Welwyn Components

Telephone: +44 (0)1670 822181 · Facsimile: +44 (0)1670 829465 · Email: info@welwyn-tt.com · Website: www.welwyn-tt.com

03. 09

UL Recognised Wirewound Resistors

ULW Series

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

b

C

ULW2

52

5

ULW3

67

10

ULW4

63

10

Ordering Procedure

Example: ULW2 at 33 ohms and 5% tolerance in ammo pack box of 2500 pieces -

U L W 2 – 3 3 R J

A25

Type

Value (use IEC62 code)

Tolerance (use IEC62 code)

Packing

A25

Ammo

ULW2

2500/box

Standard

A1

ULW3, ULW4

1000/box

J

5%

f1

f2

6

6

C

F

Body location f1 - f2 <1.4mm

Figure 1

b