Hilti Aktiengesellschaft

Karl Echtler

Wolfgang Millauer

Hanno Richter

Leopold Von Keudell

A hand held machine tool has a protective electrode (1; 1a, 1b, 1c) located within a housing with a leakage current protective switch (2; 2a, 2b, 2c) triggered by a fixed leakage current (.SIGMA.1.sub..DELTA.), for example, 10 mA, for interrupting power supply leads (4, 5) of the machine tool with a protective conductor (3) connected to the protective electrode (1; 1a, 1b, 1c) and not being switched off.

Manually guided machine tool with a safety device

A fault current protective device contains a fault current protective switch (2) for the protection of at least two circuits formed by branching subsequent to the fault current protective switch (2) and having the same number of phases. One of these circuits is looped through the fault current protective switch (2) again at least once over connections (L2, L3, and L2', L3'), respectively, of the fault current protective switch (2) which are free of use, so that a higher protection level (lower nominal fault current I.sub..DELTA.n) is obtained relative to the other circuit. Only one fault current protective switch (2) is required for this purpose, so that the fault circuit protective device is compact and economical.

Fault current protective device

A battery operated device includes a circuit connecting a DC motor (22) and a battery (9) made up of a plurality of cells (10, 11, 12) connected in series with a two-pole switch device (23) including a first switch (24) and a second switch (25). The DC motor (22) receives a lower battery voltage from an intermediate tap (17) of the battery through a first switch (24) and it receives the full battery voltage through an end tap (15) when the second switch (25) is closed so that the motor can be operated at two speeds. Further, elements are provided for preventing a short circuit between the intermediate tap (17) and the end tap (15) of the battery (9) when the second switch (25) is closed. As a result of this switching arrangement, an extensively interrupted-switching is available, so that practically no power lapses occur when switching over from one speed to the other.

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Puchheim, Germany

Karl Echtler