Amperage Interrupting Capacity (AIC) for fuses

[jcb1977]

I'm going to be adding a chartplotter/fishfinder to my sx210. I was planning on installing a new circuit back to the battery for the fishfinder and was going to copy the materials/routing for the stock radio which I believe is 16 gauge wire with a 15-amp blade style ATC fuse (see photo).

When I put this information into the blue sea circuit wizard - Circuit Wizard - Blue Sea Systems using 1 amps for load current, ~30' conductor length, with 800CCA battery, it says the blade style ATC fuses should not be used because they do not meet the AIC given the battery size. my battery is stock and came with my 2019 boat.

Does this mean the fuses that came with the boat are insufficient? I'm not an electrician but I believe the AIC is in the event of a short circuit, a heavy spike from the battery could melt a fuse with insufficient AIC and not allow it to trip, potentially starting a fire. It seems like the ATC fuses in the boat offer 1,000A AIC but the circuit wizard indicates the minimum should be 1,500AIC given the 800CCA from the stock battery.

Anyone have any insight on this? I feel like I'm missing something, like maybe there is another breaker/fuse somewhere to handle this?

 

[Beachbummer]

The only way I have ever burnt a fuse has been by shorting the battery on installation/wiring. I have yet to have one protect me on its intended use. So far the fuse has always tripped, so at least that's good.

Without removing merit behind the theoretical discussion... have you considered trying it on your boat? sacrificing one or 2 fuses may be interesting to find out for certain how a short behaves in your situation.

You may hear back differing opinions, but seeing it work, trip and burn up may be much more impressive and immediate. Of course make a separate holder and wiring for the test... don't burn up the boat on purpose, but a holder and a few feet of wiring will tell you how it will behave for real, in real life.

My personal preference is re-settable 12v breakers with push button, so they can be reset if/when they are tripped.

 

[jcb1977]

I agree it's more of a theoretical discussion as I don't see myself changing out all or most of the fuses out in the boat even if the AIC ratings are not sufficient....just seems like I'm missing something....I can't imagine Yamaha would put fuses on the boat that have insufficient AIC.

 

[Julian]

Huh....never seen anything like this before! @Mainah thoughts?

Almost looks to me like Bluesea has hit upon a way to sell more expensive products by creating a tool that recommends them....??? But I'm not an electrician and didn't stay at a Holiday Inn last night! LOL

 

[jcb1977]

Almost looks to me like Bluesea has hit upon a way to sell more expensive products by creating a tool that recommends them....??? But I'm not an electrician and didn't stay at a Holiday Inn last night! LOL

You maybe right.....I believe the wizard is using the ABYC standards but not sure if they are being correctly applied and/or are overly cautious.

 

[Mainah]

So the supposed concern is that if the fuse pops that the high current could still jump the gap. I personally don’t see the need if 30 amps or less atc fuse 12vdc with sla or agm batteries with most loads. If lifepo4 battery with high C and high peak amp rating then perhaps a concern. If an inductive load then perhaps a concern. Not sure how other folks are fusing add on ballast pumps but those would be my biggest concern as an inductive load drawing up to 30 amps. Have to imagine plenty of folks have run in line atc fuses to those off of big battery banks and I have never heard of an issue. I like distribution blocks, breakers, or fuse blocks for most stuff but in line atc fuses have a practical and safe use case.

@Julian may be right about trying to push sales. I am not an EE and I did not stay at a Holiday Inn last night. I also never bought into over marketed and insanely expensive AV cables and just bought good stuff without paying for names like Monster Cable. That said I also don’t buy anything from boss audio, or pyle.

 

[Jgorm]

That's crazy talk. I'd probably use 12g for 15a to help with the voltage drop.

 

[Sbrown]

I don't think in this case the concern would be about the high current essentially welding the fuse together as much as the concern should be about the time it takes the fuse to react to an overdraw and protect the circuit. In other words, say you have two devices being protected by the same fuse, Device A and Device B. They are wired in series in this circuit and device A is first in line, device B is second. Device B develops a short to ground which causes the circuit to overdraw current and blow the fuse. If your AIC rating isn't high enough, it's possible the fuse won't blow quickly enough to protect device A. It doesn't matter what device A is; it could simply be the wiring of the circuit, the principle is the same. Fuses don't blow "instantaneously", they do take a few milliseconds to react.

Also I'm pretty sure that the equation Blue Sea is using seems take into account the (M)CA rating (taken at 32*F) of the battery which can be significantly higher than the CCA rating which is measured at 0 degrees F. A battery rated at 800 CCA may be capable of delivering 1100 amps or more at 32*F or higher temps.

 

[Julian]

I don't think in this case the concern would be about the high current essentially welding the fuse together as much as the concern should be about the time it takes the fuse to react to an overdraw and protect the circuit. In other words, say you have two devices being protected by the same fuse, Device A and Device B. They are wired in series in this circuit and device A is first in line, device B is second. Device B develops a short to ground which causes the circuit to overdraw current and blow the fuse. If your AIC rating isn't high enough, it's possible the fuse won't blow quickly enough to protect device A. It doesn't matter what device A is; it could simply be the wiring of the circuit, the principle is the same. Fuses don't blow "instantaneously", they do take a few milliseconds to react.

Also I'm pretty sure that the equation Blue Sea is using seems take into account the (M)CA rating (taken at 32*F) of the battery which can be significantly higher than the CCA rating which is measured at 0 degrees F. A battery rated at 800 CCA may be capable of delivering 1100 amps or more at 32*F or higher temps.

This is why I put in fuse blocks at the battery and helm and run just one item of each circuit with an appropriately sized fuse.

 

[jcb1977]

I don't think in this case the concern would be about the high current essentially welding the fuse together as much as the concern should be about the time it takes the fuse to react to an overdraw and protect the circuit. In other words, say you have two devices being protected by the same fuse, Device A and Device B. They are wired in series in this circuit and device A is first in line, device B is second. Device B develops a short to ground which causes the circuit to overdraw current and blow the fuse. If your AIC rating isn't high enough, it's possible the fuse won't blow quickly enough to protect device A. It doesn't matter what device A is; it could simply be the wiring of the circuit, the principle is the same. Fuses don't blow "instantaneously", they do take a few milliseconds to react.

Also I'm pretty sure that the equation Blue Sea is using seems take into account the (M)CA rating (taken at 32*F) of the battery which can be significantly higher than the CCA rating which is measured at 0 degrees F. A battery rated at 800 CCA may be capable of delivering 1100 amps or more at 32*F or higher temps.

the circuit wizard from Blue Sea specifically asked for CCA.......the stock battery that came with my boat is 800CCA and 1000MCA.

 

[jcb1977]

That's crazy talk. I'd probably use 12g for 15a to help with the voltage drop.

even though the load for the fishfinder is at most probably 1 amp?

 

[Sbrown]

the circuit wizard from Blue Sea specifically asked for CCA.......the stock battery that came with my boat is 800CCA and 1000MCA.

I understand. I also understand they are using CCA because it is a more common standard found on almost every battery label more so than the other ratings. But I think the circuit wizard is calculating total amperage potential of the battery, among other things.

With that said, I'm not changing any of my stock system fuses out, and all my new circuit installations are protected with ATC blade fuses, so I'm not trying to tell you what you're doing is wrong or not, I'm just trying to help explain maybe why the circuit wizard came up with the results it did.

 

[jcb1977]

I understand. I also understand they are using CCA because it is a more common standard found on almost every battery label more so than the other ratings. But I think the circuit wizard is calculating total amperage potential of the battery, among other things.

With that said, I'm not changing any of my stock system fuses out, and all my new circuit installations are protected with ATC blade fuses, so I'm not trying to tell you what you're doing is wrong or not, I'm just trying to help explain maybe why the circuit wizard came up with the results it did.

Got it....I didn’t understand at first but now I know what you were getting at with the MCA. I’m not changing any of the stock fuses either and am going to use an atc fuse for my new fishfinder circuit. Just seems odd to me.

 

[Sbrown]

Got it....I didn’t understand at first but now I know what you were getting at with the MCA. I’m not changing any of the stock fuses either and am going to use an atc fuse for my new fishfinder circuit. Just seems odd to me.

I agree it does seem a bit odd. Probably just an BSS trying to sell a more expensive option, like some here have already expressed.

 

[Jgorm]

I heard a story yesterday about a guy with an experimental high power car amplifier that refused the fuse and then blew it again. Crazy!

 

[Mainah]

Lots of competition car audio types are running lithium batteries to avoid voltage drop when the bass hits and keep those amps performing at top power. The burst amps available out of a large high C rate lithium ion batteries can be huge and with basically no voltage drop. Capacitors for car audio are also able to release a whole bunch of power instantly. Fuse type/holder selection matters in these conditions.

I may help to think of this blown fuse jumping principle like welding. How close do you have to be to create an arc with X volts and Y amps and an electrode with Z resistance and C melting point. In the case of fuses refusing they are basically the electrode in this comparison. I would much rather that over an arc jumping the power feed terminals on the amp. The real concerns with refusing is when material from the fuse terminals redeposits itself in place of the broken connection making a new connection that can flow more power than the original or the arc becomes a fire ignition source.

Refusing is more rare than undersized wire overheating because of resistance and then melting the casing or becoming the electrode. I have posted my story of a big box store amp wiring kit being undersized and me being young and dumb here before. Thankfully once the wire melted through the casing and then my trunk carpet the fuse blew before the bare wire touching sheet metal caused a fire but not before I had a bunch of smoke in the cabin. This is why I preach wire size and quality to this day and always air on the side of caution. I may have only been a split second away from that wire sparking on the sheet metal igniting fumes from the gas tank directly below. Lesson learned and never repeated.

Back to what fuse to use. ATC are usually fine at or under 40 amps but I prefer sticking to 30 amps or less. Avoid ATO on the boat as the difference is closed vs open fuse element. AGU and maxi fuses are the next step up and then mini ANL and ANL. The holder or block matters too. As for the breakers out there I would be wary of the cheap ones.

The whole special holder or fuse for a 12vdc 1 amp load with a 30 ft 16 awg run because of normal battery amperage potential seems like buying asteroid insurance to me. Then again I am not an electrical engineer and I did almost blow myself up.