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 Post subject: Temporary Mechanical Jumpers
PostPosted: Mon Apr 07, 2014 9:46 am 

Joined: Mon Apr 07, 2014 9:39 am
Posts: 1
ASTM 2321-05 says that insulated jumpers can be considered good for incidental contact and MAD.
I strongly disagree and have always covered jumpers with approved cover that has been tested.
That being said many people hang their hat on the ASTM standard. I can't find anything in OSHA that would
discount what ASTM says. I need HELP education my lineman on this subject. Section 4.2 of ASTM 2321.05 States "Bypass jumpers are insulated to temporarily protect personnel from brush or accidental contact. I was always trained that in order for this to happen it had to be covered by an approved & tested cover ie:
Rubber Line hose or Blanket.
What are your thoughts?


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PostPosted: Thu Apr 10, 2014 12:43 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
There are cases where testing is not required. Case in point: roll style blanket (not the precut sheets) does NOT require testing. You just cut off what you need and use it.

Since you mentioned linemen, lets be clear about some differences here. At low voltage (<1 kV generally by standards), all you need is insulation. Tracking, PD, and similar surface effects as a result of voltage (pressure) don't happen. At that level, the ASTM standard would certainly be correct.

Above 1 kV, things change. Tracking and other PD effects certainly exist. Even if you have sufficient insulation to withstand the voltage when the conductor is in free air, when you move a grounded object close to it, the electrical lines of force bend and concentrate the voltage at one side of the cable. This causes voltage to appear OUTSIDE the insulation. Simultaneously, the grounded object has charges that appear at the surface that are opposite polarity. And once this charge difference exceeds the breakdwon voltage of the air in between, or contact is made...guess what happens next? Rapid breakdown of the insulation. This is one of the main reasons for using shielded conductors underground, inside substations, etc.

So...I would have to say that I agree with the ASTM standard at low voltages but at 4.16 kV or higher voltage standards, contact with covered (but not shielded) power lines can be pretty fatal.


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PostPosted: Mon Apr 14, 2014 11:59 am 

Joined: Thu May 10, 2012 5:00 pm
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Location: United Kingdom
Hm, the thing is, for rubber glove work, a correctly rated insulated by-pass jumper which is inspected and periodically electrically tested can be considered no different to a bare conductor with a piece of linehose covering it; good for brush contact.
Also, to put things into perspective, you rely on your gloves as a level of insulation as you do with linehose and blankets - I don't see why you would need to treat insulated by-pass jumpers as a special case.


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PostPosted: Mon Apr 21, 2014 10:43 am 

Joined: Thu Mar 10, 2011 12:14 pm
Posts: 16
Location: Denver, CO
First of all, Section 1.3 of the Scope for this standard clearly states that the use and maintenance of this equipment is beyond the scope of this standard. ASTM Standard F2321 (latest) is a design standard.
Second, Section 4.2 of the Significance and use portion of this standard states that bypass jumpers are devices designed and used ....to keep circuits energized... AND to protect personnel from brush or accidental contact ONLY. The work practice of placing additional insulation over installed jumpers is both prudent and appropriate if the personnel is within reaching distance especially if working on adjacent circuits, phases or structural components of different potentials. I suggest you look to your trade labor organizations or industry associations for common work practices that are consistent throughout your area of operation. The new OSHA final rule document for the 1910.269 re-write has some good comments/references within the preamble that you may also find interesting.


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