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gs99

02:34PM | 11/22/02
Member Since: 11/18/02
30 lifetime posts
Bvelectrical
Should the device (switch, receptacle) amp rating match the circuit breaker rating? For example, small-appliance and bathroom circuits are 20-ampere. Are the GFCI receptacles on those circuits supposed to be rated 20-ampere? Where would 15-ampere GFCI receptacles be installed?

Tom O

02:20AM | 11/23/02
Member Since: 09/17/02
487 lifetime posts
You can use 15 amp duplex receptacles on a 20 amp circuit but not 20 amp receptacles on a 15 amp circuit.

Switches must be able to handle the load that is connect to them. It is not unusual to see 10 amp or 15 amp switches on a 20 amp circuit.

Tom

gs99

10:14AM | 11/23/02
Member Since: 11/18/02
30 lifetime posts
On a 20-amp circuit, 12 gauge wire is used. Why shouldn’t 20-amp devices be used? What’s the purpose of the device rating – to assure it can handle the connected load? Is a 15-amp device not a weak link in a 20-amp circuit?
NEC 210.21.B.3 says “A single receptacle installed on an individual branch circuit must have an ampere rating not less than that of the branch circuit. (ie. on 20-ampere circuit, RR of 20); however, two or more 15-ampere receptacles or duplex receptacles are permitted on a 20-ampere general-purpose branch circuit."
> Where is there an individual branch circuit with only one receptacle? Why is exception made for a “general-purpose" branch circuit that has more than one receptacle?
> What is code for the Required Branch Circuits in 210.11(C)(1), (2), and (3) (small appliance, laundry, and bathroom)? Although you may see the lower rated devices, what is expected for new work or updates?

[This message has been edited by gs99 (edited November 29, 2002).]

Tom O

11:26AM | 11/23/02
Member Since: 09/17/02
487 lifetime posts
There is no reason not to use a 20 amp receptacle on a 20 amp circuit. But the opposite side of that coin is that there is little reason to use 20 amp receptacles at all.

Individual receptacles may be run for a window air conditioner, or an appliance installed in an area that would normally require a GFI receptacle. I'm sure if you exercise your imagination, you can think of others.

What is expected for new work? Anything the customer is willing to pay for that meets the minimum requirements of the NEC.

Purchase a copy of "Electrical Wiring Residential" by Ray C. Mullin.You should be able to find it on the web. It is well worth the money. It may not explain all your "why" questions, but it will give you an excellant understanding of your home's electrical system.

[This message has been edited by Tom O (edited November 23, 2002).]

gs99

02:40PM | 11/23/02
Member Since: 11/18/02
30 lifetime posts
Most important question not answered yet: Does the NEC specify the rating of devices (switches and receptacles) that are installed in the circuits described in 210.11(C)(1), (2), and (3) (small appliance, laundry, and bathroom)? Evidently the NEC does require 20-amp receptacles in other specific cases. I’m the owner/contractor/customer and willing to pay for the appropriate devices to meet the NEC code. What is it?

[This message has been edited by gs99 (edited November 29, 2002).]

Tom O

03:25AM | 11/24/02
Member Since: 09/17/02
487 lifetime posts
For switches, see 404.14

tdhorne

11:23AM | 11/29/02
Member Since: 09/01/02
31 lifetime posts
quote:
On a 20-amp circuit, 12 gauge wire is used. Why shouldn't 20-amp devices be used? What's the purpose of the device rating – to assure it can handle the connected load? Is a 15-amp device not a weak link in a 20-amp circuit?
NEC 210.21.B.3 says “A single receptacle installed on an individual branch circuit must have an ampere rating not less than that of the branch circuit. (i.e.. on 20-ampere circuit, RR of 20); however, two or more 15-ampere receptacles or duplex receptacles are permitted on a 20-ampere general-purpose branch circuit."
> Where is there an individual branch circuit with only one receptacle? Why is exception made for a “general-purpose" branch circuit that has more than one receptacle?
> What is code for the “special” circuits in 210.21.C.1,2, and 3 (small appliance, laundry, bathroom)? Although you may see the lower rated devices, what is expected for new work or updates?

Fifteen ampere duplex receptacles are listed to carry twenty amperes between their common contacts. That is the metal between the two screws of the same color will safely carry twenty amperes. The fifteen ampere classification is meant to tell you what pattern of cord cap it will except. This is done to prevent the connection of individual loads that the circuit can not carry to the receptacles on that circuit. As for switches it is totally impractical to require that every switch be capable of handling any load that can be supplied from a twenty ampere circuit. The switches that control the lights in your home are generally rated around ten amperes of AC. That means that they will safely open and close on a ten ampere resistive load such as 20 sixty watt incandescent light bulbs. If the circuit were DC instead of AC such as the emergency lighting circuits in some older buildings then the switch would have to be listed for ten amperes and in addition be a T rated switch. A T rated switch is tested to safely close on the cold inrush current of it's ampacity worth of tungsten filament light bulb load. If the load were a two horse power motor the switch would have to be listed for the control of the two horsepower inductive motor load. That all being true you certainly wouldn't want to pay for T rated switches, let alone two horsepower motor switches, for switching your vanity light in the bathroom. I should point out that switches are tested for the amount of current they can interrupt or connect without damage to the switch or the connected wiring. Switches can carry far more load then they can safely interrupt or connect. Conductors on the other hand need only be tested for what they will carry.

Devices such as switches are mounted in device boxes for a reason. If the device fails the failure will be confined to the box. The number twelve conductors must be capable of carrying the entire ampacity of the circuit because there is only a cable jacket or less between it and other conductors or the structure of the building.

The reason for the different ratings is to permit appropriate material selection for the job that those materials must do. If the test results are accurately reflected in the materials listing and the installing electrician selects appropriate materials for each part of the installation then it will be safe and serviceable.
--
Tom

gs99

05:07PM | 11/29/02
Member Since: 11/18/02
30 lifetime posts
No answer yet, so I'll simplify the question:
You're updating a kitchen with two 20-ampere "Small Appliance" branch circuits. Will the inspector approve switches and GFCI receptacles rated at 15-ampere?
Please provide the NEC reference with your answer.
Thanks

Tom O

03:25AM | 11/30/02
Member Since: 09/17/02
487 lifetime posts
Why are you installing switches on the small aplliance circuit? Unless you're switching a receptacle, I can't think of any reason to have a switch in a small appliance circuit.

As far as receptacles are concerned, see Table 210.21(B)(3)

JonathanGennick

04:16PM | 11/30/02
Member Since: 11/02/02
72 lifetime posts
This has actually been quite an illuminating discussion. Up until recently, I'd have argued for 20-amp switches on 20-amp circuits. However, I now understand that not only must I worry about the amperage, but what the switch controls (tungsten lighting requires T-rated, motors require a switch that supports inductive loads, etc.) Is it likely that a single switch can be 20-amp, T-rated, and able to handle inductive loads all at once? Probably not. So the logic of saying the switch only needs to be rated for the device to which it's attached makes more sense to me.

Having said all of the above, what is different about tungsten that it requires a T-rated switch? What is different about inductive loads like motors? I'm just curious here.

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