2021-2_Pages_27-35

УДК 614.841                                                DOI: 10.37657/vniipo.pb.2021.51.13.003

G.V. Bokov, A.A. Nazarov, D.G. Bokov

Mounting wires as a source of ignition in electrical cabinets

Abstract

Wires are widely used for internal installation of electrical cabinets. Number of fire cases caused by wires takes one of the first places in fire statistics. Application of wires in the cabinets has its own fire-prone aspects peculiarities as concerns initiation of electrical nature ignition source. It appears both at single wire laying and at laying in cords where wires touch each other also in connection points of electrical apparatuses and devices located in the cabinet. The article considers issues of ignition source appearance in wires taking into account specifics of their installation in electrical cabinets. Ignition source appearance in a single wire and in wires contacting each other has a difference. There are given experimental data on inflammation frequency of wire insulation material at single wire laying and also at higher resistance in electrical elements connection points. Zones that differ in characteristic features of wire as an ignition source are given in the range of possible overcurrents. Zone A is characterized by insulation ignition with low probability due to low current density that is not enough to heat the wire up to the critical temperature Т_кр, at which thermal decomposition products of wire insulating polymeric cover ignite. Zone B is designated in the range of overcurrent ratio from 2,5 to 18 compared with the long term permissible current value, in which insulation inflammation is observed due to fast conductor heating taking into account the influence of connection points with devices and apparatuses where increased transient resistance is present. It is experimentally confirmed that with the increase in transient resistance at the point of conductor connection with electrical equipment elements, the inflammation frequency of wire insulation increases. At the same time, the overcurrent range where ignition source appears reduces.

It is proposed to use the area limited by the dependence of the time before insulation inflammation from the minimum to the maximum current value at which ignition occurs as a characteristic of the wire as an ignition source.

Keywords: fire hazard, electrical cabinets, wires, components, electrical connections, overcurrent

Referenses

1. Babrauskas V. Research on Electrical Fires: The State of the Art. Fire Science and Technology Inc. 9000–300th Place SE Issaquah, WA 98027, USA.
2. IEC 332-1. Pt1 93 Test Single Vertical Insulated Wire-Cable. URL: https://ru.scribd.com/doc/259119944/IEC-332-1-Pt1-93-Test-Single-Vertical-Insulated-Wire-cable (accessed 3 April 2021).
3. GOST IEC 60332-3-21–2011. Ispytaniya elektricheskih I opticheskih kabeley v usloviyah vozdeystviya plameni. Chast 3-21. Rasprostronenie plameni po vertikalno raspolozhennym puchkam provodov ili kabeley. Kategoriya A F/R. [State Standard IEC 60332-3-21–2011. Tests on electric and optical cables under fire conditions. Part 3-21. Flame spread of vertically-mounted bunched wires or cables. Category A F/R]. (In Russian).
4. GOST IEC 60332-1-2-2011. Ispytaniya elektricheskih I opticheskih kabeley v usloviyah vozdeystviya plameni. Chast 1-2. Ispytanie na nerasprostranenie goreniya odinochnogo vertikalno raspolozhennogo izolirovannogo provoda ili kabelya. Provedenie iapytaniyz pri vozdeystvii plamenem gazovoy gorelki moahchnostyu 1 kVt s predvaritelnym smesheniem gazov. [State Standard IEC 60332-1-2-2011. Tests on electric and optical fibre cables under fire conditions. Part 1-2. Test for vertical flame propagation for a single insulated wire or cable. Procedure for 1 kW pre-mixed flame]. (In Russian).
5. Babrauskas V. Mechanisms and Modes for Ignition of Low-voltage, PVC-insulated Electrotechnical. Products, Fire & Materials 30:150-174, 2006, DOI:10.1002/fam.900.
6. Martzloff F.D., Hahn, G.J. Surge Voltages in Residential and Industrial Power Circuits, IEEE Trans. on Power Apparatus and Systems PAS-89:1049-1056. 1970.
7. Jones R.A., Liggett D.P., Capelli-Schellpfeffer M., Macalady T., Saunders L.F., Downey R.E., McClung B., Smith A., Jamil S., Saporita V. Staged tests increase awareness of arc-flash hazards in electrical equipment. IEEE Transactions on Industry Application, 2000, vol. 36, no. 2, March-April 2000.
8. Pravila ustroystva elektroustanovok [Rules for the installation of electrical installations]. Moscow, Energoservis Publ., 1998. (In Russian).
9. Guide for Fire and Explosion Investigations (NFPA 921), National Fire Protection Assn., Quincy, MA (2001).
10. GOST 27483-87. MEK 695-2-1-800. Ispytaniya na pozharoopasnost. Metody ispytaniy. Ispytaniya nagretoy provolokoy [State Standard 27483-87. MEK 695-2-1-800. Fire hazard testing. Test methods. Glow-wire test and guidance]. (In Russian).
11. Baratov A.N., Korolchenko A.Ya., Кravchuk G.N. Pozharovzryvoopasnost veshchestv i materialov i sredstva ih tusheniya [Fire and explosion hazard of substances and materials and means for their extinguishing]. Moscow, Khimiya Publ., 1990, 384 p. (In Russian).
12. Babrauskas V. How can faulty electrical wiring cause a building to catch fire? URL: http://www.interfire.org/features/electric_wiring_faults.asp. (Accessed 5 December 2020).
13. Bokov G.V., Afonin V.V., Simankin V.I. Probabilistic assessment of fire safety of the rectifier units. Pozharnaya bezopasnost – Fire Safety, 2016, no. 2, pp. 108–112. (In Russian).
14. GOST 12.1.004–91. Sistema standartov bezopasnosti truda (SSBT). Pozharnaya bezopasnost’. Obshchie trebovaniya. [State Standard 12.1.004–91. System of labor safety standards (SSBT). Fire safety. General requirements]. (In Russian).

Received April 7, 2021

Аuthors:

Gennadiy V. Bokov – Candidate of Technical Sciences, Senior Researcher, Leading Researcher. E-mail: bokoff-elektro@mail.ru;

Anton A. Nazarov – Deputy Head of  Department.

All-Russian Research Institute for Fire Protection (VNIIPO), the Ministry of the Russian Federation for Civil Defence, Emergencies and Elimination of Consequences of Natural Disasters (EMERCOM of Russia), Balashikha, Moscow region, Russia.

Denis G. Bokov – Candidate of Technical Sciences, Manager (Schneider Electric Company), Moscow, Russia.