Maximum Conductor / OCPD Rating
Maximum Conductor / OCPD Rating
(OP)
This is probably a silly question, but I am curious if someone can provide me a definitive code reference for the following situation:
Branch-circuit load of 70A continuous (type of load not listed in 240.3).
Per 210.19, ampacity of conductors sized to 125% of continuous load (no ampacity adjustments applicable) / 70A * 1.25 = 87.5A.
Per 210.20, overcurrent protection shall not be less than 125% of continuous load / 70A * 1.25 = 87.5A.
Is there a specific code reference that defines the maximum size of conductors and OCPDs utilized?
My contention is that such a reference does not exist and that obvious factors affecting the maximum conductor / OCPD would be:
- Cost
- Lugs
- Load Requirements
- Equipment Damage Curves
Am I missing something here????
Branch-circuit load of 70A continuous (type of load not listed in 240.3).
Per 210.19, ampacity of conductors sized to 125% of continuous load (no ampacity adjustments applicable) / 70A * 1.25 = 87.5A.
Per 210.20, overcurrent protection shall not be less than 125% of continuous load / 70A * 1.25 = 87.5A.
Is there a specific code reference that defines the maximum size of conductors and OCPDs utilized?
My contention is that such a reference does not exist and that obvious factors affecting the maximum conductor / OCPD would be:
- Cost
- Lugs
- Load Requirements
- Equipment Damage Curves
Am I missing something here????






RE: Maximum Conductor / OCPD Rating
RE: Maximum Conductor / OCPD Rating
It is one thing to provide a say 200A service and equipment and 200A sized wiring and OCPD for a 70A calculated load. But you can not protect a 100A rated lighting panelboard with a 200A OCPD. Look up NEC articles on panelboad overcurrent protection.
Other instances, are: LV transformer primary OCDP are limited to 125% of rated current max. The motor branch circuit protection in 430-152 are also maximum limits.
Also most UL listed HVAC equipment have maximum OCPD size listed on its nameplate or instructions, which you can not exceed.
In general, NEC does not permit underprotection of equipment or it is not the intent.
RE: Maximum Conductor / OCPD Rating
Sorry if my earlier response created any confusion on this.
RE: Maximum Conductor / OCPD Rating
It seems to me that cost and lug requirements are the main factors governing maximum conductor and OCPD for non-listed equipment, not code.
RE: Maximum Conductor / OCPD Rating
What load you think are not "Code"?
RE: Maximum Conductor / OCPD Rating
RE: Maximum Conductor / OCPD Rating
RE: Maximum Conductor / OCPD Rating