Under the 'contact ratings' of a relay datasheet, there is a row for rated load, which specifies a 10A 30VDC load on both NO and NC contacts. There is another row which is the max. switching voltage and this is specified as 250VDC (max. switching current is 10A). What is the meaning of these two specifications? Which voltage am I able to apply across the contacts for operation?

  • \$\begingroup\$ Can you provide the datasheet? I suspect that the maximum current might be 10 Amps @ 30 VDC but that if you lower the current you can switch up to 250VDC \$\endgroup\$ – Radiohead Apr 12 '18 at 14:40
  • \$\begingroup\$ Here is a link to the datasheet: www.ia.omron.com/data_pdf/cat/mk-s_ds_e_6_3_csm1382.pdf. And here is a link to the product webpage: ia.omron.com/products/family/1938. Thanks for your help! \$\endgroup\$ – Jordi Apr 12 '18 at 14:46

Rated load is essentially how much power can be carried through your relay (P = V*I = 300W). You can have a higher voltage if the current is lowered or higher current at lower voltage. This is the first limitation of your relay. If you don't respect it, your relay will simply burn out.

The second limitation is that voltage inside the relay could arc and provide a connexion even if the relay is not clamped. There is a limit point of voltage before an arc is created through thin air (air got decent insulating properties.) Therefore, voltage that pass through the relay should not exceed that limit. Otherwise, you risk damaging your relay.

The switching limit is not the max voltage required to toggle the relay! Do not confuse that data with the usually switching voltage at the control port (3,3v 5v 12v 24v typically).

  • \$\begingroup\$ Okay thank-you for the explanation. Based on this, I should apply the voltage based on the rated load spec i.e. Max 30VDC across the contacts if they are drawing 10A, or for example, I could apply 125VDC if the relay were drawing 2.4A? \$\endgroup\$ – Jordi Apr 12 '18 at 14:53
  • \$\begingroup\$ Yes, the limit would be in this case the power dissipation which is 300W \$\endgroup\$ – Radiohead Apr 12 '18 at 14:56

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