Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning cable lengths and management associated with a surge protection device (SPD), is answered by Eaton:
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| Can I reduce cable lengths of an SPD? |
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Question: Is it good practice to reduce the cable lengths of an SPD, where possible, as that would mean less cable resistance? Is it insignificant? Also, if the excess cable is coiled up, would this have an affect, or doesn't it matter how the cables are managed? Finally, would a high power cable installed next to a SPD have an affect? Answers: The key concern with cable length is the inductance of the conductor, not the impedance. Typical flexible conductor inductance is around 1 micro Henry/m, and this does not vary greatly with the CSA of the conductor. The net effect of cable is that you lose 125V of suppressor performance for every 100mm of connecting cable when testing with the 20,000V 10,000A standard waveform. This means that, if the suppressor lets through 1000V with a connecting lead length of 150mm, this rises to 1125V with 250mm of cable, 1250V with 350mm of cable, or 2250V with just one additional metre of cable.
Bends in the cable also increase inductance, particularly sharp bends, so short straight cable is the best for suppressor performance. A coil is an inductor, so please, please don't let anyone coil cables to keep them tidy. They MUST be cut down as short as possible. Grouping cables helps, so all phases, N & E bound together tightly along their length is ideal.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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