Shielding: An Effective Piece of Armor in the Battle for Power Quality

| December 4, 2017

In combination with correct grounding for the application, proper shielding can help prevent data corruption and even the limit the possibility of harmonics reaching portions of an electrical system. However, the biggest benefit of shielding is the reduction of Electro-Magnetic Interference (EMI) or “noise” in an electrical system.

Noise can be just as disruptive to an electrical system as it can be to a person. Noise can corrupt electrical signals during both transmission and reception. We use computers in most facets of daily life, reducing emails, phone calls, and any kind of data to a digital stream of 0’s and 1’s. It is not difficult to imagine a minor amount of electrical noise erroneously turning a 0 into a 1. While this doesn’t appear to be much of a disturbance to a person, to a computer that relies solely on those 2 options, it can completely alter information.

Solutions to Combating Noise

According to a 3-year study conducted by the Georgia Institute of Technology, steel conduit can protect wiring from EMI by as much as 95%. However, installing steel conduit for all wiring may not be practical for all applications due to the cost. Therefore, shielded wiring is another option that provides similar protection with a lower cost.

Both, steel conduit and shielded wires protect the wires from noise in two ways. First, they can reflect the energy from an outside source. Second, they can pick up the noise and provide it with a pathway to ground.  In either scenario, the electrical noise does not reach the wiring.

Isolation transformers can be used to attenuate noise on all wiring connected to the primary windings. An isolation transformer physically separates the primary and secondary windings, sometimes with electrostatic shield(s). Electrostatic shields are conductive sheets of nonmagnetic material (typically copper or aluminum) that use a ground connection to channel noise out of the electrical phases and back onto the system ground. Using an electrostatic shield is a smaller scale concept as the shielding used in MRI suites to protect adjacent areas from the magnetic field generated by the MRI’s magnet.

Using shielded wiring requires grounding cables on one end, both ends, or multiple locations along the length depending on performance requirements. When cable ends are shielded using ground connections through diodes or capacitors, circulating ground currents can be eliminated from the system. Single point grounding is effective in controlling noise at low frequencies (less than 1 MHz), contribution of noise from power conductors located too closely to telephone connections, for example. At frequencies above 1 MHz, such as contribution of noise from a nearby radio tower, multiple grounding points are required. Data cables must be grounded at both ends, at multiple points along the wire, or a signal reference grid must be used.

Site Specific Applications

Fitzemeyer & Tocci Associates, Inc. recently worked on a project that was located approximately an 1/8 of a mile from 3 separate radio and cell towers. The facility was plagued by data corruption that manifested in emails that were sent containing gibberish as well as a phone system that primarily transmitted static and unintelligible sounds. Using shielded wiring for all data/voice connections as well as shielded cable terminations at faceplates was a mandatory step in resolving their issues.

As a specialist in the Healthcare industry, Fitzemeyer & Tocci, Inc. is no stranger to MRI suites. As mentioned earlier in the blog, a large electrostatic shield is placed around the entire scan room. Most supporting equipment is placed outside of the shielding and connections entering/exiting the scan room utilize penetration plates to traverse the shielding.

In addition to shielding individual connections or whole MRI scan rooms, facilities have the option of taking a more aggressive shielding approach. On a recent data center project Fitzemeyer & Tocci Associates, Inc. was challenged with shielding the facility against electro-magnetic pulses. Shields for individual connections would have been extremely difficult and expensive to accomplish. Instead, the entire building was shielded using conductive concrete, multiple ground connections, and filters for any wires entering/exiting the building. Penetrations were treated with extreme care where conduits entering/leaving the building were welded at couplings in lieu of threaded connections to create continuous rigid steel shielding when bonded.

Conclusion

Whether you have a small office that could benefit from a single isolation transformer or a large data center intended to withstand a catastrophic event, Fitzemeyer & Tocci Associates, Inc. can help you protect your data and keep it free of corruption.

Abdullah Khaliqi
About

As Electrical Project Engineer, Abdullah coordinates entire systems from concept through construction, conducting site visits, systems evaluations, cost estimates and specifications. He has provided these services for a multitude of project types for various types of clients from academic to healthcare to municipal to science and technology. As the Electrical Project Engineer, Abdullah ensures the project’s electrical designs are fully code compliant and up-to-date with industry standards.

Leave a Reply

Your email address will not be published. Required fields are marked *