UL Recognised Wirewound Resistors
ULW Series
Welwyn Components
Application Notes
Application Notes
1. If the resistors are to dissipate full rated power, it is recommended that the terminations should not be
soldered closer than 4mm from the body.
2. Due to operating temperature limits imposed by some PCB materials, derating may be necessary. An
estimate of the temperature rise to be expected can be calculated using the thermal impedance figures
given under Electrical Data.
3. For the purposes of UL approval, the following points should be observed:
3.1 To protect against fire under all conditions of overload, a positive clearance of at least
13mm should be provided between the body of the resistor and any combustible materials.
3.2 A positive clearance of 13mm should be provided between the resistor body or terminations
and uninsulated parts of opposite polarity or uninsulated dead metal parts.
3.3 Limited Short Circuit testing should be performed in the complete appliance.
Packaging
The standard packaging for ULW is taped. The critical dimensions are shown in Figure 1. The component wires will not protrude beyond the outside
edge of the tapes. Taped product is then packed into ammo boxes. Alternative packaging is available by request. Pre-formed resistors are supplied
loose packed in plastic bags or boxes. For SMD leadformed option, see the Z-form datasheet.
Dimensions (mm)
Type
ULW2
ULW3
ULW4
b
52
67
63
C
5
10
Figure 1
F
C
f1
6
b
f2
6
10
Body location f1 - f2 <1.4mm
Ordering Procedure
Example: ULW2 at 33 ohms and 5% tolerance in ammo pack box of 2500 pieces -
ULW2
–
33R J
Type
Value (use IEC62 code)
Tolerance (use IEC62 code)
J
5%
A25
Packing
A25
A1
Ammo
ULW2
ULW3, ULW4
2500/box
1000/box
Standard
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· Bedlington, Northumberland NE22 7AA, UK
Telephone: +44 (0)1670 822181 · Facsimile: +44 (0)1670 829465 · Email: info@welwyn-tt.com · Website: www.welwyn-tt.com
03. 09
WELWYN [ WELWYN COMPONENTS LIMITED ]
