MICROWAVE RECEPTACLE

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BRIAN MEDWATZ

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spotsylvania, virginia
I have a job that was passed 2 + years ago. now an inspector is wanting single receptacles in the cabinet for the micro. where in the 2011 code does it expressly state this is to be a single and not a standard duplex. i have been using single receptacles for this but would like to know where it is defined in the code.
 
Unless 110.3(B) is a player here: manufacturers listing and labeling in the instructions, than the only applicable article I can think of is 422.16(B)(4), which is cord connected range hoods which are commonly dual microwave/ range hood units that require an individual/dedicated circuit, but does not denote a simplex or duplex receptacle by any means, unless one presumes that the singularity of parts of this section implies a simplex, I do not infer such, but one could......


(4) Range Hoods.
Range hoods shall be permitted to be
cord-and-plug-connected with a flexible cord identified as
suitable for use on range hoods in the installation instruc-
tions of the appliance manufacturer, where all of the fol-
lowing conditions are met:
(1) The flexible cord is terminated with a grounding-type
attachment plug.
Exception: A listed range hood distinctly marked to iden-
tify it as protected by a system of double insulation, or its
equivalent, shall not be required to be terminated with a
grounding-type attachment plug.
(2) The length of the cord is not less than 450 mm (18 in.)
and not over 900 mm (36 in.).
(3) Receptacles are located to avoid physical damage to the
flexible cord.
(4) The receptacle is accessible.
(5) The receptacle is supplied by an individual branch
circuit
 
BRIAN MEDWATZ said:
I have a job that was passed 2 + years ago. now an inspector is wanting single receptacles in the cabinet for the micro. where in the 2011 code does it expressly state this is to be a single and not a standard duplex. i have been using single receptacles for this but would like to know where it is defined in the code.
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There is no such code section. The only code that would apply is that if you do install a single receptacle and it is a 20 amp circuit it must have a 20 amp rated outlet.
I have never seen a 20 amp cord on such a Micro hood.
Ask the inspector nicely for a code section!
 
yes, been beat to death here.

no such code for single recept on a indi-bc.

its an issue with inspectors at this point
 
BRIAN MEDWATZ said:
I have a job that was passed 2 + years ago. now an inspector is wanting single receptacles in the cabinet for the micro. where in the 2011 code does it expressly state this is to be a single and not a standard duplex. i have been using single receptacles for this but would like to know where it is defined in the code.
Click to expand...

Welcome to the forum. Note that VA residential does not go by the 2011 NEC, but by the 2012 IRC:


http://codes.iccsafe.org/app/book/toc/2012 VA_Residential_HTML/index.html

There is nothing in our code that requires a simplex receptacle to serve a microwave on an individual branch circuit.
 
Local Ordinance

Local Ordinance

Some local jurisdictions require fastened in place appliances to have 20A single receptacles on dedicated circuits in my experience. I've made it common practice at this point to avoid issues.
 
Code is not always the ultimate design criteria

Code is not always the ultimate design criteria

Always check for amendments to the Code for the local jurisdiction. The Code is generally the minimal requirement.
 
BRIAN MEDWATZ said:
I have a job that was passed 2 + years ago. now an inspector is wanting single receptacles in the cabinet for the micro. where in the 2011 code does it expressly state this is to be a single and not a standard duplex. i have been using single receptacles for this but would like to know where it is defined in the code.
Click to expand...

It depends on the load the microwave is imposing on the circuit. For a duplex receptacle, NEC section 210.21(B)(2) comes into play and the type of circuit is irrelevant. For a NEMA 5-15R duplex receptacle, NEC section 210.21(B)(2) limits the maximum cord-and-plug connected load to either receptacle contained in that duplex to 12 amps. Therefore, if you've got a 1500 watt microwave plugged into one of the receptacles in that duplex receptacle, it is a violation of 210.21(B)(2). If the receptacle is a NEMA 5-20R receptacle, 210.21(B)(2) limits the load plugged into either receptacle to 16 amps.

If it was a single receptacle, NEC section 240.21(B)(1) comes into play and permits you to load that receptacle up to it's rating.
 
jrohe said:
It depends on the load the microwave is imposing on the circuit. For a duplex receptacle, NEC section 210.21(B)(2) comes into play and the type of circuit is irrelevant. For a NEMA 5-15R duplex receptacle, NEC section 210.21(B)(2) limits the maximum cord-and-plug connected load to either receptacle contained in that duplex to 12 amps. Therefore, if you've got a 1500 watt microwave plugged into one of the receptacles in that duplex receptacle, it is a violation of 210.21(B)(2). If the receptacle is a NEMA 5-20R receptacle, 210.21(B)(2) limits the load plugged into either receptacle to 16 amps.

If it was a single receptacle, NEC section 240.21(B)(1) comes into play and permits you to load that receptacle up to it's rating.
Click to expand...

Good points. Why does the code NOT require 20A receptacles in, say, bathrooms, knowing that pretty much anyone at some point will plug an 1875W hair dryer into it? Difference in fixed vs moveable appliances?
 
JFletcher said:
Good points. Why does the code NOT require 20A receptacles in, say, bathrooms, knowing that pretty much anyone at some point will plug an 1875W hair dryer into it? Difference in fixed vs moveable appliances?
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Typically the 1875 watt rating is at 125 volts. Using these values, the current is exactly 15 amps. However, the hair dryer power and associated current will be lower for the 120 volts that is actually delivered to the hair dryer. Power varies proportionally with the square of the ratio of the voltages so at 120 volts the 1875 watt hair dryer's power will actually be 92.16% (120^2/125^2) of the 1875 watt rating, or 1728 watts. With a power of 1728 watts at a voltage of 120 volts, the current is 14.4 amps. This also explains why 1875 watt hair dryers do not have NEMA 5-20P cordsets.
 
jrohe said:
Typically the 1875 watt rating is at 125 volts. Using these values, the current is exactly 15 amps. However, the hair dryer power and associated current will be lower for the 120 volts that is actually delivered to the hair dryer. Power varies proportionally with the square of the ratio of the voltages so at 120 volts the 1875 watt hair dryer's power will actually be 92.16% (120^2/125^2) of the 1875 watt rating, or 1728 watts. With a power of 1728 watts at a voltage of 120 volts, the current is 14.4 amps. This also explains why 1875 watt hair dryers do not have NEMA 5-20P cordsets.
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Makes sense, but at same time I am sure it states somewhere that we are to use nominal 120 volts for calculations, so if an appliance says 115 on nameplate then actual current at will be higher if 120 (for non inductive loads anyway) is the applied voltage:roll:
 
jrohe said:
It depends on the load the microwave is imposing on the circuit. For a duplex receptacle, NEC section 210.21(B)(2) comes into play and the type of circuit is irrelevant. For a NEMA 5-15R duplex receptacle, NEC section 210.21(B)(2) limits the maximum cord-and-plug connected load to either receptacle contained in that duplex to 12 amps. Therefore, if you've got a 1500 watt microwave plugged into one of the receptacles in that duplex receptacle, it is a violation of 210.21(B)(2). If the receptacle is a NEMA 5-20R receptacle, 210.21(B)(2) limits the load plugged into either receptacle to 16 amps.

If it was a single receptacle, NEC section 240.21(B)(1) comes into play and permits you to load that receptacle up to it's rating.
Click to expand...
Not a violation. Has to EXCEED 12 amperes to be a violation. 1500W is right at 12A. Also check the voltage at which the wattage rating is given. Can be the same as the hairdryer.

As also had been mentioned in another recent thread, one can remove the tabs on a duplex receptacle and limit the branch circuit to one receptacle, one outlet.
 
Anyone that uses a 1875 watt hair dryer on any 15 amp circuit that isn't operating at least at an actual 125 volts is in violation and will serve prison time if caught:happyyes:

Similar with their microwave ovens.

But slugging a circuit if you have an old fuse box is still acceptable.
 
kwired said:
Makes sense, but at same time I am sure it states somewhere that we are to use nominal 120 volts for calculations, so if an appliance says 115 on nameplate then actual current at will be higher if 120 (for non inductive loads anyway) is the applied voltage:roll:
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kwired, thank you and you are absolutely correct. NEC section 220.5(A) requires the use of the nominal system voltages for the purposes of calculating branch-circuit and feeder loads.

If I were designing any building other than a dwelling unit that had an appliance with a load of 1875 watts (VA) on a circuit, I would have used a load of 1875 watts (VA) for calculating the branch-circuit and feeder load rather than converting to the 1728 watts (VA). The 1 amp gain on one phase conductor is typically not enough to make a difference in the grand scheme of things and using the 1875 watt (VA) load errs in favor of a conservative design (as if the NEC wasn't conservative enough). Code requirements for dwelling units can be a completely different animal if you use the optional calcs.

My reply was simply to explain why an 1875 watt, 125 volt hair dryer is still safe to use on a NEMA 5-15R receptacle.
 
jrohe said:
kwired, thank you and you are absolutely correct. NEC section 220.5(A) requires the use of the nominal system voltages for the purposes of calculating branch-circuit and feeder loads.

If I were designing any building other than a dwelling unit that had an appliance with a load of 1875 watts (VA) on a circuit, I would have used a load of 1875 watts (VA) for calculating the branch-circuit and feeder load rather than converting to the 1728 watts (VA). The 1 amp gain on one phase conductor is typically not enough to make a difference in the grand scheme of things and using the 1875 watt (VA) load errs in favor of a conservative design (as if the NEC wasn't conservative enough). Code requirements for dwelling units can be a completely different animal if you use the optional calcs.

My reply was simply to explain why an 1875 watt, 125 volt hair dryer is still safe to use on a NEMA 5-15R receptacle.
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What you stated is likely how they can get away with not putting a 20 amp plug on it and still have it listed. Reality is it probably wouldn't be any less safe if it were rated 2000 watts at 120 or 125 volts, such appliances don't normally run long enough to become a overload issue, until there is other significant load on the same circuit anyway.
 
Call me dumb, but I thought it was watts/volts=amps. So 1875/125=15 and 1875/120=15.625. The amperage goes UP, not down.
 
jaylectricity said:
Call me dumb, but I thought it was watts/volts=amps. So 1875/125=15 and 1875/120=15.625. The amperage goes UP, not down.
Click to expand...
OK you are dumb..... but only because of your request to be called that.:)

As Bob mentioned resistance needs considered also and will remain constant so if you change voltage the wattage will also change. Inductive loads follow a little different rules, and if you increased voltage on most motors the current usually will go down, within a certain range of the design rating anyway, but power remains relatively constant with those minor voltage changes on a motor, this is disregarding what effects power factor and motor efficiency will add to the mix.
 
Smart $ said:
As also had been mentioned in another recent thread, one can remove the tabs on a duplex receptacle and limit the branch circuit to one receptacle, one outlet.
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absolutely not. article 100 says no.

Receptacle. A receptacle is a contact device installed at the
outlet for the connection of an attachment plug. A single
receptacle is a single contact device with no other contact
device on the same yoke. A multiple receptacle is two or
more contact devices on the same yoke.
Click to expand...
 
iwire said:
No, not unless you are changing the resistance of the unit.
Click to expand...

correct, as long as freq is constant the Z of the unit is constant, thus if you drop V the amps will also drop.

and yeah, hmmm, almost every 1875w dryer is spec'd at 125v. but as mentioned, for items spec'd at 115v do you apply bump up calculation to normalize their crap data back to 120v(rms) ??
 
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