distribution blocks or not

Hi please help. I've got 4 amplifiers to install in my car. do I need distribution blocks with fuses or not? Or just 1 in line fuse near the battery? Your help is very much appreciated. Thankse2cjeffoy

IMO you don't need them. But it may make it easier. You must have a fuse at the start of a power cable for the cable's protection. (And often the supply's - ie, battery protection.) Paraphrased, a cable must have a fuse whose rating does NOT exceed the cable rating (before that cable). So if splitting you main power cable into smaller cables to the amps, unless you main fuse is rated the same or lower than the smaller cable(s), each smaller cable needs to star with a suitable fuse. An exception to the above is if you rely on physical security for the small cables - ie, they cannot short to GND (cannot break or disconnect or wear thru their insulation to GND & chassis etc).

Thanks for the info. Really appreciated.e2cjeffoy

Thanks Jeff. In response to your PM(s) about installing for your 6 amplifiers and using a separate switch to power the system on/off my system (ie, bypassing the keyed ignition switch)... Firstly, apologies for posting publicly, but since this is a typical question and useful for others, and IMO it should be "public" based on the intent of this forum, and IMO there is nothing embarrassing nor personal nor private in your PM (noting the politeness of your request - with appreciation!). Secondly, I can't post diagrams unless they are copies or simple mods to existing pics. (My fault - I still haven't found an "up to speed" replacement for my old Windows2k MS Draw since I upgraded to this Win7 beast.)    However, there should be no need for diagrams. This should be quite simple - merely the use of "standard" fused switch and relay circuits which can be gleaned from other threads if not the Reference links at the top of the12volt pages (above). But anyhow, before that, some general blurb & issues... Now, I'll assume your amps (their power terminals) are all wired direct to the battery - thru fuses and cabling as per my previous reply (and a plethora of other the12volt threads) and noting that GND may be to solid chassis/body point(s) rather than - or in addition to - GND cable(s) to the battery or engine etc. [ Whether to ground "in theory" to the engine (ie, hence alternator) or battery depends what is more important from a maximum voltage POV. IE - if running with engine off, or if the alternator is incapable of supplying the load or peaks, then the battery supplies the power. In practice, the chassis/body is usually used as GND because (1) GND wiring from the engine/alternator and battery- should be appropriately sized for negligible voltage drop at the highest load; (2) the chassis is a good compromise for both battery- and alternator-supplied situations; (3) lots of or big GNDs to the battery- can be impractical and the same to the engine may have heat & vibration issues, and likewise to the alternator body plus its added cable-joining difficulty (and there should be negligible voltage drop between the metal-metal alternator body and engine - though my neighbor's Toyota 4WD with its angled Nippon Denso alternator and up to 1.5V between alternator body and engine block is testament to exceptions, but its solution lies in proper mounting of the alternator and maybe additional bonding - NOT routing all GNDs to the alternator body. ] BTW, though fuses etc and the +12V supply can be lost, losing GND can be VERY destructive. (Alternate GND paths will carry the load current and associated wiring and circuitry burns out - eg, RCA connections and internal "signal" GNDs in audio systems; alternator to external body-mounted voltage regulators (in old vehicles), throttle cables, sensor shields etc for engine GND to battery- losses.)    Hence the attraction of chassis/body grounding points, else distribution blocks from the battery-/GND. And except for exceptionally high currents (and allegedly some vehicles with poor inter-panel weld bonding), the chassis/body should be a good low resistance "equally grounded" circuit. (Being aware of loosely bonded and bolted panel and thin panel limitations.) Back to your circuit details... Hence presumably all your amps are turned on thru their remotes. And if all the remotes are +12V to turn on (as I expect they all are), then you merely need a switch and relay to turn the on. That could be a battery +12V fused switch to a relay's #86 (with #85 to GND) and fused battery +12V to #30 and out from #87 to the remotes. If the remotes are low current, the relay may not be required if the switch can handle the total current. (I know of some remotes that apparently take 2A (in normal circumstances!). IMO that is ridiculous! At most it should be a relay coil (up to 250mA, ie 1.5A for 6 remotes) but IMO it should be of the order of mA to maybe 10mA, maybe ~50mA.) Isolation diodes from #87 to each remote may be required depending on the remote circuit. EG - if the remotes are relays (coils) and one or more amps is unpowered, then the resulting +12V connection of series relay coils (with the remote-ON switch OFF) could cause some amps to turn on. The same could occur for other (IMO) badly designed remote circuits. (There is a workaround by using an SPDT aka changeover or "5 pin" relay and connecting #30 to the remotes with 87 from +12V and #87a to GND, but that could mean +12V leakage thru the remote circuit and hence battery flattening...) (BTW - most of us by SPDT relays even if using as an SPST (on-off). That's because they are usually the same price, and the one relay suits all SPST & SPDT applications.)      But the audio & amp aficionados hereon should be able to advise on the above given the amp model number(s). I am merely into electrics. That's it - in principle a +12V switch and maybe a relay that connects to the amp remotes. (A relay may be good since it could be mounted with or near the amps and manually bypassed for testing or if the switch circuit fails.) Whether you use secondary batteries for the above (as I expect you would be!) and their isolation when not in use is a different issue and topic. I hope that hasn't confustigated you, but in the interests of related background and issues... If unclear or extra info is required, just ask. And others may contribute their ideas. As to relay terminal numbering etc, refer to the Relay link above or search other threads. (Remember that a relay is just an "amplifier" for a switch - ie, it allows a 1A switch to control a 30A or 300A load etc - though they can do much more, ie voltage or circuit isolation, signal inversion, etc.)    BTW - a common 30A relay should be more than adequate. The switch or relay must be rated to carry the total remote-circuit load. Of course, you might want to use multiple switches etc if not selecting all the amps...

Thanks mate for all the info. Really appreciated. If you get some spare time. Even hand draw please send me on my email at e2cjeffoy@gmail.com. Kind regards Jeffe2cjeffoy

It depends on your configuration, really. If you run a 0 gauge wire from the battery (with a fuse within 12" of the battery of course) and split that in to smaller gauge wires to feed each amp you really should fuse the smaller wires at their proper size. The problem with wiring is if you pull too much current through a wire it will cause the wire to heat up which could lead to a fire. So, if you have a 200A fuse in your 0awg wire (just throwing out numbers here) and you split that to two 4awg wires and two 8awg wires to feed your amps you would theoretically allow your 8awg wire to pull 200A before a fuse blew - the 8awg wire can't physically do this and will heat up quickly and start melting the insulation. Now, one could argue that if keep the branch circuits short the chance of this happening is slim, but it's also beneficial to have the lowest possible fuse protecting each individual amp, that way if there is a problem instead of waiting for a large 200A fuse to blow you can have a 25A fuse blow. This may lead to other unplanned conveniences such as being able to play 3 amps when one amp is bad (as to the alternative of not being able to play any of the amps if the main fuse blows). Kevin Pierson

Thanks Kevin for the info. So if the 0awg split to 4awg what fuse rated to be used? Thankse2cjeffoy

Assuming the wire is actually the size you listed (and not undersized like is becoming more common) according to this page: https://www.the12volt.com/wiring/recwirsz.asp you 0awg max fuse size is 350A and your 4awg max fuse size is 150A. However, please note that these are MAX values and under no circumstance should you ever use a bigger fuse. Your actual fuse value should be calculated based on expected load. Your load should draw roughly 75% of your fuse rating. IE, if you have a 75A load you should use a 100A fuse (as 75A is 75% of 100A).Kevin Pierson

I've got it Kevin. Thanks a lot.e2cjeffoy