Vitreous Enamelled Heavy

Duty Tapewound Resistors

U400 Series

© Welwyn Components Limited 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

129

Issue D · 08.04

Welwyn Components

Application Notes

The recommended dissipation for the resistor hot spot

temperature applies to resistors mounted horizontally. If the

bore is completely blocked a 15% derating is recommended.

However, wherever possible, resistors should be mounted

vertically with unobstructed bore and under these conditions

can be up-rated by 10%. This makes best use of the chimney

effect of the heated tube and will encourage a cooling system

of air through the bore. Appreciable reduction of hot spot

temperature can be achieved by arranging that resistors are

subjected to some measure of forced draught. In general, it is

effective to extract air from the resistor enclosure and arrange

that an air inlet is adjacent to the bottom of the tubes.

Ordering Procedure

Specify the type reference and quantity in units.

Mounting Devices

MD5 and 6 have an ear formed in the bottom surface of the

bracket to prevent rotation on the mounting plate. The

auxiliary locking springs ensure positive retention of the tube

under severe mechanical shock conditions. See figure 8.

Ordering Procedure

Mounting clips (and auxiliary locking springs, when required):

specify the type reference and quantity in units.

Mounting Clip dimensions (mm) Fig. 8

Auxiliary

locking

Resistor

Bracket

A

B

C

D

E

F

G

H

J

K

spring

ref.

type

nom.

max

nom.

max

max

max

±0.2

dia

dia

nom

ref

U414

MD3, MD6

120

141

49

33

32.0

19.0

6.4

4.0

6.3

9.5

MD18

U415

MD3, MD6

170

191

49

33

32.0

19.0

6.4

4.0

6.3

9.5

MD18

U416

MD3, MD6

234

255

49

33

32.0

19.0

6.4

4.0

6.3

9.5

MD18

U417

MD3, MD6

285

306

49

33

32.0

19.0

6.4

4.0

6.3

9.5

MD18

Mounting bracket dimensions (mm) Fig. 7

Resistor

Bracket

A

B

C

D

E

ref.

type

nom.

nom.

max

max

nom

U412

MD42

70

81

20

25

5.2

U413

MD42

133

144

20

25

5.2

U414

MD43

124

140

28

30

5.2

U415

MD43

174

190

28

30

5.2

U416

MD43

238

255

28

30

5.2

U417

MD43

290

306

28

30

5.2

U400_D.qxd

8/9/04

4:55 PM

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