Important Features of a Bolted Pressure Switch

Bolted Pressure Switch

Almost every medium or large facility has electricity supplied through a large main switch. This switch is the main on/off point in the building and carries all the electric current used by the building. A failure at this point can be devastating to an entire operation. The bolted pressure switch (also known as the bolted pressure contact switch) was developed in the 1950′s to reliably control the massive current loads encountered in these applications. Today’s units are often rated to conduct currents up to several thousand amps and to switch these loads on and off safely. A properly installed and maintained switch will have current carrying efficiency equal to a bolted buss bar. Safety is at least as important as the load capacity when these large switches are designed.

Bolted Pressure Switch Based on Early Knives

The bolted pressure switch is based loosely on early knife or blade type switches. There are stationary contacts, moveable contacts and an operating mechanism. Operators can be manual, remote, or pneumatic. This modern design improves on the original by being faster to open or close and the fact that the contacts do not rely solely on contact spring pressure to maintain contact. The bolted pressure contact switch uses bolts and/or cams to hold the contacts together under much more pressure than the old spring contact type switch. Tighter contact means less resistance to the current and reduced operating temperature under heavy loads. Most switches are UL rated at 60 degrees C temperature rise at rated current. The large operating handle provides a mechanical advantage that loads the spring system for rapid opening and closing. There are even some motorized versions available.

Some important features that should be considered when choosing a bolted pressure switch include arc protection, UL ratings, current rating, non-magnetic mechanism to eliminate induced heating, system to lock the switch in the open position, and available accessories and renewal parts. Accessories can include shunt trip relays, ground fault detection systems, auxiliary contacts and even phase loss monitoring. Switches are available in one-, two-, three- and four-pole configuration and with connections for wires or they can be bolted direct to a buss bar. Most manufacturers of these devices offer custom design services for specific applications and a wide range of accessories. Although it is not recommended, it is possible to find used switches on the market if cost is a limiting factor.

Bolted Pressure Switch

Since a bolted pressure switch is a mechanical device, it does require a certain amount of regular maintenance to keep it working properly and dependably. Maintenance includes regular visual inspection of the switch contacts and operating mechanisms. The mechanical operators need to be cleaned and lubricated every couple of years. The electrical contacts should get a complete dis-assembly and inspection at the same time. Any questionable components should be replaced.

In any company, these devices are very important to the day-to-day operation. For this reason, regular maintenance by a knowledgeable service company is recommended. Well maintained switch gear will pay back the maintenance expense with years of uninterrupted service.