diversity and panel loading

[CPorter]

The company uses environmental chambers for product testing. The chambers are 208V, 25amp, single phase, 4 wire units with chillers & ovens combined so product can be tested from -100'F to 300'F. The chambers are spilt into two groups, one group pulls 80% FLA for for 3 minutes then drops to 5 amps for several hours. The other group pulls 60% FLA for 3 minutes, idles at 3 amps for 10 minutes and then repeats. The start times of the ovens are always staggered but I have 40+ that run all the time.

The company needs to consolidate space and move the chambers into one area. Assuming all the ovens are from the same group, have many can I realistically place on a 208V/225A panel and which parts of the NEC applies to the limit?

 

[kingpb]

Maybe I'm reading too much into this, but why are they 4-wire units, if they are 208V single phase, and does the operation you describe above also account for both operating modes, i.e. full range of temperature?

I also assume when you say 208V/225A panel, you have a 208Y/120V panel?

 

[CPorter]

It's a 4 wire circuit because the controls are 120v. The operations do include both heating and cooling, especially the one the operates at 65% for 3 minutes, idles for 10 minutes and repeats.

And yes, it is a 208Y120 circuit.

 

[CPorter]

Yes, the data reflects operations in both heating and cooling. The units that cycle and repeat are typical going from one extreme to another to see how components handle rapid temperature changes. The other units are more of soak at temperature for long term effects.

The panels are 208Y120, there are no delta secondaries in use.

 

[OTT2]

Looks to me as if your stuck with 25 amps per circuit (220.14 A) with a maximum of 9 units to this 225 amp panel. I am guessing that this feeder is supplied by 225 amp OCPD. Is this true?

Feeder load to be calculated per 220.40.

I don't see any allowance for demand factors on this type of load.

 

[benaround]

25a x 80% = 20

225/20 = 11.25 minumum units

You might want to consider recording a group of units for 30 days to get an accurate

demand. IMO, 11 units in a 225a panel is overkill.

 

[kingpb]

First off, if you have 40+ machines, you are going to need more than one panel, just to accommodate the breakers spaces, as you will want a separate breaker for each machine.

Certainly you can do feed-through lugs and still utilize the 225A feeder. As far a usage, according to Article 100, continuous is considered where a load will run for 3 hours or more drawing maximum current. Sounds like you don't have this, and that it would be more of Varying Duty.

Assuming this is motor load, which from the description I can't say for sure it is; the protection is going to based on Table 430.22(E), and 430.33. However, this is not what your asking, your looking for a load diversity.

Diversity is based on knowing the process. You have to understand what will be on, or can be on, at any given time. This will drive the feeder size. The problem is that load diversity is extremely subjective, and it would be best to have the Owner, or process Owner, tell you how many can be on at any given time, and at what intervals do they come on and off. Create a load duty cycle plot and try to determine maximum. The other suggestions, as stated earlier is to meter the current install for a month, and see what the peak usage is and plan for that.