I understand that 125% of the largest motor (continuous) load plus 100% of the remaining motor loads must be accounted for in sizing a panelboard. Does the upstream panelboard feeding this panelboard need to read that largest motor load (in addition to it's own) and take 125% of the sum of the two largest motor loads, or does the upstream panelboard only care about it's own largest motor load?
Sub-fed largest motor load question
- Thread starter ICE Eng
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billsnuff
Senior Member
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- East of 480sparky
once you have done the load calc for the subpanel and provide ocp for it in the upstream panel, then that breaker is part of the total load for the upstream panel. i would not figure the motors on the subpanel twice. JMSO
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Here is an example. On ?upstream? Panel #1, you have five motors rated 1 HP each, and one motor rated 15 HP. This panel feeds ?downstream? Panel 2, which has five motors rated 2 HP each, and one motor rated 10 HP.
When you calculate the load on Panel 2, you take 100% of the load associated with the five 2 HP motors, and 125% of the load associated with the single 10 HP motor.
When you calculate the load on Panel 1, you take 100% of the load associated with the five 2 HP motors, plus 100% of the load associated with the single 10 HP motor, plus 100% of the load associated with the five 1 HP motors, and finally 125% of the load associated with the single 15 HP motor.
When you calculate the load on Panel 2, you take 100% of the load associated with the five 2 HP motors, and 125% of the load associated with the single 10 HP motor.
When you calculate the load on Panel 1, you take 100% of the load associated with the five 2 HP motors, plus 100% of the load associated with the single 10 HP motor, plus 100% of the load associated with the five 1 HP motors, and finally 125% of the load associated with the single 15 HP motor.
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