Building Codes and Inspections/potential fire hazzard
Are there any codes or restrictions reguarding strapping high voltage electrical wiring to a natural gas line feeding a furnace in an attic space?
The gas line is copper.
Let me see what I can find out on this. It's not exactly my area of expertise, so I want you to contact your local Building Official to see what they say. They know the code in your area as well as any potential local amendments to the code that they adopted. Once you know the code, then it can be applied. Unfortunately, the code is not the same everywhere. Your local electric supplier and gas supplier may be able to give you better information.
Most building codes refer to the National Fuel Gas Code, the International Mechanical Code, and the National Electrical Code. There are also separate regulations for propane and natural gas in many areas. Whether it's residential or commercial will matter also in determining what code provisions to apply.
When you say high voltage, what voltage amount are you speaking of? What does the electric line feed? Is this natural gas or propane?
Personally, I don't think it's a good idea to have an electric line attached to a gas line, because if there is a condition resulting in an electrical arc, I don't want it on a gas line. That's not a code interpretation, just my thoughts. In a perfect world with a properly protected electrical circuit, there would probably be no issue, but in the instance of a lightning strike where current could jump from the electric to the gas line, that can't be good. Gas lines are usually bonded, which would be a bare copper conductor clamped to the gas line, but that doesn't sound like your description. Send a photo if you can and I'll see what I can find out.