250 Series
‘Thin’ Stackohm®
Vitreous Enamel Power
When limited space is a consideration, choose
Ohmite’s “thin” stackable 250 Type resistors. These
oval-shaped ceramic-core resistors feature a low
profile to permit installation in spaces with height
restrictions. They are also equipped with integral
mounting brackets so they can be fastened to a
chassis and stacked in locations with limited surface
area.
When properly fastened, the mounting brackets
add a heat sinking benefit resulting in a smaller size
per watt. Durable 250 Type resistors are fully welded
and coated with lead free vitreous enamel.
Series
F10
F20
F30
F40
F55
Wattage
10
20
30
40
55
F e at u r e S
• Small size-to-power ratio.
• Stackable
• Integral mounting bracket conducts heat to
mounting surface.
• Low profile for use in equipment where space is
limited.
• All-welded construction.
• RoHS compliant product available. Add “E” suffix to
part number to specify.
Ohms
1.0-15K
1.0-50K
1.0-10K
1.0-25K
1.0-30K
Max. Voltage*
187
815
281
655
1405
S e r i e S S P e c i F i c at i O N S
Adjustable versions and other sizes available; Consult Ohmite Also available
in low cost Centohm or Silicone coating; Consult Ohmite.
* Maximum Voltage is based on Ohm’s Law [V=√P*R] as limited by the resis-
tance value of specified product
characteriSticS
Coating
Lead free vitreous enamel
Core
Ceramic
Terminals
Tinned lug with hole. RoHS solder composition is 96% Sn, 3.5% Ag, 0.5% Cu
Derating
Linearly from 100% @ +25°C to 0% @ +350°C
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
Temperature
1 to 20Ω: ±400 ppm/°C
coefficient
Over 20Ω: ±260 ppm/°C
Dielectric with-
500 VAC: 10 and 20 watt rating. 1000 VAC: 30, 40 and 55 watt rating (mea-
standing voltage
sured from lug to mounting bracket)
Max. amps
To calculate, use the formula √P/R
Overload
10x rated wattage for 5 seconds if max. voltage is not exceeded
110
1-866-9-OHMITE • Int’l 1-847-258-0300 • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com
250 Series
‘Thin’ Stackohm®
Vitreous Enamel Power
(in. /
mm)
0.031"
0.794 mm
Diam.
0.125"
3.175 mm
0.110":
2.776 mm
0.250"
6.350 mm
0.125"
3.175 mm
Diam.
0.196"
4.979 mm
0.250"
6.350 mm
0.125"
3.175 mm
Diam.
0.109"
2.776 mm
0.188"
4.763 mm
Diam.
0.063"
1.588 mm
dimeNSiONS
0.125"
3.175 mm
0.375"
9.525 mm
0.625"
15.875 mm
0.375"
9.525 mm
Series Wattage
F10
F20
F30
F40
F55
10
20
30
40
55
Length L
0.750 / 19.050
2.000 / 50.800
1.250 / 31.750
2.000 / 50.800
3.500 / 88.900
Length A
1.000 / 25.400
2.313 / 58.750
2.000 / 50.800
2.750 / 69.850
4.250 / 107.950
10W & 20W
L
A
0.125" *
3.175 mm
0.375"
9.525 mm
*Reference dimension only; varies according to resistance
value.
Note:
When resistors are stacked, use washers or spacers
as required to insure clearance and improve power dissipa-
tion.
0.938"
23.813 mm
30W, 40W & 55W
L
A
0.250" *
6.350 mm
0.438"
11.113 mm
mOuNtiNg
In addition to the standard box bracket, stud type brackets
are available for stacking the standard size resistors. Stud
type brackets are available in two heights: standard (SS,
0.437”/11.113mm) and high (SSH, 0.531”/13.494mm). The
SSH stud is recommended when stacking the adjustable Type
260, as it assures clearance for the adjustable lugs to pass
eachother. Spacer washer No. 6027 (O.D. 0.219”/5.556mm,
I.D. 0.125”/3.175mm, thickness 0.094”/2.381mm) is recom-
mended for use with the miniature adjustable and fixed resis-
tors to provide clearance, as explained above, or increased
wattage. See chart.
0.031"
0.794 mm
Diam.
0.125"
3.175 mm
0.110":
2.776 mm
0.250"
6.350 mm
0.125"
3.175 mm
Diam.
0.063"
1.588 mm
0.625"
15.875 mm
B
W
L
A
T
0.375"
9.525 mm
0.094"
2.381 mm
Diam.
0.196"
4.979 mm
0.188"
4.763 mm
0.125"
3.175 mm
1.000"
25.400 mm
Derating for stacked mounting
Stacked resistors should be derated to prevent excessive tem-
peratures due to proximity. Approximate ratings are given in
the table.
Percent of Single Unit Rating
No. of
Resistors
Std. or Inter.
Miniature
Miniature with
0.094” (2.381 mm)
Spacer Washer
2
3
4
70
60
50
0.125"
3.175 mm
70
60
50
75
69
60
0.188"
Diam.
4.763 mm
0.109"
2.776 mm
0.125"
3.175 mm
Diam.
0.063"
1.588 mm
B
0.813"
20.638 mm
T
Core
size
L
A
Core
size
Diam.
0.196"
4.979 mm
0.250"
6.350 mm
0.125"
3.175 mm
B
W
L
A
T
Core
size
0.438"
11.113 mm
0.438"
11.113 mm
0.125"
3.175 mm
Diam.
0.196"
4.979 mm
0.250"
6.350 mm
0.125"
3.175 mm
0.188"
4.763 mm
Diam.
0.109"
2.776 mm
0.125"
3.175 mm
B
W
0.156" x0.313"
3.969 x 7.938 mm
Slot
0.188"
4.763 mm
0.188"
4.763 mm
Diam.
0.109"
2.776 mm
Brackets
cemented
in core
B
W
L
A
T
Core
size
L
A
T
0.5"
12.7 mm
Core
size
0.438"
0.531"
11.113 mm 13.494 mm
(SS)
(SSH)
(continued)
1-866-9-OHMITE • Int’l 1-847-258-0300 • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com
111
250 Series
‘Thin’ Stackohm®
Vitreous Enamel Power
cOre aNd termiNal SelectiON
For Made to Order Type 250 Stackohm Resistors
Free Air
Wattage
Rating*
Miniature
10
15
20
12
21
25
Standard
30
40
55
70
95
1.250” (31.750mm)
2.000” (50.800mm)
3.500” (88.900mm)
4.750” (120.650mm)
6.000” (152.400mm)
1.000” (25.400mm)
1.000” (25.400mm)
1.000” (25.400mm)
1.000” (25.400mm)
1.000” (25.400mm)
0.250” (6.350mm)
0.250” (6.350mm)
0.250” (6.350mm)
0.250” (6.350mm)
0.250” (6.350mm)
1
1
1
1
1
10,000
25,000
30,000
120,000
‡
150,000
‡
0.750” (19.050mm)
1.000” (25.400mm)
2.000” (50.800mm)
0.688” (17.463mm)
1.000” (25.400mm)
1.500” (38.100mm)
0.375” (9.525mm)
0.375” (9.525mm)
0.375” (9.525mm)
0.594” (15.081mm)
0.813” (20.638mm)
0.813” (20.638mm)
0.125” (3.175mm)
0.125” (3.175mm)
0.125” (3.175mm)
0.234” (5.953mm)
0.250” (6.350mm)
0.250” (6.350mm)
1
1
1
1
1
1
15,000
25,000
50,000
20,000
8,000
15,000
Core Dimensions
†
Length L
Width W
Thickness T
Max.
Min. Practical
Ohms Ohms
Code
for
Core
Dia.
TA
TA
TA
TB
TD
TD
TE
TE
TE
TE
TE
Fig.
No.
1
1
1
**
2
2
5
3, 4
5
3, 4
5
3, 4
5
3, 4
5
3, 4
Dimension A
1.000” (25.400mm)
1.250” (31.750mm)
2.313” (58.750mm)
1.313” (33.350mm)
1.813” (46.050mm)
1.750” (44.450mm)
2.000” (50.800mm)
2.500” (63.500mm)
2.750” (69.850mm)
4.000” (1.1.600mm)
4.250” (107.950mm)
5.250” (133.350mm)
5.500” (139.700mm)
6.500” (165.100mm)
6.750” (171,450mm)
Dimension B
0.375” (9.525mm)
0.375” (9.525mm)
0.375” (9.525mm)
0.594” (15.081mm)
0.594” (15.081mm)
0.938” (23.813mm)
0.938” (23.813mm)
0.938” (23.813mm)
0.938” (23.813mm)
0.938” (23.813mm)
Standard
Terminal
51
51
51
51
51
51
57
57
57
57
57
Intermediate
*Based on mounting on steeel panel 10” (254mm) x 10” x 0.040” (1.016mm).
†
Inside dimensions of core are: 0.250” (6.350mm) x 0.047” (1.191mm) for TA; 0.406”
‡
These sizes are Ohmicone (silicone-ceramic) coated–type 450-460.
**User supplies brackets.
(10.319mm) x 0.047” (1.191mm) for TB; 0.438” (11.113mm) x 0.063” (1.588mm) for TD;
0.672” (17.069mm) x 0.063” (1.588mm) for TE.
O r d e r i N g i N F O r m at i O N
Series
RoHS Compliant
Made-to-order Parts
Terminal Type
See web-
site for
See “Resistor Terminals for Tubular Cores”
custom
core info
Series
Vitreous enamel:
25 = 250 Fixed
26 = 260 Adjustable
Silicone ceramic:
45 = 450 Fixed
46 = 460 Adjustable
Wattage &
Core Code
See “Core and
Terminal Selection”
Tolerance RoHS
Compliant
J = 5%
½½½½½½½½
Coating
Wattage
Blank = Vitreous
C = Centohm
S = Silicone
Tolerance
F = 1%
H = 3%
J = 5%
K = 10%
Ohms
1R0 = 1
½
250 = 250
½
1K0 = 1,000
½
25K = 25,000
½
25K5 = 25,500
½
½½½½½½½½½½½½½½½
Mounting Brackets
(user supplies bracket for core TB)
B = Stacking box
S = Stacking stud, std. height
H = Stacking stud high
U = Unit type
Ohms
Example:
1R00 = 1
½
250R = 250
½
1K00 = 1,000
½
25K0 = 25,000
½
25K5 = 25,500
½
Standard Values
Wattage
Ohmic value
Ohmic value
F55J–––
55
F10J–––
10
F20J–––
20
F30J–––
30
F40J–––
40
F10J–––
10
Part No.
Prefix
Suffix
Part No.
Prefix
Suffix
Wattage
Ohmic value
F55J–––
55
F20J–––
20
F30J–––
30
F40J–––
40
F10J–––
10
Part No.
Prefix
Suffix
Wattage
F20J–––
20
F30J–––
30
F40J–––
40
F55J–––
55
1
–––1R0E
1.5
–––1R5E
2
–––2R0E
3
–––3R0E
4
–––4R0E
5
–––5R0E
7.5
–––7R5E
10
–––10RE
15
–––15RE
20
–––20RE
25
–––25RE
30
–––30RE
40
–––40RE
112
50
–––50RE
75
–––75RE
100
–––100E
150
–––150E
200
–––200E
250
–––250E
300
–––300E
400
–––400E
500
–––500E
750
–––750E
800
–––800E
1,000
–––1K0E
1,250
–––1K25E
1,500
2,000
2,500
3,000
4,000
5,000
6,000
7,500
10,000
15,000
20,000
25,000
40,000
–––1K5E
–––2K0E
–––2K5E
–––3K0E
–––4K0E
–––5K0E
–––6K0E
–––7K5E
–––10KE
–––15KE
–––20KE
–––25KE
–––40KE
=
tandard values;
S
check availability at
www.ohmite.com
1-866-9-OHMITE • Int’l 1-847-258-0300 • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com
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