Bosch Power Tools 1375-01, 1375AK manual Electrical Safety

Page 36

ELECTRICAL SAFETY.

For high-frequency electric tools, electrical safety is assured by the protective conductor as per EN 50144 based on protection class I. When the secondary coil of the converter is switched in the star, the star point or neutral point is extended outwards. This neutral point is earthed (earthing resistance RB Π2 ohms) and connected to the metal housing of the electric tools by way of the protective conductors so that, at an operating voltage of 265 V, the dangerous voltage between phase and earth is only

265 V = 153 V

1.73

At operating voltages of 135 V or 72 V, on the other hand, the dangerous voltage is only

135 V

= 78 V or

1.73

 

 

 

72 V

= 42 V

1.73

 

 

 

The effectiveness of the protective earthing is assured by using corre- spondingly robust plug fixtures of faultless electrical construction

together with suitably resistant cables. Careful maintenance is equally important. The electric tool itself must, in its construction design, be capable of satisfying the stringent demands of indus- trial manufacture. Under normal circumstances, the description provided above, e.g. the protec- tion measure “Earthing" as per VDE 0100 – 10 N is adhered to.

The possible protective measures may be classified and subdivided as follows:

1.0protective measures without switching device

1.1protective insulation (VDE 0100 – § 7 N)

1.2low voltage, 42 V (VDE 0100 – § 8 N)

1.3protective separation (VDE 0100 – § 14 N)

2.0protective measures with switching device

2.1protective earthing (VDE 0100 – § 9 N)

2.2reduction to zero voltage (VDE 0100 – § 10 N)

In cases 2.1 and 2.2, switch-off is effected by fuses or correspond- ing thermo-magnetically triggered station circuit breakers.

The greatest possible degree of protection is reached by using fault current (FI) circuit breakers in addition.

Protective insulation as per 1.1 is not applied to high-frequency electric tools. Low voltage as per 1.2 finds application only in special cases in which, due to existing regulations, it cannot be avoided. Because of the high currents involved, this measure is very problematic with respect to cable cross-section, switches, plugs etc. when applied to the transmission of large outputs. Small screw drivers comprise an exception. In this case, one is better off using protective sepa- ration as per 1.3, according to which every tool must have its own separator-converter. Protec- tive separation should be restric- ted to circumstances in which it is absolutely necessary.

Here we wish to focus on the protective measure “reduction to zero voltage as per 2.2" since it finds application primarily with high-frequency electric tools.The voltage reduction should continuously prevent excessive contact potential on installation parts that do not belong to the operating circuit (see Fig. 5). It requires direct earthing of a mid- point or star point conductor and is effected by connecting the in- stallation parts that are to be pro- tected either to the neutral con- ductor or to a special protective

conductor that is in turn connec- ted to the neutral conductor.

The protective measure “reduction to zero voltage" thus switches off defective installation parts since the inline fuse directly before the defective location is activated.

If the fuse is really to be activated, certain voltage reduction condi- tions as per VDE 0100 – § 10 N must be complied with. The most important voltage reduction requirement: The cross-section of the leads from the power

Fig. 4

Fig. 5

70

71

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Contents TOP HIGH-FREQUENCY Power Tools Inexpensive Power Application ContentsDrills AN Overview with a Single Click ALL Industrial Tools OnlineSelection Guide for Drills Over N/mm Iron N/mmCast180 20 to 15 to 10 to 50 to 30 to 80 to Drill diameter mmDrills Dimensional Drawings Drills Accessories for DrillsRecommended Speeds for HSS Twist Drill Bits 16 mm, B16Grinders Selection Guide for Grinders Idle rpm With abrasivesSelection Guide for Grinders Disc and Random Orbit Sanders NumberWithwheels ShapedStraight Grinders For grinding pointsTo 50 mm in diameter Complete27 to 50 mm in diameter VoltageHGS 57/50 Ls HGS 65/32Power 40 to 50 mm in diameterHGS 77/50 HGS 85/40Switchtype Remarks Comeswith For grinding wheels 50 to 80 mm in diameterComplete Speed HGS 77/75For grinding wheels 125 to 180 mm in diameterRemarks Comeswith Angle Grinders 100 to 180 mm in diameter180 to 230 mm in diameter WithHWS 85/180 HWS 88/180For grinding wheels 230 to 300 mm in diameter HWS 810/230HWS 810/300 Disc Sanders and Random Orbit Sanders Disc sanders and random orbitSanders for sanding discs with Mm diameterAccessories for Angle Grinders Dimensional Drawings Straight Grinders Dimensions mm 602 210 602 211 602 245 602 243 Dimensional Drawings Angle Grinders Dimensional Drawings Disc Sanders Random Orbit Sanders ScrewdriversSelection Guide for Screwdrivers Torque accuracy dependingOn screwdriver system Screwdriving typeWith adjustable cut-out Clutch for screws from CUT-OUT ScrewdriversTo M Impact Wrenches Impact wrenches forScrews from M 6 to M SquareTappers Tappers for threads up to 8 mm in diameterHGR 55/10 Current withoutAccessories for SHUT-OFF Screwdriver Special Accessories for ScrewdriversDimensional Drawings CUT-OUT Screwdrivers Dimensional Drawings Impact Wrenches Dimensional Drawings Angle WrenchesAccessories Loadmin Loadmax BalancerBalancer For loads From 0.3 to 17 kgPlug CONNECTIONS, Leads Stator Rotor Housing Robust Technology for LONG-TERM HEAVY-DUTY USEFan Tool installation Sample calculation for aHigh-frequency electric Network groupsDesigning AN Installation for HIGH-FREQUENCY Electric Tools Frequency converter with synchronic generatorParallel operation of frequency converters Compensating for reactive currentElectrical Safety Distribution Network Cable cross-section as a function of voltage and lead length Bosch Service Quality
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