EMI recommendations

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 Question by Victor Puyana posted 31 Mar 2006
 EMI recommendations
Hello,
I would like to know if there is any regulation/recommendation for telecom racks located at electrical rooms. We have a three phase electrical power transformer next to a telecom rack, and we would like to know if there is any rule about distance between them.

Thanks.
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 Answer by Joseph Golan posted 31 Mar 2006
Dear Victor,
Regulations (law) depends upon your local, most adopt the NEC in whole or part and has to do with safety. If the transformer needs to serviced from the side that ajoins the rack then there would be a 36" clear space requirement.

Recommendations are another thing, like the EIA/TIA Telecommunication Building Wiring Standards for one. Under the Section EIA/TIA-569-A, "Commercial Building Standard
for Telecommunications Pathways
and Spaces", there are a number of paragraphs that talk about this, such as:
13.2.1.5 Electromagnetic interference
'I'he room shall be located away from sources of electromagnetic interference. Special
attention sh.all be given to electrical power supply transformers, motors and generators, x-
ray equipment, radio or radar transmitters, and induction sealing devices.
and
10.3.3 Reducing noise coupling
In order to further reduce noise coupling from sources such as electrical power wiring,
radio frequency (RE) sources, large motors and generators, induction heaters, and arc
welders, the following additional precautions should be considered:
-- Increased physical separation.
-- Electrical branch circuit line, neutral, and grounding conductors should be
maintained close together (e.g., twisted, sheathed, taped, or bundled together) for
minimizing inductive coupling into telecommunications cabling.
-- Use of surge protectors in branch circuits that can further limit the propagation of
electrical surges. Follow guidelines in section 9.11.2 of ANSI/IEEE 1100.
-- Use of fully enclosed, grounded metallic raceway or grounded conduit or use of
cable installed close to a grounded metallic surface that will also limit inductive
noise coupling. Refer to clause 5.5.2.7 of ANSI/TIA/EIA-607 and section 9 of
ANSUIEEE 1100.

and also this out of the BICSI TDMM
TDM Manual on CD-ROM, 9th edition © 2000 BICSI®
Chapter 4: Horizontal Distribution Systems Page 197 of 253
Avoiding Electromagnetic Interference (EMI)
The designer should treat potential sources of electromagnetic interference (EMI) as a primary
consideration when selecting types of horizontal cabling and designing the layout of horizontal pathways.
Typical sources of EMI include:
• Electric motors and transformers that reside in close proximity to telecommunications cabling.
• Copiers that share space with telecommunications cables and equipment.
• Power cables that support such equipment.
One way to avoid EMI is to maintain physical separation between possible sources and the
telecommunications cabling. For additional information, see Chapter 19: Electromagnetic Compatibility.
Although optical fiber and shielded cable have been used for buildings with high levels of ambient EMI,
performance-enhanced unshielded twisted-pair (UTP) cabling, such as Category 5 or better, offers a
degree of noise immunity that ensures reliable transmission in most environments (e.g., electric field
intensity less than 3 V/m).

Almost every manufacturer of telecommunications cable and equipment will also have a reccommendation in their standards to also supply this separation.

My design rules for this is not to have them anywhere in the room and if it is impossible then get them separated by as much distance as possible (min. 4').

Sincerely,
Joseph Golan, RCDD

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