another help to understand

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aes92000

Member
Location
Katy, Texas
QUESTION
92. Determine the MAXIMUMsize overload protection required for a 480-volt, 3-phase, 15 hp,continuous-duty ac motor, where given the following related information. Assumethe value you select will permit the overload device to carry the motor loadand modification of this value is not required.

* Design C
* temperature rise - 40 deg.C
* service factor - 1.12
* nameplate ampere rating -18 amperes

A. 20.7 amperes
B. 18.0 amperes
C. 22.5 amperes
D. 23.4 amperes
ANSWER
92. A -For general motor applications, in compliance withSection 430.6(A)(2), the
ampere rating provided on the motor nameplate is used tosize the overload
protective devices intended to protect the motor. Section430.32(A)(1)
indicates where the motor has a service factor of lessthan 1.15, the rating or
setting of the overload protective device is to be notmore than the motors
nameplate ampere rating:
Motor nameplate FLA = 18 amperes x 115% = 20.7 amperes


according to Section 430.32(A)(1), I used the nameplate 18A with 40C at 125% to reach my answer of 22.5
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
aes92000 said:
QUESTION
92. Determine the MAXIMUMsize overload protection required for a 480-volt, 3-phase, 15 hp,continuous-duty ac motor, where given the following related information. Assumethe value you select will permit the overload device to carry the motor loadand modification of this value is not required.

* Design C
* temperature rise - 40 deg.C
* service factor - 1.12
* nameplate ampere rating -18 amperes

A. 20.7 amperes
B. 18.0 amperes
C. 22.5 amperes
D. 23.4 amperes
ANSWER
92. A -For general motor applications, in compliance withSection 430.6(A)(2), the
ampere rating provided on the motor nameplate is used tosize the overload
protective devices intended to protect the motor. Section430.32(A)(1)
indicates where the motor has a service factor of lessthan 1.15, the rating or
setting of the overload protective device is to be notmore than the motors
nameplate ampere rating:
Motor nameplate FLA = 18 amperes x 115% = 20.7 amperes


according to Section 430.32(A)(1), I used the nameplate 18A with 40C at 125% to reach my answer of 22.5
Click to expand...

I am inclined to agree with your interpretation.
The issue is whether the language of the section should be interpreted that both conditions must be satisfied to get the 125% value, or if either one by itself is enough. Based on normal English grammar and normal use of tables, this should be an OR condition, and your answer would be right. But although the same thing was discussed on an earlier thread here, I am not sure whether there was a clear consensus on the meaning.
If AND were intended, it would have been simpler and clearer to have one row in the table which said, in effect, "motors..... and ......" 125%
 
kwired

kwired

Electron manager
Location
NE Nebraska
aes92000 said:
QUESTION
92. Determine the MAXIMUMsize overload protection required for a 480-volt, 3-phase, 15 hp,continuous-duty ac motor, where given the following related information. Assumethe value you select will permit the overload device to carry the motor loadand modification of this value is not required.

* Design C
* temperature rise - 40 deg.C
* service factor - 1.12
* nameplate ampere rating -18 amperes

A. 20.7 amperes
B. 18.0 amperes
C. 22.5 amperes
D. 23.4 amperes
ANSWER
92. A -For general motor applications, in compliance withSection 430.6(A)(2), the
ampere rating provided on the motor nameplate is used tosize the overload
protective devices intended to protect the motor. Section430.32(A)(1)
indicates where the motor has a service factor of lessthan 1.15, the rating or
setting of the overload protective device is to be notmore than the motors
nameplate ampere rating:
Motor nameplate FLA = 18 amperes x 115% = 20.7 amperes


according to Section 430.32(A)(1), I used the nameplate 18A with 40C at 125% to reach my answer of 22.5
Click to expand...
The answer explains that the service factor is less than 1.15 and therefore you must use 115% instead of 125%. But nameplate also says the motor is 40C or less rise. Nothing in 430.32(A)(1) says you must meet either or both conditions to use the 125% - I still think 125% is allowed to be used in this case.
 
Sahib

Sahib

Senior Member
Location
India
May we say over load protection of motor at 115% as close over load protection and at 125% as coarse over load protection? :)
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Sahib said:
May we say over load protection of motor at 115% as close over load protection and at 125% as coarse over load protection? :)
Click to expand...

No, since the code does not distinguish the two. The maximum allowed will be one or the other, following the (unclear) rule, and anything beyond that is design.
 
Rewire

Rewire

Senior Member
Location
Lake of the Ozarks
aes92000 said:
QUESTION
92. Determine the MAXIMUMsize overload protection required for a 480-volt, 3-phase, 15 hp,continuous-duty ac motor, where given the following related information. Assumethe value you select will permit the overload device to carry the motor loadand modification of this value is not required.

* Design C
* temperature rise - 40 deg.C
* service factor - 1.12
* nameplate ampere rating -18 amperes

A. 20.7 amperes
B. 18.0 amperes
C. 22.5 amperes
D. 23.4 amperes
ANSWER
92. A -For general motor applications, in compliance withSection 430.6(A)(2), the
ampere rating provided on the motor nameplate is used tosize the overload
protective devices intended to protect the motor. Section430.32(A)(1)
indicates where the motor has a service factor of lessthan 1.15, the rating or
setting of the overload protective device is to be notmore than the motors
nameplate ampere rating:
Motor nameplate FLA = 18 amperes x 115% = 20.7 amperes


according to Section 430.32(A)(1), I used the nameplate 18A with 40C at 125% to reach my answer of 22.5
Click to expand...

20.7 A is the correct answer. An instructor told me along time ago that it does not matter how many times you get yes in the code because one "no" trumps all.
A motor needs to have a service rating of 1.15 or larger to size at 125% this motor does not, no trumps .
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Rewire said:
20.7 A is the correct answer. An instructor told me along time ago that it does not matter how many times you get yes in the code because one "no" trumps all.
A motor needs to have a service rating of 1.15 or larger to size at 125% this motor does not, no trumps .
Click to expand...

That assumes that you can be sure that 125% is YES and 115% is NO. Not obvious to me.
Other places in the code state it clearly as "one of..." or "all of..." The rule you suggest does not seem natural when applied to a table. With a table normal process is to stop when you find a match instead of proceeding row by row until you get to "other".
(Ridiculous example: when you look at wire types in wiring methods, do you require that a wire type match all of the entries that include "wet conditions" before you can use it for wet conditions?)

Has the CMP said anything that might clarify this?
 
K8MHZ

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Rewire said:
20.7 A is the correct answer. An instructor told me along time ago that it does not matter how many times you get yes in the code because one "no" trumps all.
A motor needs to have a service rating of 1.15 or larger to size at 125% this motor does not, no trumps .
Click to expand...

The question asks what is the maximum required.

The supposed answer gives the maximum allowed.

Section430.32(A)(1)
indicates where the motor has a service factor of less than 1.15, the rating or
setting of the overload protective device is to be not more than the motors
nameplate ampere rating:
Click to expand...

Which is also confusing, because the motor's ampere rating is 18. Where does it say you are to use the service factor?
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
K8MHZ said:
Where does it say you are to use the service factor?
Click to expand...

Look at the 2011 code:

(1) Separate Overload Device. A separate overload device that is responsive to motor current. This device shall be se- lected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating:
Click to expand...
Which points to the table based on temp rating and service factor that we have been agonizing about. The table has options for 125% and 115%.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Rewire said:
20.7 A is the correct answer. An instructor told me along time ago that it does not matter how many times you get yes in the code because one "no" trumps all.
A motor needs to have a service rating of 1.15 or larger to size at 125% this motor does not, no trumps .
Click to expand...
Read 430.32(A)(1) again.

First condition mentioned - Motors with a marked service factor 1.15 or greater - False, can't use this one.

Second condition mentioned - Motors with a marked temperature rise 40?C or less - True, 125% may be applied.

Third condition mentioned - All other motors - False, if either of the first two conditions is true then "all other motors would be false, this condition does not apply, but using 115% is not a violation either.

Nothing there says that both the first two conditions must be true to use the 125%.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The CMP had an opportunity in their action on a 2002 code proposal to clear this up, but they didn't, however their comment indicated that the 40C part of the rule is for use with motors that do not have a service factor shown on the motor nameplate.

Their lack of action lets you use the 125% value if the motor has a service factor of 1.15 or greater or if the motor has a temperature rise of 40?C or less.
 
Rewire

Rewire

Senior Member
Location
Lake of the Ozarks
kwired said:
Read 430.32(A)(1) again.

First condition mentioned - Motors with a marked service factor 1.15 or greater - False, can't use this one.

Second condition mentioned - Motors with a marked temperature rise 40?C or less - True, 125% may be applied.

Third condition mentioned - All other motors - False, if either of the first two conditions is true then "all other motors would be false, this condition does not apply, but using 115% is not a violation either.

Nothing there says that both the first two conditions must be true to use the 125%.
Click to expand...

I would apply the "why" factor. Why would I NOT be allowed to use 125% on a motor marked with a service factor less than 1.15 ?
 
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