Switchgear is usually installed in easily accessible locations and buildings, so many who are interested in such products are concerned about their safety and fire resistance. That is why in this section we present the properties of the special material (SMC) from which our partner EMITER panels are made and their proof of fire resistance.

EMITER plastic panels are made of thermosetting material consisting of polyester and various additives designed to improve certain properties of the product – ease of processing, plasticity, mechanical resistance, fire resistance, etc. In addition to components such as polyester, resin, fiberglass and other fillers, they contain a so-called “fire extinguisher”. It has a significant effect on the flammability of the product as it melts the spread of flame. This definitely increases the cost of the final product, but at the same time ensures much higher operational safety. One of the most important facts is that during combustion, these products do not emit burning drops, which is typical of thermoplastic products. This significantly reduces the risk of fires.

Fig. 1 (a) view of the transformer station; (b) transformer at the time of the accident; (c) post-extinguishing image: one burned-out cabinet and a VIT-compliant EMITER cabinet (marked with an arrow).

Flammability tests

In practice, several methods are known for checking the flammability of plastic materials: V – vertical, and HB and FH – horizontal flammability tests. Their descriptions can be found in the European standard and the American standard UL94, which is, among other things, more detailed and stricter.

During the tests, the flammability categories are ranked according to the level of severity (starting from the highest): 5VA, 5VB, V0, V1, V2 and HB = FH. As 5VA and 5VB are not used for the labeling of plastic materials, an overview of them will not be provided further.

In order to be able to compare the results of different tests, the samples used must be identical. Therefore, in the studies described below, their dimensions (125×13 mm) and burner force (50W) are the same in each of the above methods. Although it is known from the laws of physics that the thicker the sample, the more energy it will take to ignite it, PN-EN 60695-11-10 does not define the value of this parameter, but only provides a maximum of 13 mm.

V – vertical combustion test according to PN-EN 60695

10 pre-stabilized samples are used in this test (5 samples were tested in a 7-day thermal aging test at 70C and in a 5- to 48-hour test at 23C). A properly prepared sample is placed in the holder fi so that its longitudinal axis is vertical (Figure 2) and cotton wool is placed 30 cm below. A burner is then added so that its flame is in the center of the lower edge of the sample and the edge of the burner is 10 mm from the test substance.

The flame must touch the sample for 10s. If drops of molten material are emitted during the test, the burner must be tilted at an angle of 45 blades to prevent dripping. After 10 s, ignite the flame and record the burning time of the material (t1). As soon as the flame is extinguished, the burner is again placed under the sample for 10 s and the burning time (t2) and the burning time of the material after the final firing (t3) are measured in the same way. After the test, the total time for each of the samples is measured.

Test V – evaluation criteria

In summarizing the test, several criteria are used to describe the individual categories:

V0

• Burning time of a single sample: t1 + t2 ≤ 10s;
• Total burning time of all samples for each of the stabilization methods: ≤ 50s;
• Burning and flame time of each sample after the burner was added a second time: t2 + t3 ≤ 30s;
• The flame did not reach the holder;
• The cotton gasket did not ignite from falling particles or drops.

V1

• Burning time of a single sample: t1 + t2 ≤ 30s;
• Total burning time of all samples for each of the stabilization methods: ≤ 250s;
• Burning and flame time of each sample after the burner was added a second time: t2 + t3 ≤ 60s;
• The flame did not reach the holder;
• The cotton gasket did not ignite from falling particles or drops.

V2

The first four criteria are identical to category V1, while the fifth criterion has a positive result, i. the cotton gasket ignites against falling particles or drops.

If the vertical combustion method fails to assess the flammability of substance V, the standard recommends testing its properties by the HB method.

Fig. 2 Vertical combustion test according to PN-EN 60695

HB – horizontal combustion test according to PN-EN 60695

3 samples were used for the HB test, preceded by 48 h. stabilized at 23C. Mark a line on each of them at a distance of 25 and 100 mm from one end of the sample. The sample is then held in the holder fi so that its longitudinal axis is horizontal and its transverse axis is inclined at an angle of 45 degrees (Figure 3). The burner is positioned so that its principal axis is in the same vertical plane as the longitudinal axis of the sample.

If, during combustion, the flame does not exceed the limit of 25 mm (first line) before 30 s, the position of the test fire does not change and it is not drawn for that long. When the apex of the flame reaches the 25 mm mark, start measuring how long the sample burns or how long it takes for the flame to reach the 100 mm mark. In this way, all three samples mentioned above are tested.

HB test – evaluation criteria

Substances that pass the test are classified as HB40 and HB75. To be classified as HB40, they must meet one of the following criteria:

• After the fire has been drawn, the material must not burn with a visible flame;
• If the material burns even after the fire source has been drawn, the flame must not exceed the marked limit of 100 mm;
• If the flame exceeds the maximum specified limit, its burning rate must not exceed 40 mm / min.

The substance is classified as HB75 if the burning rate does not exceed 75 mm / min when the flame exceeds the maximum limit of 100 mm.

Fig. 3 Method of performing the HB test

FH – horizontal combustion test

The FH test procedure is identical to the HB test, and categories FH1, FH2 and FH3 are distinguished in the classification.

The evaluation criteria include:

• Length of the burnt part of the sample;
• Burning rate.

Summary

Looking at the problem of flammability of plastic materials, it is worth noting that flammable and flame-retardant materials are used in switchboard cabinets. We deliberately do not use the words “non-combustible material” because each substance is flammable and its rate and method of ignition depend only on the prevailing environmental factors (burning time, temperature, oxygen content, etc.).

The least stringent testing method is horizontal HB, which is recommended according to PN-EN 60439-5 (until 2007, previous publications of this standard required FB testing). The HB rate has relatively few requirements for test samples, making it difficult to speak of flammable materials in this case.

A suitable criterion for assessing the flammability of materials is criterion V – vertical combustion test. The flame formed at the bottom of the sample heats its entire surface, which is a much more realistic reflection of the operation of the junction box in the event of an accident (when a source of high temperature occurs and then a fire). This situation can occur when the screws that connect the conductive elements are loosened or, e.g. under conditions of internal arc discharge that generates a significant amount of heat.

As mentioned earlier, one of the components of a thermoset material is the “extinguisher”, which determines not only the degree of flammability of the material, but also the price. It is also known that most business partners follow it as a key criterion in public procurement, while the technical value of the product is in the background. Finally, compliance with the minimum standards is limited, although all energy products must pass the V0 flammability test with positive results before entering the market (especially in German, French and Czech energy).

In 2009, EMITER carried out comparative tests of three competitive products available on the Polish market. As the laboratory of this company is not accredited, the determination of the flammability criterion was entrusted to an independent team of German researchers. The summary report states that none of the samples met the prerequisites for V0. Only the requirements of FH2 were met: sample No 1 – FH2 / 20 mm, sample No 2 – FH2 / 10 mm and sample No 3 – FH2 / 11 mm. Meanwhile, EMITER products are made of a material that meets the standard V0 – the strictest according to PN-EN 60695-11-10 in Poland. To maintain this, the flammability properties of the material are constantly monitored in the company’s laboratory. Below are videos that clearly demonstrate the quality of EMITER products and the innovative use of SMC material.

Test No1. EMITER sample

Test No2. Analogue sample from another manufacturer

„Fire Pool” is another test of the flammability of the entire product