ambient temp/rule of thumb 80%?

[dez0178]

Hello, I am busy studing my Level 3 C&G 2330, can anyone enlighten me on the rule of thumb 80% for ambient Temperature? when does it apply and come into effect.
Cheers.

 

[ackbarthestar]

Appendix 4 Table 4B1 is one place you could look.
Usually appropriate for air temperatures greater than 30 deg C
There is no fixed ROT as far as I know - maybe someone knows more information about global warming that they haven't shared ?

 

[telectrix]

it's because you measure at ambient temp. say, 20dg.C. the 0.8 factor is to correct for the resistance of the cable being higher resistance at operating temp.

 

[ackbarthestar]

Now if he said 83.3% I might have considered both ambient and operating temperatures.......But not necessarily for ambient temperature alone

 

[SirKit Breaker]

In a nutshell, you would apply the 0.8 correction factor if you use the disconnection tables in the regs book.
If you use the On site guide you do not apply this correction factor because it has already been done for you.

If you compare the tables in the BGB and the OSG, you will see that they have different values for the same protective device. If you correct the table in the BGB, it will be roughly the same as the same table in the OSG without applying correction.

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

 

[dez0178]

Cheers for that info mate.

 

[dez0178]

Cheers, Yep looked in the OSG and found the relevant info, thanks for your info too.

 

[dez0178]

Cheers, for the help.