Prices as of April 27, 2016. Check Web site for most current prices.
Recommendations for Overcurrent Protection
UL and CSA (North American) Standards
UL and CSA (North American) Standards
North American standards, including UL 508, National Electric Code 450, and the Canadian Electrical Code, Part 1, require
overcurrent protection on all control circuit transformers. There are two options for overcurrent protection:
Option 1 (Primary only Protection)
Provide an overcurrent device in the primary circuit rated to the current of the transformer. The overcurrent limits are as follows:
• Primary 9 Amps or more: no more than 125% of rated current
• Primary 2 to 9 Amps:
no more than 167% of rated current
• Primary less than 2 Amps: no more than 300% of rated current for power circuits; no more than 500% of rated current for control circuits
Note: This method is considered less desirable, as start-up inrush to the transformer can frequently surpass the current rating of the device and result in
nuisance interruptions.
Option 2 (Primary and Secondary Protection)
The second option is to install overcurrent devices in both the primary and secondary circuits of the transformer. In this option,
the secondary device must be rated no more than 125% of rated current of the transformer and the primary no more than
250%. The Canadian Electrical Code permits 300% overcurrent on the primary for this option.
In both options listed, it is recommended that time delay fuses be considered to avoid unnecessary interruptions.
REFERENCES:
UL 508
UL 845
NEC 430-72
NEC 450-3
CEC Part 1, 26-256
Book 3 (14.3)
eTX-14
Transformers
1-800-633-0405
Prices as of April 27, 2016. Check Web site for most current prices.
Recommendations for Overcurrent
Protection UL and CSA (North American)
Standards, continued
HCTR Current Limiting Class CC Fuses
Part
Number
HCTR-25
HCTR-5
HCTR-75
HCTR1
HCTR1-25
HCTR1-5
HCTR2
HCTR2-5
HCTR3
HCTR3-5
HCTR4
HCTR5
HCTR6
HCTR7-5
HCTR8
HCTR10
HCTR15
HCTR20
HCTR25
HCTR30
PRIMARY (UL and CSA)
To assist in the selection of fuses, the following chart recommends the maximum primary fuse rating in amperes. The first
number shown is the maximum overcurrent protection when
the primary current is less than 2 amps and the overcurrent
protection device is rated for 300%. The second number
(shown in brackets) is recommended when the primary is
less than 2 amps and the overcurrent device is to be rated at
500% of rated current. Where only one number is indicated,
the primary is 2 amps or more and one rating of overcurrent
protection is shown as optimal. Choose the next higher fuse
rating if these numbers do not correspond with standard fuse
selections.
Recommended Maximum Primary Fuse Ratings in Amps Where
Primary Current is less than 2 Amps.
Primary Overload
Voltage Protection 50
115
120
220
208
230
240
277
380
440
460
480
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
300%
500%
1.25
(2.0)
1.25
(2.0)
0.6
(1.125)
0.6
(1.125)
0.6
(1.0)
0.6
(1.0)
0.5
(0.8)
0.3
(0.6)
0.3
(0.5)
0.3
(0.5)
0.3
(0.5)
AMP
Rating Pcs/Pkg Weight Price
0.25
0.5
0.75
1
1.25
1.5
2
2.5
3
3.5
4
5
6
7.5
8
10
15
20
25
30
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
$93.00
$82.00
$107.00
$84.00
$104.00
$83.00
$83.00
$93.00
$84.00
$102.00
$89.00
$87.00
$93.00
$102.00
$93.00
$90.00
$83.00
$90.00
$88.00
$91.00
Wiring
Accessories
Multi-wire
Connectors
Sensor Cables
and Connectors
M12 Junction
Blocks
Panel Interface
Connectors
Wiring Duct
Cable Ties
Wire
Bulk
Multi-conductor
Cables
Wire
Management
Products
Power Supplies
Hammond Transformers VA RATING
1.8
(3.2)
1.8
(3.2)
1 .0
(1.6)
1.0
(1.8)
0.8
(1.6)
0.8
(1.5)
0.8
(1.25)
0.5
(0.8)
0.5
(0.8)
0.4
(0.8)
0.4
(0.75)
2.5
(4.0)
2.25
(4.0)
1.25
(2.25)
1.4
(2.25)
1.25
(2.0)
1.25
(2.0)
1.0
(1.8)
0.75
(1.25)
0.6
(1.125)
0.6
(1.0)
0.6
(1.0)
8.0
–
8.0
–
4.0
–
4.0
–
4.0
–
3.5
–
5.0
–
3.5
(6.25)
3.2
(5.6)
3.2
(5.0)
3.0
(5.0)
Power
Distribution
Blocks
DC Converters
100 150 250 350 500 750 1000 1500 2000 3000 5000
5.0
–
5.0
–
4.5
(7.5)
5.0
(8.0)
4.5
(7.5)
4.0
(7.0)
3.5
(9.0)
2.5
(4.5)
2.25
(3.5)
2.25
(3.5)
2.0
(3.5)
Terminal Blocks
ZIPLink
Connection
System
Note: S
ee HCTR fuse catalog page for characteristic curves.
75
3.5
4.0
(6.5)
–
3.5
4.0
(6.5)
–
2 .0
3.2
(3.2) (5.6)
2.0
3.5
(3.5) (6.0)
1.8
3. 2
(3.2) (5.0)
1.8
3.0
(3.0) (5.0)
1.6
2.5
(4.5) (6.25)
1.125 1.8
(1.8) (3.2)
1 .0
1.6
(1.6) (2.8)
0.8
1.6
(1.6) (2.5)
0.8
1.5
(1.5) (2.5)
Company
Information
10.0
–
10.0
–
6.0
–
6.0
–
6.0
–
5.0
–
5.0
–
5.6
(9.0)
5.0
(8.0)
4.5
(8.0)
4.5
(7.5)
15.0
–
15.0
–
8.0
–
8.0
–
8.0
–
7.0
–
6.0
–
4.5
–
4.0
–
3.5
–
3.5
–
20.0
–
15.0
–
12.0
–
12.0
–
10.0
–
10.0
–
9.0
–
6.25
–
6.0
–
6.0
–
5.0
–
25.0
–
20.0
–
15.0
–
15.0
–
15.0
–
15.0
–
12.0
–
9.0
–
8.0
–
8.0
–
7.0
–
–
–
–
–
20.0
–
20.0
–
20.0
–
15.0
–
15.0
–
15.0
–
12.0
–
12.0
–
10.0
–
Transformers
and Filters
–
–
–
–
30.0
–
30.0
–
30.0
–
30.0
–
25.0
–
20.0
–
15.0
–
15.0
–
15.0
–
Circuit Protection
Tools
Test
Equipment
Enclosures
Enclosure
Climate Control
Safety: Electrical
Components
Safety: Protective
Wear
Terms and
Conditions
Book 3 (14.3)
www.automationdirect.com/power-transformers
Transformers
eTX-15
Prices as of April 27, 2016. Check Web site for most current prices.
Recommendations for Overcurrent
Protection UL and CSA (North American)
Standards, continued
MEN General Purpose Midget Class Fuses
SECONDARY
Part
Number
MEN-5
MEN-6
MEN1
MEN1-4
MEN1-5
MEN2
MEN2-5
MEN3
MEN3-5
MEN4
MEN5
MEN6
MEN7
MEN8
MEN10
MEN12
MEN15
MEN20
MEN25
MEN30
The overcurrent protection listed below, in
amperes, is 125% of the rated current of the
transformer. Choose the next higher fuse rating if
these numbers do not correspond with standard
fuse selections.
Recommended Maximum Secondary Fuse Ratings in Amps.
AMP
Rating Pcs/Pkg Weight Price
0.5
0.6
1
1.4
1.5
2
2.5
3
3.5
4
5
6
7
8
10
12
15
20
25
30
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
10/1
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
0.2 lb
$34.00
$33.50
$31.50
$40.00
$33.50
$29.00
$31.50
$29.50
$29.00
$29.50
$29.00
$31.50
$29.00
$29.50
$29.00
$34.00
$30.00
$32.00
$34.50
$32.00
Note: See MEN fuse catalog page for characteristic curves.
Hammond Transformers VA RATING
Secondary Overload
Voltage Protection 50 75 100 150 250 350 500 750 1000 1500 2000 3000 5000
12
24
110
115
120
220
230
125%
5.3
7.9
11.0
16.0
27.0
–
–
–
–
–
–
–
–
125%
2.7
4.0
5.3
7.9
14.0
19.0
27.0
–
–
–
–
–
–
125%
0.6
0.9
1.2
1.8
2.9
4.0
5.7
8.6
12.0
18.0
23.0
–
–
125%
0.6
0.9
1.1
1.7
2.8
3.9
5.5
8.2
11.0
17.0
22.0
–
–
125%
0.6
0.8
1.1
1.6
2.7
3.7
5.3
7.9
11.0
16.0
21.0
–
–
125%
0.3
0.5
0.6
0.9
1.5
2.0
2.9
4.3
5.7
8.6
12.0
18.0
29.0
125%
0.3
0.5
0.6
0.9
1.4
2.0
2.8
4.1
5.5
8.2
11.0
17.0
28.0
Book 3 (14.3)
eTX-16
Transformers
1-800-633-0405