Hello,
I work at a natural gas facility and have an existing feeder and panelboard that were originally undersized and have conductor and equipment damage due to overheating. I would like to check that I am not missing any code or design issues. The feeder is 240V 1PH, supplying a panelboard in an outbuilding that has a circuit for a 12kW immersion tank heater and two 20A circuits for a 1500W portable space heater on each circuit. Here are my calculations:
12kW heater / 240V = 50A x 125% (427.4 Continuous Load) = 62.5A
1500W heater / 120V = 12.5A x 125% = 15.625A x 2 heaters = 31.25A
Total calculated load = 93.75A
Equipment Rating will be at 75C, 100A
Existing 1 1/4" RMC, outside, some below ground
Planning on 3 - 3AWG THWN and 1 -8AWG (equipment grounding conductor), listed for wet location and good for 100A based on 310.15.(B)(16)
Wire size is good for 40% conduit fill based upon Article 344 and Table 5
No temperature or no. of conductor de-rating needed, feeder VD is 3.07%, total circuit VD is less than 5%
Do I need to move up to higher amperage equipment to have a maximum of 80% load? I have sized #1 and #2 wiring and these would still meet the 40% rule, my biggest concern is that app. 75' of conduit has been underground for approximately 20 years and I may not be able to pull the wiring through. I also don't see any additional load being applied as these circuits are only in use in the winter, any other use of the receptacle circuits would be in the summer.
Thank you,
Jim
I work at a natural gas facility and have an existing feeder and panelboard that were originally undersized and have conductor and equipment damage due to overheating. I would like to check that I am not missing any code or design issues. The feeder is 240V 1PH, supplying a panelboard in an outbuilding that has a circuit for a 12kW immersion tank heater and two 20A circuits for a 1500W portable space heater on each circuit. Here are my calculations:
12kW heater / 240V = 50A x 125% (427.4 Continuous Load) = 62.5A
1500W heater / 120V = 12.5A x 125% = 15.625A x 2 heaters = 31.25A
Total calculated load = 93.75A
Equipment Rating will be at 75C, 100A
Existing 1 1/4" RMC, outside, some below ground
Planning on 3 - 3AWG THWN and 1 -8AWG (equipment grounding conductor), listed for wet location and good for 100A based on 310.15.(B)(16)
Wire size is good for 40% conduit fill based upon Article 344 and Table 5
No temperature or no. of conductor de-rating needed, feeder VD is 3.07%, total circuit VD is less than 5%
Do I need to move up to higher amperage equipment to have a maximum of 80% load? I have sized #1 and #2 wiring and these would still meet the 40% rule, my biggest concern is that app. 75' of conduit has been underground for approximately 20 years and I may not be able to pull the wiring through. I also don't see any additional load being applied as these circuits are only in use in the winter, any other use of the receptacle circuits would be in the summer.
Thank you,
Jim