Feeder Calculation

[augie47]

ON your earlier question:
When calculating loads it's best to convert to kva.

water heater 4000w.240v = 4000 watt
Kitchen disposal 1/4hp.240v = Table 430.248 2.9 amps @ 230 = 667
Dishwasher 1200w.120v = 1200
Furnace motor 1/4hp.120v Table 430.248 5.8 @ 115 667
Attic fan 1/2hp.120v = Table 430.248 9.8 @ 115 1127
water pump 1/2hp.240v = Table 430.248 4.9 @ 230 1127
Based on 430.24 you must add 25% of largest motor 1127 X .25 282
Sub-Totaol 9070 watts

As Smart$ pointed out 220.53 allow you a demand factor of 75% for four or more appliances fastened in place.
There might be some debate/discussion as to which loads would qualify. IMO could incude all the items listed
so it possible (albeit debatable) that an adjusted calculation could be 6803 watts (9070 X .75)

 

[Jgonzalez]

Three Phase

Three Phase

You don't use 1.73 for single phase only for 3 phase motors

And of course your are right and I guess that's what had me confuse because I new 120/240v is single phase.
And 3 phase being 480 so would I take 480 X 8 amps X 1.73=6643X3=19929.6

 

[Dennis Alwon]

And of course your are right and I guess that's what had me confuse because I new 120/240v is single phase.
And 3 phase being 480 so would I take 480 X 8 amps X 1.73=6643X3=19929.6

That's correct for wattage.

 

[Jgonzalez]

Three Phase

Three Phase

ON your earlier question:
When calculating loads it's best to convert to kva.

water heater 4000w.240v = 4000 watt
Kitchen disposal 1/4hp.240v = Table 430.248 2.9 amps @ 230 = 667
Dishwasher 1200w.120v = 1200
Furnace motor 1/4hp.120v Table 430.248 5.8 @ 115 667
Attic fan 1/2hp.120v = Table 430.248 9.8 @ 115 1127
water pump 1/2hp.240v = Table 430.248 4.9 @ 230 1127
Based on 430.24 you must add 25% of largest motor 1127 X .25 282
Sub-Totaol 9070 watts

As Smart$ pointed out 220.53 allow you a demand factor of 75% for four or more appliances fastened in place.
There might be some debate/discussion as to which loads would qualify. IMO could incude all the items listed
so it possible (albeit debatable) that an adjusted calculation could be 6803 watts (9070 X .75)

I seen that on table 430.248 once you get your amps you use the volts that are on the table too.
But now that we have the total watts do I do like Augie did and take the watts and multiply by 250 to get the total amps or 2.50%

 

[Smart $]

And of course your are right and I guess that's what had me confuse because I new 120/240v is single phase.
And 3 phase being 480 so would I take 480 X 8 amps X 1.73=6643X3=19929.6

If the output is 480V, yes... but I get 19,953VA using the square root of 3.

What you have to grasp is the volt-ampere (VA) input cannot be less than the output VA. For the sake of a generic question, losses involved with the conversion process are generally ignored.

A_INPUT > 19,953VA ÷ 240V or 83A

455.6(A) will typically require an ampacity at 125%, so...

83A × 125% = 104A minimum

 

[Dennis Alwon]

I seen that on table 430.248 once you get your amps you use the volts that are on the table too.
But now that we have the total watts do I do like Augie did and take the watts and multiply by 250 to get the total amps or 2.50%

If you are just looking for wattage then you take the amps from Table 430.248 for single phase and multiply by the voltage.

Firstly it is 250% which is equivalent to 2.5 -- you have that info backwards. That 250% is to look for the size of the overcurrent protective device. If you are looking for the conductor size then you multiply the amps times 125% or 1.25. You don't multiply the wattage by any percent as that is what the wattage is for that motor, however, if you are doing a calculation then you take the largest motor and multiply by 125%.

 

[Jgonzalez]

Three Phase

Three Phase

That's correct for wattage.

I'm sorry Dennis but I'm still confuse we have single phase in the question but doing 3 phase calculations and its just messing with me a little bit.
I mean I get the math its just so many calculations and many different ways of doing it and it gets confusing.

 

[Jgonzalez]

feeder capcity

feeder capcity

If you are just looking for wattage then you take the amps from Table 430.248 for single phase and multiply by the voltage.

Firstly it is 250% which is equivalent to 2.5 -- you have that info backwards. That 250% is to look for the size of the overcurrent protective device. If you are looking for the conductor size then you multiply the amps times 125% or 1.25. You don't multiply the wattage by any percent as that is what the wattage is for that motor, however, if you are doing a calculation then you take the largest motor and multiply by 125%.

On the question it wants feeder needed for 120/240 so wouldn't that be total amps that its asking or watts or to be on the safe side couldn't I give watts and amps.

So the question says Determine the feeder capacity needed for a 120/240v

WH 4000w.240v=4000
KD 1/4hp.240v I go to table 430.248
2.9amps X 230v =667
DW 1200w.120v=1200
F.Fan 1/4hp.120v
5.8amps X 115v=667
A.Fan 1/2hp.120v
9.8amps X 115v=1127
W.P 1/2hp.240v
4.9amps X 230v=1127 X .25=282
total watts is 9070
So the question I have above is asking for watts not amps

 

[Jgonzalez]

Three Phase

Three Phase

If the output is 480V, yes... but I get 19,953VA using the square root of 3.

What you have to grasp is the volt-ampere (VA) input cannot be less than the output VA. For the sake of a generic question, losses involved with the conversion process are generally ignored.

A_INPUT > 19,953VA ÷ 240V or 83A

455.6(A) will typically require an ampacity at 125%, so...

83A × 125% = 104A minimum

480v X 8amps X 1.73=6643.2 X 3motors=19929.6 I did this a few times and come out with the same numbers.
And as far as the 480v I put that out because I know its 3 phase but it dose not have it in the question.

 

[Jgonzalez]

feeder capacity

feeder capacity

ON your earlier question:
When calculating loads it's best to convert to kva.

water heater 4000w.240v = 4000 watt
Kitchen disposal 1/4hp.240v = Table 430.248 2.9 amps @ 230 = 667
Dishwasher 1200w.120v = 1200
Furnace motor 1/4hp.120v Table 430.248 5.8 @ 115 667
Attic fan 1/2hp.120v = Table 430.248 9.8 @ 115 1127
water pump 1/2hp.240v = Table 430.248 4.9 @ 230 1127
Based on 430.24 you must add 25% of largest motor 1127 X .25 282
Sub-Totaol 9070 watts

As Smart$ pointed out 220.53 allow you a demand factor of 75% for four or more appliances fastened in place.
There might be some debate/discussion as to which loads would qualify. IMO could incude all the items listed
so it possible (albeit debatable) that an adjusted calculation could be 6803 watts (9070 X .75)

So what I wanted to know on the question it ask for feeder capacity so is that what we have total watts or are they asking for amps too..?

 

[Jgonzalez]

Tree phase

Tree phase

480v X 8amps X 1.73=6643.2 X 3motors=19929.6 I did this a few times and come out with the same numbers.
And as far as the 480v I put that out because I know its 3 phase but it dose not have it in the question.

So what Im asking when I do this calculation I use 480v X 8 amps X 1.73 to work out the three phase question or no.

 

[Smart $]

So what Im asking when I do this calculation I use 480v X 8 amps X 1.73 to work out the three phase question or no.

It's power conversion. All conversion equipment follow the equation:

• (Power In) - (conversion loss) = (Power Out)

General questions on converters regarding power in vs. power out, the "(conversion loss)" portion of the equation is typically ignored (omitted).

So being this conversion process is single phase in, three phase out we have:

• (Volts x Amperes)_IN = (Volts x Amperes x Square Root of 3)_OUT

 

[Jgonzalez]

Feeder

Feeder

It's power conversion. All conversion equipment follow the equation:

• (Power In) - (conversion loss) = (Power Out)

General questions on converters regarding power in vs. power out, the "(conversion loss)" portion of the equation is typically ignored (omitted).

So being this conversion process is single phase in, three phase out we have:

• (Volts x Amperes)_IN = (Volts x Amperes x Square Root of 3)_OUT

Just wanted to say thanks again for everyone help little hard to get on with you guys because I working all the time but I hope that in the future if I run into power problems I can count on yall again.