Steel grid resistors 3PS3 consist of resistor elements made from high-alloyed steel sheet. The resistor material is largely resistant to corrosion due to the high chromium content and resistant to scaling even at
elevated temperatures. Insulating bushings made from creepage-proof, temperaturecycle resistant ceramic material isolate the elements from each other and from the housing. Welded-in bridges connect the elements. Welded-on terminal lugs enable the connection of cables or lines by means of M12 cap screws. The housings are of the same design as those for steel grid resistors 3PR3. Therefore,
also a combination of both systems is possible. The housings are not provided with painting as all elements are made from galvanized or stainless steel sheet. The plates of the resistor elements are
punched to obtain conductors of different dimensions thus resulting in elements with different resistance values in the range from 0.01 to 3.2 ohm. As punching does not lead to material loss, the thermal capacity of all elements is the same. A reinforcement made from corrosion-free sheet insulated with mica film at the upper and lower end serves to stabilize the element.
Five sizes with up to 30 elements which can in turn be supplied in single or threestrand design are available:
Size No. of elements
3PS30 12 3 x 4
3PS32 16 3 x 5
3PS34 21 3 x 7
3PS36 26 3 x 8
3PS38 30 3 x 10
Standard resistors are equipped with a fixed number of uniform elements and provided with uniform terminal markings (cf. page 2.6). For larger units, this will facilitate spare part warehousing.
Available standard resistors:
Single-strand resistors with standard banks and uniform number of resistor group elements. Threes-strand standard bank resistors with uniform number of resistor group elements. Three-strand standard bank resistors with partly upgraded resistor group elements. Here, the first two resistor steps can take on 1.4 times the current of the value indicated in the tables. They are preferably used as the final step in resistors for intermittent operation.
The resistors shall be installed horizontally such that the resistor elements are upright and the cooling air can rise freely between these elements. The load values indicated in the tables refer to natural air cooling. Care must be taken that the cooling air has unrestricted access from below and can freely leave the resistor at the top. The place of installation must have good venting. In particular for
indoor installation care must be taken that the ambient air does not heat up to temperatures above 45°C. The indicated loads result in temperature rises of up to 260 K. For a temperature increase
of max. 200 K, the rating must be reduced by 25% (current value x 0.866). Additional external venting with a fan may increase the rating and thus also the admissible load, in particular in the case of intermittent operation with a high duty factor.
The admissible loss for three stacked resistor boxes is of about:
Size Admissible loss
3PS3 0 7.4 kW
3PS3 2 10.8 kW
3PS3 4 14.2 kW
3PS3 6 17.5 kW
3PS3 8 20.0 kW
After taking off the side panels, the incoming cables can be inserted from below and directly connected to the terminal connections of the resistor elements.
Connecting screws M12
Cable diameter up to 1 x 150 mm²
2 x 120 mm²
Adm. continuous current 400 A
The heat dissipated by the resistors must be considered for connection. Lines or cables should be inserted in each box individually from the side such that they are not located in the area of the outflowing
dissipated heat or heat radiation. For the admissible load, DIN VDE 0298 T3/4 must be observed. Where required, lines or cables suited for elevated temperatures shall be used or the ends of standard PVC cables/lines shall be covered with a heat-resistant insulation sleeve.
The resistors are maintenance-free. In case of strong dust formation, however, occasional cleaning with compressed air should be done to preserve the insulation against the grounded housing elements.