load calculation for 4 receptacle panels

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JEFF MILLAR

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This may be a very stupid question. Have a 112.5 kva xfmr feeding a 400 amp distribution panel feedeing 4 seperate 100 amp panels with only receptacle loads on each panel. . Given no other info , how would you calculate the load. Or do you just size the feeder to the 400 amp panel for 400 MPS AND THE FEEDER TO EACH 100 AMP PANEL for 100 amps. Do you calculate the total load as 112.5 kva at 480 v. ?
 
YES the conductor size is not the issue. The 112.5 kva xfmr is feeding the load. But on the 400 amp lighting panel feeding this xfmr, my question is how would you calculate that load on the lighting. panel ? not 112.5 kva, there must be a large diversity factor on the receptacle loads.
 
480sparky said:
You can't.
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I agree. WAG is about all you'll get. Not even a SEWAG.

How many receptacles are in use and what is the load for each at the time of use?

How was the transformer sized to begin with?
Conceivably someone counted the # of receptacles, multiplied it by 180 va and came up with the 112 kva. Those were divided equally into the 4 - 100 amp panels.

Or maybe they only had a budget for the 112 and danged if they were going to spend more.

Or something in between.
 
JEFF MILLAR said:
YES the conductor size is not the issue. The 112.5 kva xfmr is feeding the load. But on the 400 amp lighting panel feeding this xfmr, my question is how would you calculate that load on the lighting. panel ? not 112.5 kva, there must be a large diversity factor on the receptacle loads.
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As stated, receptacles are calculated at 180 VA per yoke. If you want the actual load, I would put a clamp on it at various times, or better yet measure it with a logger.
 
400 amp lighting distribution panel. feeds. a branch circuit. supply. to. a 112.5 kva. transformer. That feeds a 400 amp panel that only feeds. 4 receptacle panels rated 100 amp each..
Receptacle panels have 20 amp branch breakers. Max load on each branch breaker { 20 amps x 0.8 %. = 16 amps max load. per. breaker. )
Max. duplex outlets per breaker. = 16 amps / 1.5.amps. =. 10 duplex outlets. max. per 20 amp branch. circuit.
100 AMP receptacle panel / 20 amp branch. breakers. = 6 max 20 amp branch. loaded. breakers. Equals 60 duplex outlets per panel.
4 panels total max receptacles = 4 x 60. = 240.
240 x 180 va = 43200 va. 0r. 43. 2 kva.
Transformer 112.5 kva. = 112500 / 180. =. 625 X 0.8 = 500 DUPLEX OUTLETS.
Calculate the transformer. load. fed from the 400 amp panel. as. 112.5 x 0.80. =. 90 kva. or. 43.2 kva. ?
Makes the 112.5 kva transformer over sized ?
Diversity. factor. application. What do i need to. learn to correct the above and properly apply the NEC. The feeder sizes are not my issue. Basically i want to know how to calculate the transformer load. it can not be 112.5 kva. And what diversity factor should be considered for these receptacle loads. Thank you for any experience you may be willing to share.
 
NEC 220.44. NON - DWELLING. RECEPTACLE. LOAD
Estimate load on a 400 amp panel feeding only 4 - 100 amp panels with only standard 180 va duplex. receptacle loads.

Calculate duplex outlet. load on 4. 100 amp panels, ( 100 amp main. breaker )
MAX LOAD equals 80 amps on each 100 amp panel.
Max number of outlets equals 80 / 1.5 =53.33 outlets x 4 = 213 max duplex. outlets on four panels.
Total load = 213 x 180 va = 38340 va. or 38,34 kva.

Estimate load as per NEC 220.44.
FIRST 10 KVA at 100 %. the rest 28.34 kva. at 50 %. = 14.17 KVA
Total load on 4 panels. equals 24.17 kva
Why was a 112.5 kva transfurmer. used
 
This is just one of those things that will probably forever remain a mystery of the universe, similar to questions such as why is the Reuben such a delicious sandwich, why can't I seem to find Haagen-Dazs mango ice cream east of the Mississippi. Unfortunately someone has likely taken these answers to the grave.
 
Answer. NEC 220.44. FIRST 10 KVA at 100 %. Remaining kva at 50 % demand.
Design 208 / 120 volt , 100 amp distribution panel , 100 amp main breaker.
Only loads on this panel are general use ( non - dwelling, i.e Commercial application )
All duplex receptacles rated 180 va . NEC considers these outlets as non continuous loads.
Max number of out lets and circuits calculated as follows.
100 AMP MAIN BREAKER x. 208 x 1.732. = 36025.6 va
First 10 kva at 100 % = 10,000 va
Remaining va. =. (. 36025.6. minus 10000 va. = 26025.6 va
at 50 % demand = 2 x 26025.6 va. =. 52051.2 va
TOTAL va - 52051.2. +. 10000 va. =. 62051.2 / 180 va. =344.72 duplex ourlets
My design max duplex outlets per circuit. = 8
number of circuits. = 355.72 / 8. = 43.09
Use panel with 42 , 20 amp branch. circuits. Each circuit has its own neutral. No common neutral.

Comments welcome.
 
Actual load amps per panel will be 80A only, not 100A! Total actual load will be 4 x (120V X 80A x 3 phases) = 115.2 kVA. Now, you can't find a 115.2KVA in the market! The nearest is a 3-phase, 112.5kVA or 3 X 37.5kVA! That simple!
 
david luchini said:
Why?
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If not stated they have a 100% rated breakers, it's the norm to never load up to 80% of breaker rating, that's why! I am trying to find the nearest answer to the OP's question of why he got a 112.5 kVA transformer for his 4 x 100A panels. If you have another idea, shoot.
 
topgone said:
If not stated they have a 100% rated breakers, it's the norm to never load up to 80% of breaker rating, that's why! I am trying to find the nearest answer to the OP's question of why he got a 112.5 kVA transformer for his 4 x 100A panels. If you have another idea, shoot.
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My idea would be that you could put 346 receptacles on each of the four 100A panels for a 100A load on each panel instead of an 80A load on each panel.

The load on the 400A would then be approx. 360A.
 
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