Single phase ranges supplied by 3 phase service

[Jpflex]

I was wandering if I could get other peoples input of calculating total feeder load demand for single phase ranges - stoves on a three phase 480/208 volt service ?

All ranges equal at 12 KVA each

Here’s what I know:

For multi-occupancy building with 1 range per apartment, calculate the number of apartments and divide by 3

This determines the number of ranges to be placed between phase pairs for load balance

Example 30 apartments / 3 = 10 ranges per pair of phases

Next take 2 (phase legs) x 10 (ranges) = 20 ranges per adjacent phases

Look up table 220.55 column C = 35 kVA for 20 ranges

35,000 VA apparently is the load for adjacent phases and I don’t get the final parts of calculations to determine total load calculation on the three phase service. Also what is the reason for special calculations here?

 

[augie47]

You might want to look at Example D5(a) in the Annex. It illustrates that situation,

 

[LarryFine]

I was wandering if I could get other peoples input of calculating total feeder load demand for single phase ranges - stoves on a three phase 480/208 volt service ?

On a what?

 

[infinity]

On a what?

Yes it's likely he meant 208 volts.

 

[Jpflex]

On a what?

It’s no specific application just a general question of calculating total load demand for single load ranges fed from a three phase source. The voltage or range kVA is not important.

I’m going to check the annex as augie47 suggested

 

[JoeStillman]

Per 220.54 and 220.55 "Where two or more single-phase [dryers or ranges] are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases"

I find the CEILING function in excel useful for determining the three-phase currents for a number of single-phase ranges (and dryers). This is the formula in the cell where I calculate "twice the maximum number connected between any two phases"

=IF(BasicPhase=3,2*CEILING(Units,3)/3,Units)

BasicPhase and Units are range names that I use like variables in diffeerent places on the spreadsheet.

 

[Jpflex]

total load shall be calculated on the basis of twice the maximum number connected between any two phases"

this NEC statement is incomplete and makes no sense. They do not specify twice the maximum number connected if WHAT

This can be voltage, VA, watts, ranges. Etc

 

[Jpflex]

Of what not “if,” Phone changed typing

 

[kwired]

this NEC statement is incomplete and makes no sense. They do not specify twice the maximum number connected if WHAT

This can be voltage, VA, watts, ranges. Etc

Art 220 load calculations are always in VA unless otherwise specified. Column C in table is for ranges not over 12kW rating. Note 1 tells you how to deal with ranges over 12kW.

If you have 3 identical ranges and have them balanced across all three phases then there is a maximum of one connected between any two phases. Your demand value would be based on two ranges

Add a fourth range and number connected between any two phases is two - your demand value is based on four ranges.

 

[JoeStillman]

....Add a fourth range and number connected between any two phases is two - your demand value is based on four ranges.

But, curiously, add a fifth range and your demand value is still only based on four.