You are allowed to interpolate if the nameplate only provides FLA and not HP.
430.6(A)(1) in part said:
RFI the engineer and request HP rating or cutsheet for motor/equipment. He should understand if he is worth his beans.
I need help with a complex calculation
- Thread starter Huntxtrm
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RFI the engineer and request HP rating or cutsheet for motor/equipment. He should understand if he is worth his beans.
Interpolate? Does that mean, closest larger amp rating listed? Not in the current dictionary filed in my brain.
OK, it's reworked. Now is everything cool?
o 50,000sqft warehouse
o 1,000 office within warehouse
o No HVAC
o Receptacle count Unknown
o 10 hp pump 460v 14.2 amps (Name Plate)
o 10 hp pump 460V 11.5 amps (Name Plate)
o 5 hp compressor 460v
o 28 hp pump 460 v 35 amps (Name Plate)
o 100 hp compressor 460v 180 amps (Name Plate)
o 100 hp back up compressor 460v (non coincidalwith above)
o Blower 460v 78amps (Name Plate)
o Vacuum 460v 50amps (Name Plate)
o Control compressor 460v 5hp
o Waste Blower 5hp 5.72amps (name Plate), 460v
o Dryer 110v 1amp
o Tank 110v 1 amp
o Filter 110v 1 amp
o Dryer 110v 1 amp
o 120v 20amp circuit for computer
o 120v 20amp circuit for Scale monitors
o 120v 20amp circuit for LV power supply
None of the motors are continuous.o 1,000 office within warehouse
o No HVAC
o Receptacle count Unknown
o 10 hp pump 460v 14.2 amps (Name Plate)
o 10 hp pump 460V 11.5 amps (Name Plate)
o 5 hp compressor 460v
o 28 hp pump 460 v 35 amps (Name Plate)
o 100 hp compressor 460v 180 amps (Name Plate)
o 100 hp back up compressor 460v (non coincidalwith above)
o Blower 460v 78amps (Name Plate)
o Vacuum 460v 50amps (Name Plate)
o Control compressor 460v 5hp
o Waste Blower 5hp 5.72amps (name Plate), 460v
o Dryer 110v 1amp
o Tank 110v 1 amp
o Filter 110v 1 amp
o Dryer 110v 1 amp
o 120v 20amp circuit for computer
o 120v 20amp circuit for Scale monitors
o 120v 20amp circuit for LV power supply
lighting load:
warehouse 49,000sqft x .25 = 12250 va (from table220.12) x 1.25 for continuous = 15312 va 1st 12500 @ 100%, 50% there after(Table 220.42) = 12500 +(2812.5 *. .5) = 13906.25 va
Office 1000 sqft x 3.5 = 3500 va (from table 220.12) x 1.25 forcontinuous = 4375 va
Receptacle Load:
Office 1,000 sqft x 1va = 1000va (220.14k2) 1st 10kva @ 100%(Table 220.14) x 1.25 for continuous = 1250 va
Motor Loads:
1. 10 hppump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
2. 10 hp pump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
3. 5 hp compressor 480v x 7.6A (table 430.250) x 1.732 = 6,318va non-continuous
4. 28 hp pump 480v x 40A(table 430.250, 30hp) x 1.732 = 33,254 va non-continuous
5. 100 hp compressor 480v x 124A(table 430.250) x 1.732 = 143410 va x 1.25 (430.24) = 103,088va non-continuous
6. 100 hp backup compressor 480v x124A(table 430.250) x 1.732 = 103,088 va non-continuous, non-coincidalwith above, smaller of the 2 don?t count(220.60)
7. Blower 480v x 96A (T430.250) x 1.732 = 79,811va non continuous
8. Vacuum 480v x 52a(T430.250) x 1.732 = 43,230va non continuous
9. Waste Blower 480v x 7.6A(T430.250) (name Plate) x 1.732 = 4,557vanon continuous
10. 5 hp Compressor 480v x 7.6a(Table 430.250) x 1.732 = 6,318 vanon continuous
11. DesicantDryer 120v x 1A = 110va =180va (220.14L)x 1.25 (continuous)= 225va
12. Manchester Tank 120v x 1A = 110va =180va (220.14L) x 1.25 (continuous)= 225va
13. Oil filter 120v x 1A = 120va =180va(220.14L) x 1.25 (continuous)= 225va
14. Refrigerant Dryer 120v x 1A = 110va =180va(220.14L) x 1.25 (continuous)= 225va
15. Computer receptacles x 2 @180va each = 360vax 1.25 for continous = 450va
16. PLC power supply receptacle x 1 @ 180vax 1.25 for continous = 225va
17. Scale Monitor receptacles x 2 @ 180 va each x 1.25 for continous = 225va
Whichequals 321,185 VA
or 321kva.
321,185/(480 x 1.732) = 386 amps
So I would need an 800 amp rated panel board 480v
Main breaker size @ 600 amp
Actually, Iwould need a 400 amp panel breakered @ 400amps? But, I want to oversize.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Interpolate means to calculate an in-between value.
For example if 1/2 horse motor is X amps and a 1 horse motor is Y amps, then a 3/4 horse motor would (X+Y)/2 amps.
Or in this specific case, if a motor is X FLA and the the two motors on either side in the table are rated for X-Y amps and X+Y amps, then you can take the average of the two wire sizes or overcurrent devices or whatever from the table since your motor is assumed to be halfway in between.
Sometimes you are explicitlly allowed to interpolate, other times you must choose the larger value from a table.
Last edited:
Interpolate means to estimate a value between two known values.
IMO the interpolate clause is superflous and jsut outright "stupid". Even if you interpolate the HP rating, you still end up using the nameplate FLA. Say for instance you have a 460V 3? motor with a nameplate FLA of 37A and no HP rating. Interpolated, the motor would be 27.5HP... but in calculating you'd still use 37A as the FLA.
Simply put, you can use nameplate FLA but only if the nameplate has no HP rating.
Should have noted this earlier, but preoccupied :ashamed1:
A typical warehouse, as used in the NEC, IMO will not have all the processing equipment that you've listed. I don't believe using lighting load demand of 220.42 for warehouses is appropriate.
JMO...
Unless these are hardwired, just list these as "warehouse" receptacles (i.e. not office). The 125% factoring is unnecessary. For example:
Remember this is calculating the load, not a panel schedule.
Q: Are the computer receptacles for the "warehouse" and not the office?
All of the process equipment is outside, under an 20' x 30' awning. The warehouse area is just for storing bulk materials. I guess I should have mentioned that. Should I include the awning, in the calc?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I take back what I said. You are correct.
Computers are in the office. This equipment is outside as well. I am thinking, they could pe pigtailed to a receptacle, or hard wired. I will check into that.
IMO if the awning has general lighting installed, yes. Otherwise, no.
If computers are in the office part, they are part of the office receptacles already calculated by area. When you use 220.14(K)(2), it includes all the general-use receptacles, and that value must be larger than the total number of receptacles times a value not less than 180VA each. It would be a violation if you calculated by area because you do not know the number of receptacles, and after installation end up with a value greater than calculated by area.
As for the low-amperage, 120V loads. You need to decide whether they are going to be hardwired or receptacle connected. If hardwired, you may calculate at rated current times 125% for continuous operation. If receptacle connected, just omit from listing altogether and include as general-use receptacle load... and as noted, you do not factor general-use receptacles by 125%... just make sure the VA for number of receptacles exceeds the known receptacle-connected load times 125%.
Additionally, it makes a calculation easier to follow if you do not factor each listed load as continuous, or not, but rather keep continuous and non-continuous loads (and perhaps motor loads) separate, subtotal, then factor continuous at 125% en masse. See Annex D Examples.
Point taken. Thanks
Continuousloads
lighting loads:
warehouse 49,000sqft x .25 = 12250 va (from table220.12) x 1.25 for continuous = 15312 va 1st 12500 @ 100%, 50% there after(Table 220.42) = 12500 +(2812.5 *. .5) = 13906.25 va
Office 1000 sqft x 3.5 = 3500 va (from table 220.12) x 1.25 forcontinuous = 4375 va
Awning 600 sqft x 2 = 1200 va (from table 220.12) x 1.25 for continuous = 1500 va
Sum of continuous loads = 19781.25 x 1.25 forcontinuous = 24726.56 va
NonContinuous Loads
Office
NEC Calc 1,000 sqft x 1va = 1000va (220.14k2)Noderating applies.
Actual
Computerreceptacles x 2 @180va each = 360va
ScaleMonitor receptacles x 2 @ 180 va each = 360va
General usereceptacles x 4 @ 180va each = 720va
360va + 360va + 720va = 1440 va= 1440 va Largest of the 2 use this one.
Warehouse
PLC powersupply receptacle x 1 @ 180va
Scalemonitor receptacle x 2 @ 180va = 360va
General useReceptacles x 5 @ 180va = 900va
Awning
Receptacles for Dryers and tanks x 2 @ 180va= 360va
Totalof Non Continuous loads =
1440+180+360+900+360=
3240va(T220.44 for derating, less that 10kva @100%)= 3240va
Motor Loads:
1. 10 hppump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
2. 10 hp pump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
3. 5 hp compressor 480v x 7.6A (table 430.250) x 1.732 = 6,318va non-continuous
4. 28 hp pump 480v x 40A(table 430.250, 30hp) x 1.732 = 33,254 va non-continuous
5. 100 hp compressor 480v x 124A(table 430.250) x 1.732 = 143410 va x 1.25 (Largest motor430.24) = 103,088 va non-continuous
6. 100 hp backup compressor 480v x124A(table 430.250) x 1.732 = 103,088 va non-continuous, non-coincidalwith above, smaller of the 2 don?t count(220.60)
7. Blower 480v x 96A (T430.250) x 1.732 = 79,811va non continuous
8. Vacuum 480v x 52a(T430.250) x 1.732 = 43,230va non continuous
9. Waste Blower 480v x 7.6A(T430.250) (name Plate) x 1.732 = 4,557vanon continuous
10. 5 hp Compressor 480v x 7.6a(Table 430.250) x 1.732 = 6,318 vanon continuous
11. 10 hpAir wall, 480v x 14A(Table 430.250) x 1.732 = 11,639va
Total Motor loads Non Continuous = 311,493va
Total of all loads= 339,459va
Ok, this is what I have arrived at.
So, 339,459va/(480 x 1.732) = 408.31 amps
I would need an 600 amp rated panel? (is there something in the code book referencing standard panel board sizes? Like 240.6 does for breakers?)
450amp main
served by 600kcmil conductors (matched to load per 240.4c)
Or parralelled 4/0 conductors
*If I want to go big, Would i size my conductors, to my Main ocpd?
*Why do we not size the loads on the 120/208 side to a panel, then to a transformer, Then use the transformer in the service calc instead. Instead of calculating them all together?
lighting loads:
warehouse 49,000sqft x .25 = 12250 va (from table220.12) x 1.25 for continuous = 15312 va 1st 12500 @ 100%, 50% there after(Table 220.42) = 12500 +(2812.5 *. .5) = 13906.25 va
Office 1000 sqft x 3.5 = 3500 va (from table 220.12) x 1.25 forcontinuous = 4375 va
Awning 600 sqft x 2 = 1200 va (from table 220.12) x 1.25 for continuous = 1500 va
Sum of continuous loads = 19781.25 x 1.25 forcontinuous = 24726.56 va
NonContinuous Loads
Office
NEC Calc 1,000 sqft x 1va = 1000va (220.14k2)Noderating applies.
Actual
Computerreceptacles x 2 @180va each = 360va
ScaleMonitor receptacles x 2 @ 180 va each = 360va
General usereceptacles x 4 @ 180va each = 720va
360va + 360va + 720va = 1440 va= 1440 va Largest of the 2 use this one.
Warehouse
PLC powersupply receptacle x 1 @ 180va
Scalemonitor receptacle x 2 @ 180va = 360va
General useReceptacles x 5 @ 180va = 900va
Awning
Receptacles for Dryers and tanks x 2 @ 180va= 360va
Totalof Non Continuous loads =
1440+180+360+900+360=
3240va(T220.44 for derating, less that 10kva @100%)= 3240va
Motor Loads:
1. 10 hppump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
2. 10 hp pump 480v x 14A (table 430.250) x 1.732 = 11,639 va non-continuous
3. 5 hp compressor 480v x 7.6A (table 430.250) x 1.732 = 6,318va non-continuous
4. 28 hp pump 480v x 40A(table 430.250, 30hp) x 1.732 = 33,254 va non-continuous
5. 100 hp compressor 480v x 124A(table 430.250) x 1.732 = 143410 va x 1.25 (Largest motor430.24) = 103,088 va non-continuous
6. 100 hp backup compressor 480v x124A(table 430.250) x 1.732 = 103,088 va non-continuous, non-coincidalwith above, smaller of the 2 don?t count(220.60)
7. Blower 480v x 96A (T430.250) x 1.732 = 79,811va non continuous
8. Vacuum 480v x 52a(T430.250) x 1.732 = 43,230va non continuous
9. Waste Blower 480v x 7.6A(T430.250) (name Plate) x 1.732 = 4,557vanon continuous
10. 5 hp Compressor 480v x 7.6a(Table 430.250) x 1.732 = 6,318 vanon continuous
11. 10 hpAir wall, 480v x 14A(Table 430.250) x 1.732 = 11,639va
Total Motor loads Non Continuous = 311,493va
Total of all loads= 339,459va
Ok, this is what I have arrived at.
So, 339,459va/(480 x 1.732) = 408.31 amps
I would need an 600 amp rated panel? (is there something in the code book referencing standard panel board sizes? Like 240.6 does for breakers?)
450amp main
served by 600kcmil conductors (matched to load per 240.4c)
Or parralelled 4/0 conductors
*If I want to go big, Would i size my conductors, to my Main ocpd?
*Why do we not size the loads on the 120/208 side to a panel, then to a transformer, Then use the transformer in the service calc instead. Instead of calculating them all together?
You multiplied load by 125% prior to applying demand, then applied 125% to the subtotal, which doubles 125% factoring... more later.
It appears you forgot to multiply by sqrt(3).... should be 6,319 VA
No.
Yes. Concerning service conductors (or taps thereto), the OCPD must not exceed their ampacity.
Don't know... just the way it is done, as demonstrated in the examples, though I don't recall any example as including a stepdown transformer. I don't believe there is anything which prevents you from doing it the way you suggest, as long as the transformer load is equal or greater than the supplied secondary loads (as calculated separately).
I took the liberty of visually cleaning up your calculation and correcting the couple errors noted above. It seems that those corrections don't make up for the overall difference... so you may want to check double check yours and my cal's....
The Excel file is embedded in the attached Word file... I can never get the forum to upload my .xls files.
You multiplied load by 125% prior to applying demand, then applied 125% to the subtotal, which doubles 125% factoring... more later.
I see where I went wrong. I did it twice. I should only factor for continous after I do the initial demand, correct. But only for OCPD sizing, right?
It appears you forgot to multiply by sqrt(3).... should be 6,319 VA
I must have fat fingered something.
No.
Figures, any suggestions?
Yes. Concerning service conductors (or taps thereto), the OCPD must not exceed their ampacity.
Don't know... just the way it is done, as demonstrated in the examples, though I don't recall any example as including a stepdown transformer. I don't believe there is anything which prevents you from doing it the way you suggest, as long as the transformer load is equal or greater than the supplied secondary loads (as calculated separately).
I took the liberty of visually cleaning up your calculation and correcting the couple errors noted above. It seems that those corrections don't make up for the overall difference... so you may want to check double check yours and my cal's....
Thanks for doing this! It helps me to understand. I really appreciate you helping me out with this..
The Excel file is embedded in the attached Word file... I can never get the forum to upload my .xls files.
1
Point taken. Thanks again for the help.
View and/or download manufacturers' product literature.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You are not likely to find a 600 amp panel for "miniature" circuit breakers.
Something like Square D's I-line series would be no problem to find a 600 amp panel.
I am using I line as a matter of fact. That is what my supplier carries. I think I have this much ironed out. I am going to move on to motors, I think. I will start with conductor sizing and conduit, then move on to overloads. I will post on this hopefully tomorrow evening. I have a Plc cab to terminate tomorrow. If I get done early enough. I really appreciate the good help guys! It's good practice also.
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