The Sprecher + Schuh product currently being sold by NHP is from the same company however it is not necessarily the exact same product due to improvements in technology driving range changes in the years since Sprecher + Schuh was last seen in the New Zealand market.
Rockwell International acquired Sprecher + Schuh in 1993 and since then Sprecher + Schuh has operated under the direction of Rockwell Automation. NHP’s relationship with Sprecher + Schuh goes back to 1968 and continues today, when NHP was appointed the exclusive agent in Australia. In mid 2006 NHP was also appointed to sell Sprecher + Schuh in New Zealand.
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The purpose of the overload is to protect the motor from overheating. Overheating can result from numerous reasons. The more advanced the overload, the more possibilities for overheating it caters for. Another distinction between overloads is the method by which they monitor the heat of the motor and their accuracy. The decision on which overload to use comes from considering a number of issues such as budget, the replacement cost of the motor should it fail, and the opportunity cost or downtime cost while the motor is out of action. Quite often the biggest contributor is the last one - the downtime cost. Simply put, the choice of overload is 'horses for courses". The bigger the dollars involved, the more sophisticated the motor protection should be. The Sprecher + Schuh range of overloads cater for all industry requirements.
Before choosing the starting components, you need to decide on the starting method. DOL (direct on line) is the most common as it is the simplest and cheapest method. NHP provides selection guides in the Part A Catalogue to assist here. However, because of the effect of the large starting current when the DOL starting method is used, other starting methods are used. Also, the application will determine which starting method is more appropriate as each has their own pros and con's. NHP Part A Catalogue includes a table which provides assistance with which starting method to choose.
The role of a fuse or circuit breaker is to protect the downstream cable from overloads and short circuits. In motor starting circuits, their main role is short circuit protection. The fuse and circuit breaker limit the level of fault current that the other starting devices and the motor see as the fault capacity of these devices is generally much less. The decision regarding whether to choose a fuse or circuit breaker depends on the application. Circuit breakers have the advantage that they are easy to reset and break all three phases in fault conditions. Fuses provide good fault rating capacities at higher voltages and do not produce exhaust gases. A further consideration is that the Sprecher + Schuh range of circuit breakers are designed specifically for motor starting so that for general applications they provide overload and short circuit protection reducing the main starting components by one device.
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Yes, this is perfectly normal. When a contactor is brand new, its contacts are clean and flat. During their first period of usage, they undergo what is called the "bedding in" process. This causes the contacts to look at little pitted. Also, when contactors open under load, an arc is produced across the contacts. This is what causes the contact to look black.
Circuit breakers are selected based on their current rating and fault capacity. It is common to select a breaker to make the full load current (FLC) of the motor but to forget about the starting current (also called the Locked Rotor Current, (LRC)). The LRC is typically 6 times the FLC but can be in the range of 4 times to 10 times. When the circuit breaker trips during start up, it means that the circuit breaker sees the LRC as a fault. This can be overcome by upsizing the circuit breaker and using an overload to supplement the motor protection or by adjusting the magnetic (short circuit) setting, if possible, of the circuit breaker. In the case of miniature circuit breakers, MCBs, it is usual to use a "D" curve breaker for motor applications.
Coordination means that the devices will work together to clear a fault in the electrical circuit without damage to persons or property. Coordination is classified as Type 1 and Type 2. The difference between Type 1 and 2 is the condition of the devices once the fault has been cleared. In Type 1 coordination, the devices are sacrificed in the process and will need to be replaced. With Type 2, the devices are required to be serviceable after successfully clearing the fault. AS3947.4.1 details these requirements.
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The D5 series is currently being phased out by NHP as it is being superseded by the new D7 series. A lot of spares are still available from NHP for the D5 series and will be for some time, however for new installations we recommend making the change to the new D7 series. The D7 series of products have a number of technical, quality and safety advantages over the old D5 and due to more modern manufacturing processes are less expensive to purchase.
Sprecher +Schuh manufacture a dedicated thermistor protection relay - RT 7, which can directly monitor the temperature of a given object via a PTC (positive temperature coefficient) resistor acting as a temperature sensor. The outcome is an independent and reliable method of thermal protection that also takes external environmental influences into account. Alternatively you can use one of the Sprecher + Schuh electronic overloads and motor protection relays that also accept PTC inputs. This solution can provide both overload and thermistor protection at the same time.
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There are numerous methods for controlling the starting current for large motors. The key is to ensure that enough torque is provided by the starting method to ensure the motor gets up to speed as quickly as possible. In NHP Catalogue Part A, a table provides suggestions on what starting method is most appropriate. It is common to use soft starters to reduce the starting current.
The jolting that occurs when starting a motor can be overcome by changing the starting method. A soft starter or Variable Speed Drive, VSD are two such options. VSDs are generally costs prohibitive if used only to control the acceleration at start up and so a soft starter is a good choice. Sprecher + Schuh provide a range of soft starter which are easy to set up and connect easily with the other starting devices.
Overheating is the most common reason for motor failure. Motors operating in a high ambient will eventually fail unless adequately managed. An advanced motor protection relay such as Sprecher + Schuh's CET5 provides extended temperature monitoring and reporting functions to assist in this regard. Further, forced ventilation or air-conditioning are other options to ensure that the motor does not overheat.
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