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 Post subject: Shorting cable
PostPosted: Tue Sep 23, 2014 10:42 pm 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2173
Location: North Carolina
Anyone have a practice of shorting cable after disconnecting?

The theory behind the practice is to induce a dead short to trip a breaker/fuse in the event that the wrong cable is wired up during reenergization. The problem I see with it is that the shorted ends better be well held together to withstand a bolted fault or it becomes an arcing one. Open (insulated) ends don't cause arcing or bolted faults, but energized but disconnected cables could exist.


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 Post subject: Re: Shorting cable
PostPosted: Mon Sep 29, 2014 2:49 pm 

Joined: Sun Feb 14, 2010 9:28 pm
Posts: 21
Location: Queensland
Terminated, shorted and earthed. If you disconnect a motor in the field, a bolt through the lugs, taped and a j-box are often employed. Some sites require disconnection at the source end prior to disconnection at the consumer.
In Australia the wiring rules (AS 3000) Voltage in unused conductors recognises the hazard that may occur also due to induction and requires disconnected, redundant or unused conductors to be terminated and protected at both ends in the same manner as is required for live conductors.
Performed correctly, there is no risk from electro-mechanical forces or heating at the connection.

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 Post subject: Re: Shorting cable
PostPosted: Mon Sep 29, 2014 4:12 pm 

Joined: Tue Oct 01, 2013 2:56 pm
Posts: 7
We stipulate that whatever is used for shorting must be the same effective cross section as the phase conductors. If eye lugs are fitted then it should be bolted, but this is not always the case.

Yes, if the duration of the disconnection is longer the best practice is to disconnect from the supply end first. Cases have occurred where the isolation securing (lockout) at the supply end has prevented workers from gaining access to disconnect the supply end after the load end has been disconnected (for a redundant pumpset removal for example). Eventually the job is closed out after everyone has signed off, the lock is removed because the permit is closed, and at a later time the isolation is inadvertently closed back on. Splitting the job into electrical disconnection both ends first before commencing mechanical disconnection (rather than both jobs in parallel after isolation) helps prevent this scenario. A cable disconnected both ends needs to be shorted both ends but need only be earthed at one end.

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 Post subject: Re: Shorting cable
PostPosted: Tue Sep 30, 2014 10:14 am 
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Joined: Sat Feb 27, 2010 5:59 pm
Posts: 72
Location: Cincinnati, OH
Our typical preferred method is when we disconnect utilization equipment we immediately disconnect the source end of the cable as well. In almost all of the distribution equipment we use we can access the cable termination to remove the cables while LOTO devices are applied. Almost all of our motors and transformers are terminated with bolted lugs, so in most cases two phases could be bolted together quickly when they are disconnected, although we haven't made it a practice to do so.

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