WH Aluminum Housed Wirewound Resistors Welwyn / TT Electronics WH Aluminum Housed Wirewound Resistors have an all-welded construction and high-power dissipation up to 300W. Welwyn / TT Electronics WH Wirewound Resistors are suitable for severe environments and designed for excellent thermal conductivity to heatsinks. The resistors also offer a spade terminal option and are RoHS compliant.