Clearance to sign
- Thread starter carl
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bphgravity
Senior Member
- Location
- Florida
Re: Clearance to sign
These dimensions are not given by the NEC. These clearances are within the scope of the NESC. See Section 23, I believe, of the NESC for equipmnent and line clearances around structures.
These dimensions are not given by the NEC. These clearances are within the scope of the NESC. See Section 23, I believe, of the NESC for equipmnent and line clearances around structures.
charlie
Senior Member
- Location
- Indianapolis
Re: Clearance to sign
Rule 234 in the NESC covers the subject in detail. I would not tackle this without the aid of a qualified engineer due to all the detail I am leaving out of this answer and the complexities of some of the calculations such as conductor blowout. This answer will give you some guidance only.
Table 234-1 indicates for horizontal clearance of open supply conductors, over 750 V to 22 kV to signs as 7.5 feet with applicable footnotes. Some are just common sense such as being the closest point of approach of a motorized sign so I will skip those. When you calculate the maximum displacement due to wind (normally 6 pounds per square foot), the minimum clearance shall not be less than 4.5 feet. Where there is not enough space, the clearance may be reduced to 7 feet if the voltage is limited to 8.7 kV to ground.
If not readily accessible to pedestrians:
If the sign doesn't require painting, washing, changing sign letters, etc. that a person would be between the sign and the line, the clearance may be reduced by 2 feet. Where there is not enough space and the lines are covered to limit the likelihood of a short circuit in the case of a momentary contact, the clearance may be reduced by 2 feet.
Rule 234 in the NESC covers the subject in detail. I would not tackle this without the aid of a qualified engineer due to all the detail I am leaving out of this answer and the complexities of some of the calculations such as conductor blowout. This answer will give you some guidance only.
Table 234-1 indicates for horizontal clearance of open supply conductors, over 750 V to 22 kV to signs as 7.5 feet with applicable footnotes. Some are just common sense such as being the closest point of approach of a motorized sign so I will skip those. When you calculate the maximum displacement due to wind (normally 6 pounds per square foot), the minimum clearance shall not be less than 4.5 feet. Where there is not enough space, the clearance may be reduced to 7 feet if the voltage is limited to 8.7 kV to ground.
If not readily accessible to pedestrians:
If the sign doesn't require painting, washing, changing sign letters, etc. that a person would be between the sign and the line, the clearance may be reduced by 2 feet. Where there is not enough space and the lines are covered to limit the likelihood of a short circuit in the case of a momentary contact, the clearance may be reduced by 2 feet.
charlie
Senior Member
- Location
- Indianapolis
Re: Clearance to sign
Please see my previous answer and then add .4" per kV to the answer for up to 470 kV. For 69 kV it would be an additional 18.8 inches so I would call it 9.5 feet for minimum design with 6.5 feet of blowout.
Remember that icing, conductor loading, unusual conditions, specific type of installation, and the like must be taken into consideration when working with a performance standard. That is why you need the aid of a qualified engineer to do these calculations and determine the correct rules and tables to use.
I got this in a private e-mail and thought it should be shared information. The clearances and notes are just about the same as for signs.
Please see my previous answer and then add .4" per kV to the answer for up to 470 kV. For 69 kV it would be an additional 18.8 inches so I would call it 9.5 feet for minimum design with 6.5 feet of blowout.
Remember that icing, conductor loading, unusual conditions, specific type of installation, and the like must be taken into consideration when working with a performance standard. That is why you need the aid of a qualified engineer to do these calculations and determine the correct rules and tables to use.
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