10kw Range

[SonofAdam]

Got a question on my load calculations exam and need some help

3 phase utility feeding a 10 unit complex. Each unit is fed from a transformer 480/ 208/120.

The range is 10kw.

What is the maximum load of a single range? Of all of them on the service?

I guess what I'm asking is what are the rules for 1 range on a 10kw unit. I used column c and for one unit sized it at 8 kw. For all of them I sized it at 23kw since it's a multi-phase system I went 4x2=8 to balance the loads


Thanks for any help

 

[david luchini]

I guess what I'm asking is what are the rules for 1 range on a 10kw unit. I used column c and for one unit sized it at 8 kw. For all of them I sized it at 23kw since it's a multi-phase system I went 4x2=8 to balance the loads

I would say 34.5kW for all of the ranges.

23kW /2 = 11.5kW per phase. 11.5kW * 3 = 34.5kW equivalent 3 phase load.

 

[Dennis Alwon]

Got a question on my load calculations exam and need some help

3 phase utility feeding a 10 unit complex. Each unit is fed from a transformer 480/ 208/120.

The range is 10kw.

What is the maximum load of a single range? Of all of them on the service?

I guess what I'm asking is what are the rules for 1 range on a 10kw unit. I used column c and for one unit sized it at 8 kw. For all of them I sized it at 23kw since it's a multi-phase system I went 4x2=8 to balance the loads


Thanks for any help

you got part of it. Look at annex D Example D5 (a)

This is it if you haven't a code book handy

You got the 23000kw
now /2 and then multiply by 3

(23000/2) * 3 = 34,500 or 34.5kw for 3 phase

Minimum Size Main Feeder (Less House Load) (For 40 Dwelling
Units — 20 with Ranges)
For 208Y/120-V, 3-phase, 4-wire system,
Ranges:
Maximum number between any two phase legs = 7
2 × 7 = 14.
Table 220.55 demand = 29,000 VA
Per phase demand = 29,000 VA ÷ 2 = 14,500 VA
Equivalent 3-phase load = 43,500 VA
Net Calculated Load (total):
69,150 VA + 43,500 VA = 112,650 VA
112,650 VA ÷ (208 V)(1.732) = 313 A
Main Feeder Neutral Size:
69,150 VA + (43,500 VA at 70%) = 99,600 VA
99,600 VA ÷ (208 V)(1.732) = 277 A

 

[SonofAdam]

Awesome, and what about the rules for just one?
Is the 10kw to 8kw correct?

 

[Dennis Alwon]

Awesome, and what about the rules for just one?
Is the 10kw to 8kw correct?

That is correct.