Sources of Electromagnetic Interference EMI in SCS (Structured Cabling System)
EMI is stray electrical energy, radiated from any electronic system, including, cables, which can cause distortion or interference in other nearby cables or systems. EMI is sometimes referred to as “electromagnetic pollution” Electrical cables are both major producers and receptors of EMI. As producers, they radiate an electromagnetic noise field picked up by susceptible radio and TV receivers, computers, communications systems and data systems via their antennas, interconnections, lines and power supplies.
Electrical cables are susceptible to receiving this same “noise” from other nearby sources. For installations of cable lengths of up to 90 m, zero separation distance is required for branch/radial circuits that meet the following conditions :
- Limited to one power cable rated at 240V, 20A, single phase (phase-to-neutral or earth).
- The power cable or cord must have Live (L), Neutral (N) and Earth (E) conductors contained within a common sheath (that is, sheathed power
cables). If loose (individual) conductors are used as power cables, these conductors must be bunched or maintained close together to minimize inductive coupling. - A ring circuit can be considered to be equivalent to two branch circuits, eg a ring circuit of 32A is considered to be equivalent to two branch circuits of 16A each. In this case, the guidelines for 16A apply.
- Powering typical office equipment.
- The main electrical service entrance is protected with surge arresters (transient voltage surge suppressor) according to the applicable
local/national codes (for equipment safety). In addition, the following recommendations shall also be met: -
- The building itself shall be suitably protected from direct lightning strikes according to the applicable local or national codes.
- Outlet boxes or compartments where individual power conductors and Category 5/6 cabling are introduced to serve a workstation require 6 mm separation.
- If loose, open (spaced) power conductors are used and not bunched or maintained close together, a minimum separation of 50 mm is required.
- For all fluorescent light fixtures and associated power cables (in the vicinity of the light fixtures), the separation distance is 127 mm.