Insulating materials

General characteristics

For all its products ELETTROMECCANICA A. COLOMBO employs very high quality materials: particularly, the insulating parts are realized in 66 polyamide UL 94-V0, a thermoplastic with optimal thermal, electrical and mechanical characteristics.

The terminal block frame switchboard can be configured as “a derivation point” for testing, dissection or to ground operations and it must guarantee the safety connection in the most unfavourable operative conditions: for these reasons the terminal block is sized according to the restricted safety criteria, applicable also in the most critical operative conditions such as arctic and tropical climates and in environments with high risk of explosion (powder and humidity presence – pollution level “3” according to IEC 947-1).

The unique properties of the modified polyamide that we use in our products make it particularly suitable to the most critical working conditions: the strong resistance to biological (mildew, bacteria, enzymes), chemical (oils, greases, hydrocarbons) and atmospheric agents (UV light) along with the electrical characteristics (surface currents CTI > 600 V, electrical rigidity = 30 KV/mm) and the high level of mechanical robustness and elasticity (absolutely stable for temperatures from -40° up to 110° C) enable it to avoid also the typical fragility of thermosetting and ceramic materials.

Nevertheless, a high level of safety is guaranteed thanks to the absence of halogens and phosphorus, in addition to other banned flame retardant agents (polybrominated biphenyls – PBB and polybrominated diphenyl ethers – PBDE) as reported in the RoHS 2011/65/EU Directive, that can produce toxic gas emissions in case of fire.

The materials used by ELETTROMECCANICA A. COLOMBO, accredited in V0 class from the Underwriters Laboratories Inc. (USA) according to UL 94 Standard, guarantee self-extinguishing properties in a short time: in this way, “ASI” terminal blocks are not a dangerous means for fire propagation.

From the utilization point of view, the unique 66 polyamide characteristics are today fully comparable to those of thermosetting materials also in the case of extreme critical working conditions; the below chart reports the essential characteristics of the two mentioned materials.

Characteristics (at 20°C) u.m. 66 POLYAMIDE
(thermoplastic)
MELAMINE
(thermosetting)
DIELECTRIC STRENGHT kV/mm 30 10
TRACKING RESISTANCE V CTI > 600 CTI > 600
Tlim SUPERIOR, temporary °C 180 210
Tlim SUPERIOR, permanent °C 125 130
Tlim LOWER °C -50 -60
SELF-EXTINGUISH RATE Grado UL 94 VO UL 94 VO
TROPICALIZATION good good
MILDEW RESISTANCE good good

To notice:

  • wide range of operative temperature ( – 50 ÷ + 125 °C);
  • high level of surface current resistance (CTI index > 600 V);
  • high level of flame generation resistance (UL 94 degree: V0).

About “UL 94 – V0” approvals

The plastic materials belong to the category of organic materials and, as a consequence, they are combustible by nature.

In addition to the characteristics of the material, the reaction to flame depends also on environmental factors such as:

  • kind, duration and intensity of the ignition source;
  • air pressure drawn into the fire environment;
  • quantity, form and disposition of plastic materials in the area in question.

The complexity of a fire event is a reason because many different tests have been adopted: that devised in the USA by Underwriters Laboratories Inc. (UL) has received world-wide acknowledgment.

Test Execution

A defined dimension test specimen hanging horizontally or vertically in a combustion chamber is exposed, by means of a Bunsen burner, two times for ten seconds to a flame having temperature and size defined.

After every exposure the following values are being estimated:

  • combustion duration;
  • length of test specimen combusted section;
  • tester incandescence duration after flame extinction;
  • flame propagation from drops of fused material (dripping)
SELF-EXTINGUISH RATE
V0 V1 V2
Total time of combustion with flame for every group of 5 samples < 50 s < 250 s < 250 s
Residual time of combustion more time of persistence of the incandescence for every test piece, after the second application of the flame. < 30 s < 60 s < 60 s
Residual time of combustion for everyone of the samples after the removal of the flame < 10 s < 30 s < 30 s
Ignition of the hydrophilic cotton from part of incandescent drops (dripping) NO NO NO

These values allow material classification within the following self-extinguishing classes:

LOWER SELF-EXTINGUISHING HIGHER SELF-EXTINGUISHING
“no” HB V2 V1 V0 5V*

FURTHER CLASSIFICATIONS
HB – test pieces in horizontal position; it is applied to the not classifiable materials with a test’s method in vertical position.
5V – Other method with test pieces in vertical position but with a flame tilted of 20°; it is applied with a thermosetting materials.

The standard test specimen thickness are the following:

SPECIMEN’S THICKNESS (mm)
0,40 mm 0,75 1,50 3,00

ELETTROMECCANICA A. COLOMBO has adopted 66 polyamide accredited in UL 94-V0 class with a sample’s thickness of 0,40 mm, therefore to the top of the classification range.