DATA OR COMPUTER NETWORK
VICTOR A. RAMOS JR.
January 25, 1999
This power problem is incorrect bonding of electrical transformers, main electrical panels and sub-panels, uninterruptible power supplies (UPS), and generator systems. Every facility or building has an electrical distribution system that is bonded between the neutral and ground conductor which means that there is a solid metal interconnection between the neutral and ground conductor somewhere within the electrical distribution system (See drawing #1). Generally, all electrical distribution systems begin at the facilitys or buildings electrical transformer and go to the main electrical panel then to sub-panels and ultimately to a power outlet on the wall or floor. This is, of course, the most simplistic form of an electrical distribution system. In a high-tech or data/computer facility you find a more complicated electrical distribution system that includes UPSs, PDUs, generator backup capability, and automatic transfer switches (which is the actual electrical mechanism that switches from utility to generator power and vice versa). The more complicated a system is the more likely that incorrect bonding has taken place. The National Electric Code (NEC) addresses this issue very clearly and identifies where the bond should be and how many bonds should exist in the system. However, incorrect bonding does exist and can occur before, during, or after the construction phase of any facility or building. In fact, most incorrect bonding occurs after the construction phase when electrical modifications are made due to retrofitting, improvements, or enhancements of the electrical distribution system.
Incorrect bonding of any of the above mentioned components of an electrical distribution system causes several underlying problems within your site or facility. The most common problem is stray neutral current in your ground system due to multiple bonds within the electrical distribution system. When this happens, stray neutral current will establish other current flow paths in the ground system that is not the intended design path of the neutral current flow. Simply stated, stray neutral current in your ground system will interfere with the proper operation of sensitive electronic equipment, communications systems, computer systems, and local area network/wide area networks (LAN/WAN). This is referred to as objectionable current or noise in the ground system. Now stray neutral current in the ground system can produce the following symptoms:
In addition, data and computer professionals understand the need of having a true ground system. Electronic and computer equipment must have a true ground reference point for normal operation. When stray neutral current is flowing in the ground system, it will find its way back into your electronic and computer equipment via the ground wire causing the problems described above.
As a data or computer professional, you expect or assume that the electrical distribution system in your facility or building is wired correctly, but have you ever asked the question as to whether the electrical distribution system is bonded correctly? The answer is probably "no" and mostly for several reasons. First of all, how many data or computer professionals do you know that have an electrical engineering degree, are a certified electrician, or have taken electrical classes to understand the finer workings of an electrical distribution system? I would venture to say not many if any at all within your company. Secondly, we expect or assume that the electrical work was done to the highest of standards and craftsmanship. As a data or computer professional you assume that all the electrical work was done according to the specifications of the electrical prints and that the electrical inspector caught every electrical violation which was then corrected or repaired. Right! Wrong! In the real world where time is money, it doesnt always work that way. This situation can get worse when electrical modifications are made due to retrofitting, improvements, or enhancements of the electrical distribution system. Depending on the size of the work required, no electrical permit may be necessary by the electrical contractor, therefore; no electrical inspection is required to validate the work.
There are several methods of testing that will verify if you have stray neutral current in your electrical distribution system, the main indicator of incorrect bonding. The most common practice is testing each electrical computer power outlet with a specialized ground impedance tester. The most preferred method by power quality consultants is to monitor the power with the most advanced power monitoring instruments in the industry. These instruments can monitor and record any electrical disturbance at the main electrical service panel and at various sub-panels. However, in a high-tech or data/computer facility extensive power monitoring may also be required of the backup generator, UPS, and PDU. The more complicated that an electrical distribution system is the more monitoring that is required.
The first step is to locate where the incorrect bond or bonds exist within your electrical distribution system. The size and complexity of your electrical distribution system is the major factor in locating a single or multiple incorrectly installed electrical bonds. In addition, a site survey and power quality monitoring should be conducted to determine if any other deficiencies exist that could affect the operation of your electrical distribution systems and grounding systems. A power quality consultant will be able to analyze the severity of these problems and design a plan tailored to your specific bonding and stray neutral current situation. If you know or think that your building or facility has a bonding problem, please go to our "Power Problems" web page and register for your free 15 minutes of consulting.
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