maximum voltage across a wire

[tractable09]

I am a hobbyist for small electrical projects and chemical engr. by profession. I have an 18AWG wire connected to 12V DC and giving power to a load with 10A current passing through wire. I want to put a higher load with 48V DC but the current will be 10A again. In 3rd case I want to use same wire but with 220V AC and 10A current. Can the same 18AWG wire handle the 10A current in each case of different voltages? The wire specs tell me only the current rating, nowhere voltage rating is mentioned for the wire.
Is there any limit to the maximum voltage across the wire?
Thanks,

 

[wbd]

It depends on the insulation of the wire and should be on the wire or possibly the spool it came off of.

 

[itsmoked]

You can transmit any voltage equal to or less than the wire's voltage rating. And you can use any current less than the wire's capability. It varies with usage.

I often follow this table:
[URL unfurl="true"]http://www.powerstream.com/Wire_Size.htm[/url]

Keith Cress
kcress -

http://www.flaminsystems.com

 

[tractable09]

Thanks for the details, the link of powerstream.com gives me the maximum amperes, voltage rating is not mentioned.

 

[itsmoked]

Correct. Ampacity tables all assume you have the correct voltage rated wire.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[xnuke]

Voltage considerations aside, I would recommend a larger wire size for 10 A. The U.S. National Electrical Code would require a minimum size of 16 AWG for 10 A. 18 AWG is suitable for up to 7 A per the U.S. NEC, and while that code may not apply to your application or in your location, it isn't a bad idea to consider using a larger wire size.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jraef]

The "wire" doesn't care about the voltage level. It is the INSULATION on the wire that matters. Every wire insulation has a maximum voltage level assigned to it, meaning it has been tested to that level (within the testing limits of whatever authority has jurisdiction). If you are here in the US for example, that would be UL for most types of wire. Anything lower than that maximum level is fine

As a gross general rule, most "building", "appliance", "fixture" or "hookup" wire that you can buy off the shelf in a store will be rated for 300V or 600V. Wire classified as "Low Voltage", "communication" or "automotive" wire will likely be rated 50V or less. Not matter what, at 48V, you are probably fine, but at 220V, make sure you select one of the other types.

But I also agree with the others, 10A is too much for 18ga. except in some very specialized circumstances. Be careful looking up wire ampacity on Internet sources, some are referring to the ampacity of the bare coper conductors under laboratory conditions. Real world ampacity ratings are based on testing at common case ambient environments and thermal ratings of the insulation. That's why the NEC tables are what must be used. Those tables will be based on the insulation type, not just the copper inside.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ScottyUK]

With only 12V source and with a relatively high load current you should have concerns about Ohm's Law as well as the thermal rating of the conductor.

 

[tractable09]

Thanks all for the replies and giving some understanding. One thing remains is what jraef mentioned, how do i know the wire is rated for 300/600v or 50v? That is a big difference. I mean just looking at the insulation thickness for example i can differentiate between two voltages?

 

[itsmoked]

Absolutely not! A lot of 600V wire has thinner insulation than 300V wire. It all depends on what is being used as insulation.

There should be a voltage rating on the wire same as the temp and AWG. If not, it should be on the spool. If not, you should constrain the wire to low voltage service like automotive or 50V and less or to trying bags shut, hanging bird feeders, or store it in the circular file cabinet.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I'll support Keith.
You don't want to put 120 Volts on any wire that does not have a voltage rating and UL approvals.
Upgrading to #16 is a good idea. When you buy the #16 wire, select one that has the voltage rating and approval information printed on the wire.

Bill
--------------------
"Why not the best?"
Jimmy Carter