20 amp circuit required for 8.1 amp disposal

[Greg1707]

Electrical Contractor Magazine has an interesting article on sizing conductors. The example used is an 8.1 amp 3/4 horse power kitchen disposal. Since the name plate does not provide a minimum circuit ampacity 422.10a must be followed. The motor is considered continuous duty and then must also be sized 125 per cent of the FLC rating. This all sounds like a lot of trouble for a kitchen sink disposal. Why is the necessary information not included on the name plate to avoid all this?

 

[infinity]

Why can't an 8.1 amp appliance be on a 15 amp individual branch circuit? Have a link to the article?

 

[Greg1707]

Electrical contractor magazine

Electrical contractor magazine

Why can't an 8.1 amp appliance be on a 15 amp individual branch circuit? Have a link to the article?

I do not have a link but it is the July 2014 issue. The article is "Sizing Conductors, Part XXXVIII."

BTW, it also mentions in the article the 2014 requirement that all kitchen 15 and 20 amp circuits be AFCI protected. That means the kitchen circuits will require a minimum or four or five full spaces in the panel. I do a lot of work in condos and town houses that have smaller panels. We often make use of tandem breakers when we can. This will require some changes in our practices.

 

[Esthy]

Here is part of ....

Here is part of ....

Article 422 is a good place to start because it covers electrical appliances used in any occupancy. Section 422.10 specifies the ratings of branch circuits capable of carrying appliance current without overheating under the conditions specified. In accordance with 422.10(A), the rating of an individual branch circuit shall not be less than the marked rating of the appliance or the marked rating of an appliance having combined loads as provided in 422.62, which pertains to required markings on appliance nameplates. Since the branch-circuit rating shall not be less than the appliance?s marked rating, the conductor supplying power to this dishwasher shall have an ampacity of at least 10.9A. Since the conductor will be nonmetallic-sheathed cable, it is important to look in Article 334 for the appropriate requirements. Although the conductor insulation for nonmetallic-sheathed cable is rated at 90?C (194?F), the ampacity shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60?C (140?F) rated conductor (334.80 and 334.112). In accordance with the 60?C column of Table 310.15(B)(16), a 14 AWG conductor is good for 15A. In accordance with 240.4(D)(3), the overcurrent protection for a 14 AWG copper conductor shall not exceed 15A. The minimum size conductor required to supply this dishwasher is 14 AWG (see Figure 1).?
Although the minimum size conductor required for this dishwasher is 14 AWG, many electricians would install a 12 AWG conductor and protect it with a 20A overcurrent device.?
While 422.10(A) covers appliances on individual branch circuits, 422.10(B) covers circuits supplying two or more loads. For branch circuits supplying appliance and other loads, the rating shall be determined in accordance with 210.23. The first sentence states that in no case shall the load exceed the branch-circuit ampere rating. Although it may be worded differently in other locations, this same provision is located in sections throughout the Code. For example, branch-circuit conductors shall have an ampacity not less than the maximum load to be served [210.19(A)(1)]. The second sentence in 210.23 states a branch circuit supplying two or more outlets or receptacles shall supply only the loads specified according to its size as specified in 210.23(A) through (D) and as summarized in 210.24 and Table 210.24. The first provision in this section pertains to 15- and 20A branch circuits. As 210.23(A) states, a 15- or 20A branch circuit shall be permitted to supply lighting units or other utilization equipment, or a combination of both, and shall comply with 210.23(A)(1) and (A)(2). ?
The first section in 210.23(A) pertains to cord-and-plug-connected utilization equipment that is not fastened in place. The second section in 210.23(A) pertains to fastened-in-place utilization equipment. As stated in 210.23(A)(1), the total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, also are supplied. Note that 210.23(A)(2) does not specifically pertain to cord-and-plug-connected utilization equipment like 210.23(A)(1) but to utilization equipment fastened in place. If a fastened-in-place appliance is on the same circuit as lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, the ampacity of the appliance shall not exceed 50 percent of the branch-circuit ampere rating. Because the dishwasher in Figure 1 has an ampere rating that is more than 50 percent of the 20A branch-circuit, it would be a violation to install lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both on the same circuit. Even with dishwashers that have an ampere rating of 10A or less, be careful about installing anything on the same circuit. Installation instructions included with some dishwashers say to install the dishwasher on an individual or dedicated circuit. If so, the dishwasher must be installed on an individual branch circuit. In accordance with 110.3(B), listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.?
Some changes in the 2014 NEC are noteworthy when discussing certain appliances, especially dishwashers in dwellings. Before the 2014 NEC, installing ground-fault circuit interrupter (GFCI) protection for the dishwasher was not required, but now it is. In accordance with 210.8(D), GFCI protection shall be provided for outlets that supply dishwashers installed in dwelling-unit locations. The term ?outlet? in this section is not just a receptacle outlet. As defined in Article 100, an outlet is a point on the wiring system at which current is taken to supply utilization equipment. Therefore, this new GFCI requirement pertains to hard-wired as well as cord-and-plug-connected dishwashers installed in dwellings. While this is not a new requirement, the GFCI shall be installed in a readily accessible location (210.8).?
A significant change for dwelling units pertains to arc-fault circuit interrupter (AFCI) protection. In addition to the rest of the rooms and areas listed in 210.12(A), AFCI protection is now required for all 120V, single-phase, 15- and 20A branch circuits supplying outlets or devices installed in dwelling unit kitchens and laundry areas. This is significant because a dwelling-unit kitchen usually has a number of 15- and 20A branch circuits. Therefore, a dishwasher is now required to be GFCI-and AFCI-protected (see Figure 2).?
It is also necessary to reference several articles when sizing a garbage disposer. For example, a ?-horsepower (hp), in-sink waste disposer will be installed on an individual branch circuit in a dwelling unit. (In the 2014 NEC, the term ?kitchen waste disposer? changed to ?in-sink waste disposer.?) The nameplate on the disposer shows the current draw will be 8.1A at 120V but does not show a minimum branch-circuit rating. The branch-circuit conductors supplying power to this appliance will be nonmetallic-sheathed cable. What is the minimum size conductor required to supply this in-sink waste disposer??
In accordance with 422.10(A), the rating of an individual branch circuit for motor-operated appliances not having a marked rating shall be in accordance with Part II of Article 430. Not having a marked rating means not having a minimum size branch circuit on the nameplate such as 15 or 20A. In Part II of Article 430, 430.22 states that conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current (FLC) rating, as determined by 430.6(A)(1) or not less than specified in 430.22(A) through (G). Section 430.6(A)(1) states to use the FLCs values in Table 430.247 through 430.250 when determining the ampacity of conductors. The Table 430.248 FLC for a ?-hp motor at 115V is 13.8A. Therefore, instead of using the nameplate rating of 8.1A, use 13.8A to determine the ampacity of conductors. As previously mentioned, the ampacity of the conductors shall not be less than 125 percent of the motor FLC rating. Therefore, the conductors must have an ampacity of at least 17A (13.8 ? 125% = 17.25 = 17). In accordance with the 60?C column of Table 310.15(B)(16), a 12 AWG conductor is good for 20A. The minimum size conductor required to supply this electrically operated in-sink waste disposer is 12 AWG (see Figure 3).?
- See more at: http://www.ecmag.com/section/codes-standards/sizing-conductors-part-xxxviii#sthash.zeNeCjPg.dpuf

 

[infinity]

The problem here is that something is incorrect, either the 8.1 amps or the HP rating of 3/4 HP. I would go with the latter being exaggerated by the manufacturer for marketing purposes and the real number is 8.1 amps.

 

[texie]

I saw that article as well and it raised an eyebrow for me too. His argument is that it has a stated HP and has no minimum circuit ampacity on the label and as such it falls under Art. 430 ampacity tables. I'm not sure I agree with his logic. I'm inclined to think this is an appliance. Need to do a little research.

 

[infinity]

I saw that article as well and it raised an eyebrow for me too. His argument is that it has a stated HP and has no minimum circuit ampacity on the label and as such it falls under Art. 430 ampacity tables. I'm not sure I agree with his logic. I'm inclined to think this is an appliance. Need to do a little research.

My thought as well.

 

[czars]

I read the article and I question the need to treat the disposal as a continuous duty device therefore there is no need to multiply the FLC by 1.25. A disposal would never be run for a period of 3 or more hours.

 

[infinity]

I read the article and I question the need to treat the disposal as a continuous duty device therefore there is no need to multiply the FLC by 1.25. A disposal would never be run for a period of 3 or more hours.

I would guess that in the example in the article the load is being treated as a motor {430.22} which requires the 125% calculation not a continuous load.

 

[Smart $]

I read the article and I question the need to treat the disposal as a continuous duty device therefore there is no need to multiply the FLC by 1.25. A disposal would never be run for a period of 3 or more hours.

I would guess that in the example in the article the load is being treated as a motor {430.22} which requires the 125% calculation not a continuous load.

Motors are excluded from 125% continuous load factoring, even if they are operated for over three hours continuously. All the "padding" is part of the requirements for motor circuits.

The continuous duty being referred to is a motor rating, which means it can be operated continuously. Doesn't mean it will be operated continuously.

 

[Smart $]

...

The continuous duty being referred to is a motor rating, which means it can be operated continuously. Doesn't mean it will be operated continuously.

PS: See note to Table 430.22(E)

 

[kwired]

I'm inclined to think this is an appliance. Need to do a little research.

My thought as well.

I also agree. This is a motor operated appliance, not a motor.

I think it is unlikely that it would be used for 3 hours or more at a time, but I don't think they are ever marked with any duty cycle either, but again it is an appliance and not an art 430 motor.

AFAIK the HP is never marked on the actual nameplate either, just in big text on the main body of the appliance.

 

[Smart $]

... but again it is an appliance and not an art 430 motor.

Yet...

422.3 Other Articles. The requirements of Article 430 shall
apply to the installation of motor-operated appliances, and
the requirements of Article 440 shall apply to the installation
of appliances containing a hermetic refrigerant motor-
compressor(s), except as specifically amended in this article.

​

AFAIK the HP is never marked on the actual nameplate either, just in big text on the main body of the appliance.

And that is a very good point. :happyyes:

The 'rules' for no HP on the nameplate say you go by the nameplate current rating. In the case of a motor-operated appliance, that includes nameplate on motor itself, not just the appliance nameplate.

 

[kwired]

Yet...

​

And that is a very good point. :happyyes:

The 'rules' for no HP on the nameplate say you go by the nameplate current rating. In the case of a motor-operated appliance, that includes nameplate on motor itself, not just the appliance nameplate.

I agree. I knew that art 422 sent you to 430 when dealing with motor operated appliances and maybe should have mentioned it. Also don't forget the last part of 422.3 - except as specifically amended in this article.

 

[Smart $]

... Also don't forget the last part of 422.3 - except as specifically amended in this article.

Not forgetting... just not aware of any part of 422 that amends 430/440 in any pertinent manner. You?

 

[kwired]

Not forgetting... just not aware of any part of 422 that amends 430/440 in any pertinent manner. You?

Off the top of my head - no.

 

[iwire]

I did not read the article but it sure sounds like a case of a code nerd with too much time on their hands trying to fix something that has never been a problem. Too much time in the books and not enough in the field. Or they work for company that could make more money if all GD circuits had to be 20s.

My shop vac says its "3.0 Horsepower", I can only imagine the size circuit I will have to run for it now. :roll:

 

[kwired]

I did not read the article but it sure sounds like a case of a code nerd with too much time on their hands trying to fix something that has never been a problem. Too much time in the books and not enough in the field. Or they work for company that could make more money if all GD circuits had to be 20s.

My shop vac says its "3.0 Horsepower", I can only imagine the size circuit I will have to run for it now. :roll:

@ 120 volts this 3HP shop vac should have at least a 50 amp cord cap and 8 AWG supply conductors, maybe about a 70 amp breaker to make sure it doesn't trip while starting, I bet yours doesn't have anything close to that:happyyes:

 

[iwire]

@ 120 volts this 3HP shop vac should have at least a 50 amp cord cap and 8 AWG supply conductors, maybe about a 70 amp breaker to make sure it doesn't trip while starting, I bet yours doesn't have anything close to that:happyyes:

:thumbsup:


15 amp circuit, 5-15P cord cap, 16 or 18 AWG cord. It has not burned up yet, I guess I am very lucky.

 

[david]

Electrical Contractor Magazine has an interesting article on sizing conductors. The example used is an 8.1 amp 3/4 horse power kitchen disposal. Since the name plate does not provide a minimum circuit ampacity 422.10a must be followed. The motor is considered continuous duty and then must also be sized 125 per cent of the FLC rating. This all sounds like a lot of trouble for a kitchen sink disposal. Why is the necessary information not included on the name plate to avoid all this?

?Installation instructions included with some dishwashers say to install the dishwasher on an individual or dedicated circuit. If so, the dishwasher must be installed on an individual branch circuit. In accordance with 110.3(B), listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.?

I wonder if the ? HP disposal will have installation instructions calling out the size of the circuit?