Recommended clear zone around substations?

[jtinge]

What are the requirements, recommendations or guidelines for the mimimum clear zone on the outside of substation perimeter fencing?

Is the clear zone for maintenance, security, ground grid protection, or other?

Where can I find these requirements or recommendations? Looked in NESC, IEEE, without much luck. Have found some references to a mimimum recommended 20 to 30 foot clear zone for security, but not much else.

 

[karls2]

Very interesting question, I think that electrically it will depend of the hot zone you will find, after I haven't see any special request concerning the clear zone around the substation and especially when it's located inside urban area. I havent see anything in IEEE 80.

 

[jtinge]

I have also found a recommendation to maintain at least a 6' clear zone to prevent encroachment upon the ground ring usually routed on the outside perimeter of the substation fence in addition to a visible clear zone of 20' for intrusion detection. Still only a recommendation, not a hard and fast requirement. The recommendation indicates that if a clear zone is not practical, other compensatory measures may be necessary, such as increased fence height, increased lightng, or surveillance cameras or intrusion detection sensors. Makes it hard to argue against a planner who wants to locate new construction right up against your primary substation.

 

[karls2]

jtinge do you find these recomendations in standards ?
Thanks by advcance

 

[jtinge]

The information I've found related to clear zones around substations has come from several books on substation design and engineering, nothing really in codes or standards. Easy to find using the search terms "clear zone substation".

 

[bacon4life]

The grounding design should eliminate touch & step potentials between the substation fence, substation ground grid and any adjacent buildings. A 6' to 10' clear zone is a very common way to achieve this, but not the only way. Also, if you have energized equipment near the fence, NESC table 110 distances would apply as would OSHA working distances for workers constructing & maintaining the adjacent building.

An additional clear zone for security doesn't seem particularly useful in either an urban or rural setting. Some of our most expensive substation thefts have occurred from substations where we happened to own large amounts of cleared property around the substation. Vandalism damage from rock throwing has occurred at sites with large clear areas outside the substation fences.