I need to wire up a relay and have a convenient 15 amp push button breaker.
Big battery can deliver hundreds of amps.
Otherwise I have a 5 amp fuse and fuse holder, which is less convenient..
It needs to not smoke the wire before opening the breaker.

How small a wire can you go, would 17 or 18 gauge open such a breaker?
I suppose I can test with a longer section of same wire.

 

As a general rule of thumb I use a max of 8-10A/mm2

In the Netherlands we use 16A breakers by default and use 2.5mm2 cable. Which is equivelant to 14AWG. But I personally would be comfortable with using 16AWG.

I dont seem to understand why using lower awg wire open the breaker. Are you planning on using the wire as a load? Please elaborate. (A schematic would be helpfull)

 

Lots of small household appliances, lamps, etc. use 18 AWG cords in North America. It is expected that the AC mains circuit breaker will trip before the cord melts. Standard branch circuits in Canada are 15 A. I think 20 A is common in the US.

With low voltage things you always need to check to be sure the resistance in the circuit won't keep the current from rising to the trip point of the breaker in a reasonable time. 60 conductor-feet of 18 AWG will limit to about 30 amps on 12 V. That should be sufficient to trip the breaker fairly quickly. Some resistance is advantageous with small breakers because their interrupting rating usually isn't very high. If you were to put the breaker directly across the battery it might be destroyed rather violently.

 

I don't understand what the TS is trying to say. There temds to me a mimimum size because as the wire diameter gets small, the wire gets fragile. Car wireing is like 18 AWG minimum. It basically the same for fixture wiring. The circuit is usually protected against a short but if not, the weak link is accessible.

There are fuseable links in a car that are exposed. Inside a fixture or a ceiling lamp, a small amount of 18 AWG mixed with 14 AWG isn't usually a problem. Now we have AFCI breakers which helps that even more.
In an industrial cabinet, it's common to come in at say 200 A and then split to smaller circuits. The fusing is not immediate. In a house breaker panel it is.

In my opinion a few things are going on:
1. Surges/inductive loads
2. voltage loss (usually 3%)
3. Continuous (more than 4hrs a day)
4. Physical strength
5. temperature rise (current carrying Conductors in raceway)
6. Short circuit trip time.

 

I can't tell if they are asking about the "fusing current" of wire or if they are asking what size wire to use "safely" in this circuit that is just composed of a 15A breaker and a relay..
I'm going to assume the second..
As such the wire is sized based on the breaker/overcurrent device so .. In the US see NEC/NFPA 70 table 310.16 as a start..
16AWG is likely about right but there are some other factors to be considered.. Like are these wires in free air or conduit/ambient correction,etc...

for a "hobby" project.. 16AWG is good.. 18AWG is a bit too small.. 17AWG is basically non-existent.. 16, 18,20,22,24,etc...

 

AWG 16 wire has an ampacity rating of about 10 to 13 amps for a 50 foot run. You may want to consult a few wire ampacity charts. The diameter of AWG 16 Copper wire is about 0.0508" with a resistivity of about 4 Ohms per 1,000 feet. You can do the math from there since I have no clue exactly what you are asking. Note that resistivity and ampacity are also based on open air and ambient temperature.

As a general rule here in the US a 20 amp service is wired with AWG 12 and a 20 amp circuit breaker, a 15 amp service is wired with AWG 14 and a 15 amp breaker. With that in mind your AWG 16 would handle about 10 amps and should be fused accordingly or for your load.

Ron

 

Hope your not thinking of an AC house breaker for DC wiring? Their not advisable to use in DC. http://blog.gogreensolar.com/2015/02/ac-vs-dc-breakers.html

 

AWG 16 wire has an ampacity rating of about 10 to 13 amps for a 50 foot run. You may want to consult a few wire ampacity charts. The diameter of AWG 16 Copper wire is about 0.0508" with a resistivity of about 4 Ohms per 1,000 feet. You can do the math from there since I have no clue exactly what you are asking. Note that resistivity and ampacity are also based on open air and ambient temperature.

As a general rule here in the US a 20 amp service is wired with AWG 12 and a 20 amp circuit breaker, a 15 amp service is wired with AWG 14 and a 15 amp breaker. With that in mind your AWG 16 would handle about 10 amps and should be fused accordingly or for your load.

Ron

Is that for DC or AC, Ron? DC is different. Here is a link to DC wiring mostly for boats but it works for all DC cases.https://www.bluesea.com/support/art...oosing_the_Correct_Wire_Size_for_a_DC_Circuit The same site has a lot of information and sells things for DC wiring.

 

One thing not yet mentioned: 18 AWG wire is often recommended as a minimum even if it isn't required for current carrying capability simply because small gauges often have thinner insulation. It takes remarkably little insulation thickness for adequate voltage rating, but thicker insulation is obviously better able to stand up to any sort of mechanical assault.

Since the TS mentions a 5 A fuse as an alternative and a "battery", the presumption is that the normal current through the wire is less than 5 A and the voltage is probably nominally either 12 or 24. Generally people who work with batteries at higher voltages don't need to ask this sort of question and 6 V batteries aren't too common anymore. I'm assuming a lead-acid battery, since other types capable of "hundreds of amps" are generally not in the purview of the comparative novice who would ask for this sort of assistance.

I've seen people select wire based on ratings for AC mains use, which frequently means the gauge selected is far too small for low voltage DC. Wire suitable for 120 VAC is typically a nice neat order of magnitude less tolerable in a 12 volt system, in terms of voltage drop.

 

Is that for DC or AC, Ron? DC is different. Here is a link to DC wiring mostly for boats but it works for all DC cases.https://www.bluesea.com/support/articles/Circuit_Protection/1437/Part_1:_Choosing_the_Correct_Wire_Size_for_a_DC_Circuit The same site has a lot of information and sells things for DC wiring.

Now that you mention it I never gave it much thought. The original post was sort of vague to say the least. Maybe if the thread starter returns they can shed a little light on exactlt what they are trying to accomplish?

Ron

 

I am using the wire to activate a 70 amp DC breaker to run a pump.
The wire is like a brown lamp cord.
I have a boat style pull - push switch.
Use 12 VDC battery power, has to have circuit protection otherwise if the wire going to relay shorted, might catch fire.
Fuse or breaker needs to be small enough value to just trip open if wiring shorts out.
Wire is next to other wires but not in conduit, simply lays along side supported by plastic supports every so often.
Idea is run the wire from the helm area about 15 feet back to the relay near the pump to turn it on and off remotely using the relay.

I measure current flow through the relay circuit, digital amp meter said 0.14
Relay is basically cube type relay with larger lugs cause it is 70 amp DC rated.

I had it all working, but I shorted out my fuse setting the switch in place, which is why I hate fuses, now I need to find another fuse or buy a push button breaker, I saw I only have some 20 amps breakers unused. I think I could go safely to 10 amps.

 

So all this wire does is run a relay coil? The relay coil draws about 0.14 Amp? Should that be the case then any 5 amp fuse should do fine.

Ron