I've done it quite a few years ago with SA 200's. Disconnect inside the building where the service comes through the wall. you may need to solder a valve on so once you've thawed the pipe you'll have control of the water. If you don't disconnect inside and the current decides to take a route  through the building-through a conductor that is small enough to get hot and start a fire you'll have problems. It happened to an associate of mine. Use the heavest cables you have and don't rush it. set your machine where it will have the highest duty cycle. If your machine doesn't have a remote contactor be sure to hook up both +&- before starting the machine to prevent arcing on the copper pipe (or steel). Use c clamps or vise grip on the copper and hook your stinger and ground to them instead of the copper. I recall it taking several hours to thaw 100' services. You may need to dig out 100' section if it's really long and thaw in between. If it gets this far out of control you may also need an air compressor to blow out each section as you go. Also if your in the city look under the porch or stoop for exposed services you may be able to thaw them with a torch. It is rather uncommon to have water services freeze here in the mid-atlantic so I'm sure other folks will have better ideas. See Ya- Ted

P.S. it's been 25 years since I've done this- things get a little cloudy!@#$%^

Check out Lincoln's Procedure Hand book. They have a detailed section on pipe thawing.