# How To Judge the Rated Power Tolerance Of Electric Heaters

Rated power is the most important parameter of an industrial electric heater, usually we will make the corresponding power according to customer requirements.
But in the production process it will be a little deviation, which is normal. Then what is the the rated power tolerance? And how to calculate the error value? Some customers may be not clear.

According to “JB / T 2379-93 industrial electric heating pipe standard”, the deviation of the rated power is as follows:
In the case of sufficient heating, the rated power error value of the industrial heater shall not exceed the following range:
1, The electric heater rated power ≤100W : ± 10%;
2, The electric heater rated power ≥100W: +5% to -10%.
It should be noted that: when measuring the resistance, there is 10% coefficient of the difference between the cold resistance and thermal resistance.

Therefore, we had known the rated power tolerance range, we can calculate the rated power error value. Here we give you two examples:

Because when an industrial electric heater is finished, the resistance value is established, we can use the resistance meter to measure its resistance value. According to the resistance value to judge the rated power error value is within the range.
1, An electric heater power is 100W, voltage 220V.
Then the rated power error is 100 * (1 + 10%) = 110W and 100 * (1-10%) = 90W

And then according to the formula: voltage * voltage = power * resistance value
The resistance value = 220 * 220V / 110W = 440Ω and 220 * 220V / 90W = 538Ω

Finally check the measured resistance value is between 440Ω-538Ω or not
This way, you can determine the rated power error value is reasonable.

2, An Electric Heater power is 1000W, voltage 380V.
Because its rated power error is between + 5% and -10%
We can get: power = 1000 * (1 + 5%) = 1050W and 1000 * (1-10%) = 900W.

Then the resistance value = 380 * 380V / 1050W = 137.5Ω and 380 * 380V / 900W = 160.4Ω.

Finally you can check if the resistance value is between 137.5Ω- 1160.4Ω or not.

Through the above calculation, can you we determine the rated power error value now? 