what is the max overcurrent protection for a single motor

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ritelec

ritelec

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Jersey
Good morning.

A single phase blower motor 120v/9 amps was installed for a pool spa blower.
I fed it with a 20 amp single pole circuit operated through a contactor.
The owner wants more blow so the pool contractor added another 9 amp blower motor.

The pool panel is full and I am not sure if its tandem rated.
If the panels rated for tandems i can add one and feed the new blower through the contactor (it's 2 pole).
If it's not tandem rated, I'm considering feeding both motors from one 30 amp 120v single pole circuit.

My question is, does the one 30 amp circuit protect each single motor as per code?

Thank you.
Rich
 
130617-0832 EDT

ritelec:

How does a 20 A breaker protect a 9 A motor.

Suppose a motor is designed for continuous duty at full HP rating. And this motor will not stall at 50% mechanical overload. From a performance curve the current will increase by about 50% at 150% mechanical load. Thus, internal power dissipation will increase to about 1.5^2 = 2.25 or an increase of 125% over the 100% load rating. This motor will burn up if run at a continuous 50% overload, and not trip the breaker in your 20 A breaker 9 A motor example. Current will increase to 13.5 A, but power dissipation is 2.25 times full rated power dissipation. This means temperature rise will approach 2.25 times that at normal 100% load on the motor.

The breaker in the panel is not to protect the motor, but to protect the wire connected to the breaker. The motor needs its own protection.

.
 
ritelec said:
Good morning.

A single phase blower motor 120v/9 amps was installed for a pool spa blower.
I fed it with a 20 amp single pole circuit operated through a contactor.
The owner wants more blow so the pool contractor added another 9 amp blower motor.

The pool panel is full and I am not sure if its tandem rated.
If the panels rated for tandems i can add one and feed the new blower through the contactor (it's 2 pole).
If it's not tandem rated, I'm considering feeding both motors from one 30 amp 120v single pole circuit.

My question is, does the one 30 amp circuit protect each single motor as per code?

Thank you.
Rich
Click to expand...

There is a lot of critera that has to be met to feed two motors from one circuit. Also, as Gar said, the breaker size is determined by the conductor size, and the motor needs some type of overload protection.

I just went through this with an inspector. I had to feed each motor separately due to the critera not being met. One of which is, the two motors would have to be listed to be controlled by a single controller. Also, the type of overload protection comes into play as well.

Don't have time now to look up anything, but look in 430 (Motors) for info on this.
 
gar said:
130617-0832 EDT

The breaker in the panel is not to protect the motor, but to protect the wire connected to the breaker. The motor needs its own protection.

.
Click to expand...


Yes.. thank you. The motor has thermal overload protection. Would I be correct to consider then that each motor would be protected by it's built in protection?

Little Bill, Two motors would have to be "listed" to be controlled from one controller. Interesting.

There is a spare contactor I could use. And wire (or program) for both to come on at the same time.

If you could help find that reference (2 motors controlled from...) I would appreciate it. I will look also.

As far as the circ. and protection, With the TP built in I would be able to put both on one circuit. Correct me if I'm wrong.

Thank you.
 
Gar are you assuming no overload protection?

I think as long as the controller is rated for the loads then I don't see an issue. Each motor has overload protection so you are just dealing with short circuit and ground fault issues.

Is there gfci for the motors?
 
Little Bill said:
I had to feed each motor separately due to the critera not being met. One of which is, the two motors would have to be listed to be controlled by a single controller.
Don't have time now to look up anything, but look in 430 (Motors) for info on this.
Click to expand...


I will look into it. Good to know.

I believe 2 separate circs. (tandem breaker) thru two separate controllers, each motor TP, would be the way to go.

Although I do have to find that code article cause I'm sure the pool contractors gonna ask why I have to eat up another contactor to supply his blower motors which are going to come on together.

I will also check on the motor, maybe it's listed, then I'll go for the one 30 amp circ. one controller.
 
This is a spa? Is it attached to the pool and uses the pool motors? or is this a stand alone unit? 680.44 req. gfci unless it is 3 phase
 
ritelec said:
I will also check on the motor, maybe it's listed, then I'll go for the one 30 amp circ. one controller.
Click to expand...

Or two single pole circs on one controller (2 pole single throw contactor) ...............

nice... leaves me with another question. as with two circs on one device (yoke), both circs have to be disconnected to that device (two pole or three pole brks or hand ties or...)

would single poles to this one contactor need to be disconnected at the same time?

I think not.........but........

Rethinking..............how many outside lighting contactors I've seen and installed with multiple single poles feeding onto one contactor. I will also look into that for better clarity.


So the question seams to be, two motors one controller or not.

Thank you
 
Last edited:
130617-1153 EDT

Dennis:

I was trying to get across the point that the main panel breaker was not protecting the motor. Something else has to do that, or the main panel breaker has to be designed to protect the motor and that is an unlikely situation as the original post was presented.

Thus, I tried to show that the motor was not protected by the main panel breaker by picking a load that would not likely stall the motor, but if no other protection was provided the motor would burn out.

.
 
Thanks Gar.

The breaker protects the wire, the heaters protect the motor.

I forgot. Thank you for the reminder.

Checked the panel, it will accept tandems (it's an Intermatic which has breakers listed single,double,twin,quad.......guessing there term twin is tandem).

Gonna take a 20a circ. through the same 2 pole contactor for that new blower.

As the mentioned dual motor rated for a single controller, I know not.

I'll be checking,
Thanks

Rich
 
gar said:
130617-1153 EDT

Dennis:

I was trying to get across the point that the main panel breaker was not protecting the motor. Something else has to do that, or the main panel breaker has to be designed to protect the motor and that is an unlikely situation as the original post was presented.

Thus, I tried to show that the motor was not protected by the main panel breaker by picking a load that would not likely stall the motor, but if no other protection was provided the motor would burn out.

.
Click to expand...

Gotcha. :thumbsup: and I agree
 
ritelec said:
Good morning.

A single phase blower motor 120v/9 amps was installed for a pool spa blower.
I fed it with a 20 amp single pole circuit operated through a contactor.
The owner wants more blow so the pool contractor added another 9 amp blower motor.

The pool panel is full and I am not sure if its tandem rated.
If the panels rated for tandems i can add one and feed the new blower through the contactor (it's 2 pole).
If it's not tandem rated, I'm considering feeding both motors from one 30 amp 120v single pole circuit.

My question is, does the one 30 amp circuit protect each single motor as per code?

Thank you.
Rich
Click to expand...

Does the motor have internal thermal overload protection? It probably does and as such attempting to provide addition overload protect for the motor is basically redundant.
Anyway, unless the motor manufacturer specifies that a breaker is required the intent of the breaker is to protect the wire which is sized to carry the load of the motor.
Remember that breakers protect wire.
 
Rich, read through 430.53. I don't think two 9 amp motors are permitted to be on a 30 amp inverse time circuit breaker.

At the very least the breaker can't be more than values in 430.52, for any motor in the group which is 250% for inverse time circuit breakers. 9 x 2.5 = 22.5. Even a 25 amp breaker is too high.

If you had motors less than 1 HP, no more than 6 amps and 120 volts you could have them all on a 20 amp circuit.

I will let you in on this bit of information - if they don't both start at the same time, they are not too likely to ever trip a 20 amp breaker - unless they are actually loaded to a full 9 amps - then you could possibly have some tripping if run for long periods of time.
 
kwired said:
Rich, read through 430.53. I don't think two 9 amp motors are permitted to be on a 30 amp inverse time circuit breaker.

At the very least the breaker can't be more than values in 430.52, for any motor in the group which is 250% for inverse time circuit breakers. 9 x 2.5 = 22.5. Even a 25 amp breaker is too high.

If you had motors less than 1 HP, no more than 6 amps and 120 volts you could have them all on a 20 amp circuit.

I will let you in on this bit of information - if they don't both start at the same time, they are not too likely to ever trip a 20 amp breaker - unless they are actually loaded to a full 9 amps - then you could possibly have some tripping if run for long periods of time.
Click to expand...

From the OP's description, I get the impression that the motors are guaranteed to turn on and off at the same time:
I'm sure the pool contractors gonna ask why I have to eat up another contactor to supply his blower motors which are going to come on together.
Click to expand...
 
GoldDigger said:
From the OP's description, I get the impression that the motors are guaranteed to turn on and off at the same time:
Click to expand...
I got that impression too, but you can't always rob Peter to pay Paul. He either needs to spend a little more in one area or another. I myself would prefer to supply each motor from opposite 240 volt lines just to balance load some if at all possible.
 
Little Bill said:
There is a lot of critera that has to be met to feed two motors from one circuit. Also, as Gar said, the breaker size is determined by the conductor size, and the motor needs some type of overload protection.
Click to expand...

Absolutely untrue when dealing with motors. (Edit; As far as what the NEC requires)

The breaker size is determined by the motor

The conductor size is determined by the motor and will often be smaller than the breaker size.
 
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