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Old     (wakerider42)      Join Date: May 2002       02-24-2009, 7:50 PM Reply   
Hey guys,

My general understanding from some reading is that I should use a circuit breaker equal to a given amp's current (and add together for several amps together). So if I had 2 amps each pulling 80A max, I should use a circuit breaker 160A within 12" or so of the battery.

However, my MTX Thunder 81000D says to use a 150A fuse at the amp (as there are none built in) and also a fuse (or in my case a circuit breaker) at the battery. Similarly, my MTX Thunder 1004 says to use a 150A fuse at the amp and a fuse at the battery. The manual says that the 150A at each amp is for overdrive protection of the amp itself while the fuse (or breaker) at the battery is "to protect the electrical system".

So, do I need both?

Let's assume I need both. So, the total max current draw of these amps is 300A (150Ax2). I can't find any 300A circuit breakers. Seems that 200A is the limit.

What's strange to me is that my Arc 5150XXK doesn't have built in fuses, but its manual only tells me I need the one fuse within 18" of the battery.

Is this a case of just differing opinion? What do the pros think?

I'm trying to piece together an order for this system, and it's taking forever to figure out exactly what I need to buy up front. 1/0 is not friendly stuff, and none of the accessories that go with it are either!!

Old     (joe_crawley)      Join Date: Jan 2007       02-24-2009, 8:01 PM Reply   
1. you need both only if you are splitting your power out from a distribution block, which I'm quite sure you are if you are wiring with 1/0. So yes, you'll need a fuse inline at the amp and a breaker (or fuse, I always use fuses) at the battery.

2. the circuit breaker at the battery should be selected based on the less of A) the summed amplifier fusing or B) the current carrying capacity of the wire. If you have 3 150A fuses, you might put a 450A breaker at the battery. THIS IS A DISASTER WAITING TO HAPPEN. You will never trip a 450, there should probably be a 200 there. I would put a 200 at the battery even if I have two 150s and see if it becomes a problem. If it does and you get some spurious trips while listening, which it likely won't, you can change it to a 300.

When in doubt ALWAYS fuse low, not high.
Old     (loudsubz)      Join Date: Aug 2001       02-24-2009, 8:20 PM Reply   
this should sum it all up.

Like said, the fuse from the battery is to protect the wire, do not go larger than what the wire is rated for.

When you break the wire into smaller lengths you should fuse them as well as the current capacities of the smaller gauge wires is going to be less.
Old     (wakerider42)      Join Date: May 2002       02-24-2009, 8:43 PM Reply   
Thanks guys, this is ringing a bell now. Makes sense from a current carrying capacity of wire standpoint. That website is good. Makes sense that you should technically fuse anytime you go to smaller gauge.

I don't really want to try to model my situation and calculate it out, so I think I'm gonna go with what seems right.

I'll be running 2 Optima Blue Tops into a Perko. I will run a main 1/0 line from the common Perko through a 200A breaker, then to a distribution block. 2 1/0's out of the distribution block, 1 to MTX 81000D, 1 to MTX1004, each with inline 150A fuse as recommended by MTX. Probably overkill on separate 1/0 lines for each amp since I am limited by the upstream 1/0, but that is what fits nicely into the amp, and bigger won't make a difference.

I will also have a separate 4 ga line from common Perko to ARC with just an 80A breaker (or fuse, we'll see). No need for another fuse since not downsizing.

Old     (philwsailz)      Join Date: Feb 2009       02-25-2009, 7:21 AM Reply   
Good morning all!

I want to chime in here. As a member of the American Boat and Yacht Council, (ABYC) AND a member of the National Marine Manufacturers Association, (NMMA) I am intimately familiar with this topic. Safety is a priority of these organizations, and safety is important to me too.

The ABYC and the NMMA have a set of standards by which most new boats are manufactured. Lots of times these standards exceed what the U.S. Coast Guard sets forth as law regarding new boat production. In this instance, the ABYC standards found in the July 2008 revision of "E-11 AC and DC Electrical Systems on Boats" toes the line and agrees with the U.S. Coast Guard law. Specifically, U.S.C.G. CFR 33 183.425 table 5 speaks to maximum current capacity for electrical conductors. It is interesting to understand that the Coast Guard defines current capacity both by size AND by the temperature rating of the conductor's insulation. If you are using really crummy 1/0 wire with low-temp insulation, (60C /140* F) the max current allowed is 195 Amps. If you use1/0 wire with a very hi-temp insulation, (200C / 392* F) the max current is 325 Amps.

Again, be reminded this is the law for new boat production. You are not going to be arrested if you do not follow it.

Additionally, the law says that the over-current device, (fuse or circuit breaker) next to the battery can be sized up to 1.5 times the combined circuit load as long as it does not exceed the max current allowed based on the insulation temperature rating. Finally, the Coast Guard law says that the over-current device be located no more than SEVEN INCHES from the battery! That is tough to do, and again, you will not be arrested if you are further from the battery than this... Still, get it as close as you can. It is there to protect the wire, to prevent it from catching on fire, or catching something else on fire, or causing an explosion, harming you, your passengers or anyone else nearby. Oh it is there to protect the boat too....

Sorry for the long preface, but I want to make sure that we all understand that my recommendations are going to be based on what the law is for new boat production.


You are right on the breakers size being maxed out at 200A in my opinion. I have searched for larger ones too, and cannot find them. If you want to go with a breaker, you will be limited to 200A. BE SURE TO USE AN IGNITION - PROTECTED BREAKER!!! SAE J-1171 RATING IS WHAT YOU ARE LOOKING FOR. You do not want a device, (that is there to protect everything) starting a fire due to a spark it created while trying to do its job.

As Gangstar says, fusing to 450A in his scenario is not an option. In his scenario based on 3 amplifiers, one would be better served with two or three pulls of 1/0 to power the amps, with each run of 1/0 protected at the amp with its own fuse or breaker. I do however know that under-fusing can be problematic, and I like to have a battery fuse slightly higher than the combined current load on the wire, as long as the wire is rated for it and I do not exceed the 1.5x allowed by the law.

Your particular situation and installation are right on the gray edge. Your 200A breaker will adequately protect your wire, if even it has the lowest thermal rating. However, if you are really hammering on the stereo, there is a chance that you will pop the breaker. I think the chance is remote, as it is pretty common for the amp manufacturers to put in some extra fusing "just in case" it is needed. In normal operation even at max output, most amps operate at a level that is less than the total fuse rating; otherwise we all would be changing fuses a lot more than we do. If after you install the system you find that you are regularly popping your breaker in the system you are going to do, the safest recommendation I have will be to split the amps up and wire each one on their own pull of 1/0, with a 200A breaker on each wire right at the battery or Perko.

What you have set forth as a plan though is totally safe, and I recommend you go ahead with your plan and see if it runs without popping the breaker. It certainly is going to be a lot cheaper to try it first! Again, just as a reminder, make sure that breaker is ignition-protected and has the SAE J-1171 rating on it.

Good Luck and let us know!!!


(Message edited by philwsailz on February 25, 2009)
Old     (wakerider42)      Join Date: May 2002       02-25-2009, 7:55 AM Reply   
Thanks Phil. That makes sense. I do believe I will be okay as only 1 of the 2 1/0 powered amps is really going to be doing any driving. The MTX1004 is just driving 4 in-cabin "hi-end" Pioneeers, so it won't be working very hard. The MTX81000D, however, will be pounding 2 MTX9500 10" subs, so it could be working pretty hard. I think in total, the pair won't be drawing near the max, so I shouldn't have any problems with popping the breaker.

Thanks again guys. I'll be sure to post the final product, when I finally freakin' get around to finishing. Just can't find the time! Finally bought all my interconnects, distribution blocks, etc. MAN that stuff adds up really fast.



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