What guage of wire?

[dbfd588]

Ok guys. I have a main power lead coming from my battery. Its run to my switch box. Im running a 45 watt radio, 180 strobe system, a few led lights and im wantin to add a 100watt siren. The main lead is like 12 gauge I think. It is a power cable for a spectra. Is this a big enough wire to supply all my stuff?

[dbfd588]

can anyone tell me how many amps for each gauge of wire.
18 gauge = ? amps
16 gauge =
14 gauge =
12 gauge =
10 gauge =

[Tom in D.C.]

Look here:

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

Your projected load figures out roughly to 380 to 400 watts at
full load. You're looking at about 30+ amps and the #12 wire
will not handle it according to the chart.

[FireCpt809]

To do things right . The radio, siren, strobe supply and lights should be run independant of each other and fused at the rated amprage. Running one main wire to supply everything is a fire wating to happen.

[dbfd588]

thats what I wanted to know. I dont like fireballs on wheels! Looks like I got some wireing to do. Thanks guys

[W8RW]

Running separate conductors for the radio and other equipment is also a good idea because some of the lights and sirens can put noise on the power lead. There is less chance of it getting into your radio with separate conductors.

[RKG]

To do things right . The radio, siren, strobe supply and lights should be run independant of each other and fused at the rated amprage. Running one main wire to supply everything is a fire wating to happen.

Not necessarily so: fuses or breakers ("Circuit Protection Devices") are sized to protect the wire that is downstream of the fuse or breaker. Only wire that is upstream of a subsequent CPD need be considered.

There is nothing wrong with, for instance, bringing a #8 AWG feed, through a 30A breaker, to a fuse block that would subdistribute power to various devices. The fuses in the block are sized based on the wire that runs from the block to the device.

The notion that a fuse should be sized relative to the draw of a device, as if the fuse is to protect the device, is incorrect. There is no risk in powering, say, a 5A device via a #12 feed through a 15A fuse. In fact, that is what you do every time you plug a low-draw device into a wall outlet in your house.

[Batwings21]

The fuse under the hood serves one purpose only, to protect the wire that runs from the battery to the individual device fuses. For instance say a 8 gauge can handle 80 amps, you would fuse the under hood fuse at 75, then inside the vehicle, have a fuse panel, or multiple individual fuse holder attached ( preferably by soldering) to the bigger lead coming from under the hood. One device, say you siren goes bad, it pops its fuse and the rest of your stuff goes on its merry way. That is the was most automobile electrical systems are designed. Under certain circumstances, running a radio or other device direct to the battery is desirable, it is most of the time not necessary. Just remember NEVER run the ground lead and direct to the battery, NEVER over fuse your wires, and ALWAYS make sure each device inside has its own fuse.

[dbfd588]

Hey you guys have been alot of help. Im only running 180 watts worth of strobes and 4 leds. So thats roughly 25amps. But when I add a radio and siren I will add another main lead from the battery just to be safe. Thanks guys. Another quick qustion. Is there a type of meter to measure how many amps is being pullde through a wire. When I have all my stuff powered on it would be nice to be able to check how many amps its pulling.

[thebigphish]

it's called an ammeter.

If you have a lot of goodies (like most of our installs around here), we just get an ammeter from a parts store and wire it in next to the fusebox - this way you know whatchya' got cranking.

There are some inductive ammeters which are designed for point of testing.

[fineshot1]

Not necessarily so: fuses or breakers ("Circuit Protection Devices") are sized to protect the wire that is downstream of the fuse or breaker. Only wire that is upstream of a subsequent CPD need be considered.

There is nothing wrong with, for instance, bringing a #8 AWG feed, through a 30A breaker, to a fuse block that would subdistribute power to various devices. The fuses in the block are sized based on the wire that runs from the block to the device.

This is what I normally do - although I use a 40A fuse at the batt + post for the console distrubution panel and also run a seperate 10 gage + lead to the batt and 40A fuse that also for the LED Light Bar. The console dist panel supplies DC to the siren, radio's. I use the maxi fuses with the very heavy duty fuse holders - all very heavy duty. I have never had anyone come back due to any problems such as heated wires or shorting. The dist panels also get insulated in case anyone else sticks there fingers inside or drops something into the console.

[kf4sqb]

Strange, I added a post to this thread, and it apparently didn't show up. Oh, well, a few other people have already made most of the points I wanted to make anyway. I've been doing electrical work in an industrial setting for years, so do have some qualifications in this area. As stated earlier, fuses and circuit breakers are used to protect the wire, not the device being powered, in most cases. All devices should have their own fuse for their own protection, of course, but most times when a device like a radio or siren pulls enough current to blow a properly sized fuse, it already has a problem, else it wouldn't have blown the fuse. When running a large-gauge wire to a distribution point as has been discussed here, the main thing to remember is to put a fuse as close as possible to the power source, in this case the battery of a vehicle, and not to oversize the fuse. It is, of course, OK to put a fuse in rated at less than the wire is capable of carrying, but never, NEVER!!! put in a fuse with a higher ampacity than the wire is intended to carry. I have seen too many problems caused by jack-leg electricians putting in too large a fuse. "What? The fuse keeps blowing? No problem! We'll just put in a bigger one!" Then, you wind up with a fire, or damaged equipment, or both. If the fuse is blowing, there is a problem. Find it! In general, the capacity of various different wire sizes is:

#14=15 amps
#12=20 amps
#10=30 amps
#8 =40 amps

There are some exceptions and variations on those numbers, but that will cover most applications with a little bit of a margin of safety. For example, #10 will actually safely carry almost 40 amps in certain applications, but I wouldn't recommend doing it unless you know what you are doing. The type of insulation on the wire, as well as the environment everything is installed in, start coming into play if you want to run more current than whats recommended above.

[misawatech]

I agree with kf4sqb. The list he provided is closer to the accepted ratings listed in the National electic code. I've been working in some sort of electrical field for 26 years now and I've never seen that table in the link above. Most of the tables I've used listed the more common guages of 6, 8, 10, etc. I know I have seen the other sizes but they are hardly ever used or available.

In addition to the maximum current rating you have to take into account the area of the installation. The current ratings in the NEC are listed in separate columns for temps of 65, 75, 85, and 90 degrees C. They are further broken down by wire type such as solid copper, aluminum, or copper clad aluminum and whether a stranded wire or solid wire is used.

My point is that each situation may call for a different installation. If you did want to run a large guage conductor from the battery then I would recommend you install a busbar for your individual connections. I am seeing this in all the new emergency response vehicle and some of the standard work trucks. From this bus you would then run your individual circuits to the equipment and fuse for it's current draw.

Lastly, and I may have misunderstood, but it is my guess that you won't get any current reading from an inductive meter. An inductive meter, what we in the business call a clamp on, wraps around the conductor but needs a magnetic field that is only found in an Alternating current circuit.

Just my opinion

[jackhackett]

Lastly, and I may have misunderstood, but it is my guess that you won't get any current reading from an inductive meter. An inductive meter, what we in the business call a clamp on, wraps around the conductor but needs a magnetic field that is only found in an Alternating current circuit.

They make DC clamp on ammeters. They're good if you need to measure high current that a normal meter won't handle, and to get a quick reading without having to disconnect anything. Not usually good for low current readings.

[Jhadds117]

Well I have learned quite a bit by reading the posts. However now I ask for an opinion. I have a Ford Excursion. I was planning on running 6 Gauge Wire from the battery to my Center Console to a Distribution Block, About 20 ft of wire I am guessing. From there each radio will be powered off the block with the appropriate wire and fuse that came with the radio. Also a ground block will be installed and 6 Gauge ground run to the frame. I am looking to hook up and power 1 MaxTrac Low Band - 60Watt, and 2 Spectra UHF 45 Watt Models, Range 3 & 4 along with a BC-796D Scanner. I already have 1 Spectra VHF 45W in use and positive run directly to the battery. And a BC-780Xlt running off a power point behind the dash. I do not plan on changing that wiring at all. At no point in time will I be transmitting on more than 1 radio at a time, and I know that the most draw is pulled when transmitting, will this be sufficient? If it is overkill that is cool too. Just don't want a fire breaking out. Eventually I will be dropping down to 1 40Watt UHF radio that covers the 450-512 all in one, but for now, I will use what I have and fit that into the budget hopefully by July or August this year. Thanks in Advance.

[kf4sqb]

Yeah, what JackHackett said. Just FYI, the clamp-on ammeter that can be used on AC or DC current is based on a hall effect sensor.


Jhadds117, #6 should be quite sufficient for what you need. A bit of overkill, in fact. When it comes to wiring, overkill is our friend!

[RADIOMAN2002]

I may be wrong but the listing of amperage rating that kf4sqb gave, are I believe for 110v 60cycle AC. DC ratings are different, especially for 12VDC. Since AC current uses only about .7 what DC does.

[smokeybehr]

There's nothing wrong with a little overkill in running your electrical system.

I run 1/0 as my main bus wire from the battery to the fuse block. Under the hood is an 80A fuse. From there runs all my high-amperage equipment (T83 Spectra, car stereo amps) and the run to the front console, which is a #4. From there, I have another fuse block with appropriate sized fuses for each piece of equipment. Give yourself more power than you think you need, and you'll be safe.

[kf4sqb]

I may be wrong but the listing of amperage rating that kf4sqb gave, are I believe for 110v 60cycle AC. DC ratings are different, especially for 12VDC. Since AC current uses only about .7 what DC does.

You are absolutely correct, that is for AC. You can actually use a smaller wire for a given current at DC as opposed to AC, due to what's called "skin effect" with AC. However, I give, and use, the ampacities listed above because they offer quite a bit of a margin of safety. As a volly firefighter, I've seen enough car fires started by p!$$-poor wiring jobs that I can assure you that you don't want to skimp in the wiring department. You're asking for trouble if you do.