decreaseing current carrying capacity

[lofty84]

how does one decrease the current carrying capacity of a cable

 

[IQ Electrical]

how does one decrease the current carrying capacity of a cable

You could stretch it or run it through very thick thermal insulation.

 

[telectrix]

bury it in insulation, warm it up, squash it ( LOL).

 

[Amp David]

Bunching with other cables, running through insulation, higher ambient temps. Its all about installation methods.

 

[benji]

you could reduce in size the fuse/mcb thats protecting it

 

[IQ Electrical]

I Think you mean how do you apply derating factors to cables?

You need to be aware of:

The design current
The tabulated current carrying capacity of the cable
The ambient temperature
The grouping factor
Any thermal insulation factor
Voltage drop

 

[lofty84]

I think ive confussed my self as I thought that how this question was worded was saying that if part of the run was to go through an area which has a 40 degrees C amient temperature from a 25 degreees C ambient temperture run I would need to decrease the current carrying capabilities of the cable. But what I think it is saying is that the current carrying capabilities of the cable will be reduced when it enters this 40 degrees area and therefore I will need to up my cable size.......


here was the question


a 70 degrees thermoplastic insulated and sheathed cable to bs6004 is installed in an ambient temperature of 25 degreees for part of the run and then enters an area at 40 degrees. the effect on the cable will be to

a) require clips at greater intervals
b) reduce the voltage drop
c)increase the bending radius
d)decrease its current carrying capacity

 

[telectrix]

well if you think logically, the part of the cable installed in the higher ambient temperature will require less current to increase it's temperature to it's rated maximum operating temperature, so effectively, you will be reducing its CCC.

 

[lofty84]

so does that mean you would need to concider uping the overall size of the cable. I mean if the current carrying capabilitie of the cable are to decrease will it effect the operation of the load or am I way of the mark

 

[telectrix]

you need to apply the relevant rating factor according to the installation method. if the load current is less than the derated value of CCC , then the cable is OK for that situation.

e.g. 2.5mm is rated at 27A clipped direct. if it's installed ref. method 101, say, then the CCC is reduced to around 18A ( guesstimate as i not got osg handy) . so if you load is <18A you're OK. if it.s 23A, then you would need to increase the cable size.