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electric outlet for window AC question

E

ehsjr

Jan 1, 1970
0
That's 80 percent of the BRANCH CIRCUIT rating. 80 percent of 20 amps
is 16 amps. So in theory, if I have multiple NEMA 5-15R receptacles on
a 20 amp branch circuit, I could draw up to 16 amps from one outlet and
not violate this rule. I would not worry about it in a technical sense
with respect to the receptacle since I know it is rated to 20 amps. The
plug in use might not be, but 20 amp plugs don't appear to be any more
robust than 15 amp plugs; they just have a twisted neutral.

So which rule would I be violating if in this case a single cord-and-plug
connected appliance draw more than 12 amps? What rule requires equipment
over 12 amps to use a NEMA 5-20P or larger? A UL listing requirement?

Don't lose the concept in the minutae. The 20 amp T slot
receptacle serves two purposes: it allows devices with
NEMA 5-20 's to be plugged in, and it also identifies
the receptacle as being on a 20 amp branch. Manufacturers
have to follow a host of rules/standards/practices etc,
and to get UL listing, nust use the correct plug on
cord and plug connected devices they make.

The violation would occur if you wired a 20 amp receptacle on
a 15 amp branch, regardless of what gets plugged in. As you
noted in another post, 210.21(B) with a multiple receptacle
(or receptacles) on the branch. A dedicated (meaning serving
a single receptacle) 15 Amp circuit is ridiculous enough on
its own without compounding it by makeing the receptacle
20 amps.

Ed
 
R

Roy Q.T.

Jan 1, 1970
0
One Last Thing, For Ed & Phil : What you are saying is, You can't
install a 20A Receptacle on a 15A circuit, but, you can install a 15A
receptacle ona 20A circuit is that what you are saying the NEC allows
here ? Roy


From: [email protected] (ehsjr)
[email protected] wrote:
That's 80 percent of the BRANCH CIRCUIT rating. 80 percent of 20 amps is
16 amps. So in theory, if I have multiple NEMA 5-15R receptacles on a 20
amp branch circuit, I could draw up to 16 amps from one outlet and not
violate this rule. I would not worry about it in a technical sense with
respect to the receptacle since I know it is rated to 20 amps. The plug
in use might not be, but 20 amp plugs don't appear to be any more robust
than 15 amp plugs; they just have a twisted neutral.
So which rule would I be violating if in this case a single
cord-and-plug connected appliance draw more than 12 amps? What rule
requires equipment over 12 amps to use a NEMA 5-20P or larger? A UL
listing requirement?
Don't lose the concept in the minutae. The 20 amp T slot receptacle
serves two purposes: it allows devices with NEMA 5-20 's to be plugged
in, and it also identifies the receptacle as being on a 20 amp branch.
Manufacturers have to follow a host of rules/standards/practices etc,
and to get UL listing, nust use the correct plug on cord and plug
connected devices they make.
The violation would occur if you wired a 20 amp receptacle on a 15 amp
branch, regardless of what gets plugged in. As you noted in another
post, 210.21(B) with a multiple receptacle (or receptacles) on the
branch. A dedicated (meaning serving a single receptacle) 15 Amp circuit
is ridiculous enough on its own without compounding it by makeing the
receptacle 20 amps.
Ed
 
E

ehsjr

Jan 1, 1970
0
| One Last Thing, For Ed & Phil : What you are saying is, You can't
| install a 20A Receptacle on a 15A circuit, but, you can install a 15A
| receptacle ona 20A circuit is that what you are saying the NEC allows
| here ? Roy

A 15 amp circuit with exactly one outlet: NEMA 5-15R or NEMA 5-20R
A 20 amp circuit with exactly one outlet: NEMA 5-20R only
A 15 amp circuit with multiple outlets: NEMA 5-15R's only
A 20 amp circuit with multiple outlets: NEMA 5-15R's and NEMA 5-20R's

Change "5-" to "6-" for 240 volt circuits, or to "14-" for 120/240 volt
circuits. The rules are not specific to a particular voltage.

It's the 5-20R on a 15 amp circuit with one outlet that most people believe
is a bad idea. But 210.21(B)(1) sure appears to permit it. I sure hope
there is some other code that I have overlooked that would prohibit this,
but that is the part where such code should be.


A situation encountered in the field does not necessarily need
to have a specific prohibition in the NEC in order for it to
be rejected by the AHJ. See 110.3(A)(7). 110.3 (A) requires that
the inspector evaluate the installation for the items listed.
Item (7) does not prohibit a 20 amp receptacle on a 15 amp
branch, per se, but does prohibit it, de facto .

Ed
 
E

ehsjr

Jan 1, 1970
0
Roy said:
One Last Thing, For Ed & Phil : What you are saying is, You can't
install a 20A Receptacle on a 15A circuit, but, you can install a 15A
receptacle ona 20A circuit is that what you are saying the NEC allows
here ? Roy

Yes.
Ed
 
R

Roy Q.T.

Jan 1, 1970
0
From: [email protected] (ehsjr)
Roy Q.T. wrote:
One Last Thing, For Ed & Phil : What you are saying is, You can't
install a 20A Receptacle on a 15A circuit, but, you can install a 15A
receptacle ona 20A circuit is that what you are saying the NEC allows
here ? Roy

Yes.
Ed

Then : You are right per se, and quite wrong de facto };-) Okay', and I
understand this very well , but I just hate it when posters assume that
the cat has 5 legs and start slinging crap around, like we have time to
toss the ball around in here. Roy
 
E

ehsjr

Jan 1, 1970
0
Roy said:
From: [email protected] (ehsjr)
Roy Q.T. wrote:
One Last Thing, For Ed & Phil : What you are saying is, You can't
install a 20A Receptacle on a 15A circuit, but, you can install a 15A
receptacle ona 20A circuit is that what you are saying the NEC allows
here ? Roy

Yes.
Ed

Then : You are right per se, and quite wrong de facto };-)

A 15 amp receptacle is manufactured to the same specs as a 20
amp receptacle, in terms of the current carrying capability.
The only difference is that the 20 amp receptacle has a T slot
so it can accept flat blades at 90 degress to one another.
The 15 amp can't accept those 90 degree offset blades.

The idea that a 20 amp receptacle can handle more current
than a 15 amp receptacle, without burning/melting or otherwise
becoming defective, is incorrect.

Ed

Okay', and I
 
R

Roy Q.T.

Jan 1, 1970
0
I don't think so Ed; There are a variety of them and i read recently
that the specs for a 15 & 20 amp receptacles are different, they might
seem the same but the metals employed are tempered differently and their
capacity is limited to there rating.

Believe me I am not making this up: A 15 Amp circuit will trip if it
goes over the rated current with both 15 & 20A with no ill effects on
them, but, the study specifically mentioned that 15A units on a 20A
circuit can suffer as any underrated equipment used on the supply or
convenience outlet circuitry., I do not think much of it either and have
bought random duplex receptacles without minding there current ratings
and am just a little self conscious about it now since this came up on
this thread.,Given my past observations I am just reiterating the
concept of careful circuit component matching to myself };-)
®oy
 
E

ehsjr

Jan 1, 1970
0
Roy said:
I don't think so Ed; There are a variety of them and i read recently
that the specs for a 15 & 20 amp receptacles are different, they might
seem the same but the metals employed are tempered differently and their
capacity is limited to there rating.

Believe me I am not making this up: A 15 Amp circuit will trip if it
goes over the rated current with both 15 & 20A with no ill effects on
them, but, the study specifically mentioned that 15A units on a 20A
circuit can suffer as any underrated equipment used on the supply or
convenience outlet circuitry., I do not think much of it either and have
bought random duplex receptacles without minding there current ratings
and am just a little self conscious about it now since this came up on
this thread.,Given my past observations I am just reiterating the
concept of careful circuit component matching to myself };-)
®oy

Thanks, Roy!

I would love to read the article if you can find it.
My information came from UL and is dated 1991 - so
if there is something new that superceeds it, I am
eager to learn.

Ed
 
J

John Gilmer

Jan 1, 1970
0
..
Then, you don't have any of these T-slot plug appliances in your house?
Does anybody here have a T-slot plug appliance in their house?

I doubt it.

Seems that "no one" makes a 120 volt gadget that draws more than 15 amps!
(Even if it claims to have severl horse power motor!)

With the exception of electric stoves and clothes dryers, 240 outlets are as
rare as hen's teeth with only a few being put in to support larger sized
window air conditioners. Often these just "patch" onto the electric dryer
circuit.

Must of this thread has been quite silly and pointless.
 
J

John Gilmer

Jan 1, 1970
0
| With the exception of electric stoves and clothes dryers, 240 outlets are as
| rare as hen's teeth with only a few being put in to support larger sized
| window air conditioners. Often these just "patch" onto the electric dryer
| circuit.

I've never actually seen such a patch job, and certainly would never
recommend it.

Well, I saw on in a house that was "modern" in 1958 but had a fuse box. It
did have the "heavy" circuits for the stove and dryer, however.

Folks put in these BIG window units because they don't have the money to put
in Central Air and install an entirely new service. I never "opened up"
such an installation, but dryer circuits are often/usually just 30 amps so
#10 romex would be protected. It may not be "code" but it's not asking
for trouble either.
But in DIY type forums, I've seen a number of people
ask how to do it (IMHO, that would not be a project for someone with
so little experience in wiring they would have to ask how to).

True. But even if you are taking short cuts it doesn't mean you don't want
to be a safe as you can manage without spending an arm and a leg.

It seems to me that the folks who create the NEC sometimes DO worry about
economy and DO reason that it's better to have GOOD safety at reasonable
cost over GREAT safety at a cost that encourages folks to just jury rig. But
when they mandated the "arc detection breaker" I wondered.
| Must of this thread has been quite silly and pointless.

Most threads seem quite silly and pointless to me when discussing something
that I don't happen to need. This particular thread certainly has gone off
on a tangent (both in subject and in plug blades).

Well, since we are on the subject:

I notice that the "dryer and stove" outlets with only three wires
(chassis/neutral are bonded in the appliance) don't make any effort to
connect neutral before hot. Of course, for the last 30 years dryers are
completely "off" until you push the start button and the only 120 volt loads
in the stove are the lamp and the timer so ...)
But it has shaken up
some dust that probably shouldn't be where it has settled long ago. I am
considering making an information web page on the subject "15 vs 20 amps".

Fine. Put in a "questions and comments" BB if you can.
 
J

John Gilmer

Jan 1, 1970
0
I've been thinking of setting up a whole "code comments" forum board.
It would be oriented to issues about complying with, or changing, the
electrical code, and targeted to electricians, engineers, and others
with an interest. It wouldn't be a DIY forum.

Why not?

http://ka9wgn.ham.org/ |
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E

ehsjr

Jan 1, 1970
0
HorneTD said:
The UL standard is unchanged. Both 15 and 20 ampere receptacles must be
capable of carrying 20 amperes continuous without damage.

Thanks, Tom!
 
B

Bud

Jan 1, 1970
0
HorneTD said:
Phill has a point. 210.21 (B) (3) would not appear to apply to branch
circuits that only have one outlet. I strongly suspect that was not
what the code making panel intended but the way 210.21 (B)(1) reads now
you could put a twenty ampere receptacle as the only outlet on a fifteen
ampere circuit.


Hard to believe but apparently true. A single outlet just has to have a
higher rating than the branch circuit. Not only can you put a 20 amp
single receptacle on a 15 amp circuit you can put a 30 amp, 100 amp ....

This appears to have been in effect at least back into the 1980s.

One way to see check the reasoning behind a code item is to look for
proposed changes and see how the code making panel responds. There were
no proposed changes to this rule as far back as 1983 (1996 and 1993 are
unknown). This rule was invisible?

Bud--
 
J

John Gilmer

Jan 1, 1970
0
Pa. code is now saying 15 amp circuits to all rooms. Receptacles and lights
for that room on the same circuit, direct feed. No junction boxes.

WTF do you mean by "no juction boxes?"

What IS a "junction box" according to PA these days?
 
W

w_tom

Jan 1, 1970
0
indago said:
Plus the fact that a lamp cord has a tough enough time tripping
out a 15 amp breaker, let alone raising the ante to 20 amps. I
heard a rumor that an Ohio town is demanding that general
outlets in living rooms, bedrooms, and such be on 15 amp
circuits.

Where do these numbers come from? 15 amp wire cannot blow a
20 amp breaker? Nonsense. From Automatic Electric, the
continuous current for fusing a copper 18 AWG wire is 82.9
amps. Therefore an 18 AWG wire can carry more than 82
intermittent amps - for the milliseconds necessary to trip a
breaker.

15 amp receptacles must installed in those rooms. Idea
being a six foot power cord on any appliance would always be
long enough to connect to a wall receptacle. Those 15 amp
receptacles can be powered by 20 amp circuits.

But again, how reliable is the source when short term
amperage for an 18 AWG zip cord is more than sufficient to
safety trip a 20 amp breaker. The important parameter is
time. Those 'more than 20 amps' must exist only for a short
period. 18 AWG wire is more than sufficient to trip a 20 amp
breaker during a short 'short circuit'.
 
B

Bud

Jan 1, 1970
0
w_tom said:
indago wrote:


Where do these numbers come from? 15 amp wire cannot blow a
20 amp breaker? Nonsense. From Automatic Electric, the
continuous current for fusing a copper 18 AWG wire is 82.9
amps. Therefore an 18 AWG wire can carry more than 82
intermittent amps - for the milliseconds necessary to trip a
breaker.

It actually takes a lot longer than one might guess to trip a breaker
(or fuse). Most circuit breakers have a thermal trip element, which is
like a fuse with a time delay - it won't trip, for example, on a motor
start. For Sqare D, 80 amps on 20 amp breaker has a minimum clearing
time of 6 seconds. Above 200 amps the maximum clearing time is 1 cycle.

Bud--
 
B

Bud

Jan 1, 1970
0
w_tom said:
But again, how reliable is the source when short term
amperage for an 18 AWG zip cord is more than sufficient to
safety trip a 20 amp breaker. The important parameter is
time. Those 'more than 20 amps' must exist only for a short
period. 18 AWG wire is more than sufficient to trip a 20 amp
breaker during a short 'short circuit'.


You may be interested in this - from the Product Safety Technical
Committee of the IEEE EMC Society:


In North America, wire sizes
for power cords, including extension
cords, are selected to always
be capable of blowing the 15 or
20 amp building fuse in the event
of a steady-state short-circuit at
the end of the power cord.

The power cord wire size together
with its insulation rating
must have a sufficiently low
impedance to withstand the
overheating of the short-circuit
until the 20-amp circuit breaker
clears the circuit. (Cord-connected
electrical heating appliances often
have high temperature insulation
on their power cords to account
for steady-state high current conditions.

To meet this criterion, the
minimum wire size for flexible
cords is AWG 18, except for
specific applications, in which
case there are extensive insulation
robustness tests designed to
preclude insulation failure.
Ampacity ratings of cords and
cordsets are given in UL 817,
Table 90. These ratings are for
normal conditions.
 
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