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#150736 - 08/31/05 10:06 PM Bolted shorts for protection..  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
On another thread:
https://www.electrical-contractor.net/ubb/Forum2/HTML/002236.html

the idea was brought up to have a "bolted short" intentionally placed while working on equipment to protect against someone energizing the circuit while work was in progress. (Primarily to protect against those Darwin candidates who don't understand lockout/tagout.)

While the logic may seem sound {any inadvertant energization would be shunted to ground or cleared by the OCP device} I feel the risks aren't worth it.

For example:

Possible explosive failure or dangerous heating of the device(s) used to act as the bolted fault;

Possible violent failure of the circuit breaker/disconnect/fuse while closing in on the fault;

Additional damage to equipment/feeders by the above or failure of the OCP device to open;

Impression of dangerous voltages/currents on metal enclosures/parts if the impedance of the grounding path is not adequate;

The possibilty of workers forgetting to remove the bolted fault upon completion of work.

It would be hard to imagine many work situations where one couldn't tape up/cover/isolate the equipment being worked on. And testing with a volt-tic or meter as many times as needed for safety during performance of the task would be a better option IMHO.

As I'd mentioned in the referenced thread, I'm not talking about POCO work, where grounding rigs are commonly used. All the POCO guys I've talked to say the grounding rig must also be placed out of the work area but as close as practical (on overhead work, usually within one span.) Mainly, to keep it out of the way, but also in case the line is heated up and the rig blows it'll be out of harm's way.

What do you folks think?


Stupid should be painful.

Arc Flash PPE Clothing, LOTO & Insulated Tools

#150737 - 09/02/05 06:05 AM Re: Bolted shorts for protection..  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Mxslick,
I think to a degree what could cause problems here is nothing short of bad communication.
We use Shorting and Earthing (Grounding) of Overhead LV,MV and HV lines here, during maintenance work as part of our Health and Safety practice, it's been like that for years here.
If some idiot was to throw the controlling switch(which would never happen here, it's controlled by the PoCo Control room).
Other side of the coin, make sure that you only use a multi-person lock on your gear.


Let's face it, these days if you're not young, you're old - Red Green grin

#150738 - 09/02/05 04:43 PM Re: Bolted shorts for protection..  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Trumpy:

Quote
I think to a degree what could cause problems here is nothing short of bad communication.


Exactly!! When someone is working on equipment, and locks it out, it is presumed that a tag or note is also present explaining the "whats" and "whys" for the lockout.

It would seem that in most cases of people ignoring LOTO as related on this site, it is usually those who have no clue that work is taking place, they just know that their power went off. Mind, this doesn't excuse the removal of LOTO devices or resetting breakers without knowledge of cause/effect, but explains why these incidents seem to keep happening.

Short of stationing someone at the disconnect or breaker, there is no 100% way of assuring that some fool won't hit the power. Posting someone at the LOTO is exactly what I would do if working on equipment remote from the disconnect/breaker. Give that person a walkie-talkie and orders to not allow anyone near the disconnect/breaker.

Overkill? I don't think so. If I were working on equipment such as a panel, transformer or MCC where the fault potential is high, even paying some one $10+/hour is still a lot cheaper than the consquences of unwanted energization. I wouldn't place my safety on the idea of creating a short in the very equipment I'm working on.

Quote
If some idiot was to throw the controlling switch(which would never happen here, it's controlled by the PoCo Control room).


Which is why the practice is a great idea for utilities, the nature of control and operations makes it a lot safer than what would happen in a commercial/industrial envrionment.

edited to add:

And the standards of training and qualification are a lot higher at most utilites.


[This message has been edited by mxslick (edited 09-02-2005).]


Stupid should be painful.

#150739 - 09/19/05 10:53 AM Re: Bolted shorts for protection..  
Big Ed  Offline
Member
Joined: Apr 2004
Posts: 55
Roxboro, NC, USA
I work at a generation facility. We ALWAYS apply grounding rigs to high/med voltage circuits prior to work (de-engergized of course).

This is not primiarily for re-energization protection but for "stray" voltage protection. When working with very high voltages it is easy to get an induced voltage on tagged and locked conductors.

I don't personally work the poles, but I have discussed this very topic with linemen, and they ground for re-energization. Not by the utility, but by homeowners with generators.

Ed


#150740 - 09/22/05 03:21 AM Re: Bolted shorts for protection..  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
Mxslick, putting spiritual issues aside, whom would you rather it be in this situation. You, who took the time to lock and tagout, or the other guy who grabbed a bolt cutter, cause he thinks he owns the terrritory? Have you never come across one of those "who said anybody could work on this without my say so" types. Lucky , we have come much a long way in this industry as far as safety goes in the 3 decades I have been in the trades. Those kind of guys aren't much of a problem anymore, but still......


#150741 - 09/22/05 06:04 AM Re: Bolted shorts for protection..  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I will not intentionally short or ground fault wiring, IMO doing so puts more people at risk.

Yeah we can say the person hurt may be the one that was breaking the rules and deserves what they get. However I do not want to be part of burning or killing anyone, no matter how much of an idiot they may be.

Beyond that there would be litigation and no doubt the subject of intentionally shorting the wiring would come up.


If I have doubts that LOTO will keep me safe I would rather take the time to disconnect the wiring from the source than to short the circuit.

I do understand that the those that work with higher voltages than I do need to ground out the wiring for their safety. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#150742 - 09/23/05 03:06 PM Re: Bolted shorts for protection..  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
macmikeman:

Actually in my line of work I can play both roles to an extent. (Not the bolt cutter part, but the "who said.." part.)

Many are the managers/projectionists who have gotten the wrong side of my temper when they take it upon themselves to try to help while I get a tool/take a break, etc. So every now and then I puff up and play the part. [Linked Image]

Thankfully as you said, there are fewer of those types around anymore which makes all our work safer.

Like I mentioned above, I'd rather pay to have someone stationed at the lockout if I felt there was any chance of some bozo tampering, rather than use a short for protection. It's my butt that I want to take home in one piece every day.

iwire brought up the best solution of all to this whole debate:

Quote
If I have doubts that LOTO will keep me safe I would rather take the time to disconnect the wiring from the source than to short the circuit.


Even if that means dealing with some of the horrid deadfront designs out there, I agree.


Stupid should be painful.

#150743 - 10/04/05 10:51 PM Re: Bolted shorts for protection..  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Take a look at this:

https://www.electrical-contractor.net/ubb/Forum5/HTML/001094.html


Even though this incident apparently did not start with a bolted fault for protection, think carefully about all of the consequences here. Read all of togol's posts, noting especially that the transformer involved had NO relay {overcurrent/fault} protection.

A graphic illustration of why LOTO and disconnecting feeders (the secondary of the trans in this incident was disconnected) if necessary is the safest way to work.

From the intro, it also appears that the whole thing started due to lack of communication.

[This message has been edited by mxslick (edited 10-04-2005).]


Stupid should be painful.

#150744 - 11/04/05 04:02 PM Re: Bolted shorts for protection..  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Bump.


Stupid should be painful.

#150745 - 11/04/05 05:24 PM Re: Bolted shorts for protection..  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
I don't believe that there really is a hard and fast answer to this one; instead the circumstances need to be evaluated in terms of the equipment involved. This is all a statistics game; the chance that some fool will energize a locked out circuit, the chance that the intentional ground bond will cause serious damage, etc. These risks will be very different for different pieces of equipment.

The philosophy of 'if this bolted ground connection causes a problem, it is the fault of the fool who bypassed the LOTO' is really dangerous; essentially justifying a 'mantrap'. As others have noted, such a bolted connection can itself cause risk for the EC when the time comes to re-energize the equipment. (Though I guess that this latter issue could be dealt with by placing a key for the LOTO lock on the ground bolting apparatus, so that you _couldn't_ re-energize without removing the ground connection.)

But the other side of the coin: shouldn't equipment be _designed_ from the very start to properly deal with ground fault condition? Shouldn't the supply OCPD or GFP simply open?

It seems to me that if the supply equipment is known to _safely_ disconnect in the event of a ground fault or line-line fault, then intentionally bonding a circuit to ground is a low cost method of adding additional safety. If the supply equipment has a reasonable chance to fail in the event of a bolted fault, then doing so is a dangerous practise.

We _know_ that there is equipment which cannot properly tolerate solidly bolted fault. Sometimes this is through poor design, age, etc. There is at least one story here of an arc injury caused by working on a fuse feeding a bolted fault (presumably not an intentional fault, but still...) But IMHO modern service equipment, possibly including GFP protection, properly designed for available fault current, etc., should be able to safely tolerate and open against a bolted fault with minimal damage and no life safety issues.

The system which I worked on this past summer was a high impedance grounded neutral system. A phase to ground fault would cause about 5A of current flow, and the ground fault protection would trip in a couple of cycles. On such a system, intentionally grounding a _single_ phase would _safely_ and swiftly de-energize the system if some fool bypassed LOTO.

-Jon


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