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what is the long wire can i use with arduino uno and Relay Answered

hii every body

i will use arduino uno as Microcontroller and i will use this controller to control my devices like (lights,tv,redio) etc

i will put my arduino uno on my living room and will put many relays on other rooms of my house 

my relay is 5 v DC input and control (250V/10A) 

and i will make arduino put (HIGH) as 5 volt to make relay work  and (LOW) to stop relay from working

as i described before i will put arduino on my living room and put relays on others rooms so i have 2 questions

first :
- what is the high power that relay can Load it (How Much Watt)  ?

 - what is the long wire and how much its width can i use to connect arduino uno to relay on others rooms , 
that wire i will send 5 vol from arduino to relay to work

- some one tell me that i can use the network cable that have (8 wires inside it) to send 5 volt from arduino to relays is that right ?
and if its right how much long can i use 

Thanks to every body


Power = current x voltage, you can work it out from that.

Cable length ? Very hard to say. Its not a good idea to have digital outputs being fed long distances without some kind of buffer. "Try it" is probably simplest, it depends on the sensitiivity of the relay - is that relay opto-isolated ?

Hi! Can you give an example of "some kind of buffer" that you refer to? Thanks.


1 year ago

A RJ485 cable Cat5 has four pairs of wires easily a total of 8 wires..

BTW a relay is a great isolated mechanical amplifier.. A small DC 5volt and low current can control 2500 Watt AC or 300 Watt DC...

You need to tell us the what the relay current is ? Then we can specify the wire size you might need...

And be cautious about relay kickback damage to your uP without an inverse parallel diode across the relay coil..

thank you

arduino output 5 v and 20 MA current , and i need to send this signal to relay to work

but i dont know what is the size of wire can i use and how long the wire that will be the maximize long to not reach it to not loss the power of 5 v with 20 MA

can you tell me ?

and if i will use the cat 5 to transfer 5 volt with 20 MA from arduino to relay is is good idea or use classic wire

about the relay i use the relay like that on the picture that come with board on it , so is i need diode with that board or that will enough

thanks again ......

Here are two relay versions the optically isolated input one is what you have posted. That style of relay coil will draw about 15ma to 25ma.

You will need three wires. A +5v Red about a #16 gauge =.051" diameter this size wire adds an ohm every 250' of length you run it. A Ground Black wire is also a #16 gauge wire.. The third wire that goes to a uP output port pin can be a smaller #20 gauge = .032" diameter..

Be sure to click the second pic to see the whole image


BTW because each relay needs two power wires +5 and ground. That means you will be adding 2 ohms every 250' of wire distance..

Use WiFi and modules for everything.
No use trying to have an arduino and then using wires and relays to to the work.
Or simply get a home automation kit....

Also there is one more thing to consider with long wires: Interference!
Two old analog phones connected with a long wire and a battery can even get your local radio station ;)