How Much Current Can 30/40 Amp Relay Hold?

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=2215
Printed Date: July 27, 2025 at 7:01 AM

Topic: How Much Current Can 30/40 Amp Relay Hold?

Posted By: 2000vsm
Subject: How Much Current Can 30/40 Amp Relay Hold?
Date Posted: July 25, 2002 at 12:04 PM

I'm planning on using a relay to power about 5 sirens.. is it ok to just use one relay? cuz like the headlights and foglights use only one relay and the lights are like 55 watt each, so 110 watt.. and each of my sirens are only 15watt and only 3 of them are in use most of the time so that's 45watt and total is 75 watt

Replies:

Posted By: mobiletoys2002
Date Posted: July 25, 2002 at 6:24 PM

well your post tells how much current 30/40 amp yes 30 amps of curent a relay can handle .thats more than enough for sirens make sure your wire is big enough to supply all the current required. use a 14 guage or so as the wire to the relay this wire will be used to supply the relay with enough curent for the sirens.

Posted By: topinstaller
Date Posted: July 31, 2002 at 4:09 AM

This is where Ohm's Law comes in handy. I = P/V or Current(Amps) = Power(Watts)/Volts . Well we know that you have approximately 75 Watts of power. We know that your battery Volts is about 12V. So therefore your maximum current draw will be approximately 6.25Amps. 75 / 12 = 6.25. Your typical relay is rated at 30Amps continuous and 40Amps peak or max. Go ahead and add about 10 more sirens you have plenty more in that relay. LOL.

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