40 Degree C...Is it just ambient temperature?

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ibew441dc

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It is very common to see a smaller motor....say 5 HP or less to have an ambient temperature rating of 40*C (104*F).

But what is the maximum operating temperature rating of the motor? If I used a temp gun an shot a motor and it said it was 90*F, Is that too hot (It is very hot to the touch).

Or is 104*F the hottest the motor can get without starting to break down?
 
It is very common to see a smaller motor....say 5 HP or less to have an ambient temperature rating of 40*C (104*F).

But what is the maximum operating temperature rating of the motor? If I used a temp gun an shot a motor and it said it was 90*F, Is that too hot (It is very hot to the touch).

Or is 104*F the hottest the motor can get without starting to break down?

am⋅bi⋅ent

 /ˈ?m
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bi
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ənt/ Show Spelled Pronunciation [am-bee-uh
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Use ambient in a Sentence

?adjective



1.of the surrounding area or environment: The tape recorder picked up too many ambient noises. The temperature in the display case was 20? lower than the ambient temperature.



So the 'ambient' does not refer to the temperature of the motor but to the maximum surrounding temperature in which the motor is designed to operate. The maximum temperature reached by the motor depends on the ambient temperature, the load of the motor, the insulation material used on the winding and the motor design. There are different insualting materials that have a target maximum design temperature. The design ususally stays well below that. Class A is 105C*, B is 130C*, H is 155C* and F is 180C*. These are the maximum operating temperatures, so the lower the ambient temperature, the mor load the motor can take, thermally.

There is a great difference between manufacturers.

Of eight 20HP motors from different manufacturers, built to IEEE841 specifications, the actual temperature rise varied between 46C* to 69C*.
 

ibew441dc

Senior Member
am⋅bi⋅ent

 /ˈ?m
thinsp.png
bi
thinsp.png
ənt/ Show Spelled Pronunciation [am-bee-uh
thinsp.png
nt] Show IPA

Use ambient in a Sentence

?adjective



1.of the surrounding area or environment: The tape recorder picked up too many ambient noises. The temperature in the display case was 20? lower than the ambient temperature.



So the 'ambient' does not refer to the temperature of the motor but to the maximum surrounding temperature in which the motor is designed to operate. The maximum temperature reached by the motor depends on the ambient temperature, the load of the motor, the insulation material used on the winding and the motor design. There are different insualting materials that have a target maximum design temperature. The design ususally stays well below that. Class A is 105C*, B is 130C*, H is 155C* and F is 180C*. These are the maximum operating temperatures, so the lower the ambient temperature, the mor load the motor can take, thermally.

There is a great difference between manufacturers.

Of eight 20HP motors from different manufacturers, built to IEEE841 specifications, the actual temperature rise varied between 46C* to 69C*.

I get the ambient part...I'm just a little confused as to how one is to determine the worst case scenario max temp rating of a motor....
 

rbalex

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Go to this webpage: http://www.nema.org/stds/ and search by TITLE for: Condensed MG 1. You will be rewarded with a link to a free download. Check Section 9.8, pg 21 and Table 38, pg 57. Note the rise is based on a 40C ambient.

You may have to sign-up for an account. BTW, many NEMA Standards are available for free.

UL does NOT have such a standard for common motors because they are not listed.
 
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Go to this webpage: http://www.nema.org/stds/ and search by TITLE for: Condensed MG 1. You will be rewarded with a link to a free download. Check Section 9.8, pg 21 and Table 38, pg 57. Note the rise is based on a 40C ambient.

You may have to sign-up for an account. BTW, many NEMA Standards are available for free.

UL does NOT have such a standard for common motors because they are not listed.

The OP question: "But what is the maximum operating temperature rating of the motor? If I used a temp gun an shot a motor and it said it was 90*F, Is that too hot (It is very hot to the touch)." can not be answered as I tried to explain it in my original response to him. There is NO standard that will limit how hot the external surface can get. The limits of physics, the motor design and the insulation class will define an upper limit, the lower limit is defined by the ambient - at standstill - but where the actual surface temperature will be at any given load is undefined.

MG-1 does not contain any more information on the temperature issue than the Smart$ posted link does. It does not - because it can not - tell you how hot the motor surface temperature will be, or even what the winding temperature will be as it varies by manufacturer, type and design. Only the manufacturer can tell you this and it will be within certain manufacturing tolerance limits.

One thing puzzles me though. OSHA has a definition of maximum surface temperature (140*F?) that an employee can be subjected to touch. Equipment operating above that level is supposed to be guarded. It seems to me that many motors, especially the high efficiency ones exceed that temperature, yet the manufacturer does not give warning in the OM's.
 

Besoeker

Senior Member
Location
UK
It is very common to see a smaller motor....say 5 HP or less to have an ambient temperature rating of 40*C (104*F).

But what is the maximum operating temperature rating of the motor? If I used a temp gun an shot a motor and it said it was 90*F, Is that too hot (It is very hot to the touch).

Or is 104*F the hottest the motor can get without starting to break down?

40C ambient isn't all that uncommon for larger motors also.
The 40C refers to the maximum ambient temperature in which the motor can be run at rated load. The surface temperature that you measure would generally be higher than the ambient. How much depends on the motor design, particularly ventillation and cooling - how waste heat is removed.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Your point is well taken; I was just validating Smart $'s assertion that such a product standard exists (NEMA MG-1) and that the link's information was consistent with it.

There are fundamentally two approachs to establish a temperature rating: a stated absolute maximum temperature or a stated temperature rise over a specified ambient - which still ultimately leads to an absolute maximum. (See NEMA MG-1 Condensed, Table 38, note 3)

As the link notes, the laws of physics prohibit the enclosure surface temperature from exceeding the internal temperatures; but, as you pointed out, there are still too many other varibles, to conclusively state what it will be - even if you knew exactly what the internal maximums were.
 
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