In a certain Technical Standard, there is a clause for underground cable with regards to Single core cables, when laid in trefoil formation, shall be braced by preformed non-magnetic clamps or cleats designed to withstand the mechanical forces caused by short circuit currents.
Upon checking with electrical colleagues and counterparts, for underground (UG) cables, they rarely see use of cleats or clamps to secure the 1C cable trefoil formation. The use of cleats and clamps are normally seen at cable bending and when entering building to secure the above ground cables. Most of the times, the contractors propose to use cable ties made with SS316 coated with PU.
So are these SS316 cable ties non-magnetic type?
There are actually many types of stainless steel categories, which are:
1. Austenitic
2. Ferritic
3. Martensitic
4. Duplex
5. Precipitation-hardened.
We'll be focusing on austenitic and ferritic stainless steel material. What do they mean?
>>> Ferritic – generally magnetic
Ferritic stainless steels are classified in the 400 series, usually with 10% to 30% chromium content, and are often chosen for their excellent corrosion resistance and elevated temperature oxidation resistance.
>>> Austenitic – non-magnetic in the annealed condition
Austenitic stainless steels are chromium-nickel-iron (series 300) or chromium nickel-manganese-iron (series 200) alloys. Austenitic stainless steels are non-magnetic in the annealed condition but, depending on the composition (mainly the nickel and manganese content), they become slightly magnetic when cold worked. Austenitic stainless steel cannot be hardened by heat treating but only by cold working.
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For specification of non-magnetic stainless steel cable ties to brace the 1C cables trefoil formation, one should specify it to be made of Austenitic Stainless Steel to address the non-magnetic material requirement.
What are your experiences with regards to this requirement? Do share in the comment below.
