1/4hp motor

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hhsting

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I have 1/4 hp 120V single phase lab exhaust fan motor direct connect on dedicated circuit with 20A breaker. The drawings say to provide thermal overload protection.

I dont see where in NEC 2017 it says where overload is not provided the breaker should be sized for overload? I dont also see where breaker can be sized 20A breaker either?
 
In the beginning of article 430 it says to use the tables not the nameplate to determine the motor ampacity.
So your motor is in table 430.248, looks to be 5.8 Amps
Then see Part IV of 430 and table 430.52 in particular.
For the overlaod see 430.32 (D) and (B)
 
tortuga said:
In the beginning of article 430 it says to use the tables not the nameplate to determine the motor ampacity.
So your motor is in table 430.248, looks to be 5.8 Amps
Then see Part IV of 430 and table 430.52 in particular.
For the overlaod see 430.32 (D) and (B)
Click to expand...

If thermal overload is not provided where does it say breaker need to size per thermal overload protection? U cant size the breaker based on short circuit and ground fault?
 
hhsting said:
If thermal overload is not provided where does it say breaker need to size per thermal overload protection? U cant size the breaker based on short circuit and ground fault?
Click to expand...
Why wouldn't you use an external overload device?
 
infinity said:
Why wouldn't you use an external overload device?
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All the plans are saying it provide thermal overload so i am assuming it is not factory install. However if no overload thermal is provided can the breaker act as both thermal overload and short circuit fault protection? Where it says in NEC 2017 section 430?
 
Every exhaust fan i have ever seen in 1/4 HP has protection thats either thermal or Integral with Motor.
If no overload is provided its sized per 430.33(B)(1)
 
hhsting said:
Can the breaker be sized 20A for 1/4 ho 120v motor dedicated direct connection only one motor?
Click to expand...
it depends on the motor, like I said every one I have ever seen has built in overload of some type, If the over load is provided 430.32 then yes.
 
hhsting said:
But if its not then what 430 section applies for sizing of breaker?
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2017 NEC said:
430.42 Motors on General-Purpose Branch Circuits. Overload protection for motors used on general-purpose branch circuits as permitted in Article 210 shall be provided as specified
in 430.42(A), (B), (C), or (D).
(A) Not over 1 Horsepower. One or more motors without individual overload protection shall be permitted to be connected
to a general-purpose branch circuit only where the installation
complies with the limiting conditions specified in 430.32(B) and
430.32(D) and 430.53(A)(1) and (A)(2).
Click to expand...

430.32 (B) is for One Horsepower or Less,
Automatically Started and or permanently Installed motors.
430.32(D) send you to 430.32 (B) if its a permanently Installed motor.
That gives you 4 options for the overload protection, none are the breaker.

Sorry I meant to reference 430.32(B)(1) in post# 6 where i typed 430.33
 
tortuga said:
430.32 (B) is for One Horsepower or Less,
Automatically Started and or permanently Installed motors.
430.32(D) send you to 430.32 (B) if its a permanently Installed motor.
That gives you 4 options for the overload protection, none are the breaker.

Sorry I meant to reference 430.32(B)(1) in post# 6 where i typed 430.33
Click to expand...

Ok but what section says breaker can be 20A? I see it minimum 15A even with thermal overload?


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hhsting said:
1/4hp 120V has FLA 5.8a. 5.8x2.5=14.5A next size is 15A???
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I was going to say 430.53 but then you said its on a dedicated circuit.
So without more info leading to the exceptions, yes that what I come up with.

hhsting your a inspector / plans reviewer right?
In my area the plans examiner would redline the motor and have the commercial electrical inspector verify it complies with article 430 in the field.

If thats not the way it works in your area perhaps inspectors are outsourced / private underwriters, then I think you need to request more info on this motor.
 
OK hold on well in post #10 technically I am wrong:
2017 NEC said:
430.55 Combined Overcurrent Protection. Motor branch circuit short-circuit and ground-fault protection and motor over-
load protection shall be permitted to be combined in a single protective device where the rating or setting of the device provides the overload protection specified in 430.32.
Click to expand...

If you for some reason had a very old motor with no overload built in, and say it was connected to a very old fuse box, they might have used a
8 amp Edison fuse to protect the motor. As you still end up back at
430.32(A)(1).

But this is just a old historical fact in late 2021.
 
tortuga said:
OK hold on well in post #10 technically I am wrong:


If you for some reason had a very old motor with no overload built in, and say it was connected to a very old fuse box, they might have used a
8 amp Edison fuse to protect the motor. As you still end up back at
430.32(A)(1).

But this is just a old historical fact in late 2021.
Click to expand...

Alright but lets say thermal overload protection IS provided then i still dont see how 20A breaker as short circuit fault protection is good for 1/4 HP 120V single phase?
 
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