Touch Potential Between Substation and Customer Fence
Touch Potential Between Substation and Customer Fence
(OP)
I understand that there can be some touch potential between a substation fence and a customer's metal fence near by, but how do you determine how close it can be before it becomes a problem? I have seen 6 Feet online. Are there any regulations for this? I know that you could connect the customer's fence to the substation ground, but how about an isolating fence? What type of material should the isolating fence be between the two fences?
Thanks
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RE: Touch Potential Between Substation and Customer Fence
There are several standard such as the IEEE Std 80, NESC, and others. However, may not be a direct regulation that address your concerns with fence directly.
There are a few option to isolate fence such as isolation metallic chain link section (using MV insulator) or non conductive fence section (search for Amico Fence)
I hope this could help
RE: Touch Potential Between Substation and Customer Fence
RE: Touch Potential Between Substation and Customer Fence
RE: Touch Potential Between Substation and Customer Fence
Thank you for all the responses.
RE: Touch Potential Between Substation and Customer Fence
Another thing to watch: The foreign fence may not be up to the substation required height. A low fence attached in any way to the perimeter fence will be a climbing aid nullifying the primary purpose of the perimeter fence.
RE: Touch Potential Between Substation and Customer Fence
Thanks for the info
RE: Touch Potential Between Substation and Customer Fence
The inner and outer fence will be jumpered and hence for the earth faults, the potential of outer fence would also rise along with the inner fence. But, inner fence is safe, as the earth mat is supposed to encompass the inner fence. So the potential difference between the ground and the structure are within the acceptable value.
In the mean time if you are not spreading the ground mat along the outer fence, there could be a higher potential difference between the metal structure (here in this case the outer fence) and the found. This could be dangerous.
RE: Touch Potential Between Substation and Customer Fence
RE: Touch Potential Between Substation and Customer Fence
NESC 384 C: Bonding should be provided between all aboveground metallic supply and communications enclosures that are separated by a distance of 6 feet or less. For the purpose of this rule, pole grounds are not required to be bonded to the communication enclosure.
IEEE 80: Substantial metal-to-metal touch voltages may be present when a person standing on or touching a grounded object or structure comes into contact with a metallic object or structure within the substation site that is not bonded to the ground grid. Calculations of the actual metal-to-metal touch voltage are complex. In practice, hazards resulting from metal-to-metal contact may best be avoided by bonding potential danger points to the substation grid.
It is impractical, and often impossible, to design a ground grid based on the touch voltage caused by the external transferred voltages. Hazards from these external transferred voltages are best avoided by using isolating or neutralizing devices and by treating and clearly labeling these circuits, pipes, etc., as being equivalent to energized lines.
OSHA: The employer can use a grounding grid to equalize the voltage within the grid or bond conductive objects in the immediate work area to minimize the potential between the objects and between each object and ground. (Bonding an object outside the work area can increase touch potential to that object, however.)
OSHA also referenced ANSI C2 which is NESC as above.