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Power Separation Guidelines



Introduction


A tutorial looking at Power Separation Guidelines, and the issues when separating power and data cabling. As well as looking at what distance between power and data should be adhered to, we look at the effects of Electromagnetic Interference (EMI).

This document details the requirements with regard to installing the Commscope (formerly Avaya) SYSTIMAXTM Structured Cabling Systems (SCS) in the vacinity of power circuits normally associated with Customer Premises. These guidelines should be followed in order to ensure compliance to the requirements of the SYSTIMAXTM Application Assurance Programme. Much of this information has been sourced from Commscope and relevant industry standards documents.

Electro Magnetic Compatibility (EMC)


Radio Interference has been known about since the 19th century, however it wasn't until radio and television began to be widely used in the 1930s that organisations such as the GPO in the UK were tasked with arbitrating between the frequencies allowed to be used for transmissions. This arbitration role has become more complex as Electromagnetic Interference (EMI) has become more prevalent with the growth in car ignition systems, Citizen's Band radio and faster computer processor clock speeds.

EMC requires the consideration of the following:
  • Electric Field strength - E-field
  • Magnetic Field strength - H-field
  • Effectiveness of the receiver's shielding
  • Frequency range of the transmitter and the receiver
In the UK and Europe, regulatory frameworks have been established:
  • Wireless Telegraphy Act (2006) originally conceived within the UK in 1949
  • Verband Deutscher Elektrotechniker (VDE) - the Association for Electrical, Electronic & Information Technologies The first electro-technical standard (VDE 0100) was passed in Germany in 1895
  • Comité Européen de Normalisation Electrotechnique (CENELEC)
  • EEC Directive 89/336/EEC is Statutory Instrument 992 No 2372 - The Electromagnetic Compatibility Regulations. This directive was implemented in the UK with effect from the 1st Jan 96. It has two components; Protection and Interference - properly installed equipment should not suffer from or cause electrical interference. There are no measurement limits, the compliant equipment is able to carry the CE mark.

EMC Protection


EMC protection requirements are:
  • The electronic disturbance generated must not exceed a level that prevents radio and telecommunications equipment and other relevant apparatus to operate as intended.
  • There must be a level of intrinsic immunity which enables it to operate as intended when it is properly installed and maintained and used for the purpose intended. This means a reasonable level of performance is expected to be maintained and a measure of expected degradation declared. The immunity measures put in place must not cause the item to be dangerous.
Well known EMC standards are listed below:
  • TC247/WG3 - Building management products for HVAC
  • BS EN 61000-4 - Basic standard covering immunity test methods
  • BS EN 50082-1 - Generic immunity standard for residential, commercial and light industrial environment
  • BS EN 50082-2 - Generic immunity standard for industrial environment
  • BS EN 60801 - Immunity of process control equipment
  • BS EN 55101 - Immunity of Information Technology equipment
  • BS EN 55104 - Immunity of household and other similar equipment
  • BS EN 50081-1 - Generic emission standard for residential, commercial and light industrial environment
  • BS EN 50081-2 - Generic emission standard for industrial environment
  • BS EN 55014 - Radio frequency emissions from household and other similar electrical appliances
  • BS EN 55011 - Radio frequency emissions from industrial, scientific and medical equipment
  • BS EN 55015 - Radio frequency emissions from fluorescent lamps
  • BS EN 55022 - Radio frequency emissions from IT equipment
  • BS EN 60555 - LF emissions onto supply systems (household)
  • BS EN 60439-1 - Low voltage switchgear and control gear assemblies
There some exclusions, some because the devices are covered by other directives. These are listed below:
  • Export to country outside EEC - general exclusion
  • Excluded installations - general exclusion
  • Spare parts - general exclusion
  • Supply to authorised representative - general exclusion
  • Second hand apparatus - general exclusion
  • Benign apparatus - general exclusion
  • In sealed electromagnetic environment - specific exclusion
  • Radio amateur apparatus - specific exclusion
  • Military equipment - specific exclusion
  • Implantable medical devices (90/385/EEC)
  • Medical devices (93/42/EEC)
  • Electrical energy meters (76/89/EEC)
  • Spark ignition engines (72/245/EEC)
  • Spark ignition of tractors (82/890/EEC)
  • Non-automatic weighing machines (90/384/EEC)
  • Telecommunications terminal equipment (91/263/EEC)

EMC Interference


Typical Low frequency interference sources are as follows:
  • Intermittent Magnetic fields - radiated
  • Continuous Magnetic fields - radiated
  • Electric fields - radiated
  • DC in AC networks - conducted
  • DC ground circuits - conducted
  • Slow variations of supply voltages - conducted
  • Power frequency variations - conducted
  • Harmonics - conducted
  • Signalling voltages - conducted
  • Voltage unbalance - conducted
  • Voltage fluctuations - conducted
  • Induced low-frequency voltages - conducted
Typical High frequency interference sources are as follows:
  • Electric fields - radiated
  • Magnetic fields - radiated
  • Electromagnetic fields - radiated
  • Induced continuous wave voltage or current - conducted
  • Continuous waves - radiated
  • Transients - radiated
  • Oscillatory transients - conducted
  • Unidirectional transients - conducted

UTP and Power Cabling


Separation between SCS Structured Cabling and Power systems should be as large as possible, but available space will always be a limiting factor. Especially sensitive systems or systems that will emit Electromagnetic interference should be identified and adequate provisions made in the design with the advice of the system manufacturer. All cable systems should be easily identified as necessary for ease of future modification and maintenance.

Network equipment, controllers and cabling needs to be located as far as practicable from noisy electrical circuits which can include:
  • Lifts
  • Air handling units
  • Chillers
  • Variable speed motors
  • Switched loads
  • Relays
  • Contactors
Display screens that are based on CRTs, need to be located 5m away from sources of 50 Hz magnetic fields, such as transformers, busbars, and lift equipment. This is because fields > 0.5µT can cause displayed images to distort. Steel is a good barrier for shielding against 50 Hz magnetic fields; 5mm thickness will attenuate the field by a factor of 100 (40dB)

When you are in sensitive locations such as close to radars; airports, seaports or close to broadcast transmitters, hospitals or heavy electrical plant - then it is prudent to have an EMC survey carried out.

Power supplies within a building can suffer from its own EMC problems such as conducted disturbances: RF noise, harmonics, transient over-voltages, dips, surges, frequency variations, RMS fluctuations and interruptions. Good earthing and lightning protection are essential to provide stable power within a building.

All copper type cables that are carrying AC electrical currents will have an Electro Magnetic Field (EMF) surrounding the cable, this magnetic field is susceptible to interference from other magnetic fields that are in close proximity. The greater the current being carried then the greater the EMF produced, this therefore will cause an induction effect upon adjacent cables which may well result in induced noise/voltage transients etc. All cables are aerials, thus any adjacent signal cables (data/voice) will very lightly suffer from data corruption in data/Lan cables and line noise in voice circuits.

The criteria for the maximum induced longitudinal voltage into SCS UTP cabling from one or more power cables is 50 mv (0.050V) under normal power cable operating conditions. The induced voltage from more than one power cable is added in phase.

High voltage system cables should be segregated from cables of other systems and clearly identified for a general safety precaution, as well as for EMI reasons. If a wide separation cannot be achieved some form of protection barrier may be required.

Applicable local and national safety regulations will have procedures whenever the required distances are larger than the requirement for SYSTIMAX SCS. For the UK & Ireland, the IEE Wiring Regulations (BS 7671) and Installation of Apparatus Intended for Connection to Certain Telecommunication Systems (BS 6701) are two such documents to be referenced.

SYSTIMAX Guidelines


For SYSTIMAX installations of cable lengths of up to 90 metres, zero separation distance is required for branch/radial or ring circuits that meet the following conditions:
  • Limited to 250 volts, 20 amperes, single phase, less than 5 KVA
  • Power cables and cords with Live, Neutral and Earth conductors contained within a common sheath (that is, sheathed power cables).
  • Powering typical office equipment.
  • The main electrical services entrance is protected with surge arresters (transient voltage surge suppressor) according to the applicable local/national codes (for equipment safety).
  • If open (spaced) power conductors are used, a minimum separation of 50 mm is required.
Additionally, the following recommendations should be considered:

If compartment trunking is used, the barriers (metallic or non-metallic) are also suitable for separating individual power conductors (live, neutral and earth conductors) from SYSTIMAX high performance cables. These power conductors must be maintained close together for minimising inductive coupling into the SYSTIMAX cables.
  • The use of surge suppressors in branch circuits can further limit the propagation of electrical surges. These must be installed according to the applicable local/national codes (for equipment safety).
  • The use of fully enclosed metallic trunking or conduit will also limit inductive coupling, but if properly grounded and bonded in accordance with the IEE Wiring Regulations (BS7671).
For power Systems in excess of the above and less than 480 Volts, the minimum separation distances between cable routes and power wiring are as shown in Table A below :

Table A - Minimum Separation Distances


Conditions Minimum Separation Distance
Greater Than > 5kVa
Unshielded power lines or electrical equipment in proximity to SYSTIMAX cables in open or non metal containment. 610mm(24") Unshielded power lines or electrical equipment in proximity to SYSTIMAX cables in open or non metal containment. 610mm(24") Unshielded power lines or electrical equipment in proximity to SYSTIMAX cables in open or non metal containment. 610mm(24")
Unshielded power lines or electrical equipment in proximity to SYSTIMAX cables in a grounded metal conduit or fully enclosed trunking. 305mm(12")
Power lines enclosed in a grounded metal conduit (or equivalent shielding) in proximity to SYSTIMAX cables in open or non metal containment.(i.e. SWA power cables contained on traywork) 305mm(12")
Power lines enclosed in a grounded metal conduit (or equivalent shielding) in proximity to SYSTIMAX cables in a grounded metal conduit or fully enclosed trunking. 152mm(6")

Proper bonding and grounding of the metal conduit or fully enclosed trunking should be in accordance with the IEE Wiring Regulations (BS 7671), which are applicable to all electrical installations and are not unique to SYSTIMAX SCS. Installations of Power Circuits are outside the SYSTIMAX SCS footprint and consequently, the electrical suppliers or other appropriate qualified personnel are responsible for proper grounding and bonding.

In addition, the following requirements shall also be met:
  • The building itself shall be suitably protected from direct lightning strikes according to applicable local/national codes.
  • For fluorescent light fixtures and associated power cables, the separation distance is 127 mm.

Additional Information


For high voltage 3 phase 415v SWA @ 100 to 400A per phase the minimum recommended separation should be 1 metre providing the cables were enclosed within a steel conduit/trunking along the length of parallel exposure. In event of a riser situation then SCS cabling and power cabling must be adequately separated , i.e. SCS cabling contained within vertical trunking/traywork.

In event of very high i.e. transformer main input voltages 6.6 KV SWA @ 50 to 250 A, then SCS cabling must be contained within steel conduit with a minimum separation of 2 metres.

Note 1. - All steel conduit/ trunking must be fully bonded to the building safety earth in accordance with IEEE 16th edition wiring regulations.

There are special conditions affecting separation. The separation of SCS cables can be avoided/reduced if they are enclosed within a metallic conduit. Experience indicates that low carbon steel (not stainless steel) of 0.8 mm thickness or aluminium of 1.6 mm thickness will provide satisfactory EMI isolation. The conduit or trunking must completely enclose the SCS cables, be continuous and be fully grounded (earthed to the building safety earth).

Note 2. - This statement above (special conditions affecting separation) is applicable to Comscope's document regarding European Power Line Separation Guidelines and calculations providing all stated criterion are satisfied.

In event of a new installation where a traywork containment system is installed then it is recommended that all power cabling and data/voice cabling are contained within separate tray sub-systems with a reasonable separation distance apart.

The above guidelines are as recommended by many data cabling installers and should be applied in conjunction with local building regulations and installation standards to ensure the requirements of EMC directives are complied with.

Table B - BS6701 Separation Guidelines (1994)


BS 6701 (1994) Section 7.7.4.1 (a) :  
> 600 VAC or 900 VDC  
>= 150mm No divider present
>= 50mm non-conducting divider present
Section 7.7.4.1 (b) :  
> 600 VAC >= V >= 50 VAC or 900 VDC >= V >= 120 VDC  
>= 50mm No divider present
0 mm non-conducting divider present

Table C - BS 7671 (1992) Separation Guidelines (IEE Wiring Regulations, 16th Edition)


BS7671 (1992)      
Voltage (V) Distance (mm) Current (A) Distance (mm)
240 450 15 350
415 580 50 500
3300 1100 100 600

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