Adding 1000/2000 W 240v Heater To 15 Amp 240v Circuit Running 1/2 HP Well Pump - Electrical - Page 2 - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum Adding 1000/2000 w 240v heater to 15 amp 240v circuit running 1/2 HP well pump
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01-01-2014, 10:54 PM   #16
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Here's what the code has to say; this is not a direct quote, just the parts that pertain to the OP.

430.24 A motor and other load. Conductors supplying a motor and other load shall have an ampacity of 125% of the motor plus the ampacity required for the other loads.

Here are the figures; the well pump motor draws 5 amps. 5 X 1.25 = 6.25

Since this motor is on a basic circuit breaker, the maximum size, according to 430.52, is 250% of the motor current. 5 X 2.5 = 12.5 Therefore, a 15 is the maximum.

Now, since the heater is considered a continuous load, it must be figured at 125%, just like the motor.

2000W ÷ 240 = 8.3

6.25 (pump motor)+ 8.3 (heater) = 14.55 Therefore, it would be code-compliant to connect both the 2000 watt heater and the 1/2HP motor to a 15 amp 240 volt circuit. Changing the breaker to a 20 would violate 430.52

According to my Franklin Motor spec book, the 1/2HP 230 volt 3 wire model draws 23 amps at startup. The 2 wire model draws 32 amps. I seriously doubt this would trip a 15 amp breaker even with 8.3 amps already on it.

Even though I'm a serious advocate of well pump motors being on their own circuit, if a new circuit is difficult to run, I would very likely connect the heater to the well pump circuit.

Be careful though, as noted, the pump controller is located downstream of the pressure switch. Depending on how the wire is run, there's a good chance that there is no power available at the controller when the pump is not running.

Rob

01-02-2014, 04:22 AM   #17

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Quote:
 Originally Posted by micromind Here's what the code has to say; this is not a direct quote, just the parts that pertain to the OP. 430.24 A motor and other load. Conductors supplying a motor and other load shall have an ampacity of 125% of the motor plus the ampacity required for the other loads. Here are the figures; the well pump motor draws 5 amps. 5 X 1.25 = 6.25 Since this motor is on a basic circuit breaker, the maximum size, according to 430.52, is 250% of the motor current. 5 X 2.5 = 12.5 Therefore, a 15 is the maximum. Now, since the heater is considered a continuous load, it must be figured at 125%, just like the motor. 2000W ÷ 240 = 8.3 6.25 (pump motor)+ 8.3 (heater) = 14.55 Therefore, it would be code-compliant to connect both the 2000 watt heater and the 1/2HP motor to a 15 amp 240 volt circuit. Changing the breaker to a 20 would violate 430.52 According to my Franklin Motor spec book, the 1/2HP 230 volt 3 wire model draws 23 amps at startup. The 2 wire model draws 32 amps. I seriously doubt this would trip a 15 amp breaker even with 8.3 amps already on it. Even though I'm a serious advocate of well pump motors being on their own circuit, if a new circuit is difficult to run, I would very likely connect the heater to the well pump circuit. Be careful though, as noted, the pump controller is located downstream of the pressure switch. Depending on how the wire is run, there's a good chance that there is no power available at the controller when the pump is not running. Rob
Thats 125% of the motors RLA/FLA. So 5 amps may not be the motors rated amp draw.

You also forgot to multiply 8.3 times 1.25

So, 5 X 1.25 = 6.25, 8.3 X 1.25 = 10.375, 6.25+10.375=16.625 amps.
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01-02-2014, 08:40 AM   #18
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Quote:
 Originally Posted by beenthere Thats 125% of the motors RLA/FLA. So 5 amps may not be the motors rated amp draw. You also forgot to multiply 8.3 times 1.25 So, 5 X 1.25 = 6.25, 8.3 X 1.25 = 10.375, 6.25+10.375=16.625 amps.
You're right about the heater amps. My mistake.

According to the OP, the pump draws 5 amps which is above the 4.9 listed in 430 as the current for a 1/2HP motor. So 5 is the correct number to use.

01-02-2014, 10:12 AM   #19
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Quote:
 Originally Posted by micromind Since this motor is on a basic circuit breaker, the maximum size, according to 430.52, is 250% of the motor current. 5 X 2.5 = 12.5 Therefore, a 15 is the maximum.
Can you explain what concept is in play that would require a maximum circuit breaker size? Obviously a minimum size is easy to understand.

01-02-2014, 01:59 PM   #20
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Quote:
 Originally Posted by micromind Here's what the code has to say; this is not a direct quote, just the parts that pertain to the OP. 430.24 A motor and other load. Conductors supplying a motor and other load shall have an ampacity of 125% of the motor plus the ampacity required for the other loads. Here are the figures; the well pump motor draws 5 amps. 5 X 1.25 = 6.25 Since this motor is on a basic circuit breaker, the maximum size, according to 430.52, is 250% of the motor current. 5 X 2.5 = 12.5 Therefore, a 15 is the maximum. Now, since the heater is considered a continuous load, it must be figured at 125%, just like the motor. 2000W ÷ 240 = 8.3 6.25 (pump motor)+ 8.3 (heater) = 14.55 Therefore, it would be code-compliant to connect both the 2000 watt heater and the 1/2HP motor to a 15 amp 240 volt circuit. Changing the breaker to a 20 would violate 430.52 According to my Franklin Motor spec book, the 1/2HP 230 volt 3 wire model draws 23 amps at startup. The 2 wire model draws 32 amps. I seriously doubt this would trip a 15 amp breaker even with 8.3 amps already on it. Even though I'm a serious advocate of well pump motors being on their own circuit, if a new circuit is difficult to run, I would very likely connect the heater to the well pump circuit. Be careful though, as noted, the pump controller is located downstream of the pressure switch. Depending on how the wire is run, there's a good chance that there is no power available at the controller when the pump is not running. Rob
Yes I would prefer to have the well pump se

01-02-2014, 02:06 PM   #21
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Quote:
 Originally Posted by micromind Here's what the code has to say; this is not a direct quote, just the parts that pertain to the OP. 430.24 A motor and other load. Conductors supplying a motor and other load shall have an ampacity of 125% of the motor plus the ampacity required for the other loads. Here are the figures; the well pump motor draws 5 amps. 5 X 1.25 = 6.25 Since this motor is on a basic circuit breaker, the maximum size, according to 430.52, is 250% of the motor current. 5 X 2.5 = 12.5 Therefore, a 15 is the maximum. Now, since the heater is considered a continuous load, it must be figured at 125%, just like the motor. 2000W ÷ 240 = 8.3 6.25 (pump motor)+ 8.3 (heater) = 14.55 Therefore, it would be code-compliant to connect both the 2000 watt heater and the 1/2HP motor to a 15 amp 240 volt circuit. Changing the breaker to a 20 would violate 430.52 According to my Franklin Motor spec book, the 1/2HP 230 volt 3 wire model draws 23 amps at startup. The 2 wire model draws 32 amps. I seriously doubt this would trip a 15 amp breaker even with 8.3 amps already on it. Even though I'm a serious advocate of well pump motors being on their own circuit, if a new circuit is difficult to run, I would very likely connect the heater to the well pump circuit. Be careful though, as noted, the pump controller is located downstream of the pressure switch. Depending on how the wire is run, there's a good chance that there is no power available at the controller when the pump is not running. Rob
Yes I would prefer to have the well pump separate as well but running a new circuit to this location is gonna be a PITA! But I will only go the other rout if is actually safe. The only thing I don't understand fully is the maximum amperage at 15, what would be the case for not using 20 amp? Just curious

01-02-2014, 03:09 PM   #22

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Quote:
 Originally Posted by micromind You're right about the heater amps. My mistake. According to the OP, the pump draws 5 amps which is above the 4.9 listed in 430 as the current for a 1/2HP motor. So 5 is the correct number to use.
Actually, its suppose to the RLA that is listed on the pump that is used.
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 01-02-2014, 05:29 PM #23 Newbie   Join Date: Jan 2014 Posts: 14 Rewards Points: 10 Just took this pic from inside the controller Attached Thumbnails
01-02-2014, 07:45 PM   #24
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Quote:
 Originally Posted by beenthere Actually, its suppose to the RLA that is listed on the pump that is used.
430.6(A)(1) states Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for multispeed motors, the values given in tables 430.248, 430.249, and 430.250 shall be used to determine the ampacities of conductors or amp ratings of switches, branch circuit short circuit and ground fault protection, instead of the actual current rating marked on the motor nameplate.

01-02-2014, 08:17 PM   #25
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Quote:
 Originally Posted by JKeefe Can you explain what concept is in play that would require a maximum circuit breaker size? Obviously a minimum size is easy to understand.
I'll try to not screw this one up........lol. I should know better than to post something relatively simple while I'm designing a fairly complex control scheme for a bunch of VFDs at an oil refining plant.

Lol.

The maximum breaker rating is given because motors draw more current for starting than for running. Most motors will draw roughly 6 X their full-load current for starting.

With a few exceptions, every motor is required by code to have some type of protection from overloading and/or failure to start. This will protect both the motor and the wire feeding it.

If the breaker were to be sized to the wire, there's a fair chance that the breaker would trip before the motor came up to speed. So breakers are allowed to be larger than the wire. The only purpose of a breaker in a motor circuit is short circuit and ground fault protection. The motor overloads are not quick enough.

I'm pretty much guessing here, but I suspect that the reason there's no minimum breaker size listed is because it would make the code more of an installation manual rather than a safety manual. 90.1(C) states This code is not intended as a design specification or an instruction manual for untrained persons.

As to why a 20 is not compliant when a 15 is required it's mostly because a 15 will trip at a slightly lower fault current than a 20. In real life though, I can't think of even one instance where a 20 would be more hazardous than a 15 for a motor.

It's just one of the quirks in the code, I guess.

Kind of like why is it compliant to use #14s to supply a 16 amp motor and it's not compliant to use the same #14s to supply a 1500 watt 120 volt heater that draws 12.5 amps. It makes no sense, especially given that a motor is more abusive to wire than a heater.

 01-02-2014, 08:18 PM #26 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,401 Rewards Points: 7,792 And wouldn't a water pump be a low speed, high torque motor. __________________ When posting in certain forums, knowing your location will help others give better feedback/advice/solutions to your questions.
01-02-2014, 08:20 PM   #27
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Quote:
 Originally Posted by beenthere Thats 125% of the motors RLA/FLA. So 5 amps may not be the motors rated amp draw. You also forgot to multiply 8.3 times 1.25 So, 5 X 1.25 = 6.25, 8.3 X 1.25 = 10.375, 6.25+10.375=16.625 amps.
If the heater were connected for 1000 watts, it'd be compliant.

5 X 1.25=6.25, 4.2 X 1.25 = 5.25 + 6.25= 11.5

01-02-2014, 08:24 PM   #28
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Quote:
 Originally Posted by beenthere And wouldn't a water pump be a low speed, high torque motor.
The vast majority of the ones I've seen, and certainly a submersible pump motor would be 2 pole; roughly 3450 RPM. And normal torque.

Though I have seen sewer pump motors that were 590 and 885 RPM.

 01-03-2014, 09:42 AM #29 Newbie   Join Date: Jan 2014 Posts: 14 Rewards Points: 10 Thank you everyone for your time, I did learn a few things! One more question, can I run 14/3 wire to my heater or do I stay the same and run 12/3. I have lots of 14/3 hanging around.
01-03-2014, 12:06 PM   #30

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14/3 is fine for 1000 or 2000 watts at 240 volts.

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