PVC is the most common insulation material used for wiring in low-voltage (LV) service. ‘Low-voltage’, in the context of this paper, is taken to be 120–240 VAC. The electrotechnical products considered include insulated wires, cables and cords, and also appurtenant termination devices, e.g. male plugs or female taps. Well-known factors leading to the ignition of PVC-insulated wiring and related products include: (a) manufacturing defects; (b) grossly excessive current; (c) over-insulation, sometimes augmented by overcurrent; (d) localized heating due to strand breakage; (e) localized heating due to mechanical strand severing by staples or nails; and (f) localized heating due to failed terminations. Other failure modes are known but have received only limited study. These include (i) excessive force and creep; (ii) chemical interaction effects; and (iii) breakdown under voltage surge conditions. Additional research is needed in these areas. The proximate cause of ignition involved with many of the above mechanisms is arc tracking (arcing across a carbonized path). In turn, it is shown that PVC is especially susceptible to becoming charred, it requiring only approximately 160°C for the material to become semiconducting during short-term exposure (around 10 h), while longer-term exposure (around 1 month) may cause failures at temperatures as low as 110°C. Some limited data exist which suggest that standard UL and IEC temperature classifications are unduly optimistic, as applied to PVC. Fire can originate if wiring or equipment cannot withstand a powerline surge. Mains-connected electrical appliances need to be designed to resist 6000 V surge voltages, even though this is not mandated in most of the current UL and IEC standards. Data are presented showing that the IEC 60112 wet-tracking test gives especially misleading results for PVC and should be improved or abrogated. Copyright © 2005 John Wiley & Sons, Ltd.

Mechanisms and modes for ignition of low‐voltage, PVC‐insulated electrotechnical products

PVC is the most common insulation material used for wiring in low-voltage (LV) service. “Low-voltage,” in the context of this paper, is taken to be 120 – 240 VAC. “Wiring” is taken to include not only insulated wires, cables, or cords, but also the appurtenant termination devices, e.g., male plugs or female taps. Well-known factors leading to the ignition of PVC wiring include: (a) manufacturing defects; (b) grossly excessive current; (c) over-insulation, sometimes augmented by overcurrent; (d) localized heating due to strand breakage; (e) localized heating due to mechanical strand severing by staples or nails; and (f) localized heating due to failed terminations. Other failure modes are known but have received only limited study. These include (i) excessive force and creep; (ii) chemical interaction effects; and (iii) breakdown under voltage surge conditions. Additional research is needed in these areas. The proximate cause of ignition involved with many of the above mechanisms is arc tracking (arcing across a carbonized path). In turn, it is shown that PVC is especially susceptible to becoming charred, it requiring only approximately 160oC for the material to become semiconducting during short-term exposure (around 10 h), while longer-term exposure (around 1 month) may cause failures at temperatures as low as 110oC. Some limited data exist which suggest that standard UL and IEC temperature classifications are unduly optimistic, as applied to PVC. Mains-connected electrical appliances need to be designed to resist 6000 V surge voltages, even though this is not mandated in most of the current UL standards. Data are presented showing that the IEC 60112 wet-tracking test gives especially misleading results for PVC and should be improved or abrogated.

Mechanisms and modes for ignition of low-voltage pvc wires, cables, and cords

It was shown that uniaxial deformation of polyvinyl chloride, plasticized with dibutyl phthalate retards the molecular mobility of the plasticizer, displacing the correlation time spectrum towards higher values and distorting its shape. Appreciable anisotropy of the motion of dibutyl phthalate molecules is not observed. The behaviour of the parameters of nuclear relaxation of the polymer under strain is explained by the assumption of the existence of a 3-dimensional network in plasticized PVC.

The effect of deformation of plasticized polyvinyl chloride on molecular mobility

Dynamic calorimetry has yielded the thermograms of commercial PVC S-70 as a function of the prehistory of the samples. From the heat characteristics the authors isolate three stable states of PVC marked by constant parameters of melting and vitrification. Comparison of the PVC structure from the results of DSC and IR spectroscopy shows that the structural states of PVC isolated constitute three stable isomeric forms corresponding to the different conformational organization of PVC with complete identity of the configurational structure.

Phase and relaxational states of polyvinyl chloride

Creep and necking processes of PVC have been studied using the direct structural methods: birefringence, X-ray structural analysis and electron microscopy. It is shown that the creep process is associated with the disruption of the supramolecular organization of the polymer. A structural pattern of the processes developing at different stages of creep of PVC is proposed. It is shown that the structural conversions on creep of PVC are based on the process of the local orientation rearrangement with formation of distinctive micronecks on reaching a certain critical concentration of which the macroscopic neck begins to form. The supramolecular organization of the polymer to the point of crystallites in the region of the neck is disrupted.

Deformability of polyvinyl chloride in creep conditions

Heat treatment of quenched specimens of polyvinyl chloride containing small amounts of dioctylphthalate (3–20 wt.%) is accompanied by changes in the viscoelastic properties of the polymer (in the shape durability τs and in the rate at which forced-elastic deformation dϵdt develops). Changes in τs and in dϵdt during heat treatment are most marked in the vicinity of the glass temperature of plasticized PVC (transitional region). These effects are explained in terms of meromorphic type supermolecular structures emerging in the PVC/plasticizer system under heat treatment.

S.V. Pichugina

Papers

Deformability of polyvinyl chloride in creep conditions

Change in the structural state and viscoelastic properties of plasticized polyvinyl chloride under heat treatment