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#42028 - 09/15/04 03:32 PM Poco clearances  
velect  Offline
Member
Joined: May 2004
Posts: 81
st joseph mi usa
What kind of clearance must a power company have with their primary lines to a residential roof?

Also what height must they maintain off the ground with primary power?


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#42029 - 09/15/04 04:09 PM Re: Poco clearances  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
velect,
It depends on the voltage, the type of wire involved (Insulated vs Un-insulated) and also the type of roof.
Sag under high temperatures also comes into the calculation.
Also, it depends upon whether the area (roof) can be stood on or not.
Not that it will be much help NZECP34 gives Bare wires of -650V - 3.7metres above the peak of the roof.
+650V - 5.0mtrs. Sorry I can't be of more help.


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

#42030 - 09/15/04 04:38 PM Re: Poco clearances  
CharlieE  Offline
Member
Joined: Apr 2004
Posts: 200
Indianapolis
Velect, Trumpy's absolutely correct. You need a lot more information to answer that question. Exactly what is the problem that is prompting this question? Have you contacted the serving electric utility? I am assuming these are electric utility wires and the NESC covers the installation.

You actually need the location in the span, the length of the span, the attachment heights at both poles, the low point of the sag, and the temperature when measured just to calculate the blowout and maximum sag under hot weather loading or winter ice (whichever is worse).

If the wires are actually over the house, all the same information is needed as well as the height of the roof where the wires pass over, the type of roof so to ascertain whether it is accessible by pedestrians (by the NESC rules, forget the definition of accessible in the NEC for this application).

Trumpy did a good job of answering your question but you really need the services of the serving electric utility's trained engineer who is familiar with the NESC or his company's standards since they are based on the NESC and will either meet or exceed the Code. [Linked Image]

- - - - - - - - - - - - - - - - - - - - - - - - - - -
Charlie Eldridge, Indianapolis, Utility Power Guy


Charlie Eldridge, Indianapolis Utility Power Guy

#42031 - 09/15/04 09:20 PM Re: Poco clearances  
velect  Offline
Member
Joined: May 2004
Posts: 81
st joseph mi usa
Wires are uninsulated.....7200 volt.
Eave of the roof is 11 feet from one of the phases
A local roofer was electrocuted Friday when he was moving a shingle conveyor (lifts bundles on the roof) and hit one of the phases. The house is two story with a 4/12 pitch

The three phase feeds a lumber yard a few hundred yards down the road.
Poles are approximately 200 feet apart

[This message has been edited by velect (edited 09-16-2004).]


#42032 - 09/16/04 08:32 AM Re: Poco clearances  
CharlieE  Offline
Member
Joined: Apr 2004
Posts: 200
Indianapolis
The standard required clearance is 7.5 feet for 12470Y/7200 volts. I don't understand why this would not be enough clearance for normal conditions. If any maintenance is to be done, it would be time to call the electric utility and have them de-energize the line or cover it. Our policy is to de-energize since people seem to think that the line is safe if it is covered (it is not, it is just safer).

I am really sorry for the fatality but you can't walk out into traffic and expect not to get hit. [Linked Image]


Charlie Eldridge, Indianapolis Utility Power Guy


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