wiring question.

[RBRONKEMA GHTFD]

Okay guys I have a question, which has been stumping me. I installed a MX7k on a guys truck over the weekend. I custom made a switch box for him and put 7 rocker switches in it. I started at the battery with a 30 amp fuse. Then ran a 10 ga wire to a fuse block inside the switch panel. then I put 2 30 amp fuses on the block and ran a 12 ga to power the switchs and relays. The first 4 switchs have relays. I fugured I'd put relays on the first 4 being they are going to be on the most running the lower flashers, sweeps, and 5 rotators. Also the 4th switch is for the take downs. (they do not flash I just thought I'd put a relay on it because those get used more than alley lights and rear work lights.) Now my question is why does the fuse at the battery keep blowing? It only blows if he has more than 4 switchs on at once. I had this bar hooked up the same way on a different truck and had no issues before. Should I add a relay to the main power wire or what? Thats what I am thinking about doing but I am not sure what I should use to "trigger" the power. (trucks a 02 dodge ram.) I don't want to add a bigger fuse at the battery as I am afraid it may cause a fire. Also everything including the bar is grounded at the battery. Everything is ran thru groments and in loom also so it wont chaffe on anything. Any thoughts. Thanks in advanced. Like I said this has been bugging me and has been hooked up on a different truck before the same way and the guy never had a issue.

 

[ff_emt_820]

Sounds to me like you are pulling more than 30 amps when you flip a 4th switch. I would suggest a higher amperage circuit breaker. Imho a circuit breaker is more help in preventing fires etc than a fuse.

 

[firemedic105]

ff_emt is correct. If you look at the amps that you are pulling, you are using enough with just the rotators in the bar to nearly max your fuse. I was taught, maybe I am wrong, that each rotator pulls approximately 5.5amps when activated. Multiply that by 5 and you get 27.6A approximately just with the rotators. Add an additional 11 A when u turn the sweeps on


Each flasher and takedown would draw approximately 4.5 amps based of my standard figures, so I am surprised that he isn't blowing more fuses with fewer switches on.


Looking at the requirements for power, and someone can correct me if i am off slightly.


5 x rotators, 27.5 A


2 x sweeps 11 A


2 x takedowns - 9A


4 x Flashers 18A


Total usage = 65.5A


Add in 25% safety = 80A approximately.


Now remember, these are standard figures i use.

 

[RBRONKEMA GHTFD]

Sounds to me like you are pulling more than 30 amps when you flip a 4th switch. I would suggest a higher amperage circuit breaker. Imho a circuit breaker is more help in preventing fires etc than a fuse.

Where might one get a circut breaker thats the correct size for this application?

 

[shues]

Where might one get a circut breaker thats the correct size for this application?

Blue Sea Systems: http://bluesea.com/category/3/10/productline/overview/150


[Broken External Image]:http://bluesea.com/files/images/products/thumbs182/7102_182x182.jpg


Bussmann: http://www.cooperbussmann.com/6/HeavyDutyFuses.html (scroll down)


[Broken External Image]:http://www.cooperbussmann.com/images/vertimagesec-276ac54e-09bd-448e-8cb7-183b08f1c942.JPG

 

[wfd67]

I've dropped a few of these into our fire rigs over the years, using the existing breakers (self-resetting). We wire them into two separate switch boxes to allow the engineer/captain to cut out lights once on scene (calling for ROW vs. blocking ROW). The box with the rotators is wired using an 8ga wire into a 40 amp breaker, the second with 10ga wire into a 30a breaker. (The flip of the switch on each relay gets us lit up in a hurry, but we can dial it down as needed; a bit overkill in your setup, though).


I'd agree with the others that it's a load issue (and the fuse thing; you spend a lot of time replacing those little things). I got a bag full of self-resetting fuses on eBay a while ago and have been using 'em whenever the one in the rig isn't where I want it or I just can't get to the dang thing.


The rotator load is about what I use (the 5.5a per rotator noted earlier; I use 5.4a, but my safety factor is baked into assuming 12.8V and knowing the engines run 14V when running.) The flashers may be lower depending on the bulb; 1156s at 28 watt will bring you closer to 2.35a @ 12volts, but if it's S795 you're darn close to his number of 4.5. On our 69" bar (6 rotators, 1 oscillator, pairs of takedown, flasher and sweeps, no rear lower lighting) the bar calculates out to about 65 amps by my math, and we've never run into a cut-out or breaker issue across running this setup for the past several years and with the lights spinning for an hour or longer at a time (though again, once parked a pair of rotators and the oscillator are cut out minimally, easing back by ~ 18 amps or so).

 

[RBRONKEMA GHTFD]

So should I get a 80 amp and call it good? Or go higher? I think autozone by me has the 120s or something.

 

[AZEMT]

Don't want to go too high, or the breaker becomes useless. I'd say 80 sounds about right for your application. Perhaps 100. But if you pad it too much, it won't save you if something overloads the system by less than your safety factor, which for an 80 amp draw would be 40A if you put in a 120. 40A is more than enough to start a fire (not to mention take you for a pretty good ride) if it gets loose in the wrong place.

 

[RBRONKEMA GHTFD]

I just ordered a 80 amp.

 

[firemedic105]

I've dropped a few of these into our fire rigs over the years, using the existing breakers (self-resetting). We wire them into two separate switch boxes to allow the engineer/captain to cut out lights once on scene (calling for ROW vs. blocking ROW). The box with the rotators is wired using an 8ga wire into a 40 amp breaker, the second with 10ga wire into a 30a breaker. (The flip of the switch on each relay gets us lit up in a hurry, but we can dial it down as needed; a bit overkill in your setup, though).

I'd agree with the others that it's a load issue (and the fuse thing; you spend a lot of time replacing those little things). I got a bag full of self-resetting fuses on eBay a while ago and have been using 'em whenever the one in the rig isn't where I want it or I just can't get to the dang thing.


The rotator load is about what I use (the 5.5a per rotator noted earlier; I use 5.4a, but my safety factor is baked into assuming 12.8V and knowing the engines run 14V when running.) The flashers may be lower depending on the bulb; 1156s at 28 watt will bring you closer to 2.35a @ 12volts, but if it's S795 you're darn close to his number of 4.5. On our 69" bar (6 rotators, 1 oscillator, pairs of takedown, flasher and sweeps, no rear lower lighting) the bar calculates out to about 65 amps by my math, and we've never run into a cut-out or breaker issue across running this setup for the past several years and with the lights spinning for an hour or longer at a time (though again, once parked a pair of rotators and the oscillator are cut out minimally, easing back by ~ 18 amps or so).

Thanks for the confirmation of the numbers I use. I always have things a little higher since you never know when a bulb or circuit will throw you for a loop.


Thanks. JJ