What amp relay do i use???

[19266022]

Hi guys
I already have installed a 25amp cable from my crank battery into the cab I intend on hooking it up to a fuse block for multiple accessories.
I only want the power available when the ignition is on, so I guess I need a relay to power up the fuse block once the key is turned. I'm guessing just a 25amp standard relay but i'm not sure. I have a 40 amp relay in the shed but I don't want to just hook it up and hope for the best. Also is 15amp cable ok to use to my uhf, led work lights and tv tuner from the fuse block??
can someone help me please

[Steveyb]

15 amp is more than enough for your accessories mate.

Use the 40A relay, that will be fine as the relay isn't a safety device. Just have a fuse that will blow before your 25a cable will melt.

[john253a]

the fuse is there to protect the cable and not the item being wired,
the max amp ratting on the fuse is the max amp ratting of cable minus efficiency lose and length

ie a 4g cable is rated at 200amp @ 6" but only 10 amps @ 50"

[VMN]

Might be overkill but when I have used a relay like this, I have put a fuse on both the battery and the low current side. I'd aim for say a 30 amp fuse before the 40 amp relay so the relay itself is protected and say 3 amps on the low current side (smaller would be fine but hard to find). If you only need three protected circuits, you could use the spare fuses on your fuse block and you will still have one spare circuit. In theory, the 30 amp fuse should never ever blow but it is defensive design.

[wyworrie]

You say you have 25A cable, then a 20 -25 A fuse MUST be fitted as close as possible to the battery. The relay (40A is quite ok) can be mounted and connected anywhere to supply fuse block. Fuses in the block MUST be lower than the wire they supply and NOT exceed the size recommended for the equipment supplied.

Good luck mate

[19266022]

Thanks everyone for your reply's. Got the info I needed