Guidance to configuring enclosures – from Rittal

Isolator door covers for the US market now easier to install than ever before

When a plant constructor receives the order to construct low-voltage switchgear for the US market, the differences between the standards in force in Europe and the USA have to be taken into account. For example, enclosure doors have to be effectively prevented from being opened when the system is under voltage. Rittal’s new, UL-certified isolator door cover shows how the complex requirements of UL 508A can be easily implemented.

Security plays a major role in the US market. Machinery and equipment may only be commissioned once acceptance has been granted. Acceptance is generally made much simpler, faster and inexpensive when only UL-approved components are used. A number of special design considerations, not found in the normal IEC standards, also need to be observed. One typical example is outlined in the UL 508A standard: In low-voltage switchgear, design measures have to be taken to prevent components in the unit being under voltage when the door is open. It is necessary to ensure that the door cannot be opened when the system is subject to voltage. In addition, the system must not be live if any of the doors are unlocked/open.

The new isolator door cover from Rittal, in conjunction with the adjacent door locking system, is currently the only solution on the market that meets all the requirements of the UL 508A standard. The manufacturer offers an isolator door cover of this type for its TS 8 bayed enclosure system. An actuator for an isolator switch is integrated in the 125 mm-wide isolator door cover. The door can only be opened when this has been activated and the electricity supply to every component in the enclosure has been cut off. This function is achieved via an actuating mechanism that is easy to assemble and adjust. A complete combination of enclosures can be made safe using just one isolator door cover. The door of the neighbouring enclosure is also operated via the adjacent door locking. This solution only calls for a very small amount of additional space. The door of the enclosure directly adjacent to the isolator door cover can only be shut when all the other doors are already closed. This way, the user can see directly if all the doors have been closed properly. Only then can the actuator supply the switchgear with voltage.

Simple assembly

While developing the new isolator door cover, Rittal went to great lengths to ensure it was easy to assemble. As with most assembly operations on the TS 8, the isolator door cover can be mounted by just one person. It is first suspended instead of a side panel, and it can then be easily screw-mounted without needing to be held in place by a mechanic. The operating mechanism and locking rod are then mounted and adjusted. Here too, great emphasis has been placed on ease of assembly. All the steps can be performed by just one technician. Finally, the enclosure’s standard side panel is mounted onto the isolator door cover. In the process, a potential equalisation is established automatically. No additional earthing straps are needed if no active components are installed in the side panel. Video tutorials are available on the Rittal website so that every step of the installation can be visualised: