SUSTAINABLE ELECTRICAL SYSTEMS
Sensitive electronic systems and equipment should be powered by an electronics grade electrical distribution. The term “electronics grade electrical distribution system” is a upgraded version of what would be called a minimal code compliant electrical system. The average commercial building is more than 50+ years old. The PC computer is less than 30-years old.
It is very possible the electrical system in your building could have been installed long before the PC computer was invented. Forget the 50+ year old building, do you think the electrical design of a 30+ year old building is capable of supporting a computer network? It was designed to support what is now “obsolete” technology, incandescent lights and
hard start electric motors. Today’s microprocessor based technology? It was not even a dream when many buildings were constructed. Do you want to rely on an electrical distribution system for proper equipment and systems operation that is not capable of that support?
The major di!erences between what we will call a “standard” electrical distribution system and an “electronics” grade electrical distribution system is the installation design that will include the grounding specification, electrical panel selection, wiring design and installation methods.
The NEC (National Electric Code) allows for an electrical system that is not capable of properly supporting sensitive electrical and electronic loads. It allows shared neutrals & grounds, mixing sensitive loads on panels with inductive, dirty or outside circuits and overloaded circuits. The system we just described is “legal” as it follows the NEC, but it is not proper to support sensitive electrical and electronic loads. The ground in a standard
electrical distribution is focused upon life safety but not the support of sensitive systems. Life safety is the focus of the NEC, as it should be. However the NEC does not define the proper support of systems that can be impacted by electrical noise, energy flow on ground or mixing of panel loads.
Some of the issues or conditions in a minimum code compliant electrical distribution system are listed below:
- The electrical ground resistance far exceeds the stated NEC 25-Ohm recommended (but not required) standard.
- The primary neutral conductor and the neutral lug are sized per the NEC (not over-sized as they should be for electronic loads).
- The neutral conductors in branch circuits are o”en “shared” (common or used by more than one circuit).
- The ground of the circuits and case ground (conduit & panel) are common (bonded) and not isolated. (older systems relied on conduit for ground or had no ground)
- Circuit breakers are most o”en builder’s grade “snap in” and seldom electronics grade “bolt in” breakers or rated at 100%.
- Electrical outlets will be builder’s grade “three wire” outlets (phase neutral & ground).
- Electrical outlets may be the “back stab” type and prone to issues and can be dangerous and are the known source of building fires!
- Electrical circuits will have added based upon the “180VA” rule. So you could have more than 10 duplex outlets on one 20-ampere circuit.
- Parking lot light circuits are on the same panel as the outlets that power PC Computers.
- Air conditioning equipment and other “motor” loads will be on the same panel as sensitive devices and electronic loads.
Read the above list to an IT person or your data center manager you know and ask if they would power their equipment if the electrical system were as code allowed to be installed system above to be installed.
Electronics grade power distribution systems have a number of primary di!erences (a few are listed below):
- The ground resistance will be <5-Ohms (fall of potential tested).
- The panel loading will be logical. Dirty loads will not be mixed with sensitive loads.
- Outside circuits such as; parking lot lights, out side sign lights, sprinkler system controls, etc. will not be mixed with sensitive loads.
- The load segregation will place the sensitive load panel(s) as far away from any outside or inside source of electrical problems as possible.
- The primary neutral conductor and the neutral lug are over-sized, (sized two times or greater the NEC requirements), to deal with harmonic currents generated by switch mode power supplies.
- The neutral conductors in branch circuits are home runs (never shared or used by more than one circuit).
- Panel grounding and conduit ground is case ground and a separate isolated ground buss bar will be installed. This isolated ground buss bar will be connected directly (and only) to the service entrance ground buss bar with a stranded and insulated copper conductor sized appropriately for the distance involved.
- Circuit breakers are electronics grade “bolt in” breakers and breakers will be 100% rated.
- Only Isolated Ground outlets will be used (phase, neutral, ground & case ground) for all sensitive circuits.
The reasons for installation of an electronics grade power distribution system are numerous. A few key points are:
- The ability to handle high harmonic voltage and currents.
- Separation of case and equipment ground to eliminate noise and provide an e!ective low resistance path for equipment shielding.
- Elimination of circuit failure from loose snap in breakers.
- Elimination of shared circuit equipment problems (unbalance loads with shared neutrals).
- Reduction of Common Mode voltage. (between neutral & ground)
- Isolation of sensitive equipment from inductive loads (AC systems, copy machines, lights, etc.)
- Reduction or elimination of common mode noise (neutral to ground voltages at high frequency)
- Reduction of lightning damage exposure.
A detailed description of an electronics grade electrical distribution panel will not add to this information. If you are not familiar with these panels, contact a power quality professional or your consulting electrical engineer for assistance. They are readily available and the additional cost (small) is well worth the investment.
At the branch circuit level, electronic grade distribution systems do not have shared neutrals and employ a four wire topology. (Phase, neutral, case ground & isolated ground) The phase (hot) wire will most commonly be black, red or blue. The neutral will be white or yellow. The case ground wire will be bare copper. (See note below) The isolated ground wire normally be will be insulated green or insulated green wire with a trace stripe (yellow and pink are the most common).
It is important to note “dissimilar metals will electrolyze” is a problem common to electrical distribution systems. The result will be corrosion (high resistance) and can lead to both equipment problems and life safety problems such as fires. Galvanized conduit connected to copper is but one example. In the case of dissimilar metals the wire should be tinned or nickel chrome coated wire. The best option is to upgrade so there is not a problem with dissimilar metals.
To understand the importance of an “electronics grade” electrical distribution system for sensitive electronics you should consider how microprocessor equipment operates and what it is looking for.
One of the most frequent problems are common mode events (neutral to ground) and can cause significant disruption to the operation of microprocessor based equipment. Modern logic circuits do not enjoy the electrical isolation that was part of the older “linear power supply” technology. The microprocessor circuits are constantly measuring logic voltages against the “zero voltage reference” or safety ground. The microprocessor’s decisions are the result of discrimination of one rapid voltage transition from another, ultra-clean and quiet electrical safety grounds are essential. The microprocessor expects to see less than .5 volts of neutral to ground voltage. If the microprocessor sees more than .5 volts it will cause system lockups, communication errors, reduce operating throughput, unreliable data, fragment hard drives and operational problems that can not be duplicated or explained. If high enough, neutral to ground voltages will damage equipment.
In an “isolated ground outlet” the case ground wire (usually bare copper) is not connected to the ground pin. Case ground is connected to the outlet frame Conduit and outlet box only. Continuity can not be measured between the ground pin and conduit, outlet box or the outlet frame.
In new construction or during remodeling project it is o”en easy and cost e!ective to install electronics grade electrical distribution panels and isolated ground circuits. The cost in existing construction can be prohibitive and point of use products are available for those instances. (Reference: Isolation Power Conditioners)