Cone Probe with UL 1278 Figure 10.1

Guarding of Heating Elements

General

The heating element and any part of the element assembly (such as an element support, sheath, and similar parts) shall be so guarded that flammable material as well as persons will be protected against contacting it.

Any heater projections such as guards or grilles that are intended to guard hot heater surfaces shall be positively secured to the heater such as by screws, rivets or welding or being engaged in slots so that they cannot be removed without the use of tools, breaking or permanent bending or distortion.

The acceptability of a guard is judged with respect to its general serviceability and with respect to the shape and size or both of the openings in it, in conjunction with the distance of the guard from the heating element and the other high-temperature parts mentioned in 10.1.1. Except as noted in10.1.5, an opening in a guard is considered to be acceptable if, with the heater in any intended operating position, the following conditions are met:

a) The shape and size of an opening are such that a test gauge in the form of a right-circular cone having a base diameter of 2-3/4 inches (69.9 mm) and an altitude of 5-1/2 inches (139.7 mm), see Figure 10.1, is prevented from touching the heating element and the other high-temperature parts when the cone probe is inserted, apex first, in any manner. See 10.1.4.

UL1278 Fig.10.1

b) The shape and size of an opening which permits the vertically downward entrance of a bar probe 1/2 inch (12.7 mm) wide and 1/16 inch (1.6 mm) thick, see Figure 10.2, are such that a triangle probe 1/16 inch thick and in the form of an isosceles triangle having a base of 2-3/4inches and an altitude of 5-1/2 inches, see Figure 10.3, is prevented from touching the heating element and the other high-temperature parts when the triangle probe is inserted, apex first, in any manner. The testing of an opening with the triangle probe applies also where the vertically downward insertion of the bar is prevented by the construction of the guard, the use of an additional barrier, or both, unless the vertically applied bar tends to be deflected outward – that is, away from the guard.

UL 1278 Figure 10.2

UL1278 Fig.10.3

c) The area of an opening in a substantially vertical face of a guard is not more than 3-1/4 square inches (2100 mm²) if the size and/or shape of the opening permits the entrance from any horizontal direction of a vertically oriented rod probe 1/16 inch in diameter and 2-3/4inch long, see Figure 10.4. 

                                                                     UL1278 Fig.10.4

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

Our main products are Goniophotometer, Integrating Sphere, Spectroradiometer, Surge Generator, ESD Simulator Guns, EMI Receiver, EMC Test Equipment, Electrical Safety Tester, Environmental Chamber, Temperature Chamber, Climate Chamber, Thermal Chamber, Salt Spray Test, Dust Test Chamber, Waterproof Test, RoHS Test (EDXRF), Glow Wire Test and Needle Flame Test.

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