Load for 100 A/C Units

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gboles01

Member
Location
Ft Worth, TX
I have a somewhat unusual industrial load question.

A client is wanting to install 100 Conex boxes (large shipping containers 10' X 40') with air conditioning for each box. The A/C units are 208 Single phase at 7.25 FLA. This give me a total continuous load of 725 Amps of load for just the A/C Units. There will be a monitoring system that is also a continuous load but this will require only 30 Amps (presumed 208 single phase). This give me a total of 755 Amps of continuous single phase loads. I am not counting the noncontinuous loads yet (approx 40 convenience receptacles per the AHJ)

I plan on brini8ng in a three phase, Y, service feeder. This brings me to my question - should I use the sq Root of 3 to determine the service size needed?

Thanks in advance
 

Npstewart

Senior Member
are you asking because you have almost a 100% single phase LOAD, your wondering if you should use a 3 phase voltage to figure out the load on the panel itself?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Yes to calculate the load for 3 phase you would use 208 * 3 sq.rt or 360.

The single phase units hopefully will be installed so that you have a fairly balanced load on all three phases.

Obviously, if you install all the units on the A & B phase that would be a problem but it is not likely to be install that way.
 

One-eyed Jack

Senior Member
I have a somewhat unusual industrial load question.

A client is wanting to install 100 Conex boxes (large shipping containers 10' X 40') with air conditioning for each box. The A/C units are 208 Single phase at 7.25 FLA. This give me a total continuous load of 725 Amps of load for just the A/C Units. There will be a monitoring system that is also a continuous load but this will require only 30 Amps (presumed 208 single phase). This give me a total of 755 Amps of continuous single phase loads. I am not counting the noncontinuous loads yet (approx 40 convenience receptacles per the AHJ)

I plan on brini8ng in a three phase, Y, service feeder. This brings me to my question - should I use the sq Root of 3 to determine the service size needed?

Thanks in advance
The short answer would be Yes.
 

gboles01

Member
Location
Ft Worth, TX
Thanks

Thanks

That's what I thought, just needed to confirm it. I will be trying to balance the loads as much as possible. as of right now it looks that the loads will be pretty evenly balanced. So thanks again.
 

PhaseShift

Senior Member
You could calculate the total connected load by taking your 755A * 208V = 157kVA.

So assuming you used a 157kVA transformer (not a typical size however) you would take 157kVA / .208 / 1.73 = 428A. You could then size your service feeders for 428A and then balance the loads.
 

BJ Conner

Senior Member
Location
97006
Been there,done that

Been there,done that

Calculate the load in VA
208 volts x 7.25 amps = 1,508 VA/unit
total load = 1,508 VA/unit x 100 units = 150,080 VA Total (AC load only).
Each unit is going to need 2 poles in a 208/120 panel so you need 200 breaker spaces for the ac units.
At a minimum just AC units will require 4 complete panels (42 circuit) and 16 in the fifth.

I would spot a 30 KVA 3 phase transformer and a 125 amp- 42 ciruit panel for every 10 connexs. Twenty circuits of each panel would be for AC units and the remaining 22 for recepticals, lights, spares, tools, microwaves, refridgerators etc.

This based on my experience on construction projects. Loads and uses grow and change on connexs. If the use and occupancy is defined and enforced the need for contingencies goes away. YMMV
 
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