Surge Protection Measures and NEC Requirements

This webinar, given by Mark Hendricks, Technical Director at DEHN Inc, provides a detailed review of the applications where surge protective devices (SPDs) are required to be installed on the electrical distribution system in order to meet the National Electric Code. Over the past several code cycles, the National Electrical Code (NFPA 70, NEC), has added sections requiring that surge protective devices (SPDs) SHALL be used on all dwellings, wind generation systems (Article 694), emergency systems (Article 700) and power systems impacting homeland security (article 708). 

Article 708 covering mission critical homeland security systems further requires a risk assessment and mitigation plan for meteorological hazards such as lightning. This is a continuing and ongoing process of recognizing the importance of lightning and surge protection for critical services and for facilities which although not critical, are at above average risk for loss of life or property due to lightning. 

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Answers to Q&A Following Live Webinar

Question Answer (Mark Hendricks at DEHN Inc)
Do you have comments on surge protection for high-rise buildings? SPDs should be on the main service entrance and each main panel for each floor.  Mandatory on emergency lights, fire control, alarms and elevator/door safety interlocks.
Could you please briefly explain its working operation/ principle? SPDs act as voltage control to divert only the surge current between two electrodes, in parallel or series. The surge current is diverted away from the victim, safely to ground. 
For an ungounded 480 Volt Delta connected service at 480 volts, 3-phase, what should the MCOV rating be? MCOV should be 550V L-G, 1100V L-L., SPD model 908 350 The voltage to ground for ungrounded circuits is the greatest voltage between the given conductor and any other conductor of the circuit. For a 3-phase, 3-wire ungrounded 480-volt system the voltage to ground is 480-volts
How to protect external RFID reader 8' high on a pole the best? I know DEHN (I'm a German enegineer) has devices for mobile phone and security cameras, but not sure if that can be used? We need to know the specific RFID reader model, but if it is RJ45 connected then our SPD model 929 221 is ideal for outdoor POE appliances. It might be a 4-20mA hard wired circuit.
If the main distribution panel has surge protection, do the downstream panels require it too, or does this just add cost to the project? Any panel more than 10m away can be considered beyond the effective range of the voltage control offered by another SPD IEC 60364-4-53 Clause 534.4.9.
Is it recommended to install SPD on line side or load side of a service disconnect? An SPD on the line side offers greatest protection of the internal systems due to direct strike ground potential rise. An SPD on the load side, like on the panel board will offer slightly better protection from outdoor sources like street lights that attract the surge and pollute the load center panel.
Can the master bar be separate to lightning down conductors? Yes, the Master Bar should connect to the earth electrode with a dedicated same size wire as the burred wire. The lightning down conductor should connect to the electrode with enough separation to any other bonded metal by a minimum calculated separation distance.
On the topic of lightning, is it safer to use a down conductor or use the body of the pole/mast to dissipate the electrical energy during a lightning strike? Unless you want to avoid any side flash into pole mounted equipment, the pole mast can be used if it meets IEC 4mm and NFPA 3/8" . High Voltage Isolated down conductor methods are preferred to provide equivalent air space separation from the down conductor.
What is live of surge protection equipment? Barring an uncontrolled overvoltage from the main service, the life of the surge protector depends on the technology of the device and strike environment. In Florida you will want to inspect metal oxide varistors every year, replace ever 10 years. Well made voltage switching gap devices can last decades. Several of our SPDs have life sense to advise as they suffer degradation and most will tell you when they die.
What is the recommended procedure of grounding the shield wire, drain wire etc in low voltage applications? Is it accepted to bond at both ends or only at one end? If it is only one end, then what is the recommended end (source or load side)? The treatment of shield has three scenarios with pros and cons:
  • Ground both ends - very resilient against noise, but subject HUGE ground currents if the chassis are not bonded to same reference.
  • Ground remote end - less stray ground currents flow into cabinet side, good for outdoor plants.
  • Ground at the cabinet - more stray currents enter the cabinet across a larger outdoor plant, good for indoor plants.
Would our world be better off if the world had never heard of isolated grounding systems? This is a good philosophical discussion!! But from the point of view of an aircraft or space ship, every thing has to have a common chassis reference or it doesn't work.
Are remote indications available to determine the deterioration of the SPD? DEHN has excellent predictive failure features on our Biltzductor dataline protector.
If an SPD is installed on the main incomer breaker on the MCC, do it again required on the downstream feeders? 75ft or greater is two runs min. NFPA 780 class 2 (about 1/2"), if lower class 1 (about 7/16") is allowed, IEC 62305 allows 8mm depending on number of conductors.
Which type of surge protection should be used on fire protection system in multi story building? All of the data lines and the incoming ac power in the panel must be protected. Specific device selection depends voltage and application, but DEHNrail 953 201 and 953 204 are popular.
Following the question on the use of the down conductor: In a play field (football) lighting system, will it be safer to use the down conductor instead of the mast itself? Unless you want to avoid any side flash into the lighting power circuits, the pole mast can be used if it meets IEC 4mm and NFPA 3/8". High Voltage Isolated down conductor methods are preferred to provide equivalent air space separation from the down conductor.
Surge protection Device can reduce arc flashing in LV Systems? It is reasonable to assume surge protection alleviates part of the dielectric stresses on the LV wires and switchgear. Arc flash is so dangerous that any mitigation methods like SPD application, house keeping, rodent control and electric conservation are worth implementing.
DEHN have Arc flashing protection systems and that can reduce or limit Short-circuit limits? Yes, DEHN has a very effective DEHNshort product line like our model 782 030 that sense the developing arc and trip the mains before the full asymmetric fault current inrush can propagate.
What is the sizes of down conductors in multi story building? 75ft or greater is two runs min. NFPA 780 class 2 (about 1/2"), if lower class 1 (about 7/16") is allowed, IEC 62305 allows 8mm depending on number of conductors.