Abstract: An electrical heater comprising a heating element, a tubular metal sheath surrounding the heating element and spaced therefrom, insulation inside the sheath for electrically insulating the heating element from the sheath, and a closure closing one end of the sheath. A passaging extends through the closure in a direction generally lengthwise of the sheath. At least one power lead adapted for connection to a source of electrical energy extends through the passaging for conducting electrical energy to the heating element. The power lead includes an electrical conductor, a metallic sleeve surrounding the conductor, and insulation for electrically insulating the conductor from the sleeve. The conductor has a terminal portion electrically connected to the heating element. A seal between the closure and the sheath around the one end of the sheath seals against the passage of contaminants between the closure and the sheath.