Origination of40 degree C

Status
Not open for further replies.

bjkenlx

Member
Location
Eatontown, NJ
We are trying to find the origination of the 40 degree C used in electrical equipment.

We have been asked by a client where this came from.

Any thoughts?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You mean as it relates to the ambient temperature used in testing electrical equipment?

Welcome to the forum.
 

bjkenlx

Member
Location
Eatontown, NJ
You mean as it relates to the ambient temperature used in testing electrical equipment?

Welcome to the forum.

I am looking for the origin for the "40 oC maximum ambient" that we all use in temperature calculations for items such as transformers.

Another question, i am listed as a Junior Member, how do I become a Member?

Thanks for your help.

Ken Lennox
 

stew

Senior Member
the 40 c rating is mostly shown on electric motors. It is the ambient at which the motor can safely be operated at full horsepower continously without exceeding whatever the temperature rating of the motors insulation system is. In other words adding the ambient of 40 deg c to the heat of the motor itself and you get the temperature at which the motor can be operated full hp cont.Its also shown as 40 degree c rise. This is essentially the same operating in a higher ambient with a totall rise above ambient of 40 deg c. This standard was developed I think around 1940 when doulble coated magnet wire was introduced to replace enamel covered wire.
 

zog

Senior Member
Location
Charlotte, NC
I am looking for the origin for the "40 oC maximum ambient" that we all use in temperature calculations for items such as transformers.

Another question, i am listed as a Junior Member, how do I become a Member?

Thanks for your help.

Ken Lennox

Transformer tempature ratings are listed as "max rise" above ambient, in order to not exceed the max temp rating of the insulation the max ambient should not be exceeded. There are 2 concerns, rise, which leads to uneven expansion from the ineer and outer part of the coils, and max temp which can damage the insulation. (That is the cliff notes version)
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Yes, that is what I am asking.

Where did the 40 degree C come from.

why did they pick the 40 degree C or who picked it?
Temperature ratings of equipment is basically an economic compromise: cost increases exponentially with temperature.

But I don't know if the definitive answer is discoverable any longer, it's a very very old specification. Most likely it stems from a Centigrade equivalent to 100F since that is a nice round number that would be indicative of a non-residential temperature. In other words if you were making something to be used indoors in habitable spaces, most likely the ambient temperature would not be over 100F very often. But if you rated a piece of electrical equipment for 75F (around 25C), there is a high likelihood that ambient would be exceeded on a regular basis. If you designed everything residential for 50C or 60C (122F and 140F), as a lot of industrial equipment is, then the cost would be exponentially higher and unaffordable to the greatest number of consumers.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
In 1904 the NEC used an ambient temperature of 25?C (yes they used ?C just like they do now).
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
To the best of my knowledge the following is true.......

ASHRAE has selected 40 deg C as the temp most closely corresponding to the maximum average ambient temperature for most of the US.

ANSI/IEEE and NEMA have used this as a baseline and standardization for equipment design because the impact of solar radiation varies by geographic location, degree of exposure to sunlight, time of day, and season. It would not be economical to design electrical equipment with custom ratings to correspond with a particular set of solar radiation conditions. For similar reasons, it is usually not appropriate to design for all the other influences to simultaneously fall into their most adverse ranges, e.g., maximum ambient, highest load current, maximum solar radiation, or zero wind.

Therefore, it becomes the responsibility of the designer to understand and determine appropriate solar radiation correction factors for the particular installation.
 

bjkenlx

Member
Location
Eatontown, NJ
To the best of my knowledge the following is true.......

ASHRAE has selected 40 deg C as the temp most closely corresponding to the maximum average ambient temperature for most of the US.

ANSI/IEEE and NEMA have used this as a baseline and standardization for equipment design because the impact of solar radiation varies by geographic location, degree of exposure to sunlight, time of day, and season. It would not be economical to design electrical equipment with custom ratings to correspond with a particular set of solar radiation conditions. For similar reasons, it is usually not appropriate to design for all the other influences to simultaneously fall into their most adverse ranges, e.g., maximum ambient, highest load current, maximum solar radiation, or zero wind.

Therefore, it becomes the responsibility of the designer to understand and determine appropriate solar radiation correction factors for the particular installation.


Thanks for this information. It is the best answer I have received so far.

Ken (bjkenlx)
 
Status
Not open for further replies.
Top