I design a simple control system using MCU, ECU and a relay to control an 220vac inductive load of 20A max current So i decided to use a 30A relay

I found two relays JQX-16F(T91) - write on them the following

The first:

30A/20A 250vac

30A/20A 28vdc

The second :

H : 40A 250vac

Z : 30A 28vdv


For the first one i dont get why there are two ratings 30A and 20A , it should be 30A or 20A?!

For the second one i dont get the H and Z terms


If you have a 20 A inductive load, then a '30 A' relay may still be far too small.

Why 30/20A ratings? You'll need to look at the data sheet to see what they refer to. It may be that it's 10000/1000000 operations, or resistive/inductive load, where the inductance is specified somewhere in the data sheet. With no data sheet you're guessing.

When in doubt, assume the figures written on the relay are for the most benign (resistive) conditions.

  • \$\begingroup\$ Thanks @Neil_UK i really tried to find datasheet with no luck, for H and Z terms for the second relay, any guessing? \$\endgroup\$ Jul 16 '21 at 13:13
  • 1
    \$\begingroup\$ No guessing, but if at all possible you should choose a part that has an adequate datasheet. In many countries (US, Commonwealth, probably all of Western Europe), the manufacturer or seller is at least somewhat bound to provide what the datasheet says they're providing. So in such countries, if the datasheet says it, you can trust it. If there's not datasheet, then the best you can really trust that you're getting is a relay-shaped object that may or may not work at all, and if it works at all, may or may not work the way you think it will. \$\endgroup\$
    – TimWescott
    Jul 16 '21 at 14:16
  • \$\begingroup\$ Thanks. The chinese products only available in our market cnqianji.net/… \$\endgroup\$ Jul 16 '21 at 14:22
  • \$\begingroup\$ There's a lot of difference between 10k operations and 10 million, and some relays are 'rated' at the lower figure. It won't take long to get to 10k if you're switching at all frequently. \$\endgroup\$
    – Neil_UK
    Jul 16 '21 at 15:13

After contacting with the both relays suppliers I get the following information : 1- For first relay 30A/20A it refers to No/ Nc contacts ratings

2-for the second relay , H refers to NO and Z refers to NC contacts, so the NO Contact has 40A current capacity, and the Nc has 30A


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