Vertical Clearance for an Overhead Line (NEC or NESC)

[James Rowe]

We have a project that is planning on running a pipe bridge from one building to another, this pipe bridge would be passing directly below a 69kV line. This line is an owner line not a utility line. I am just trying to determine if/what the clearance should be between the pipe bridge and the overhead line.

 

[kwired]

If it is not a utility owned line then generally NEC is what will apply to it.

 

[augie47]

Seems to be covered by 225.61

 

[James Rowe]

So if I understand this correctly then: 225.61 (B) States that above 22kV we increase the distance listed in the table by 0.4" per kV, 69kV - 22kV = 47kV, 47kV x .4" = 18.8" = 1.57' So, Add 1.6' (rounding up).
In the table I am assuming a pipe bridge would fall under "Over or under roofs or projections not readily accessible to people" ?? ; Vertical clearance 12.5' + 1.6' = 14.1'
So, If the existing 69kV line is at 30' then the maximum height of the pipe rack is 30' - 14.1' =15.9'?

 

[augie47]

appears correct. still scary when you figure most pipe is 21'
You might want to research OSHA rules......

 

[James Rowe]

Yes, I am just glad that our process group is asking the question before the design/install the pipe rack.
In regard to OSHS, what I have found is that Over 50kV to 200kV the Minimum Approach Distance is 15', So they can not get closer than 15' when constructing? The line would either need to be de-energized or some other precautions would need to be implied?

Thanks!

 

[tw1156]

So if I understand this correctly then: 225.61 (B) States that above 22kV we increase the distance listed in the table by 0.4" per kV, 69kV - 22kV = 47kV, 47kV x .4" = 18.8" = 1.57' So, Add 1.6' (rounding up).
In the table I am assuming a pipe bridge would fall under "Over or under roofs or projections not readily accessible to people" ?? ; Vertical clearance 12.5' + 1.6' = 14.1'
So, If the existing 69kV line is at 30' then the maximum height of the pipe rack is 30' - 14.1' =15.9'?

The line sag needs to be factored in as the worst case distance as well (think wind, summer time heating, ice loads, etc factoring in); so it would be the 14.1' during the lowest point of worst case scenario, not during conditions that you may measure today.

 

[James Rowe]

So if I understand this correctly then: 225.61 (B) States that above 22kV we increase the distance listed in the table by 0.4" per kV, 69kV - 22kV = 47kV, 47kV x .4" = 18.8" = 1.57' So, Add 1.6' (rounding up).
In the table I am assuming a pipe bridge would fall under "Over or under roofs or projections not readily accessible to people" ?? ; Vertical clearance 12.5' + 1.6' = 14.1'
So, If the existing 69kV line is at 30' then the maximum height of the pipe rack is 30' - 14.1' =15.9'?

OK, Looking at this again while working through NESC Table 234-1 I am noticing both NEC and NESC are referring to Phase to Ground Voltage 69kV/1.73 = 40kV. So 40kV - 22kV = 18kV
18kv x 0.4"/kV = 7.2" (0.6')
12.5' + 0.6' = 13.1' (13'-1.2")
30' - 13.1' = 16.9' (16'-10.8") between pipe rack and 69kV line.

NESC 234-1 (2)(b)(2) Does list the clearance for 22kV as 8' so the clearance from pipe rack (I am changing bridge to rack based on the wording in the NESC table) works out to be 8'-7.2".