Mike Dolt Enterprises
Mike Dolt Enterprises
User: sw_ross, Location: NoDak
Asked on: Friday, January 31, 2025 at 9:35 am EST
Answered on: Thursday, March 6, 2025 at 8:04 am EST
Question: A local contractor has several Fostoria 15kW heaters that they use during the construction phase for temp heat in each structure (1 per structure).We’ve told them that the size of the heater is way overkill for the size of the structure. Anyways, they must have gotten a deal on them because they have a number of them. Amongst our company we are having discussions about the size of the OCPD.It’s obvious that it’s considered a continuous load so circuit size is based off 125% 210.19(A)(1). We set them up with #4awg SO cord. Our discussion is about the OCPD. The nameplate rating is stated as 62.5 amps, and in fact it pulls that amount of amps. One of our guys says that it should be protected by a 70 breaker (nameplate rating with next size up). Most of us think it should be an 80 amp breaker (62.5 x 125%=78 amps, next size up = 80 amps)?I’m looking for a code reference for the branch circuit OCPD being 125% of load for continuous load for a branch circuit (as opposed to the feeder size)? I’m sure it’s right in front of me as I look at the 2020 code book but can’t find it.Please help with reference…, thanks!
You're on the right track with your thinking! The key code section you're looking for is 210.20(A), which specifically addresses overcurrent protection for branch circuits. Let's break down why you need that 80 amp breaker
Understanding the Code
210.20 Overcurrent Protection
This section states that branch-circuit conductors and equipment shall be protected by an overcurrent protective device having a rating or setting that complies with 240.4
210.20(A) Continuous Loads
This is the critical part:"Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load."
Applying the Code to Your Situation1. Continuous Load
Your Fostoria heaters are used for temporary heat during construction, meaning they operate for extended periods. Therefore, they are considered continuous loads.2.
Calculating Minimum OCPD Size
Heater Load: 62.5 amps 125% of Continuous Load: 62.5 amps 1.25 = 78.125 amps Required OCPD Size: Since you can't have a 78.125 amp breaker, you must use the
next standard size up, according to 240.4(B), which is 80 amps.
The Code Supports the 80 Amp Breaker
The code clearly requires the OCPD to be rated for at least 125% of the continuous load. While the "next size up" rule is applied for the conductor, it is also applicable to the OCPD in this instance. Therefore, the 80 amp breaker is the correct choice to ensure both safety and code compliance.
Important Considerations
Conductor Ampacity
You've already addressed this by using #4 AWG SO cord, which should have sufficient ampacity for 62.5 amps, even with derating for temperature if necessary. Ensure the cord is rated for the environment and installation method.
NEMA Ratings: Ensure that the equipment and wiring method is appropriate for the environmental conditions.By using the 80 amp breaker, you are adhering to the NEC guidelines, and prioritize safety in this electrical installation. Flag for review