Feature: Impreza WRCar Electricals

Feature: Impreza WRCar ElectricalsFrom Subaru Press [ 20/04/2004 ].
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The wiring loom in the Subaru Impreza WRC2004 can be described as the car's heart and veins. Running from a console unit located in the centre of the car, it includes 4040 metres of cable, 108 joins and 2100 separate crimp connections, and is painstakingly hand-built at the Subaru Rally Team's base in Banbury, UK. Using a high-grade copper wire that is known as 55A, each WRC Impreza loom is hand laid by a SWRT technician onto a complex paper diagram, which instructs exactly where each wire should be.

Unlike Impreza road car looms, which use upvc insulated cables cut by a machine and then grouped together, the wires in the WRC loom are concentrically twisted by hand into a predetermined pattern to ensure that the loom has maximum flexibility once it is complete. As Craig Trim, the electrical supervisor told us, "While road car looms are buried under the trim and, once installed, often never seen again, WRC looms are constantly being moved around and re-tested."

The wire and connectors used in the WRC loom are also stronger, tougher and more durable than those used in the road car, in order to cope with the extreme conditions of the WRC. "The WRC cars have to compete on a variety of extreme surfaces", explains Craig, "so in the WRC looms we use a specialist single insulation wire that can operate at any temperature between -65°C and 150°C. It's more flexible than the wire used in a road car and weighs 85 per cent less." He offers an example "To carry 12 volts in a road car you would use a 2.5mm diameter cable wire which is very heavy, yet to carry 12 volts in the rally car we use a 1.09mm diameter cable that's much lighter and designed to cope with extreme, hard wearing conditions." The wire also conforms to military and aviation specifications.

"Once the wires have been concentrically twisted, we heat shrink them for protection, before they're fixed into military specification waterproof connectors," he continues. "These connectors are similar to those used in F1 and far more effective (and expensive!) than the plastic connectors used in road cars."

With each complete Impreza WRC2004 wiring loom taking 505 man-hours to produce, and including 53 electrical assemblies, it's good to know that the looms aren't only used once. " A good loom should last the life of a car," Craig tells us. "The only serviceable item is the glue that we use to fix the waterproof rubber seal to the connector, which can wear after three or four years. The looms are tested using a high technology electronic circuit tester known as cirrus, the same system that's used to test the harness on the space shuttle. "It's very reliable," says Craig, "and checks every aspect, such as voltage leakage or insulation failures. Not that there are ever too many problems! There's eight of us working in the department and they're a very reliable bunch."

They will be a few more features on the Subaru WRT soon.