m sleem

I want to confirm that:

for example: Breaker size is 80 AT

feeder size should carry out 80A

OR feeder size should carry out 90A

OR feeder size should carry out 70A

480sparky

A feeder with an ampacity of 70a on an 80a breaker is a violation.

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mbednarik

Cable size should be enough to carry the load applied. example, you have a 50 amp continuous load. 50 X 125% = 62.5 amp load. The conductors would have to be large enough to carry 62.5 amps after any/all derating for temp or bundling. Now reference standard OCPD (overcurrent protection device) sizing in 240 to find that would would put that general load on a 70 amp OCPD. If the type of load is any found in table 240.4 G special OCPD dizing applies, refer to the corresponding art.

m sleem

but i know we can size the feeder by the previous step of the breaker....but i'm not sure this in regard to all type of loads or only motors.

mcclary's electrical

Way too broad of a statement.

What if it's an outside tap? What if it's a tap? What if these are transformer secondary conductors with no overcurrent protection?

mcclary's electrical

If your feeders ampacity is not corresponding to a common size breaker, you can got to the next size up as long as you're not over 800 amps.
There is a standard size 70 amp breaker, so you can't just go to 80.

Speedy Petey

Depends on who's code you are referring to.
I am only familiar with the NEC.

480sparky

The OP is way to ambiguous for anything else.

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Aussielec

This statement confuses me(along with everybody else). You size your circuit breaker to be less than the maximum current carrying capacity of your cable.

Your ciruit breaker is there to protect the cable and nothing else.

If you put an 80amp CB on a cable that is rated to a maximum of 70amps that is violation of any code in any country through out the world period....(sorry drunk)

m sleem

could you show an example for this case ?.......our friends deny it.

wildleg

as I posted in your other thread on almost the same subject, the NEC does not apply to your situation if you are in a Saudi Territory

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Chris Kennedy

From the 2008 NEC

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m sleem

so clear .....very nice

m sleem

so clear .....very nice

Chris Kennedy

Interesting, not something you hear often about the NEC.

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erics37

As you can tell from extensively researching the Saudi electrical code, it is rather lacking, which is probably why the OP is here asking this stuff. Why do you care what guideline they are under?

B4T

This goes along with post #12..

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard
ampere ratings for fuses and inverse time circuit
breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50,
60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300,
350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000,
2500, 3000, 4000, 5000, and 6000 amperes. Additional
standard ampere ratings for fuses shall be 1, 3, 6, 10, and
601.The use of fuses and inverse time circuit breakers with
nonstandard ampere ratings shall be permitted.

wildleg

Don't you think that it is appropriate to apply the code that specifically applies to the situation ? the Saudi code was initiated in 2007, and the section I quoted specifically references three other codes to use if the letter of their Article 401 isn't clear. The IEC is one of the codes that applies, but nowhere is the NEC referenced. Would you be so quick to quote European codes for work in the US ? I doubt it. I can't for the life of me understand why you would be so quick to defend the quoting of a code that doesn't even apply to the installation, given the information that was stated ? If there is no reference in their code to the NEC, doesn't it make you consider the notion that there is a reason for that ?

__________________
As President Roosevelt said: "We have nothing to fear but fear itself. And Chuck Norris. And 滿口胡言. And Grabthar's hammer. And Gort. and 江南 Style. and rotting in the street and Zombies . . . and Wayne Griffen "

1capybara

ok but what about 20% spare capacity for the feeder and the breaker size.
50A continuous load x 125% = 62.5 amps
20% spare capacity = 75 amps
use 80 amp breaker and size feeder to carry not less than 80 amps= 4 awg
[not counting deration for temp or bundling]

erics37

Nothing in the code requires that you size for spare capacity. If you have a calculated continuous load of 62.5 amps and you could find a 62.5 amp overcurrent device then you could use that. Otherwise you can adjust the OCPD size to one of the sizes on the standard list in 240.6. Some feeders (like ones supplying motors for instance) don't allow you to size to the next standard OCPD up, so in those cases you're stuck using the next size down.