In the industrial equipment world, covered by standards such as UL508 and UL347, as well as IEC 60204, it is "standard practice" to provide a ground conductor that is of sufficient size that the potential of the equipment ground bus, under foreseeable ground fault conditions, does not rise to a hazardous decisive voltage. In practice, this means ensuring that the resistance of the ground path is low enough to ensure that the rise in potential is less than, say, 50 volts (although we use a figure of 24 volts for safety) before either the upstream protection operates, or after the current level reaches short-circuit fault levels (which is the safer course, but may not be practical in all cases when dealing with heavy equipment). The 35 sq.mm ground wire size that you specify is probably not an unreasonable requirment at 500kW, but it depends on the ground loop resistance at the lengths that you are using. Chris Gilks
-----Original Message----- From: Janne Engström <[email protected]> To: [email protected] <[email protected]> List-Post: [email protected] Date: Sunday, November 21, 1999 1:26 PM Subject: Earth Potential Equalizing > >Hi all, > >We are manufacturing heating equipment for industrial use. >Our equipment is one part in an "in line" setup of machines. > We are required, by one company we deliver to, to provide a wire >for equalizing the earth potential between our control cabinet and >the frame of the main machine. > >The heater is about 50kW at 400V. > >The required wire is 35 square millimeters copper wire. > >The equiment in this case is for the European market. > >I think what they are afraid of is that current will flow in the shields in >the control cables between the different parts of the setup, creating problems. > >Are there any standards that require this? Is this "standard procedure"? > >Best regards > >Janne Engstrom > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
