Affect of ambient temperature on Current Capacity of Wires

[MDGroup]

My basic understanding is that the higher the ambient temperature in a device, the lower the current capacity of a wire. So, the current capacity has to get de-rated by a certain percentage based of how high the temperature is. That is as far as I get.

But, how do you figure out how much the elevated temperature impacts the wire? A lot of internet searching gave me a lot of non-conclusive results.

Here's my set up:
Our device will pull about 13 Amps Max continuously.
The conductors inside of the unit that carry full current are all 16 AWG (105'C Jacket).

1 - 16awg wire should be able to handle 22 Amps, Correct?
2 - Temperature inside of the unit can reach approximately 65'C. Does that de-rate that current carrying capacity? By how much?

3 - If we are borderline with our ratings, could a missed strand in a crimp, or a loose crimp put us on over the limit?

(I'm a Mech E, so please don't get too techincal in your answers)

Thanks.

 

[Compositepro]

The temperature limitation is on the insulation jacket of the wire. If your ambient happens to be 105C then the ampacity limit on your wire becomes zero. There are tables that give the ampacity limits of wires vs ambient temperature.

 

[cuky2000]

Beware that there are limiting factor at the equipment connector and protective devices that can not operate the cable above 90oC even if the cable insulation is rated for 105 oC. Other limiting factors is voltage drop or sometimes the short circuit thermal or mechanical stresses imposed on the cable.

Below is a sample table with derating factors for ambient temperature and a link for a cable calculator.

Good luck

http://www.electrician2.com/calculators/wireocpd_ver_1_reverse.html

 

[waross]

When using higher temperature ratings junction boxes may be used near each end of the run.
A larger wire with adequate ampacity at a lower temperature rating is run from the breaker and transitioned to the smaller, higher temperature rated wire. At the far end a similar j-box is used to transition to a wire suitable for connection to the load.
Hopefully the breakers are located in a lower temperature ambient than the area transitted by the wires.

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

 

[7anoter4]

The current carrying capacity [ampacity] of a wire in an enclosure it is calculated and tested in the device manufacturer workshop. Since there are so many factors to take into consideration no standard could state the conductor cross section area.

 

[waross]

The Canadian Electrical Code (for electrical installations) has two sets of Ampacity Tables.
Tables for different temperature ratings in free air,
and
Tables for different temperature ratings in a raceway or cable.
Approved conduit fittings and approved junction boxes are normally suitable for use at the ampacities listed in the raceway or cable tables.
Larger enclosures encompassing equipment as well as wires are covered under manufacturing codes.

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

 

[cherryg222]

Your post doesn't specify the standards being followed, but since you have mentioned the wire size as 16AWG, we will assume that you are following NEC (N America). Normally the smaller sized wires in NEC ampacity tables do nnot follow 105degC insulation. The range there is 60, 75 and 90degC insulation. Now since you are terminating the wires on 75degC rated terminals (can be checked with manufacturer of equipment), you may need to follow ampacity for 75degC temp rating of conductor. Now as per Table 310.15(B)(16) of NEC, 16AWG rating has not been listed. The next best available value is the 90degC value of 18Amps. Now this is on the basis of ambient of 30degC. Since you specify the ambient as 65degC, Table 310.15(B)(2)a provides the derating factor as 0.65 for 90degC rating. Thus derated ampacity for a 16AWG conductor is 0.65 x 18A = 11.7A. You load current is 13A max. I believe your cable size is under rated for the application. Somebody else can comment on my values above.