried...that's it. So it became common practice to always have two journeymen working together on 277V circuits, but I've recently been told that's not what OSHA says they have to allow us to do. The only instance I've found where it's mandated to have two journeypersons working together is over 600V High Voltage. But doesn't OSHA also put 277V into the 600V "OTHER" catagory for High Voltage?

Steve from NY

 

[jim dungar]

Unless they have adopted a specific rule, OSHA uses "accepted industry standards" as their major references when issuing citations.

In the case of electrical safety OSHA is citing NFPA 70E(2004) rather than creating their own rules. NFPA 70E is about an entire Electrical Safety-related Work Practices program not just arc flash.

NFPA 70E acknowledges that "testing, troubleshooting, and voltage measuring" requires some parts to be energized, and so does not require a "live work" permit for these tasks provided the provisions of Chapter 1 (including training and PPE) are followed.

NFPA 70E makes reference to NFPA70B Recommended Practice for Electrical Equipment Maintenance, so it would be possible for OSHA to also cite this as a standard.

 

[don_resqcapt19]

The following is from the OSHA site.

General." Safety-related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts, when work is performed near or on equipment or circuits which are or may be energized. The specific safety-related work practices shall be consistent with the nature and extent of the associated electrical hazards.

[URL="http://www.osha.gov/pls/oshaweb/owalink.query_links?src_doc_type=STANDARDS&src_unique_file=1910_0333&src_anchor_name=1910.333(a)(1)"]1910.333(a)(1)[/URL] "Deenergized parts." Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations. Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs.

Note 1: Examples of increased or additional hazards include interruption of life support equipment, deactivation of emergency alarm systems, shutdown of hazardous location ventilation equipment, or removal of illumination for an area.

Note 2: Examples of work that may be performed on or near energized circuit parts because of infeasibility due to equipment design or operational limitations include testing of electric circuits that can only be performed with the circuit energized and work on circuits that form an integral part of a continuous industrial process in a chemical plant that would otherwise need to be completely shut down in order to permit work on one circuit or piece of equipment.

 

[muskiedog]

Rule #1

Rule #1

Check, check , check. Assume it is never a dead curcuit.

 

[Jim W in Tampa]

Always use your hot stick and test it first

 

[jim dungar]

Remember, until you have verified it as de-energized, you must follow all of the "live work" practices. If you are following the task tables of NFPA 70E voltage testing is a 2*, which means normal Category 2 PPE and also a "double layer switching hood".

 

[marinesgt0411]

a way too far simplified answer to your question is OHMS law if resistance is the same (your body) and you increase voltage 120,240 to 277 what happens to current? I=E/R

 

[ramsy]

something about the differences in the sine waves between Line and High Voltages..

The 277vac sine wave originates from a 3-phase xfrmr peaking 3-times per 60Hz cycle vs twice for single-phase 240vac. So, peak power hits at least 33% more times during the entire contact duration.

As marinesgt0411 says, another reason it hurts worse, besides delivering more peaks, may be higher voltage. Less than 50 volts is a threshold for PPE, so if an extra 50 volts overcomes more resistance and body mass, more nerves may absorb more watts with 277 vs 240vac, ~40 volt difference.

1910.333(a)(1) "Deenergize or dawn PPE"

Contractor safety record, OSHA 300 log, is becoming decisive in commercial bids. OSHA also enforces employee rights to "Refuse to work in unsafe conditions" and "to view an employer's OSHA 300 log of occupational injuries & illnesses. I agree, this assertive kind of task ownership, excercised responsibly, will be more successful and respected when marketing a business or resume.

 

[George Stolz]

The first time I was hit with 277V was in a hospital here in NYC. We were working on the emergency lighting circuit and had properly shut the circuit down and locked/tagged out the breaker. We made our run into the 1900 box and I was splicing the neutral (first) when the outer pad of my hand made contact with the box. BAMMMMMMMMMM

After recovering, much swearing, finding my linesmans from where I threw them....we found out that Building Maintenance TAPPED the neutral and added another 277V line to supply the lights in a shanty they built. Instead of pulling another pair of wires to the panel, they found a spare where they were working but apparently couldn't "fit" another neutral into the splice in their box. So they ran a line into the closest 1900 box they could find to pick up another neutral...right outside the door of the shanty.

And you lived to learn (and teach others) a lesson.

When you seperate neutrals on a presumed dead circuit, slap a tick tracer against them one more time to be sure they're not in use. Look for small sparks when you seperate them.

(Not picking on you.)

 

[yanici]

New member here so don't kill me. Don you mention Osha 1910.333(a)(1). One of the exceptions to working live in Osha is "loss of illumination for an area". There is a conflict in NFPA 70-E, that exception was removed. I'm not sure if it was intentional on the NFPA's part or not. It is my understanding that OSHA has not formally adopted 70-E but is enforcing it if a violation occurs.

At my place of employment we regularly change ballast live, even 277 volt. I think it's wrong. Any other opinions?

 

[muskiedog]

I did ballast live soa snot to shut down the lighting over production operations

I did ballast live soa snot to shut down the lighting over production operations

I recieved a shock from doing them live. I had done it 100's of times until the insulation was cracked and I happened to be resting my arm on the metal rafts. Dropped me to the bottom of the cage and my arm hurt for a week. Never did anything alive again. You can always bring in task lighting.