A naturally occurring phenomenon when the electromagnetic field of one device disrupts, impedes or degrades the electromagnetic field of another device by coming into proximity with it.
When cable is in close proximity to strong electromagnetic fields, unwanted current and voltage may be induced on it. If the power level is high enough, the electrical "noise" can interfere with voice and data applications running on the cabling.
Electromagnetic Interference (EMI)
Electromagnetic Interference (EMI)
Cabling plant can be susceptible to Electromagnetic Interference, usually known as EMI. This is a naturally occurring phenomenon when the electromagnetic field of one device disrupts, impedes or degrades the electromagnetic field of another device by coming into proximity with it.
When cable is in close proximity to strong electromagnetic fields, unwanted current and voltage may be induced on it. If the power level is high enough, the electrical
"noise" can interfere with voice and data applications running on the cabling.
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Electromagnetic Interference (EMI) cont’
• In data communication, excessive electromagnetic interference (EMI) hinders the ability of remote receivers to successfully detect data packets.
• The end result is increased errors, network traffic due to packet retransmissions, and network congestion.
• For analogue voice communication, EMI can create psophometric noise, which degrades transmission quality.
Electromagnetic Interference (EMI)
In data communication, excessive electromagnetic interference (EMI) hinders the ability of remote receivers to successfully detect data packets.
The end result is increased errors, network traffic due to packet retransmissions, and network congestion.
For analogue voice communication, EMI can create psophometric noise, which degrades transmission quality.
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Protecting against EMI:
There are two methods of protecting against EMI:
Shielding
Physical separation
Electromagnetic Interference (EMI)
The two main methods of reducing noise without having to resort to noise-cancelling electronics are shielding and physical separation.
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Protecting against EMI:
Shielding
In shielding, noise voltage is induced into a foil or braid surrounding the twisted pairs, instead of onto the conductors.
A properly installed shielded cabling system performs about 20dB better than UTP cabling system performance in terms of interference immunity (coupling attenuation).
Electromagnetic Interference (EMI)
In shielding, noise voltage is induced into a foil or braid surrounding the twisted pairs, instead of onto the conductors. The shielding must be properly earthed so that the resultant current is carried away from the shield.
A properly installed shielded cabling system performs about 20dB better than UTP cabling system performance in terms of interference immunity (coupling attenuation).
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Protecting against EMI cont’
Physical separation:
The following slides specify the minimum separation recommended for both 100 Ohm UTP and Shielded/Screened cabling, as well as the pathways and spaces used to carry or house the telecommunications cabling.
Electromagnetic Interference (EMI)
By applying the proper physical separation distances, U/UTP cabling can be used in a cabling system, while still avoiding EMI. In situations where minimum separation distances cannot be met for U/UTP cabling, F/UTP, F/FTP or S/FTP cable can be used.
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Electromagnetic Interference (EMI)
• Power Separation – BSI 6701:2004
50Va.c. – 600Va.c.
120Vd.c – 900Vd.c. to earth
Not less than 50 mm
Or a divider meeting the requirements of BS 7671 Exceeding
600Va.c. – 900Vd.c. to earth
Not less than 150 mm Or 50 mm with a divider meeting the requirements of BS 7671
But see exceptions
Power Separations
BSI 6701
The separation distances shown in the slide are specified in the British Standards Institute BSI 6701:2004 standard and provide a good reference. It should be noted however that other national standards have different specifications for separation which should be applied where appropriate.
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Electromagnetic Interference (EMI)
• Power Separation – BSI 6701:2004
Exceptions(apply to voltages 50Va.c. – 600Va.c. / 120Vd.c. – 900Vd.c. to earth) If one or more of these conditions is met, separation is not deemed to be necessary
• the electricity supply cables are enclosed in a separate conduit or trunking which, if metallic, is earthed in accordance with BS 7671;
• the electricity supply cables are of a mineral-insulated type;
• the electricity supply cables are of an earthed armoured construction;
• the electricity supply cables are of a flexible double insulated type (e.g.
“kettle leads” supplying 240 V mains power to telecommunications equipment in cabinets).
NOTE: Standard electrical 240 V “twin and earth type” cabling is not flexible double insulated.
The exceptions to the separation requirements for voltages 50Va.c. – 600Va.c. / 120Vd.c. – 900Vd.c. to earth shown on the previous slide are,
If one or more of these conditions is met, separation is not deemed to be necessary
the electricity supply cables are enclosed in a separate conduit or trunking which, if metallic, is earthed in accordance with BS 7671;
the electricity supply cables are of a mineral-insulated type;
the electricity supply cables are of an earthed armoured construction;
the electricity supply cables are of a flexible double insulated type (e.g. “kettle leads” supplying 240 V mains power to telecommunications equipment in cabinets).
NOTE: Standard electrical 240 V “twin and earth type” cabling is not flexible double insulated.
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CENELEC EN 50174-2:2008 Segregation requirements:
• The standard defines 4 Segregation Classifications –a, b, cand d– for cables
• Classifications are based on Coupling Attenuation performance (screened cables) or Transfer Conversion Loss (unscreened cables)
• Category 7 cable complies with Classification “d”
• Screened Category 6 and 5 cables comply with Classification “c” but may comply with Classification “d”if Coupling Attenuation met
• Unscreened Category 6 and 5 cables comply with Classification “b”but may comply with Classification “c”or “d”depending on Transfer Conversion Loss performance
• Classification “a” is applied where
– The mix of applications or the cabling to be installed is unrestricted – The type of cabling to be installed is unrestricted
– The cable performance with regard to the relevant parameters is unknown
Electromagnetic Interference (EMI)
Power Separations
CENELEC EN 50174-2
The European EN 50174-2:2008 standard defines 4 Segregation Classifications – a, b, c and d – for cables
Classifications are based on Coupling Attenuation performance (screened cables) or Transfer Conversion Loss (unscreened cables)
Category 7 cable complies with Classification “d”
Screened Category 6 and 5 cables comply with Classification “c” but may comply with Classification “d” if Coupling Attenuation met
Unscreened Category 6 and 5 cables comply with Classification “b” but may comply with Classification “c” or “d” depending on Transfer Conversion Loss performance
Classification “a” is applied where
- The mix of applications or the cabling to be installed is unrestricted - The type of cabling to be installed is unrestricted
- The cable performance with regard to the relevant parameters is unknown
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CENELEC EN 50174-2:2008 Segregation requirements
No segregation is required between IT cabling and mains power cabling (other than that required by national or local regulation) provided that all the following conditions are met:
• The environmental classification for the IT cabling complies with E1 of EN 50173-1:2007
• The power conductors – Form single phase circuits
– Provide a total current of 32A (max)
– Comprising a circuit are maintained in close proximity (e.g. within an overall sheath or twisted, taped or bundled together)
And either
Electromagnetic Interference (EMI)
No segregation is required between IT cabling and mains power cabling (other than that required by national or local regulation) provided that all the following conditions are met:
The environmental classification for the IT cabling complies with E1 of EN 50173-1:2007. This is part of what is known as the M.I.C.E. classifications which cover the Mechanical, Ingress protection, Climatic and chemical and Electromagnetic characteristics of the environment. E1 is a relatively benign EMI environment which should be found in most office situations. However, as it defines specific limits for radiated and conducted interference signals, it cannot be assumed that an E1 environment exists without inspection. It is usually considered that screened or shielded cabling complies with the E1 requirements.
The power conductors
o Form single phase circuits
o Provide a total current of 32A (max)
o Comprising a circuit are maintained in close proximity (e.g. within an
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CENELEC EN 50174-2:2008 Segregation requirements cont’
a) The information technology cables meet the requirements of Segregation Classifications “b”, “c” or “d”
or
b) In circumstances where the cabling is application specific, the application(s) supports a zero segregation relaxation.
This allowance should be not applied in spaces allocated to distributors in accordance with EN 50173 series or equivalent concentrations of transmission equipment.
Electromagnetic Interference (EMI)
The information technology cables meet the requirements of Segregation Classifications “b”, “c” or “d”
or
In circumstances where the cabling is application specific, the application(s) supports a zero segregation relaxation.
This allowance should be not applied in spaces allocated to distributors in accordance with EN 50173 series or equivalent concentrations of transmission equipment.
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Electromagnetic Interference (EMI)
CENELEC EN 50174-2:2008 Segregation requirements cont’
• In all other cases, the results of the following table multiplied by the power cabling factor shall be applied
Containment applied to IT or mains power cabling Segregation
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20A 230V 1-phase 1 to 3 0.2
4 to 6 0.4
7 to 9 0.6
10 to 12 0.8
13 to 25 1.0
16 to 30 2
31 to 45 3
46 to 60 4
61 to 75 5
> 75 6
Electromagnetic Interference (EMI)
CENELEC EN 50174-2:2008 Segregation requirements cont’
Electrical Power Cabling Factor P
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ANSI/TIA/EIA 569-B power separations
Table 1: Minimum power separation for UTP cabling systems
Power Level < 3 kVA 3 < 6 kVA > 6 kVA
Pathways 50mm (2 in) 1.5m (5 ft) 3m (10 ft)
Spaces 50mm (2 in) 3m (10 ft) 6m (20 ft)
Electromagnetic Interference (EMI)
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Electromagnetic Interference (EMI)
ANSI/TIA/EIA 569-B power separations
Table 2: Minimum power separation for screened and shielded cabling systems
Power Level < 3 kVA > 3 < 6 kVA > 6 kVA
Pathways 0m (0 in) 0.6m (2 ft) 1m (3 ft)
Spaces 0m (0 in) 0.6m (2 ft) 1m (3 ft)
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