Multi motor

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Large dairy with circulating fans originally installed about 20 years ago.

Fans are 1/2 hp 480v with internal thermal protection. About 15 to 20 fans per branch circuit protected via an AB1489 mini 30 amp CB. #12 AWG. They were all started with single motor starter.


Trying to determine if it was ever a legal install.


I do not see it passing 430.53 (B). Table 430.52. NEC 2014, but what about years ago?
 

jap

Senior Member
I'm just curious what amperage the heaters are in the Starter not that it matters much, but if they're sized heavy its acting as nothing more than a contactor.
Each motor has overload protection and even with 20 of them (if they're 480v 3ph) I'd guess the FLA somewhere around 22.5 amps.
So the wire size seems adequate and the Short Circuit / Ground fault protection device seems to be in line, so why would it have not been legal to begin with?

JAP>
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
We do not know what the heater size is, like you say it doesn't matter.

Inverse Time Breaker, Table 430.52, indicates the branch circuit protection should not be higher than 2.5 times the full load current of the motor. 1.1*2.5= 2.75 amps. Next standard size is 15. I take it that I can put on as many 1/2 hp motors as I want as long as the 15 amp breaker is capable of starting them.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
We do not know what the heater size is, like you say it doesn't matter.

Inverse Time Breaker, Table 430.52, indicates the branch circuit protection should not be higher than 2.5 times the full load current of the motor. 1.1*2.5= 2.75 amps. Next standard size is 15. I take it that I can put on as many 1/2 hp motors as I want as long as the 15 amp breaker is capable of starting them.
agreed.
 

Cow

Senior Member
Location
Eastern Oregon
We do not know what the heater size is, like you say it doesn't matter.

Inverse Time Breaker, Table 430.52, indicates the branch circuit protection should not be higher than 2.5 times the full load current of the motor. 1.1*2.5= 2.75 amps. Next standard size is 15. I take it that I can put on as many 1/2 hp motors as I want as long as the 15 amp breaker is capable of starting them.
That's how I do it Tom, 15 amp breakers or fuses, and then load the circuit up.

We just finished a 6 fan install in a dairy holding pen today. 1 hp 480v motors. The way we did this one was a single 3p 15 amp breaker feeding a control cabinet with three AB IEC contactors each starting 2 fans, each fan has an individual manual motor protector in a plastic 4x rotary disconnect enclosure mounted on the fan.

In the past when I've had quite a few fans to wire, I've taken a single feeder into a control cabinet but split it into multiple circuits fused down to 15 amps or so before going through the contactors and out to the motors.

I definitely wouldn't like the idea of putting a bunch on a 30 amp breaker with no individual OCPD. It sounds like a ground fault in one motor would give you a hard time troubleshooting trying to figure out which one of the 15-20 fans it was.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
...

I definitely wouldn't like the idea of putting a bunch on a 30 amp breaker with no individual OCPD. It sounds like a ground fault in one motor would give you a hard time troubleshooting trying to figure out which one of the 15-20 fans it was.
Exactly the problem. Now the equipment supplier wants to install 1hp fans and asked if he could just put in a larger breaker. :happysad:
 

augie47

Moderator
Staff member
Location
Tennessee
Large dairy with circulating fans originally installed about 20 years ago.

Fans are 1/2 hp 480v with internal thermal protection. About 15 to 20 fans per branch circuit protected via an AB1489 mini 30 amp CB. #12 AWG. They were all started with single motor starter.


Trying to determine if it was ever a legal install.


I do not see it passing 430.53 (B). Table 430.52. NEC 2014, but what about years ago?
'99 Code is earliest I have on hand at the moment and it would not have been allowed then either (430.52, 53)

That's how I do it Tom, 15 amp breakers or fuses, and then load the circuit up.

We just finished a 6 fan install in a dairy holding pen today. 1 hp 480v motors. The way we did this one was a single 3p 15 amp breaker feeding a control cabinet with three AB IEC contactors each starting 2 fans, each fan has an individual manual motor protector in a plastic 4x rotary disconnect enclosure mounted on the fan.

In the past when I've had quite a few fans to wire, I've taken a single feeder into a control cabinet but split it into multiple circuits fused down to 15 amps or so before going through the contactors and out to the motors.

I definitely wouldn't like the idea of putting a bunch on a 30 amp breaker with no individual OCPD. It sounds like a ground fault in one motor would give you a hard time troubleshooting trying to figure out which one of the 15-20 fans it was.
IMO, you have a different scenario with fuses as 15 amps is not the smallest standard fuse.
 

kwired

Electron manager
Location
NE Nebraska
Exactly the problem. Now the equipment supplier wants to install 1hp fans and asked if he could just put in a larger breaker. :happysad:
Of course you can, the larger fans will cool the conductors better allowing you to load them to a higher lever - it is an "air over" application:cool:
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
'99 Code is earliest I have on hand at the moment and it would not have been allowed then either (430.52, 53)



IMO, you have a different scenario with fuses as 15 amps is not the smallest standard fuse.
IIRC, the code specifically allows for 15A OCPD on this kind of group motor install and does not restrict it to CBs.
 

jap

Senior Member
We do not know what the heater size is, like you say it doesn't matter.

Inverse Time Breaker, Table 430.52, indicates the branch circuit protection should not be higher than 2.5 times the full load current of the motor. 1.1*2.5= 2.75 amps. Next standard size is 15. I take it that I can put on as many 1/2 hp motors as I want as long as the 15 amp breaker is capable of starting them.

I see,,, I missed that part and I agree with you.

JAP>
 

augie47

Moderator
Staff member
Location
Tennessee
450.53 (A) and (B) would both appear to allow this.
Certainly possible under "A", but the few times I have encountered this, (A)(2) was a problem but in those cases they were using individual controllers which were marked for a lower SCGF protection.
It seems to me that (B) would be a problem as a 1/2 HP 480 motor calls for a 3 amp standard fuse so using a larger fuse for multiple motors would exceed the max for the smallest.
Kinda silly since the 15 amp breaker would be allowed.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Certainly possible under "A", but the few times I have encountered this, (A)(2) was a problem but in those cases they were using individual controllers which were marked for a lower SCGF protection.
It seems to me that (B) would be a problem as a 1/2 HP 480 motor calls for a 3 amp standard fuse so using a larger fuse for multiple motors would exceed the max for the smallest.
Kinda silly since the 15 amp breaker would be allowed.
I forgot we were talking about fuses. I think you are right.
 
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