Is this safe?

I am going to be running 3 amps off a remote wire. I bought a 30 amp automotive relay today from radio shack. I am going to use the remote wire off the back of the radio for the trigger point on the relay, and then run the power from a distro block already in the back. Do I need to put a fuse between teh relay and the distro block or will the fuse under the hood for the main power lead be sufficient? (I am just unsure of the safey of the relay with it having the potential to pull 30 amps of current through such a small remote wire) If a fuse is necessary, what size fuse should I put on it?

Wait, are you saying that you're going to run the remote turn on lead to the power distribution block? If so, then you're going to fry your HU. Most "new" amps have a remote turn on "pass through" that allows you to "daisy chain" amps on a single lead.

why would you relay a remote?

From what I gather, evanc is going to use the remote turn on lead to close the coil on the relay. One side of the coil would be grounded, the other from the HU. He would then run +12 to the common pin (terminal 30) and then another wire to the remote in on the amps from terminal 87. This will not fry the HU. If you are going to do this, I would fuse the wire coming from the distribution block. Reason being, the wire could fry if it shorted. So pick a fuse that allows the maximum amount of current through the wire. For example, if you choose to use a 16 cauge wire from the block, use a 15 amp fuse. However, the remote turn on into the amp requires very low current(not sure how low), you would still be safe using a fuse smaller than the allowable current through the wire. WTB: Black Leather Acura GSR seats

what is ultimately trying to be accomplished?

I'm using a 1/2 amp fuse on a 20 ga. wire that splits to remote turn on two amps.  It has never blown.  The current is tiny, and all it needs is a 12 volt signal.  There is too much amperage at the distro block for the purpose of supplying this 12 volt supply.  Find a constant 12 v in a nearby wire in the car's wiring to supply it.  Then you'll need a total of 4 small fuses:  all three wires out of the relay should be fused separately, and the main remote wire. You can use 49 cent fuse holders and a pack of fuses for a couple of bucks, 500 milliamps up to 2 amps each...very small.

ss-installer, A relay is used with the remote turn on lead when there are numerous accessories that require its signal. Since the remote turn on current is so low from the head unit, the added draw from each accessory can damage it. So to be safe, the relay is used since it allows for more current draw. It seems that when there are 3 or more accessories (amps, signal processors, fans, etc.) people use relays.    WTB: Black Leather Acura GSR seats

makes sense.

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Most remote leads off of head units supply 300mA of current. A relay generally requires about 100 mA to trip the coil.  Each amp has an internal relay attached to that remote wire that allows power to flow from the larger power cable to power the amp.  So using a separate relay, you only have 100mA of current draw on that remote lead, and you can run up to 30 amperes of current through the relay.  With this you can turn on multiple amps, fans, neon, any number of 12V accessories, provided the total current draw does not exceed 30 amperes.  With small electrics, like fans and small neon tubes it would be hard hard to exceed 30 amps, as most dont draw more than 1 or 2 amps.Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.