multiple motors

[bubbarocco]

I have to hook up 5) 230v 1/2hp sf. 1 and code letter K with internal overloads.. These motors are all the same, they are fans and continuously used.
I was checking to see if I can put three of these motors on one branch circuit.


Per T430.248 my full load current is 4.9

4.9x1.25 continous=6.125
+4.9 2nd motor
+4.9 3rd motor
15.92 Amps on a #12 awg wire
4.9x250% inverse time breaker = 12.25
+ 4.9
+ 4.9
=22.05 so I would round down to 20 A and if it doesn't hold put it on a 25A Breaker

 

[augie47]

Note that 430.52 gives you the Maximum GF-SC protection at 250% (with non-applicable exceptions) which would be a 15 amp C/B, so your 20 amp would not be compliant.

 

[kwired]

You can fput them on one feeder and make a tap to each one with appropriate overcurrent protection, if that helps with what you wish to do. If the overcurrent protection is placed right it takes care of motor disconnect requirements at same time.

 

[Volta]

If they are all used continuously then they each will have the 25% added, not just the largest/first.

 

[mbeatty]

It looks like this falls under 430.53.

Regards,

Mark

 

[kwired]

If they are all used continuously then they each will have the 25% added, not just the largest/first.

430.24 says 125% of largest plus sum of all others. Exception 1 addresses what is allowed if one or more are not continuous duty.

It looks like this falls under 430.53.

Problem with that section is OP says his motors are 230 volt and 430.53 allows up to 20 amp but it has to be 120 volt motors. OP still needs to limit each motor branch circuit to a 15 amp overcurrent device max. I think he can put them on one 30 amp feeder and put a 15 amp breaker near each motor then he has proper overcurrent protection as well as a disconnect within sight of each motor.

 

[Volta]

430.24 says 125% of largest plus sum of all others. Exception 1 addresses what is allowed if one or more are not continuous duty...

That may be true, but don't confuse "continuous duty" rating with used continuously. The OCPD needs to be 25% larger than the continuous load 210.20 / 215.3. As you know, Chapter 4 minimums do not override Chapter 2 requirements, only supplement or modify them.

 

[kwired]

That may be true, but don't confuse "continuous duty" rating with used continuously. The OCPD needs to be 25% larger than the continuous load 210.20 / 215.3. As you know, Chapter 4 minimums do not override Chapter 2 requirements, only supplement or modify them.

The sections you mention are for overcurrent protection, 430 does modify this for motors and actually permits short circuit and ground fault protection to be much higher than 125% in some cases.

The 125% of largest plus all others is for minimum conductor ampacity and does not matter what the fuse or breaker size is going to be at that point.

If motor is not continuous load then 100% full load current is used. If multiple motors and some are continuous and some are not then 125% of highest rated continuous is used plus 100% of all others.

Chapter 4 minimums do not override Chapter 2 requirements, only supplement or modify them.

I don't agree with this

210.2 Other Articles for Specific-Purpose Branch Circuits.
Branch circuits shall comply with this article and also with the applicable provisions of other articles of this Code. The provisions for branch circuits supplying equipment listed in Table 210.2 amend or supplement the provisions in this article and shall apply to branch circuits referred to therein.

How can you meet both chapter 2 requirements and chapter 4 permissions for a circuit breaker supplying a motor circuit? That is the reason the chapter 4 permissions are there because the chapter 2 requirements create an unacceptable performance condition for this particular circuit. They could just put exceptions in chapter 2 for everything that is already covered in chapter 4 and kind of have the same requirements on many things but isn't it better to just say 'we have a motor here, we need to go to art 430 and see what is different from the otherwise general rules'?

 

[Volta]

....

How can you meet both chapter 2 requirements and chapter 4 permissions for a circuit breaker supplying a motor circuit? That is the reason the chapter 4 permissions are there because the chapter 2 requirements create an unacceptable performance condition for this particular circuit. They could just put exceptions in chapter 2 for everything that is already covered in chapter 4 and kind of have the same requirements on many things but isn't it better to just say 'we have a motor here, we need to go to art 430 and see what is different from the otherwise general rules'?

I don't see the conflict. And you're right in that you were speaking of conductors and I responded about OCPD, but that doesn't mean, and nothing in 430.24 allows- for protecting the conductors at less than 125% of any continuous load.

 

[kwired]

I don't see the conflict. And you're right in that you were speaking of conductors and I responded about OCPD, but that doesn't mean, and nothing in 430.24 allows- for protecting the conductors at less than 125% of any continuous load.

Did you mean what you said? Protecting conductors at less than 125%? Again you are mentioning overcurrent protection when the section is about conductor ampacity.

I don't see where it says anything about 125% needed for all motors. I also don't see the reason for including the words "highest rated motor" if the intention is to use 125% of all motors. If you wish to use 125% of all you do not create any hazard you are just exceeding minimums.

 

[Volta]

Did you mean what you said? Protecting conductors at less than 125%? Again you are mentioning overcurrent protection when the section is about conductor ampacity.

I don't see where it says anything about 125% needed for all motors. I also don't see the reason for including the words "highest rated motor" if the intention is to use 125% of all motors. If you wish to use 125% of all you do not create any hazard you are just exceeding minimums.

Well I did mean that, though I said it clumsily. I don't know what section would allow us to protect the wires at less than 125% of the continuous load.

Do you feel that 5 @ 10 FLA motors, running continuously, can be fed from an OCPD of less than 62.5 amps, or do you feel that 52.5 is sufficient?

 

[kwired]

Well I did mean that, though I said it clumsily. I don't know what section would allow us to protect the wires at less than 125% of the continuous load.

Do you feel that 5 @ 10 FLA motors, running continuously, can be fed from an OCPD of less than 62.5 amps, or do you feel that 52.5 is sufficient?

Conductor needs to be 62.5 amps. Feeder breaker can be 60 amps, or more if 60 will not hold during starting.

2.5 times largest plus all others. 430.62.

May be a good idea to run a larger feeder but this is code acceptable.

As far as protecting conductors at less than 125% of continuous load it doesn't create a hazard as much as it creates an inconvenience from the possible tripping of the overcurrent device.

 

[kwired]

Conductor needs to be 62.5 amps. Feeder breaker can be 60 amps, or more if 60 will not hold during starting.

2.5 times largest plus all others. 430.62.

May be a good idea to run a larger feeder but this is code acceptable.

As far as protecting conductors at less than 125% of continuous load it doesn't create a hazard as much as it creates an inconvenience from the possible tripping of the overcurrent device.

(Waited to long to make changes to post)

Wanted to add: since the minimum required conductor ampacity is 62.5 it can be protected by next higher size standard overcurrent device so a 70 amp breaker would be fine. I wouldn't have a problem feeding the five 10 amp motors with 6 AWG and a 70 amp breaker.

 

[Volta]

Conductor needs to be 62.5 amps.

Now that confuses me. What section requires that? I was under the impression that you were making the case via 430.24 that we only need an ampacity of 52.5 ((5x10)+(.25x5)).

Feeder breaker can be 60 amps, or more if 60 will not hold during starting.

2.5 times largest plus all others. 430.62.

May be a good idea to run a larger feeder but this is code acceptable.

As far as protecting conductors at less than 125% of continuous load it doesn't create a hazard as much as it creates an inconvenience from the possible tripping of the overcurrent device.

Well, except for the first sentence segment I would generally agree with that.

(Waited to long to make changes to post)

Wanted to add: since the minimum required conductor ampacity is 62.5 it can be protected by next higher size standard overcurrent device so a 70 amp breaker would be fine. I wouldn't have a problem feeding the five 10 amp motors with 6 AWG and a 70 amp breaker.

I would accept that too. Perhaps our only difference here is that I see nothing that allows us to ignore 215.3 or 210.20, and I don't think the OCPD can be less than 62.5, in my scenario.

 

[kwired]

Now that confuses me. What section requires that? I was under the impression that you were making the case via 430.24 that we only need an ampacity of 52.5 ((5x10)+(.25x5)).

I really don't know how I came up with that. Checking again I have 52.5. Thought I did it the right way, maybe it was inflation