250 Series
Thin Stackohm
Vitreous Enamel Power
FeatureS
When limited space is a consideration, choose
Ohmites thin stackable 250 Type resistors. These
Small size-to-power ratio.
oval-shaped ceramic-core resistors feature a low
Stackable
profile to permit installation in spaces with height
In te gra l mo unt in g br ac ke t c ond uct s he at to
restrictions. They are also equipped with integral
mounting sur face.
mounting brackets so they can be fastened to a
chassis and stacked in locations with limited sur face
Low profile for use in equipment where space is
area.
limited.
When properly fastened, the mounting brackets
All-welded construction.
add a heat sinking benefit resulting in a smaller size
RoHS compliant product available. Add E suffix to
per watt. Durable 250 Type resistors are fully welded
part number to specify.
and coated with lead free vitreous enamel.
SerieS SPeciFicatiONS
Series Wattage Ohms Max. Voltage*
F10 10 1.0-15K 187
F20 20 1.0-50K 815
F30 30 1.0-10K 281
F40 40 1.0-25K 655
F55 55 1.0-30K 1405
Adjustable versions and other sizes available; Consult Ohmite Also available
in low cost Centohm or Silicone coating; Consult Ohmite.
* Maximum Voltage is based on Ohms Law [V=P*R] as limited by the resis-
tance value of specified product
characteriSticS
Lead free vitreous enamel
Coating
Core Ceramic
Terminals Tinned lug with hole. RoHS solder composition is 96% Sn, 3.5% Ag, 0.5% Cu
Derating Linearly from 100% @ +25C to 0% @ +350C
Tolerance 5% (J)
Power rating Based on mounting a single resistor on a metal surface measuring 10
(254mm) square by 0.04 (1.016mm) thick. Reduce rating by 15% when
mounting on non-metallic surface
Overload 10x rated wattage for 5 seconds if max. voltage is not exceeded
1 to 20: 400 ppm/C
Temperature
coefficient Over 20: 260 ppm/C
500 VAC: 10 and 20 watt rating. 1000 VAC: 30, 40 and 55 watt rating (mea-
Dielectric with-
sured from lug to mounting bracket)
standing voltage
Max. amps To calculate, use the formula P/R
110 1-866-9-OHMITE Intl 1-847-258-0300 Fax 1-847-574-7522 www.ohmite.com info@ohmite.com250 Series
Thin Stackohm
Vitreous Enamel Power
dimeNSiONS
(in. / mm)
0.125"
0.625"
3.175 mm Series Wattage Length L Length A
15.875 mm
0.031" Diam.
F10 10 0.750 / 19.050 1.000 / 25.400
0.794 mm 0.063"
1.588 mm
F20 20 2.000 / 50.800 2.313 / 58.750
Diam. F30 30 1.250 / 31.750 2.000 / 50.800
10W & 20W
0.125"
F40 40 2.000 / 50.800 2.750 / 69.850
3.175 mm
L F55 55 3.500 / 88.900 4.250 / 107.950
0.110":
A
0.125" *
2.776 mm *Reference dimension only; varies according to resistance
3.175 mm value.
0.375" Note: When resistors are stacked, use washers or spacers
0.250"
as required to insure clearance and improve power dissipa-
9.525 mm
6.350 mm
tion.
0.188"
4.763 mm
0.125" Diam.
3.175 mm 0.109"
2.776 mm
Diam.
30W, 40W & 55W
0.196"
4.979 mm
L
0.250"
A
6.350 mm 0.250" *
6.350 mm
0.125"
3.175 mm
0.438"
11.113 mm
mOuNtiNg
Derating for stacked mounting
In addition to the standard box bracket, stud type brackets
are available for stacking the standard size resistors. Stud Stacked resistors should be derated to prevent excessive tem-
peratures due to proximity. Approximate ratings are given in
type brackets are available in two heights: standard (SS,
0.437/11.113mm) and high (SSH, 0.531/13.494mm). The the table.
Percent of Single Unit Rating
SSH stud is recommended when stacking the adjustable Type
Miniature with
260, as it assures clearance for the adjustable lugs to pass
No. of 0.094 (2.381 mm)
eachother. Spacer washer No. 6027 (O.D. 0.219/5.556mm, Std. or Inter.
Resistors Miniature Spacer Washer
I.D. 0.125/3.175mm, thickness 0.094/2.381mm) is recom-
2 70 70 75
mended for use with the miniature adjustable and fixed resis-
3 60 60 69
tors to provide clearance, as explained above, or increased
4 50 50 60
wattage. See chart.
0.125" 0.125"
0.625" 0.188"
3.175 mm 3.175 mm
15.875 mm
4.763 mm
0.031" Diam. 0.094" Diam. 0.125" Diam.
0.794 mm 0.063" 2.381 mm 0.063" 3.175 mm 0.109"
1.588 mm 1.588 mm 2.776 mm
B B B
Diam. Diam. Diam.
0.813"
W W
0.125" 0.196" 0.196"
20.638 mm
3.175 mm 4.979 mm 4.979 mm
L L L
0.250"
0.110": 0.188"
Core Core Core
A A A
2.776 mm T 4.763 mm T 6.350 mm T
size size size
0.125" 0.125"
0.375" 0.438"
0.250" 3.175 mm 3.175 mm
0.438"
9.525 mm 11.113 mm
6.350 mm
11.113 mm
0.188" 0.188" Brackets
4.763 mm 4.763 mm cemented
0.125" Diam. 0.125" Diam.
in core
3.175 mm 0.109" 3.175 mm 0.109"
2.776 mm 2.776 mm
B B
0.156" x0.313"
Diam.
W W
3.969 x 7.938 mm
0.196"
Slot
4.979 mm
L L
0.250" 0.188"
Core Core
A A
6.350 mm T 4.763 mm T
size size
0.125"
0.438" 0.531" 0.5"
3.175 mm
11.113 mm 13.494 mm 12.7 mm
(SS) (SSH)
(continued)
1-866-9-OHMITE Intl 1-847-258-0300 Fax 1-847-574-7522 www.ohmite.com info@ohmite.com 111
0.938" 0.375"
23.813 mm 9.525 mm
1.000" 0.375"
25.400 mm 9.525 mm