250 Percent Sizing OCP

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ritelec

ritelec

Senior Member
Location
Jersey
Hello,

Been thinking about something.

When sizing a circuit for a thermally protected motor, from what I understand the ocp can be up to 250% of the hp (current)

So I read here..

T430.248 1.5HP @ 230 volt = 10 amps
T430.52 10 amps * 250% = 25 amps Maximum cb.. so that works.

Not sure the hp but... a 9 amp motor x 2.5 would be 22.5 amps. A 25 amp breaker would be too high.

So the question is, a 1/2 HP motor at 4.9 amps * 2.5 = 12.25 amps. Even though a 15 amp breaker is the next size up, wouldn't it be too high as the 25 amp was on the 9 amp motor above?

Thank you
 
Was thinking

at 250% of a motor, 14 wire could be on 30 or more amp breakers,
12's could be on 40's or more.

So where would that leave egc and 250.122

eg: run a number 14 circuit conductor, on a 30 amp brker with a 10 ground ???

Somethings not right?

Thank you
 
The EGC is not required to be larger than the circuit conductors.

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case shall
they be required to be larger than the circuit conductors sup-
plying the equipment.
Click to expand...
 
While you are contemplating such things.....
(a) If you use a dual-element to protect the same 1/2 HP motor you would need a 10 amp fuse. :)
(b) If you protect the motor with a motor starter and the starter list the maximum short-circuit protection as a 10 amp fuse, can you still use the 15 amp breaker in lieu of the fuse.
 
augie47 said:
While you are contemplating such things.....
(a) If you use a dual-element to protect the same 1/2 HP motor you would need a 10 amp fuse. :)
(b) If you protect the motor with a motor starter and the starter list the maximum short-circuit protection as a 10 amp fuse, can you still use the 15 amp breaker in lieu of the fuse.
Click to expand...

now your confusing me..
(but then again that's not hard to do)

lieu?

I once knew a lieu, he had an eye like this

(Totally respectful to people with eyes like this)
 
Webster:

lieu

/lu/ Show Spelled [loo] Show IPA
noun 1. place; stead.


Idioms 2. in lieu of, in place of; instead of: He gave us an IOU in lieu of cash

I thought you friend was Igor (or Egor, depending) !:D
 
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