20 amp circuit breaker and wiring

baymeeAugust 31, 2010

Forgive me if this has been posted before.

If I am adding a switch and light to a 20 amp circuit, does the light switch, as well as the wiring to the switch and on to the light fixture have to be 20 amp as well? 12 ga. wire?

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bus_driver

The wire must be 12 gauge. The switch can be of rating less than 20 so long as it is adequate for the load it supplies.

    Bookmark   August 31, 2010 at 7:18AM
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baymee

Just to clarify, the wire from the 20A receptacle that powers the switch must be 12 ga., the switch can be 15A, and the wire from the switch to the light can be 14Ga?

    Bookmark   August 31, 2010 at 11:12AM
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hendricus

yes

yes

no All wires on a 20 amp breaker must be 12ga.

    Bookmark   August 31, 2010 at 12:01PM
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smithy123

correct, but you really should be using a 20a switch

    Bookmark   October 16, 2010 at 11:37PM
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spencer_electrician

No, a 20 amp switch is not needed here, it would be a waste. Unless the light the poster from 2 months ago installed uses more than 1800 watts, a 20 amp switch is not needed.

    Bookmark   October 16, 2010 at 11:48PM
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brickeyee

"correct, but you really should be using a 20a switch"

The NEC allows the use of 15 A receptacles and switches on 20 A circuits as long as it is not the ONLY receptacle (and a duplex counts as two) on the circuit.

If the load is over 15 A on the switch, you would also have to increase the rating of the switch.

15+ amps of lighting (1800+ watts) is a lot of lighting on a single switch in a residential application (it is not uncommon in large halls (think commercial/church/school).

    Bookmark   October 17, 2010 at 11:31AM
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smithy123

I stick to whatever size the cb is. What if a rec would be added later down the line saves work. 20a switches also last longer.

    Bookmark   October 18, 2010 at 12:05AM
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baymee

I had to read what brickeyee said, about 10 times, until it sunk in.

We are now talking about a circuit that uses 12 ga. wire in its entirety, a 20A circuit breaker, but a mixture of 15A and 20A receptacles and switches. The weak link appears to be the 15A receptacles. This is rather confusing to most people.

    Bookmark   October 18, 2010 at 6:12AM
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petey_racer

Baymee, you are misreading what Brick is saying.
The 15A receptacles are NOT a weak link. A 15A receptacle IS rated for 20A feed through.
The only thing 15A is the slot configuration on the front.

Smithy, 20A switches do NOT last longer. Heavy duty, or spec-grade, switches do.
The only reason people think this is because there are no cheap 20A switches. If you buy 15A spec-grade switches they last just as long as 20A spec-grade switches.

    Bookmark   October 18, 2010 at 6:37AM
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hexus

"I stick to whatever size the cb is. What if a rec would be added later down the line saves work. 20a switches also last longer."

you aren't going to get very far in this field with your way of thinking....

    Bookmark   October 18, 2010 at 8:41PM
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smithy123

How arent i going very far into the Field? I have added lots of switched recs off of lights and drew almost 20a.

    Bookmark   October 18, 2010 at 10:58PM
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baymee

I wasn't aware about the amperage capability of a 15A receptacle being the same as a 20A. Is this stated in the code?

When you think about it, look at a radio. It plugs into a 15A receptacle, but has tiny wires that wouldn't even support 5 amps, and they never burn up.

I'm definitely keeping info on this topic.

    Bookmark   October 19, 2010 at 6:10AM
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ontariojer

it is written on the rec. normally.

    Bookmark   October 19, 2010 at 7:14AM
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brickeyee

See Table 210.21(B)(3) Receptacle rating for Various Size Circuits.

It clearly shows that a 20 A branch circuit is allowed to use 15 A or 20 A receptacles.

210.21.(B)(3) Receptacle Ratings starts off with "Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes..."

You have to remember that the #14 15 & #12 20 A limit is not based on the actual wire size and insulation temperature, but one intended to make sure that the most commonly used circuits(15 A & 20 A) have extra margin.

This is why they can be used at their full rating for motor circuits, hermetic compressors, and start off higher for derating in conduit.

    Bookmark   October 19, 2010 at 7:01PM
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baymee

Here's a link to a discussion of this issue. It apparently causes problems for more people than me.

http://forums.mikeholt.com/archive/index.php/t-112623.html

    Bookmark   October 20, 2010 at 5:52AM
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smithy123

i was arguing with the kauffman's chicken guy because he did not have a 20a plug on his trailer that draws 20a. it is a safety hazard because he could plug it into a 15 amp extension cord. the chicken is good, though.

    Bookmark   October 20, 2010 at 6:07PM
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brickeyee

"... trailer that draws 20a. "

Did you measure the current?

Or just feel to see if the cable was warm?

    Bookmark   October 20, 2010 at 8:52PM
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smithy123

the trailer has hubbell 20a twist lock connectors

    Bookmark   October 20, 2010 at 9:01PM
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smithy123

the plugs were p&s knockoffs of hubbell hbl5266c. they had twist lok females rated for 20a/240v, single phase. he said the 5-15 plugs were rated at 20a, but they were marked 15a. he said the 20a plugs were for heavy duty use, but they were for anything draving more than 15a.

    Bookmark   October 20, 2010 at 9:16PM
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k27k

When I was at a fair i seen that this one stand had A J-BOX MOUNTED TO THE SIDE OF THEIR OVEN!!!!!! I THINK THAT THAT IS A VERY BAD IDEA! The wires inside it are probably not rated for that high of a temp. althought th j-box was metal.

    Bookmark   October 20, 2010 at 9:19PM
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smithy123

the wires running from the oven were probably rated for that temperature, kyle.

    Bookmark   October 21, 2010 at 5:34PM
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