working hot

[kthbrwn]

I have never had to make hot connections. Though, I have heard when one does, it should be done by making up ground first, then the neutral, and finally the hot.
Why would this be any different than making up ground first, then the hot, and finally the neutral?
Seems if a load is present, getting between the hots as in the former, would cause just as severe injury as in the latter, if one would get caught between the neutrals.

 

[ryan_618]

Re: working hot

If you do the grounds then nuetrals then hots, you only have one live wire to deal with (the hot). If you were to do the ground then hot then nuetral, you would have two live wires to deal with (the hot, then the open nuetral).

 

[hurk27]

Re: working hot

There's nothing like getting inbetween open neutrals of a 277 ballast circuit "OUCH"
Or even at 120 volts

 

[don_resqcapt19]

Re: working hot

Making connections to a live source is almost always a violation of the OSHA rules. If the hot work is permitted by the rare exceptions to the OSHA rules PPE for the level of fault current available must be worn. The absolute minimum protection would be fire retardant clothing including a long sleeve shirt, safety glasses, 1000 volt rated tools and 1000 volt rated gloves. If the available fault current is high a full blast suit would be required.
Don

 

[ryan_618]

Re: working hot

Don, when you say available fault current, at which point do you mean? Are you talking about at the breaker protecting the circuit (AIC), or at the transformer?

Also, wouldn't this change depending upon the voltage, length and size of conductors?

I am not condoning anyone to work "hot" here, just trying to learn. It seems to me that a 200 foot run of 480 would have less fault current potential thn a 10 foot run of 120.

 

[gwz2]

Re: working hot

Arc Flash 110.16 and Fault Current 110.9, 110.10 seem to be subjects that no-one want to follow-up on.

The http://www.bussmann.com site has some good reading material to obtain and much of the info is downloadable for free.

But, I think that a knowledgeable instructor with the information is very helpful for discussion.

Try downloading their SPD booklet and study it for the fault current ( Kair ) info.

They also have several Arc Flash topics to download.

OSHA has certainly improved the " working hot " conditons since what was the practice in the field in the fifties.

I am sure that I, and many - many others, of that area are very lucky to be alive today by the work ethics of that time period.

Maybe I'm to linient, but more more current than 20 millamp ( 0.020 amperes ) of current going through a persons body in the heart area is in serious jeopardy for their life.

gwz2

[ November 23, 2003, 09:44 PM: Message edited by: gwz2 ]

 

[hurk27]

Re: working hot

I remember some very hairy times about 25 years ago when we had a supervisor shove a 1/4" metal fish tape into a 400 amp 480 buss I think that was the last time I pulled wire into a hot panel. I was just lucky that I wasn't in front of the panel yet. as it caught carbord box's on fire 20' away. it would probly have put me in the hospital for sure. Of course It was my fault for not catching the fish tape . But thoses were my younger days.

[ November 24, 2003, 01:59 AM: Message edited by: hurk27 ]

 

[don_resqcapt19]

Re: working hot

Ryan,
Yes, the available incident energy determines the level of PPE required. Remember that the PPE must provide protection from both electric shock and the arc blast. The energy available at the point in the circuit must be use in the PPE calculation. These number must be accurate. The fault clearing time is a very important part of the calculation and sometimes the use of a higher fault current number then what is actually available will result in a level of PPE that is not adequate for the actual conditions. This is because the seriousness of skin burns is directly related to the length of time that the fault exists. The use of a available current number that is higher than what is actually available will in some cases show a shorter clearing time for the OCPD and could result in the selection of PPE that will not provide enough protection.
In a fault the arc blast energy often causes the most serious injuries. The temperature of the arc at a fault can be up to 35,000?F. The pressure caused by the electrical explosion can exceed 2000 psi. Look at the type of protection that is required for high energy faults. http://www.mitchellinstruments.com/c6096.pdf
Don

 

[ron]

Re: working hot

Don,
You are right on target. You cannot guess the number of arguments I have had recently with engineers/electricians attempting to perform arc flash calcs, by using the infinite primary calculation on the upstream transformer. It will offer an artificially high available, and hence an artificially faster clearing time of the protective device, and thus result in an artificially lower PPE requirement.
Not to be too excited, but this 70E standard is going to mean some more work for the engineers to perform short circuit calcs.

[ November 24, 2003, 10:00 AM: Message edited by: ron ]

 

[karl riley]

Re: working hot

OK, here is a question I have been avoiding asking for 14 years: am I violating safety rules by just taking bare handed ammeter measurements of hot conductors, uninsulated busses, etc. in panels, switching cabinets, etc.?

Karl

 

[don_resqcapt19]

Re: working hot

Karl,
Yes. You cannot have the energized parts exposed unless you have the correct PPE or are outside of the hazard area. It would be impossible to be out side of the hazard area and use any type of test equipment in almost all cases.
Don

[ November 24, 2003, 01:21 PM: Message edited by: don_resqcapt19 ]

 

[keeper]

Re: working hot

OSHA allows voltage testing with the proper PPE, as many have mentioned in these threads. What about with clamp on ammeters in conjunction with voltage clips? Basically, scenarios where you are installing a power data logger temporarily/permanently?

 

[karl riley]

Re: working hot

Thanks, Don. Do you have an internet reference for this OSHA requirement?

Karl

 

[don_resqcapt19]

Re: working hot

Karl,
Look at 1910.333.
Also look at this letter of interpretation. There are additional interpretation letters here. OSHA has not directly adopted NFPA 70E, but has recoginized it as a standard to be followe when working on or near energized electrical equipment.
Don

[ November 25, 2003, 11:58 AM: Message edited by: don_resqcapt19 ]

 

[karl riley]

Re: working hot

Don, thanks. I have downloaded the sites and will study them. Does OSHA have jurisdiction only on employees? It sounds like it.

Of course safety proceedures should be followed, but it is good to know the law.

Karl

 

[Guest]

Re: working hot

Personally I think PPE is very good PR. It's pretty cool for the client when you show up with jack boots; leather aprons; leather chaps; face shields; hearing protection; huge gloves; then you throw down some rubber mats; loop "danger" tape around every column, tree, or desk. That's fun stuff!

 

[hurk27]

Re: working hot

Wayne you forgot to tell the good part, When you ask the home owner which wire is the hot one. LOL
I would of loved to see there face.

Now I know what Roger was talking about starting the post with my own name LOL

 

[pierre]

Re: working hot

This has been a very good thread, especially with the links provided by Don. Wow what a lot of info!! You wonder why when you talk to electricians they avoid this like the plague

Pierre

 

[brian john]

Re: working hot

This year alone I have been involved with three seperate situations where electricians were pulling feeders into energized switchgear. In order to save time they had terminated the other end (load) including the EGC in all three cases the EGC shorted to the bus. This was three seperate contractors, three seperate jobs all 480/277 all included a trip to the hospital.


HURK
There's nothing like getting in between open neutrals of a 277 ballast circuit "OUCH"
Or even at 120 volts

Well pretty much like getting between a open hot and a load.

 

[larryl]

Re: working hot

grounds first
neutral second
then hot
you dont want to loose a neutral,,trust me on this,,NEURTAL= FIRST ON LAST OFF,,sorry for yelling at ya,,
be safe,,
larry