Problems with running electrically noisy cables close to sensitive cable
Do not route electrically noisy cables close to sensitive cables.
Split cables up into groups, e.g….
- Transducer (signal input ) cables (e.g. from platinum resistance thermometers, thermocouples, strain gauges, microphones, tachogenerators)
- Analogue signal cables (e.g. 4-20mA, 0-10V, 24Vdc from local power converters)
- Digital signal cables (e.g. Ethernet, Profibus, ASI, RS485)
- Office quality’ electrical power cables (e.g. supplying equipment up to 1kW such as printers, PCs, VDUs, photocopiers, lighting, small machines such as domestic vacuum cleaners, washing machines, small resistive loads up to 3kW, variable-frequency drives and UPSs up to 1kW, etc.)
- “Industrial quality’ electrical power cables (e.g. supplying large rotating machines, pumps, HVAC, welding equipment, robotic manufacturing, large resistive loads, large power converters whether AC-DC or AC-AC such as motor drives, automatically adjusting power factor correction capacitors, etc.)
- The motor cables associated with variable speed AC and/or DC motor drives (unless using sinusoidal filters, in which case they become category d or e depending on the quality of the filter), welding cables
- Medium-voltage mains distribution (1-32kVac)
- High-voltage mains distribution (1-32kVac)
Only bundle members of each group together.
Never place different groups in the same trunking.
Always use a solid metal cable support structure (ducts, trunking, trays, even structural steelwork) along the entire length of all insulated cables, and constructed it to be a PEC (see below). Basket or wire cable trays are no use.
If routed in parallel routes, lie the different bundles along a metal wall, girder or cable tray that is designed as a PEC (see below) and maintain at least Xmm spacing (whether horizontal or vertical) between each bundle in turn from a) through to h). If this means digging a new cable trough in a concrete floor, so be it – the effort will be worthwhile.
- For cable lengths < 3m: X = 100mm (at least)
- For cable lengths 3-30m: X = 150mm (at least)
- For cable lengths > 30m: X = 150(length/30) mm (at least)
For instance, if X is 150mm then the a-b spacing is 150mm but the b-e spacing is 450mm.
Routing cable categories in dedicated metal conduit PECs or covered metal duct PECs can allow these spacings to be reduced.← Back to FAQs