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| | I am being told by a P.E. that it is not an NEC code requirement to ground equipment racks, cabinets, or cable tray in a data center with a dedicated grounding system separate from the ground wire provide for equipment power. The P.E. states that the ground wire in the power cord is all that is required by NEC. My response is the racks, cabinets, cable tray and other metal equipment should be bonded to a TIA 607 compliant grounding system in a data center, equipment rooms and all telecom rooms and that the power cord ground and TIA 607 ground should be bonded to the electrical power ground and building steel to comply with TIA 607 and NEC and that the racks/cabinets, cable tray and conduit that carries low voltage cabling must all be bonded to ground to assure that if a lighting or other faulted power circuit comes into contact with the metal racks/cabinets, cable tray, and conduit then personnel are protected. If this is not done then there is a potential liability issue. Any comments will be appreciated. |
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| | The PE is coorrect that there is not a requirement from the NEC to ground all of the metallic ocmponents that are in the TR. But you need to understand that the NEC (a code) is only concerned with safety, not performance. TIA (a standard) is meant to enhance performance. The NEC is something that you are required to follow in order to protect the safety of the equipment operators. The NEC does not have any concerns for the performance of the equipment. The TIA standards should be followed to be assured that the performance is as designed into the system. The TIA is a set of best practice standards that should be followed, but you are not required to follow. I hopr this is helpful Dave Golner RCDD/NTS |
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| Actually, I think communications grounding is covered a little bit on both article 250 and article 800 of the NFPA 70. (NEC) Not sure if it specifically mentions grounding the racks/ ladder rack etc; I would reference the code book. I have heard the 2008 NEC also incorporates more telecommunications into it than the 2005 code but have not had a chance to read it yet.
David Fulford
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| | Well as a PE myself who works for a large telecom company and specializes in protective grounding systems and co-author of IEEE Emerald Book, I can tell the PE you spoke to is mostly correct, and maybe 100% correct In your equipment racks/cabinets assuming you have AC power supplied to them, there is absolutely no NEC requirement to ground then with a supplemental ground. To take it one step further if the cabinets are in a line-up, bolted together, and each rack has an AC circuit supplied to them, the multiple EGC’s supplied with each AC circuit to every cabinet supply a far superior ground in terms of both performance and safety than any supplemental ground you could provide from a TRGB. The only question in my mind would be the cable tray and the manner it is supported and what it connected too. If it is physically integrated into the cabinets or supported by them, there is no NEC requirement to bond them or technical performance reason top do anything further. Now on the other hand if the cable tray is supported by threaded rod from ceiling inserts or stanchion poles without any physical connection to an approved electrical raceway or cabinet, there would be a NEC requirement to bond it to an approved grounding means. The best way is to bond it to building steel and one jumper from the AC panel ground bar serving the area. Much of what is in TIA is a myth or antiquated practice today. It is from the days when the equipment was powered from a DC battery plant, and I/O communications was done with ground reference signal protocols like RS-232. Today most of what you work with is AC powered and has a ground conductor provided with the circuit and all I/O communications is no done via balanced signals methods like Ethernet or optics in which a ground reference has no function or purpose.
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| | I agree that the NEC does not speak to grounding of the racks themselves, however, almost every manufacturers installation instructions state that a ground is required for many of the switches, etc that are installed. This is separate from the equipment grounding conductor contained in the power cord. Cicso likes to cover-up their grounding pads, but they are there. It is my belief that properly grounding all metallic parts, i.e. cable tray, racks, etc as discussed in TIA is just good practice. Panduit has a good publication on grounding and quite an extensive grounding products line. |
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| | I'm pretty sure that any electronics that have a grounding lug MUST be grounded. I think that's in the NEC 645.15. This article does apply to you if you're mounting the equipment. I recommend installation of a rack-mounted ground bar in each rack and have each bonded to the TGB. Also, I'm pretty sure that the ethernet encoding schemes rely pretty heavily on a nice solid reference voltage. This is particularly true with the high through-put schemes such as PAM-5. |
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| tchristison (4/2/2008)
I'm pretty sure that any electronics that have a grounding lug MUST be grounded. I think that's in the NEC 645.15. This article does apply to you if you're mounting the equipment. I recommend installation of a rack-mounted ground bar in each rack and have each bonded to the TGB.
Nope this is not true and a myth, the lug you are referring to is completly optional and serves no purpose other than customer demand. In fact using as such can add problems. Article 645 is for IT Equipment Rooms and very strict requirements of 645.2 must be met to take advantages of the leniencies allowed to article 645. Telephone rooms do not satisfy the requirements, and most Data centers do not qualify, nor would any engineer design a site to use it because of the EPO switch requirement. FWIW your interpretation is 645.15 is incorrect. It basically says all non-current carrying metal parts shall be grounded in accordance with article 250 or double insulated. Power systems derived within listed ITE that supply ITS through receptacles supplied as part of this equipment shall not be considered separately derived for the purpose of applying 250.20(D). Where signal reference structures are installed, they shall be bonded to the AC equipment ground (aka EGC) What that is telling you is if you have something like just a DSX panel where it is just passive components (no AC or DC powered equipment in the rack with an EGC equipment ground conductor supplied with the AC/DC circuit), then you are required to ground the equipment rack by some approved means like a bond to your TRGB. The purpose of this bond is just for life safety in the event the rack becomes energized so the over current protection device (circuit breaker) will operate. In addition it is permitted if necessary for a signal reference source to add a supplemental ground, but it must be sourced or bonded to the AC equipment ground for the area served, or in other words from the nearest AC panel ground bar. tchristison (4/2/2008)
Also, I'm pretty sure that the ethernet encoding schemes rely pretty heavily on a nice solid reference voltage. This is particularly true with the high through-put schemes such as PAM-5.
Not true, Ethernet is a balanced signal topology that requires no signal or ground reference that is why it was developed and replaced ground referenced topologies like RS-232 and 485. If that were true your laptop and other batteried powered equipment like test equipment would not work.
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| waboyd (4/2/2008)
I agree that the NEC does not speak to grounding of the racks themselves, however, almost every manufacturers installation instructions state that a ground is required for many of the switches, etc that are installed. Not true you just have not found it and that would be contained in 250.4(A)(2) which says: Non-Current carrying conductive materials enclosing electrical conductors or equipment. or forming part of such equipment, shall be grounded as to limit the voltage to ground on these materials. So if you have AC powered equipment installed in the rack, it is grounded. Otherwise passive equipment racks and cable trays are required to be grounded per NEC. The reason CISCO covers up the ground lug is because it is optional and not needed for proper operation.
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| dereckbc (4/2/2008)
tchristison (4/2/2008)
I'm pretty sure that any electronics that have a grounding lug MUST be grounded. I think that's in the NEC 645.15. This article does apply to you if you're mounting the equipment. I recommend installation of a rack-mounted ground bar in each rack and have each bonded to the TGB.
Nope this is not true and a myth, the lug you are referring to is completly optional and serves no purpose other than customer demand. In fact using as such can add problems. Article 645 is for IT Equipment Rooms and very strict requirements of 645.2 must be met to take advantages of the leniencies allowed to article 645. Telephone rooms do not satisfy the requirements, and most Data centers do not qualify, nor would any engineer design a site to use it because of the EPO switch requirement. NEC Article 645 Information Technology Equipment. I think your both right. Seeing that the NFPA 70 is meant for life as well as property protection, it seems to me that tchristison is correct from one point of view. Code states the following: NFPA 70 645.15 Grounding. All exposed non-current-carrying metal parts of an information technology system shall be bonded to the equipment grounding conductor in accordance with Article 250 or shall be double insulated. Power systems derived within listed information technology equipment that supply information technology systems through receptacles or cable assemblies supplied as part of this equipment shall not be considered separately derived for the purpose of applying 250.20(D). Where signal reference structures are installed, they shall be bonded to the equipment grounding conductor provided for the information technology equipment. --------- What are we talking about here? The "lug" is used for protecting the equipment when in service and under maintenance. When under maintenance (opened up), the AC power is removed as per manufacturers instructions and it is the "lug" that protects. Just because the equipment is installed (mounted) in the rack doesn't mean it is plugged in. If it is not plugged in...what protects it? Kevin J
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| Kevin J (2/23/2009)
dereckbc (4/2/2008)
tchristison (4/2/2008)
I'm pretty sure that any electronics that have a grounding lug MUST be grounded. I think that's in the NEC 645.15. This article does apply to you if you're mounting the equipment. I recommend installation of a rack-mounted ground bar in each rack and have each bonded to the TGB.
Nope this is not true and a myth, the lug you are referring to is completly optional and serves no purpose other than customer demand. In fact using as such can add problems. Article 645 is for IT Equipment Rooms and very strict requirements of 645.2 must be met to take advantages of the leniencies allowed to article 645. Telephone rooms do not satisfy the requirements, and most Data centers do not qualify, nor would any engineer design a site to use it because of the EPO switch requirement. NEC Article 645 Information Technology Equipment. I think your both right. Seeing that the NFPA 70 is meant for life as well as property protection, it seems to me that tchristison is correct from one point of view. Code states the following: NFPA 70 645.15 Grounding. All exposed non-current-carrying metal parts of an information technology system shall be bonded to the equipment grounding conductor in accordance with Article 250 or shall be double insulated. Power systems derived within listed information technology equipment that supply information technology systems through receptacles or cable assemblies supplied as part of this equipment shall not be considered separately derived for the purpose of applying 250.20(D). Where signal reference structures are installed, they shall be bonded to the equipment grounding conductor provided for the information technology equipment. --------- What are we talking about here? The "lug" is used for protecting the equipment when in service and under maintenance. When under maintenance (opened up), the AC power is removed as per manufacturers instructions and it is the "lug" that protects. Just because the equipment is installed (mounted) in the rack doesn't mean it is plugged in. If it is not plugged in...what protects it? Kevin J 645 is very specific in scope, and is applied to allow certain exceptions to other parts of the code. A (generic) telecom room, equipment room, entrance room (as described in EIA/TIA standards) does not automatically rise to the level of the 645 prescribed Information Technology Equipment Room. 645.4 describes those special requirements. If the room doesn't meet all of them, it does not qualify, and the code exceptions allowed within 645 may not be applied.
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