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April 6, 2012 / Jane Awittor

What is a Pilot Duty Rating & How is it Obtained?

A relay can be assigned a pilot duty rating when it’s used for switching loads on another relay or solenoid valve coils. It can be a direct current (DC) rating or an alternating current (AC) rating as shown in the table at the bottom of this post.

The pilot duty ratings are obtained after performing product qualification tests.  These tests are performed at the voltage and current values provided using the information in table 1 below with a 0.35 power factor.

During product qualification test, the Make Current is applied for a very short period and it’s used to simulate inrush current of an inductive load.

When an application load voltage is less than 120 volts the following steps are followed to obtain the Make and Break Currents:

Step1: For voltages of 120V and below use the table below to determine the Make Current. For voltages above 120V, proceed to step 2 to determine the Make Current.

Step 2: Break Current is obtained by dividing the Break (Max Volt-amps) by the application load voltage but the current cannot exceed the Thermal Continuous Test Current Amps. 

The number following the letter helps to determine the maximum load voltage rating of 150, 300 or 600 volts while the letter indicates the maximum continuous current as shown in the table below: These ratings and current information are obtained from UL 508 standard. 

Example 1: B300 rating on a relay would represent a Make Current of 30A while the Break Current is 3A at 120VAC and Thermal Continuous Current is 5A, per Table 1 below. 

In order to apply for Pilot Duty Ratings two tests are performed: Overload and Endurance Testing:

  1. Overload Testing:

    The overload testing consists of 50 operations making and breaking a circuit of 110 percent of the maximum rated voltage.  The load is to consist of an electromagnet representative of the load that the device is intended to control AT pf = 0.35

  2. Endurance Testing:

    The endurance testing is conducted after the overload testing to ensure the contacts can perform acceptably when subjected to a 6,000 cycle endurance test at rated voltage at PF=0.35

Table 1: Rating Codes for AC Control-circuit Contacts at 50 and 60 Hz

Contact

Rating

Code

Dsga

Thermal

Continuous

Test

Current

Amps

Max

Current Ampsb

 

120 V

240 V

480 V

600 V

Max

Volt-amps

 

 

Make

Break

Make

Break

Make

Break

Make

Break

Make

Break

A150

10

60

6.00

7200

720

A300

10

60

6.00

30

3.00

7200

720

A600

10

60

6.00

30

3.00

15

1.50

12

1.20

7200

720

B150

5

30

3.00

3600

360

B300

5

30

3.00

15

1.50

3600

360

B600

5

30

3.00

15

1.50

7.5

0.75

6

0.60

3600

360

C150

2.5

15

1.5

1800

180

C300

2.5

15

1.5

7.5

0.75

1800

180

C600

2.5

15

1.5

7.5

0.75

3.75

0.375

3.00

0.30

1800

180

D150

1.0

3.60

0.60

432

72

D300

1.0

3.60

0.60

1.80

0.30

432

72

E150

0.5

1.80

0.30

216

36

Panasonic has a wide range relays that have pilot duty ratings, including: DK, DSP, LD, LZ, JQ, JS, JW, S, ST, PE, PA and JS relays.

More information can be obtained on our relay product pages.

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