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If machines and systems are to be exported to the US or Canada, the associated control panels must be constructed and certified in accordance with the regulations of UL 508A or CSA C22.2 No. 286. cUL certification for Canada also conforms to CSA (Canadian Standards Association) standards, which is why this certification is considered and recognized by the Canadian authorities as a CSA certification. UL and CSA are applicable in both markets. The technical details of the control panel are a crucial factor in attaining UL 508A compliance. Manufacturers should therefore already be taking the requirements of the standard into account during the project planning stages. In order to construct a control panel in accordance with UL 508A, each individual area should be adapted or designed according to the North American control panel standard.
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The nominal current of the feeder is determined by the cumulative nominal currents of the branch circuits, such as the full load currents of motors and other loads.
When planning the feeder, it is also crucial that main switches (circuit breakers and molded case switches), which are equipped with door coupling rotary handles, have an additional rotary handle. Only then are the requirements of UL 508A fulfilled.
UL 508A includes provisions for protecting several motors with only one set of fuses or circuit breakers (section 31.4.1.c). However, all devices in the electrical circuit must be designed for group protection (this must be indicated on the devices or in the instructions).
In addition, the conductors for the individual loads must have a minimum nominal current of 1/10th the nominal current of the branch circuit protection used for the individual electrical circuits with manual motor controllers (MMC).
The MMC must be marked as "suitable as tap conductor protection in group installations." The conductors on the load side of the MMC must also have a minimum nominal current of 125 % of the full load amperes (FLA) of the motor.
When designing branch protection, the following values must be observed:
The nominal current of the BCP must not exceed the nominal current described in the component group protection marking and must correspond to the specified type.
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There are several ways to create a branch circuit for a motor feeder. Each of these methods includes short-circuit protection, overload protection and the ability to start and stop the motor. Some methods also include the ability to isolate the branch circuit for repair and maintenance purposes (disconnectors).
UL 508 Type F combination motor controllers (CMCs) are the most efficient solution for a branch circuit for a motor: They combine motor-protective circuit-breakers, contactors and feeder adaptors in one device.
The branch circuit protection for heating loads should:
The design of controllers (e.g. contactors) for heating control depends on the full load current of the heating system using the general purpose ratings or the resistive load ratings.
The branch circuit protection for normal incandescent lamp or fluorescent lamp loads should:
Control circuits must be primarily protected in accordance with UL 508A. If the control circuit is built with a separate power supply, the following applies:
Fuse protection for "Class 1" and "Class 2" control circuits should be implemented according to Table 42.2 of UL 508A. Low-voltage limited energy circuits should be protected in accordance with the 100-VA rule using special time delay fuses or miniature circuit breakers.
According to UL 508A, non-motor loads must be protected as specified by the respective manufacturer in the UL report. Circuit breakers compliant with UL 489 or fuses compliant with UL 248-4...12 must be used.
Fuses are additionally of interest because they can also be used to very easily increase the SCCR of the switchgear system so that it attains an SCCR that is compliant with the National Electric Code.
UL 508A also defines specific requirements for main and control current wiring, including the cross section, color and current carrying capacity.
Detailed information on this can be found in the "Design guide for control systems according to UL 508A," which can be downloaded from the Eaton website.
Machines that meet IEC standards are often exported to North America (the US and Canada). However, the codes and standards that must be adhered to in North America differ considerably from those in other regions of the world. For this reason, it is important for control panel manufacturers to take the requirements of UL 508A into consideration from the beginning, during the project planning stage. This will simplify commissioning and reduce costs later.
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