# Current capacity of wire

1. Aug 17, 2011

### jaymin nayak

I have wire of 1.5 mm2(Flexible). Now i want to measure it's current carrying capcity how i can measure it's current carrying capacity?

2. Aug 17, 2011

### sophiecentaur

Re: Simple wiring query.

If you were prepared to operate it at a high temperature then its current would be much more than if you needed to have an undetectable temperature rise. So you would need to specify your conditions.
In practice, the rating is very conservative and will have been reached by experiment and drastically based.
Bottom line is that there is no real answer to this very real problem.

3. Aug 17, 2011

### jaymin nayak

Re: Simple wiring query.

I have to measure current carrying capacity just at room temperature(27'c). I just need simple practical. The wire is PVC insulated.

4. Aug 17, 2011

### sophiecentaur

Re: Simple wiring query.

But it's not simple. Do you want to melt the PVC? How thick is the insulation? What is the thermal conductivity of the PVC sleeving? What temperature do you want to operate at?
All you can do is to calculate the resistance of a length of cable and that will tell you how much power it will dissipate when carrying a given current. That will not tell you anything about it's 'current capacity'.
This is why they publish recommended current ratings - based on experiment and experience. Sums are not enough.

I am not just being difficult. You are not (or, whoever sets the question, is not) specifying what is actually needed to answer the question. Or do you just want to melt the wire? Even that is not straightforward unless the conditions are specified.

5. Aug 17, 2011

### Staff: Mentor

Re: Simple wiring query.

....and did you really mean "measure"?

6. Aug 17, 2011

### jaymin nayak

Re: Simple wiring query.

I have been given u some data which I have. Thickness of insulation is 0.70 mm. Ambient air temperature is 40'c. Max. conductor temperature is 70'c.Thermal resistivity of PVC is 620'C cm/W. The length of the cable is 1m. & it's max. resistance is 12.1 ohm per km. Sir i have only that data & I have to learn simple practical for measuring current carrying capacity of PVC insulated wire. In above data The ambient temp, The max.conductor temp & Thermal resistivity of PVC are common.if u cant understand please give me more detail about current carrying capacity of cable. Yes i have to melt the pvc. I want to also know which cable has more current carrying capacity PVC insulated or Rubber insulated? Why? Plaese explain it in detail

Last edited: Aug 17, 2011
7. Aug 18, 2011

### sophiecentaur

Re: Simple wiring query.

I really don't want to get involved in this. Use VERY thick wire (1.5mm) and a 2A fuse with a Powerbreaker in the mains socket. That will avoid a lethal shock or a fire. You haven't the manufacturing skills or facilities to go for an economical solution.

8. Aug 19, 2011

### jaymin nayak

Re: Simple wiring query.

Which wire has more current carrying capacity PVC insulated or Rubber Insulated ? Why?

9. Aug 19, 2011

### sophiecentaur

Re: Simple wiring query.

Look over the list of factors. Which ones are relevant? As you haven't committed yourself by giving a full specification them I cannot tell you. This seems too much like a h/w assignment for me to be able to give you more specific advice but I could point out that one type of insulation is much more common.

10. Aug 21, 2011

### Redbelly98

Staff Emeritus
Moderator's note: the above posts have been moved here from an unrelated thread.

11. Aug 21, 2011

### Redbelly98

Staff Emeritus
There are several factors that go into this, including:

the ambient temperature
natural vs. forced convection
the thermal resistance and melting point of the insulation
how many wires will there be in the cable?

As a starting point, you could google wire current capacity

12. Aug 21, 2011

### Mbert

I think what this author is asking is relatively simple. How to measure (observe) the current capacity of a wire around 16 AWG gauge with different insulations in ambient conditions.

From what I remember, such an experiment was made in an episode of DIY network's Deconstruction to compare copper wires to aluminum wires. To actually melt the copper wire, (if I remember well) it took quite some current and was provided by a welding power supply. In your case, if you're only melting the insulation, you won't probably need that much current. Remember to perform this experiment in a safe environment, since toxic fumes will most likely be released and there's always a possibility of starting a fire. Also, remember that you are dealing with thermal time constants, so heating the cable with a very fast high-current spike is different than heating the cable with a dc current (or 60 Hz AC).

M.

13. Aug 22, 2011

### sophiecentaur

How long is a piece of string?

14. Aug 22, 2011

### dillonjerry

There are many tables out there for the current carrying capacity of wire based on its gauge. If its area is 1.5mm^2 that puts it some where in between 15 and 16 gauge wire. Here is an example table.

http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

Obviously this depends on how long the wire has to maintain this current, and what the acceptable heat threshold is. For what reason do you need this data? Is this a personal project, or homework?