Rises In ambient temperature

[fretfingers123]

I'm not sure if this is posted in the right section but its part if the regs so ill go for it.

I have a question on my AM2 exam paper which reads "If an area within an installation undergoes a 10 degrees Celsius rise in ambient temperature, the effect on the current-carrying capacity of cables will be to:
A) decrease the value of Iz
B) increase the value of Iz
C) level of Iz unchanged
D) increase the fault current by 10%

I can't find the answer in my 17th Ed regs book anywhere. Under section 523 (current-carrying capacity of cables) there is nothing stated about ambient temperatures of 10 dC. Not is there anything under section 522.1 ( ambient temps) and I wouldn't know where to start with the appendixes. Any help as to where to FIND the answer in the regs book would be greatly appreciated.
Cheers,
Al

 

[Deleted member 72666]

Think more on the lines of increase in cable temp = increase in cable resistance. From that you should have your answer.

 

[mechelec]

You need to be looking in your college books not in the regs. This is basic electrical theory.

 

[fretfingers123]

Thanks for your help!

 

[HandySparks]

So, what's the definition of Iz?

 

[telectrix]

You need to be looking in your college books not in the regs. This is basic electrical theory.

not even that. stands to reason that cables get warm. if it's 'otter outside, they get even warmer. it's schoolboy physics.

 

[fretfingers123]

Well the answer is that of course, resistance increases in relation to temperature increases. However, the exam is "the use of the regs book" I just couldn't find the values of Iz in circumstances such as a temp increase of 10 degrees. Thanks for the help!

 

[SirKit Breaker]

So, what's the definition of Iz?

It is irrelevant in the question, as is the increase in fault current in the answers.

This question ( i dont know who wrote it) is very City and Guilds style, and is only looking for the basic electrical knowledge understanding.

Cheers..................Howard

 

[HandySparks]

Well the answer is that of course, resistance increases in relation to temperature increases. However, the exam is "the use of the regs book" I just couldn't find the values of Iz in circumstances such as a temp increase of 10 degrees. Thanks for the help!

You won't find tables of Iz against temperature, but you will find tables of Ca against temperature, which you should be able to draw some conclusion from.

 

[Richard Burns]

If you have a look at appendix 4 paragraph 2 this covers ambient temperature changes and gives you the table numbers to look at for rating factors to apply to the values of It to give Iz.