Abstract: A flow heater (11) has a stainless steel tube (1Z), around which is externally placed a polyimide (KAPTON) insulating film (14) with an overlap (15). Under pretension is wound onto the same a metallic resistance material heating tape (17), so that the resulting elasticity reserve, also at operating temperature, ensures a good application of the heating tape to the film. Temperature switching devices for preventing excess temperatures or running dry can be fitted in the overlap area (15).

Abstract: In the manner of a tubular heater, a temperature sensor comprises a metallic tubular jacket with internal resistance wire coil embedded in insulating material and closing pieces having electrical connection members, so that a very simple, robust and high temperature-resistant temperature sensor with a measuring range up to e.g. approximately 750.degree. C. is obtained. The temperature sensor jacket can be earthed or grounded. For operating the temperature sensor there is appropriately a test current in the mA range in the case of a test voltage in the mV range, whose temperature-dependent changes are processed by means of an electronic amplifier.

Abstract: A load selector for switching over from one tap of a step transformer to the next includes fixed step contacts disposed on a circle and connected to taps of a step transformer. At least two switch contacts per phase are disposed in common on a pivotable contact carrier and are simultaneously pivotable on the circle. Two vacuum switches per phase are electrically built into the contact carrier and connected in series with the switch contacts. A cam race is disposed along the circle. Rollers run along the cam race for actuating the vacuum switches. The cam race and the rollers are current free. A slip ring is coaxial with the cam race and the circle. The cam race is disposed axially between and spaced apart from the fixed step contacts and the slip ring. Slip contacts slide on the slip ring. Each of the vacuum switches are eletrically connected between a respective one of the switch contacts and a respective one of the slip contacts.