20 amp circuit required for 8.1 amp disposal

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kwired

Electron manager
Location
NE Nebraska
?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?
I will say true, and will also reluctantly say most of those mentioned appliances will likely come with such instructions, and IMO for no good reason other then for them to have an excuse to not honor a warranty if not installed according to instructions.:(
 

mbrooke

Batteries Included
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United States
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Technician
I read it and its not technically correct. It would be correct if HP was just used along with use (ie continuous duty process motor). But this is a disposal, intermittent with an 8 amp rating already determined by the manufacturer.



Around here disposals have 2 options. 1 separate 15 amp circuit usually part of a MWBC when dishwasher resides near, or 1 20 amp circuit with both disposer and dishwasher sharing it. 40 year practice that has proved fail safe.
 

kwired

Electron manager
Location
NE Nebraska
I read it and its not technically correct. It would be correct if HP was just used along with use (ie continuous duty process motor). But this is a disposal, intermittent with an 8 amp rating already determined by the manufacturer.
So do you think OP's disposer is an art 422 appliance or an art 430 motor? If it is a motor and is a true 3/4 hp motor nameplate amps means nothing unless you need to provide overload protection, you default to table 430.248 to find full load current and it says 13.8 amps there. Then comes the issue of if it is not considered a continuous load - exactly what method is used to select conductor ampacity? If we go back to 430.22, we need to actually apply 140 up to maybe 200 percent of rated current to come up with conductor ampacity, unless it is a motor with a rated duty cycle. I can't recall if I have ever seen a "continuous duty" marked on a disposer, but am fairly certain I have never seen any duty cycle ratings - so it still defaults to it being considered continuous duty motor AFAIK. But if it is a 422 appliance instead of a 430 motor - that could change how this is determined, need to dig a little deeper before confirming that though.



Around here disposals have 2 options. 1 separate 15 amp circuit usually part of a MWBC when dishwasher resides near, or 1 20 amp circuit with both disposer and dishwasher sharing it. 40 year practice that has proved fail safe.
As long as both appliances are 10 amps or less it works with code also, get one above 10 amps - real world applications have worked with little or no issue many times, code may not always agree.
 

mbrooke

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Technician
So do you think OP's disposer is an art 422 appliance or an art 430 motor? If it is a motor and is a true 3/4 hp motor nameplate amps means nothing unless you need to provide overload protection, you default to table 430.248 to find full load current and it says 13.8 amps there. Then comes the issue of if it is not considered a continuous load - exactly what method is used to select conductor ampacity? If we go back to 430.22, we need to actually apply 140 up to maybe 200 percent of rated current to come up with conductor ampacity, unless it is a motor with a rated duty cycle. I can't recall if I have ever seen a "continuous duty" marked on a disposer, but am fairly certain I have never seen any duty cycle ratings - so it still defaults to it being considered continuous duty motor AFAIK. But if it is a 422 appliance instead of a 430 motor - that could change how this is determined, need to dig a little deeper before confirming that though.



As long as both appliances are 10 amps or less it works with code also, get one above 10 amps - real world applications have worked with little or no issue many times, code may not always agree.


IMO the disposer is an appliance. Its a packaged UL listed unit sold as such. There is no way an undersized 3 minute a day motor would be a true 3/4 horse power. The label might say so, but appliance makers like to stretch claims. Putting a true 3/4 HP motor in a disposer would be nice but the cost would bring price up considerably. I see one as an advertising claim (3/4 HP) and the other as an actual established amperage (8.1 amps). Not sure if it changes anything but some disposer don't even use induction motors, rather rectified permanent magnet DC or universal motors.

Also consider the fact that if one looks at the advertising literature of most older washing machine or dishwasher they will often find "Ultra Heavy duty 1/2 HP" or "Super 1/3 HP motor". Under the NEC these would need 20 or 30 amp circuits with oversized breakers for starting inrush if considered motors. Dishwashers would get even messier with their onboard heating coil. But because they are listed as appliances max amperage is used.


I could be wrong but that how Ive always assumed it.


"real world applications have worked with little or no issue many times, code may not always agree" :D You bring up a good point here. It may not even be code from the start. On new installs I have never seen the combined rating of the two go above 20amps, certainly not in the last 10 years with energy efficient dishwasher not going over 6 amps. Rarely are builder disposers anything extravagant to begin with, however I have seen kitchens with some 70s or 80s dishwashers that pull 12 amps with a HO latter replacing the 5 amp builder disposer with a 12 amp Insinkerator (A must have disposer;)). Violation here no doubt, but again one could argue the NEC doesn't consider possible future changes.
 
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GoldDigger

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IMHO a motor load which does not have a duty cycle specified is still not a continuous load as that multiplier does not apply to motors. Maybe to appliances, but for motors it has already been factored into demand and hopefully circuit loading.
 

david

Senior Member
Location
Pennsylvania
On/Off Control Wall Switch
Motor Single Phase
HP 3/4
Volts 120
HZ 60
RPM 1725
Amp. (Avg. Load) 8.1
Time Rating Intermittent

From internet search of one manufactures specs
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
UL 430 covers household disposals. It's a little long and laborious, but it is clear that you do not calculate the branch circuit using Art. 430 rules. For starters, the HP of a disposal per UL is calculated from the line current stated on the label. The line current on the label is determined from testing under conditions described in the standard. It is makes clear that the line current regardless of any HP markings (even if on the data plate) is to be used for branch circuit sizing. The standard says that a disposal must start and operate on a circuit that is at least the stated current on the data plate and that the next standard size OCPD is OK. The most direct answer to the MCA is given in Section 59.6.
Assuming a typical disposal such as the one mentioned in the article of 9.8 amps and you use the manufacturer optional cord set (that by the way has a 5-15 cord end) and you want to put it on an individual outlet and branch circuit you would be required to use a 15 amp circuit with a 15 amp single receptacle. In fact, under these conditions you could not use a 20 amp circuit even if you wanted to.
So to sum up, I think the author the the article in question is clearly not correct on the subject at hand.
For those so inclined here is a link to the UL standard: http://www.clearfwd.com/uploads/File/UL 430-2004(1).pdf
 
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Smart $

Esteemed Member
Location
Ohio
UL 430 covers household disposals. It's a little long and laborious, but it is clear that you do not calculate the branch circuit using Art. 430 rules. For starters, the HP of a disposal per UL is calculated from the line current stated on the label. The line current on the label is determined from testing under conditions described in the standard. It is makes clear that the line current regardless of any HP markings (even if on the data plate) is to be used for branch circuit sizing. The standard says that a disposal must start and operate on a circuit that is at least the stated current on the data plate and that the next standard size OCPD is OK. The most direct answer to the MCA is given in Section 59.6.
Assuming a typical disposal such as the one mentioned in the article of 9.8 amps and you use the manufacturer optional cord set (that by the way has a 5-15 cord end) and you want to put it on an individual outlet and branch circuit you would be required to use a 15 amp circuit with a 15 amp single receptacle. In fact, under these conditions you could not use a 20 amp circuit even if you wanted to.
So to sum up, I think the author the the article in question is clearly not correct on the subject at hand.
For those so inclined here is a link to the UL standard: http://www.clearfwd.com/uploads/File/UL 430-2004(1).pdf
The UL Standard has no bearing on NEC requirements unless the pertinent part(s) is(are) included on the product nameplate (such as MCA) or in the product documentation (i.e. its instructions)... or otherwise imposed such as a manufacturers-included or -optional 15A plug.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
The UL Standard has no bearing on NEC requirements unless the pertinent part(s) is(are) included on the product nameplate (such as MCA) or in the product documentation (i.e. its instructions)... or otherwise imposed such as a manufacturers-included or -optional 15A plug.

I beg to differ. The NEC, UL and other NRTL organizations are always trying to harmonize requirements to avoid conflicts. As recent example of this is a change made in NEC 2014 404.8(C) regarding snap switches. The NEC was changed to reflect what the listing standard required. And do you ignore 110.3?
The disposal question is a perfect example of where one needs to look at the testing standard to determine what is required. It is clear the the standard does not view a disposal by it's stated horsepower and the label current is to be used.
The idea that a disposal has to be wired using the stated HP and Art. 430 is pure nonsense when the testing standard says that it will not draw more current that is stated on the label under the design load it is tested under.
 

kwired

Electron manager
Location
NE Nebraska
It is also clear (to me anyway) that the NEC views a disposal in the same way as the standard (430.6(A)(1) Ex. No. 3.)
Good find, exception 3 makes most of this conversation meaningless IMO.

It is easy to skip some of this early information at times and go straight to the later sections, then find out later that reading some of the early content in a particular code section actually gives information that was needed for the problem you are trying to solve. I know it never crossed my mind to look at such early sections in art 430, I think I did start reading nearly from beginning of 422 when researching the discussion in this thread.
 

david

Senior Member
Location
Pennsylvania
The article mentioned 8.1 amps. I couldn?t find the appliance nameplate on line but the spec sheet says
Amp. (Avg. Load) 8.1 If the average load amps is 8.1, the exception states FLA.
I wonder if there will be a significant difference between the two.

The spec sheet said continuous feed and the video said that met once you turn the switch on feed it until you turn the switch off verses ones that you feed first add a safety cap before they will operate.

The time rating was labeled Time Rating Intermittent, the article said continuous duty
I am wondering if the article used 8.1 average load amps verses nameplate FLA , and used continuous feed verses Time rating Intermittent
 

david

Senior Member
Location
Pennsylvania
The article mentioned 8.1 amps. I couldn?t find the appliance nameplate on line but the spec sheet says
Amp. (Avg. Load) 8.1 If the average load amps is 8.1, the exception states FLA.
I wonder if there will be a significant difference between the two.

The spec sheet said continuous feed and the video said that met once you turn the switch on feed it until you turn the switch off verses ones that you feed first add a safety cap before they will operate.

The time rating was labeled Time Rating Intermittent, the article said continuous duty
I am wondering if the article used 8.1 average load amps verses nameplate FLA , and used continuous feed verses Time rating Intermittent

Sorry I was referring to post #26 in the thread there is no spec sheet in the article or video,
I did an on line search of ? HP disposals until I found a spec sheet that referenced 8.1 amps since 8.1 is pretty specific I assume it is real similar to the one referenced in the article
As far as the video I just looked at a couple and the one happened to explain what continuous feed met.
It also showed turning off a 15 amp breaker before disconnecting your older model and made no mention of changing the 15 amp circuit when upgrading to the 3/4 HP one.

EDIT: I also looked at insulation instructions , there was a lot of concern for the equipment ground but when it came to the branch circuit, cover all statement in accordance with the latest addition of the NEC
 
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Smart $

Esteemed Member
Location
Ohio
I beg to differ. The NEC, UL and other NRTL organizations are always trying to harmonize requirements to avoid conflicts. ...
You are mistaking what I'm saying... and what I said was in a generalized context, not topic-item specific. Where the NEC requires or takes a listed item into account, the standard is included by reference... yet where there is a conflict, the NEC supersedes the listing standard (i.e you're installing to the NEC 'standard, not NRTL standard?a safety testing standard; not an installation standard), and this is especially true where the item is not required to be listed.

But as replies following yours have revealed, this discussion is quite moot regarding a listed disposal. Yet we can continue the debate for a non-listed disposal if you wish... :angel:
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
OK, seems we are all on the same page now. If I could only get everyone onboard on the proper use of a busbar in relation to 250.64(D) and (F)......:p
 
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