Relay Ratings and Current Changes

It's not clear to me, is 30V a supply voltage?

I think these parametres are related to relay contacts. So it can be applied for 24V/5A contacts' load.

As caramba said - is this the rating of the relay contacts or the rating of the relay coil?

If contacts - no issue. You can operate at 24V, the max current is still 5A.

If coil - yes the current will increase if you drive a 30V coil with 24V. Be sure that the minimum closing and holding voltage for the coil is less than 24V, or it won't work reliably.

Do you have a part number for that relay, and have been to the manufacturers web site to look up the tech specs for that relay?

For contact currents, there shouldn't be a probem with the current flow (voltage will not matter as long as you don't get "flash-over")

If the current is too much, you will burn out your contacts (inductive loads can do this)

If the current is under the recommended minimum for those contacts, you could get the contacts "gumming" up, where the current is used to keep the contacts clean from muck.

Relays usually have two ratings printed on them.

One for the coil voltage , in which case you may not see a current rating.

The rating with two or three voltages and currents ( some may even specify resistive loads as distinct from inductive loads) are for the contatcs.

Your 5A 30V is most certainly for the contacts.

Typical coil voltage in this range is 24 or 28V.

I=E/R current has nothing to do with your relay rating. Very elementary stuff.

If this is the coil rating then if you drop the voltage to 24 V the Resistance will stay the same and the watts will go down and the relay may not be able to operate.

If it is the contacts that is rated at 30 V and you are lowering the voltage across the points to 24-volts and the load is the same then the amps will go down as per ohms law.

If 5 amps is the contact rating, the voltage is irrelevent, up to the maximum voltage rating of the relay contacts .It does make a difference whether the rating is for A/C or D/C current.Most relays give a dual rating.The coil can be either dc rated or ac rated.If not indicated on the coil, look for a single heavy copper turn,called a shading coil, on the core(the stationary part) of the coil.The presence of a shading coil indicates it is designed for AC. It's purpose is to prevent buzzing of the contacts due to zero-crossing of the AC voltage.The AC voltage induces an equal and opposite magnetic field in the shading coil when it crosses zero voltage, and the collapsing magnetic field holds the armature of the coil in position for the short interval when no voltage is present. The shading coil is not required for a DC relay coil.

D/C usually is rated at lower amps for the same contact construction, because the current never crosses zero, and consequently is harder to break the circuit. Anyway, 5 amps at 1 volt,2,volts,10 volts,20 volts,up to 30 volts does not matter to the relay contacts.The load, however will respond differently to the applied voltage,depending on type of load,whether it is purely resistive,inductive,capacitive, or a combination.

Hope this helps.

HTRN