Square D Thermal Unit Selection

 

General

All tables are based on the operation of the motor and controller in the same ambient temperature, 40° C (104° F) or less. Always be certain the correct thermal units are installed in the starter before operating the motor. Each thermal unit shall be installed such that its catalog number is visible.  Figure 1 for complete thermal unit installation instructions. On melting alloy thermal units the ratchet wheel must engage the pawl assembly.


 
Selection Procedure

1.

Determine motor data:

a.

Full load current rating

b.

Service factor

Note: If motor full load current (FLC) is not known, a tentative thermal unit selection could be made, based on horsepower and voltage. 

2.

Motor and controller in same ambient temperature:

a.

All starter classes, except Class 8198:

1.

For 1.15 to 1.25 service factor motors use 100% of motor FLC for thermal unit selection.

2.

For 1.0 service factor motors use 90% of motor FLC for thermal unit selection.

b.

Class 8198 only:

1.

For 1.0 service factor motors use 100% of motor FLC for thermal unit selection.

2.

For 1.15 to 1.25 service factor motors use 110% of motor FLC for thermal unit selection.

3.

Motor and controller in different ambient temperatures:

a.

Multiply motor FLC by the multiplier in Table A. Use the resultant full load current for thermal unit selection.

4.

Locate proper selection table from index

a.

The proper thermal unit number will be found adjacent, to the right of the range of full load currents in which the motor FLC or resultant full load current falls.

Slow Trip Thermal Unit Selection

To select Type SB slow trip thermal units, the selection table for a standard Type B thermal unit may be used with the following modifications: For continuous rated motors having service factors of 1.15 to 1.25, select thermal units from the standard Type B table using 93% (102% for Class 8198) of the full load current shown on the motor nameplate and then substitute an SB for the B in the thermal unit type number.

Example: A motor with a full load current of 12 amps controlled by an 8536SCG3 would require B22 thermal units for standard trip applications and SB19.5 thermal units for slow trip applications. The SB is selected by multiplying 12 amps times 93% for 11.16 amps and using this value to select B19.5. Then add the S prefix to arrive at SB19.5.

For continuous rated motors having a service factor of 1.0, select thermal units in the same manner using 84% (93% for Class 8198) of full load current shown on the motor nameplate.

Note: SB thermal units are used on Size 0, 1, 2 and only some Size 3 applications. Check thermal unit tables for current ranges.

Table A: Selection of Thermal Units for Special Applications

Class
of
Controller
Continuous
Duty
Motor
Service
Factor
Melting Alloy and
Non-Compensated
Bimetallic Relays
Ambient
Temp.-
Comp.
Relays
Ambient Temperature of Motor
Same as
Controller
Ambient
Constant
10° C
(18° F)
Higher
Than
Controller
Ambient
Constant
10° C
(18° F)
Lower
Than
Controller
Ambient
Constant
40° C
(104° F)
or less,
for Any
Controller
Ambient
Full Load Current Multiplier
All
Classes,
Except
8198  
1.15 to
1.25  
1.0  
0.9  
1.05  
1.0  
1.0  
0.9  
0.8  
 .95  
0.9  
Class
8198  
1.15 to
1.25  
1.1  
1.0  
1.15  
1.1  
1.0  
1.0  
0.9  
1.05  
1.0  


Controller
Thermal Unit Selection Table Number
Hand Reset Melting Alloy
Bimetallic
Starter Type
Class
Type
Seriesa
Size
Standard
Trip (20)
Quick Trip
(10)
Slow Trip
(30)
Non-
Compensated
Compen-
sated
Manual
Starters
FHP
2510
2512
8908
F
A  
FHP
43h  
...  
...  
...  
...  
Manual Starters
(Small
Enclosure)
2510
M, T
A  
M–0
M–1
M–1P
  1 
  1 
  1   
72
72
72  
j
j
j  
...
...
...  
...
...
...  
Manual
Starters
(Large
Enclosure)
2510
2511
2512
8925
M, T
A  
M–0
M–1
M–1P
  2 
  2 
  2   
73
73
73  
j
j
j  
...
...
...  
...
...
...  
Manual
Loom Sw.
2510
MBL, TBL
A  
M–0
  7   
...  
j  
...  
...  
DC
Magnetic
Starters
7135
7136
7735
7736
C, D
...  
1,2
 65   
...  
j  
...  
...  
E
...  
3
  9   
...  
...  
...  
...  
F
...  
4
 10   
...  
...  
...  
...  
G
...  
5
 12   
...  
...  
...  
...  
AC
Magnetic
Starters
(Small
Enclosure)
 
8536
8904b
(Starter
In Own
Enclosure)
8933
8998
8999
(Model 3
Control Center)
I-LINE®
and QMB
Motor
Starter
Centers
A
(8536
only)
B, C  
00
 17h  
...  
...  
...  
...  
SA
A, B  
00
 13   
...  
j  
...  
...  
SB
A  
0
 13   
74  
j  
 8  
 33   
SC
A  
1
 13   
74  
j  
 8  
 33   
A  
1P
 41   
...  
j  
...  
...  
SD
A  
2
 56   
75  
j  
62  
 70   
SE
A  
3
 18   
76i  
134ij  
63  
 37g  
B  
3
...  
...  
...  
142  
...  
SF
A  
4
 54   
77i  
...  
11  
 29g  
B  
4
...  
...  
...  
144  
...  
SG
A  
5
 49   
...  
...  
38  
 46   
Bl  
5
 59   
83  
...  
23  
42  
SH
A, B  
6
 21   
...  
...  
39  
 47   
8998
8999
(Model 4
Control Center)
SC
A  
1 Fusible
 66   
74  
...  
64  
 33   
1 Circuit Breaker
 15   
74  
...  
SD
A  
2 Fusible
 67   
75  
...  
57  
 70   
2 Circuit Breaker
 58f  
75  
...  
SE
A  
3 Small Enclosure
 16   
76i  
134ij  
51  
 37g  
3 Large Enclosure
 68f  
76i  
133ij  
 
 
B  
3
...  
...  
...  
141  
...  
SF
A  
4
 61   
77i  
...  
35  
 29f  
B  
4
...  
...  
...  
143  
...  
SG
A  
5
 24   
...  
...  
52  
 46   
SH
A  
6
 20   
...  
...  
48  
 47   
8998
(Model 5 and
Model 6 MCCs)
SCk
A  
1
109   
...  
...  
...  
 97   
1 COMPAC 6
104   
...  
...  
...  
...  
SDk
A  
2
110   
...  
...  
...  
 98   
SEk
A  
3
111   
...  
...  
...  
 99   
SFk
A  
4
112   
...  
...  
...  
100   
SGk
A  
5
113   
...  
...  
...  
101   
Bl  
5 CT
103   
...  
...  
...  
...  
SHk
A  
6
114  
...  
...  
...  
102  
8911
DPSG
A  
20–30 A
135   
...  
...  
...  
...  
40 A
145  
...  
...  
...  
...  
50 A
146   
...  
...  
...  
...  
60–90 A
149  
...  
...  
...  
...  


Continue

Controller
Thermal Unit Selection Table Number
Hand Reset Melting Alloy
Bimetallic
Starter Type
Class
Type
Seriesa
Size
Standard
Trip
Quick Trip
(10)
Slow Trip
(30)
Non-
Compensated
 Compensated
AC
Magnetic
Starters
(Large
Enclosure)  
8198
G, S
...  
...
  5  
...  
j  
...  
  6  
8536
(Starter Used in
Multi-Motor Panel)
8538   8904e
8539   8906
8606   8907
8630c  8920
8640d  8922
9089   8924
8647   8925
8650   8930
8736   8941
8738   
8739   
A
(8536 only)
B, C  
00
 14h  
...  
...  
...  
...  
SA
A, B  
00
 53  
...  
j  
55  
25  
SB, NB
A  
0
 15  
78  
j  
64  
33  
SC, NC
A  
1
 15  
78  
j  
64  
33  
SD, ND
A  
2
 58  
79  
j  
57  
70  
SE, NE
A  
3
 16  
80i  
133ij  
51  
37g  
B  
3
...  
...  
...  
141  
...  
SF, NF
A  
4
 61  
81i  
...  
35  
29g  
B  
4
...  
...  
...  
143  
...  
SG
A  
5
 24  
...  
...  
52  
46  
Bl  
5
 59  
83  
...  
23  
42  
SH
A, B  
6
 20  
...  
j  
48  
47  
8810
8811
8812
CB, DB, SB, UB
A  
0
 15  
78  
j  
64  
33  
CC, DC, SC, UC
A  
1
15  
78  
j  
64  
33  
CD, DD, SD, UD
A  
2
58  
79  
j  
57  
70  
CE, DE, SE, UE
A  
3
16  
80i  
133ij  
51  
37g  
CF, DF, SF, UF
A  
4
61  
81i  
...  
35  
29g  
SE
B  
3
...  
...  
...  
141  
...  
SF
B  
4
...  
...  
...  
143  
...  
CG, DG, SG, UG
A  
5
24  
...  
...  
52  
46  
Bl  
5
59  
83  
...  
23  
42  
CH, DH, SH, UH
A  
6
20  
...  
j  
48  
47  
8940
WELL-GUARD®
Control
WC, XC
A  
1
13  
78  
...  
...  
33  
WD, XD, MD, RD, VD
A  
2
56  
79  
...  
...  
70  
WE, XE, ME, RE, VE
A  
3
18  
80i  
...  
...  
37  
PF, WF, XF, MF, RF, VF, PE
A  
4
54  
81i  
...  
...  
29  
XSG, NSG, MG,RG, VGh
A  
5
...  
...  
...  
...  
 46  
Bl  
5
...  
...  
...  
...  
42  
XSH, VH
A  
6
...  
...  
...  
...  
 47  
8911
DPSO
A  
20–30 A
136  
...  
...  
...  
...  
40 A
147  
...  
...  
...  
...  
50 A
148  
...  
...  
...  
...  
60–90 A
150  
...  
...  
...  
...  
AC
Magnetic
Part-
Winding  
8998
(Model 5 and
Model 6 MCCs)
SCk
A  
1
127  
...  
...  
...  
121  
SDk
A  
2
128  
...  
...  
...  
122  
SEk
A  
3
129  
...  
...  
...  
123  
SF
A  
4
105  
...  
...  
...  
117  
SG
A  
5
115  
...  
...  
...  
118  
Bl  
5 CT
116  
...  
...  
...  
...  
Separately
Mounted
Overload
Relays  
9065
AF
B  
4(133 A)
...  
...  
...  
30  
...  
AG
A  
5(266 A)
...  
...  
...  
36  
...  
AR
A  
1(25 A)
...  
...  
...  
32  
...  
AT
A  
2(45 A)
...  
...  
...  
60  
...  
AU
...  
3(86 A)
...  
...  
...  
50  
...  
DA
A  
1(25 A)
...  
...  
...  
140g  
...  
GA
A  
2(60 A)
...  
...  
...  
139g  
...  
HA
A  
3(100 A)
...  
...  
...  
138g  
...  
JA
A  
4(180 A)
...  
...  
...  
137g  
...  
C
A  
1(25 A)
44  
82  
j  
...  
...  
F
B  
4(133 A)
19  
85i  
...  
...  
...  
G
A  
5(266 A)
22  
...  
...  
...  
...  
MEO
A  
(32 A)
86  
...  
...  
...  
...  
S
A  
1(26 A)
59  
83  
j  
23  
42  
2(45 A)
69  
84  
j  
27  
71  
3(86 A)
34  
...  
...  
...  
...  
4(133 A)
28  
...  
...  
...  
...  
T
A  
2(45 A)
31  
...  
j  
...  
...  
U
...  
3(86 A)
40  
...  
...  
...  
...  

a Series letters listed refer to the marking on the nameplate of the basic open type starter. When the starter is supplied in a controller containing other devices, the controller may have a different series letter marked on the enclosure nameplate.
b Small enclosure tables apply for Class 8904 non-combination and non-reversing starters. For combination and reversing Class 8904 starters refer to the large enclosure selections, index above.
c For Class 8630 starters divide the delta connected motor full load current by 1.73, and use this quotient to select thermal units.
d For Class 8640 and Class 8940 (MD, PD, ME, PE, MF, PF, MG and PG) starters use the full load current of each motor winding as a basis for thermal unit selection—normally one-half total motor current.
e Large enclosure tables apply for Class 8904 combination and reversing starters. For non-combination and non-reversing Class 8904 starters refer to small enclosure selections,
f Use for Autotransformer Starters (Fusible and Circuit Breaker).
g Order Type E thermal units by number from Square D/Schneider Electric, Furnas Electric Company, Batavia, Illinois or a Furnas distributor at $9.00 each, subject to motor control discounts.
h Type A thermal units for full load currents lower than those listed in this table are available. For complete information, consult your nearest Square D/Schneider Electric sales office.
i Form Y81 must be specified to use quick trip (Class 10) or slow trip (Class 30) thermal units on Size 3 starters and quick trip (Class 10) thermal units on Size 4 starters.
j This device will accept Type SB slow trip (Class 30) thermal units.
k Refers to type number of starter in MCC, not actual type number of MCC.
l Divide the motor FLC by 60 and use this quotient to select the appropriate thermal units.
4/1/04