I have 5 evap coolers. 10hp 460v 3 phase 12.2 amps. FLC is 14 amps. I want to make sure I size my feeder right. We are gonna put a panel board on roof. FLC 14ampsx1.25 =17.5 amps. 4 more motors at 14 amp @ 100%=56 amps. 56x17.5=73.5. Conductor size 4awg cu or 2awg AL. 80 amp breaker. I was gonna put each motor in its own 3/4 emt 10 awg thhn on a 3 pole 20 amp breakers thanks
Evap coolers
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The individual motor branch circuit, the #10 looks big and the 20 amp breaker looks small. Using the old code rules could be #12 with 30 Amp breaker. Did not check it with the new code rules. Feeder looks OK by eye but I might try to go up on the breaker size if I can find a code rule for it, to carry motor locked rotor starting current.
More importantly, the evap fan could be a typical winning drive application. If your rooftop panelboard is outside with no allowance to add drives now or later, I might look it as, well IDK but maybe not useful over the expected useful life.
If the rooftop panelboard is going inside in the rooftop penthouse and you have an allowance for footprint to add drives now or later, I might say that's providing something useful or reuseable when the time comes. I would plan for an inside footprint at the panelboard location where drives can be added in easily.
More importantly, the evap fan could be a typical winning drive application. If your rooftop panelboard is outside with no allowance to add drives now or later, I might look it as, well IDK but maybe not useful over the expected useful life.
If the rooftop panelboard is going inside in the rooftop penthouse and you have an allowance for footprint to add drives now or later, I might say that's providing something useful or reuseable when the time comes. I would plan for an inside footprint at the panelboard location where drives can be added in easily.
MAC702
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- Clark County, NV
Agree, and add to make sure they don't all start at the same time. Evap coolers are often not t-stat controlled, but just run the entire time the area is occupied. You don't want every morning to see all 10 just flipped on at the same time to start the day.
Ok thanks I will go 100 amp feeders #2 cu on a 100 amp breaker. Are you also saying that I should go 30 amp 3 pole breakers for the units, I went with 20amp OCPD because 14 amps @1.25= 17.5 would be 20 amp, I’m only going with #10 cause of the Ambient temperature. I know it changed in the 2014 how rate wire for Ambient temperature but I don’t have my codebook.
kwired
Electron manager
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- NE Nebraska
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- EC
14 AWG @ 75C is acceptable for a 10 HP 480 volt motor. Many run 12 AWG anyway.
Square D motor slide chart says 25 amp breaker - but that is a suggestion and not a requirement. I've seen many 10 HP motors that start with no issues on a 15 amp breaker. Application conditions will effect this. Long circuit run and smaller conductor will have a soft starting effect to some degree.
Square D motor slide chart says 25 amp breaker - but that is a suggestion and not a requirement. I've seen many 10 HP motors that start with no issues on a 15 amp breaker. Application conditions will effect this. Long circuit run and smaller conductor will have a soft starting effect to some degree.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
There is not much difference in cost between #14 and #10 wire so if you want to use #10 feel free. But you really only need #14 by code.
I would be inclined to use at least 20A CBs on the individual motors. Just to avoid nuisance trips. You could use 30A Cbs if you wanted to. They cost the same as 15 or 20 A CBs so why not give yourself the best chance at no nuisance trips.
I think I would install a 100 A MCB panel and feed it with #2 AL protected by a 90 A breaker at the source.
Will you need to have a small xfmr to provide 120V single phase to feed receptacles to use for service work?
I would be inclined to use at least 20A CBs on the individual motors. Just to avoid nuisance trips. You could use 30A Cbs if you wanted to. They cost the same as 15 or 20 A CBs so why not give yourself the best chance at no nuisance trips.
I think I would install a 100 A MCB panel and feed it with #2 AL protected by a 90 A breaker at the source.
Will you need to have a small xfmr to provide 120V single phase to feed receptacles to use for service work?
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- Connecticut
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- Engineer
kwired
Electron manager
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- NE Nebraska
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- EC
That is what the "magnetic" is about in "thermal-magnetic" circuit breaker. Most will hold for a few seconds at 6-8 times the rating, this is what allows motor starting and some other high inrush applications to work without nuisance trips.
As mentioned 35 is the max code allows as the general rule, I earlier mentioned I have seen 10 HP motors that work just fine on 15 amp breakers. Most of those were I-Line type FA breakers (FWIW) All depends on conditions at the install and the actual trip curve of the breaker.
High efficiency motors have a lower impedance, higher starting current. There were code letters for starting current that went up. For example you could upsize to 175% time delay fuse for a high locked rotor code letter, to get it to hold with the high efficiency motor.
It seems there's a lot missing from the given information. 10 hp is big for an evap tower fan but not so big if it's an entire package unit. It's not clear what equipment is being wired. 10 hp in a tower fan is a big blade. You want to be able to ramp to speed and modulate speed with demand.
It seems there's a lot missing from the given information. 10 hp is big for an evap tower fan but not so big if it's an entire package unit. It's not clear what equipment is being wired. 10 hp in a tower fan is a big blade. You want to be able to ramp to speed and modulate speed with demand.
kwired
Electron manager
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- NE Nebraska
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- EC
Which increases likelihood of it being VFD driven, and then there is no starting surge as severe as across the line starting has.
Well, trying to say this in a gentle way, breaker and fuse size for a motor load is one of my tells.
50 hp of evap tower fan points to a sufficiently large installation to have field and factory engineering, along with inhouse facility engineering. It's a lot of people and a large capital project. It does not make sense that there would be no plans and specs. What is on the plan for starter or drive. No drawing would be another tell.
50 hp of evap tower fan points to a sufficiently large installation to have field and factory engineering, along with inhouse facility engineering. It's a lot of people and a large capital project. It does not make sense that there would be no plans and specs. What is on the plan for starter or drive. No drawing would be another tell.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You don't do farm work do you?
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