sizing overloads and fuses

[mcalidl]

I am a young engineer and have a simple question. I am putting a 6KW 3 phase 480 v heater on a size 1 starter. I know this will work on a size 0 but that is not very common around here. I have a question about properly fusing and setting the overloads. What size and how do I go about figuring this out. Which one is instantaneous and which is time delay?

 

[nonuke]

Take a look at the table bellow. You can also find lots of other useful information.

http://www.wiringmanual.com/norm040.html

 

[allscott]

Find yourself a copy of the US electrical code (sorry I don't have one in front of me). Overloads are for motors, you need branch circuit protection for a heater.

You can calculate the current for the heater using the formula.

P=Sqrt3 * EL * IL

IL= 7.3A

Follow the code from there

 

[rsdoran]

I do believe he was refering to heater as in an overload "heater element" that is used with a motor starter. http://www.ab.com/en/epub/catalogs/12768/229240/229248/3005006/3178797/229411/

That page will provide info on heater elements and the class. The type, class, etc will depend on what is needed.

 

[allscott]

I do believe he was refering to heater as in an overload "heater element" that is used with a motor starter. http://www.ab.com/en/epub/catalogs/12768/229240/229248/3005006/3178797/229411/

That page will provide info on heater elements and the class. The type, class, etc will depend on what is needed.

Woops, your probably right, nevermind..........

 

[milldrone]

The way the question was asked it could go either way. Ron might have the regional dialect advantage.

 

[rsdoran]

I am a young engineer and have a simple question. I am putting a 6KW 3 phase 480 v heater on a size 1 starter. I know this will work on a size 0 but that is not very common around here. I have a question about properly fusing and setting the overloads. What size and how do I go about figuring this out. Which one is instantaneous and which is time delay?

I do not know about regional dialect but the OP did state size 1 starter; which usually references NEMA motor starters and heaters are a common term for the overload elements. There can be crossover points between starter sizes but all should be relevant to the motors FLA and class for the overload protection.

 

[stasis]

I am a young engineer and have a simple question. I am putting a 6KW 3 phase 480 v heater on a size 1 starter. I know this will work on a size 0 but that is not very common around here. I have a question about properly fusing and setting the overloads. What size and how do I go about figuring this out. Which one is instantaneous and which is time delay?

all of the info requested is calculated using the motor nameplate data. The overload may fit physically, but to be properly 'sized' is another matter. The FLA of the motor will determine the size of fuses & overloads required. Instantaneous & time delay uses are as diferent as manuacturers.

 

[rsdoran]

all of the info requested is calculated using the motor nameplate data. The overload may fit physically, but to be properly 'sized' is another matter. The FLA of the motor will determine the size of fuses & overloads required. Instantaneous & time delay uses are as diferent as manuacturers.

Part of that was not exactly right.

Anyway take a look at this: http://www.mikeholt.com/mojonewsarchive/EC-HTML/HTML/Motor_Calculations_-_Part_1~20030303.htm