Ron,
That is a good question. The answer is that one is not supposed to connect
any load greater than 12 amperes to an outlet rated at 15 amperes, that is,
a NEMA 5-15R receptacle. The NEC allows two or more 15-ampere-rated outlets
to be installed on a 20-ampere branch circuit (wired with 12 AWG conductors
and a 20A fuse or circuit breaker), but the limit of 12 amperes on each
outlet still applies.
Proof of this restriction is evident in the "vacuum cleaner wars" of a
decade or so ago. Hoover came out with a vacuum cleaner with "7 amperes of
cleaning power." Then Bissel came out with a unit claiming 9 amperes of
cleaning power. Other vacuum cleaner makers entered the fray until all of
the brands had units with "12 amperes of cleaning power." The reason that
nobody offered a unit with 13 amperes of cleaning power is because they
would then have to equip that unit with a NEMA 5-20P plug and at least a
14/3 power cord. Most older homes do not have NEMA 5-20R outlets, so such a
vacuum cleaner could not be plugged in to the outlets in most homes.
Besides, there is no credibility to a laughable rating of "cleaning power"
expressed in amperes! That is about as silly as claiming that a mobile
radio has "13.8 volts of talk power!"
Back to your second question. By definition, a 15-ampere-rated branch
circuit has circuit conductors of #14 AWG or larger, and is protected by a
fuse or circuit breaker rated at 15 amperes. The fuse or circuit breaker
should hold indefinitely at 15 amperes, but the NEC recognizes that allowing
100% of rated current is never a good idea, since wiring in attics may
already be in a very hot environment. Therefore, the NEC requires that no
ordinary branch circuit be permitted to be loaded more than 80% of the
circuit rating. That's where the 12 and 16 ampere limits come from.
Another issue is voltage drop, which is directly proportional to circuit
loading. Circuits that are loaded to 100% of rating will probably have
excessive voltage drop, which leads to inefficient operation. Good
electrical design dictates that the wire size be increased for long runs, to
keep the voltage drop below 3%. Moreover, an adequate electrical supply
system should never experience more than 80% loading of any circuit. Very
heavy single loads should have a dedicated branch circuit of suitable
capacity, with a single outlet.
73, Eric Lemmon WB6FLY
-----Original Message-----
From: [email protected]
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Thursday, July 17, 2008 8:07 PM
To: [email protected]
Subject: Re: RE: [Repeater-Builder] Re: RadioShack Recalls Power Supplies
Eric,
Question about the outlets. Is the only reason one cannot get more than 12
amp from a 15 amp outlet is the rules so if one is designing a power system
if more than 12 amps is required one has to put in 20 amp outlet to meet
code???
I would think one could get 15 amps due to the breaker able to handle it or
are 15 amp breakers designed to trip at just above 12 amps???
73, ron, n9ee/r
From: Eric Lemmon <[EMAIL PROTECTED] <mailto:wb6fly%40verizon.net> >
Date: 2008/07/17 Thu PM 11:00:53 EDT
To: [email protected]
<mailto:Repeater-Builder%40yahoogroups.com>
Subject: RE: [Repeater-Builder] Re: RadioShack Recalls Power Supplies
Wayne,
That is not exactly true. An outlet rated at 15 amperes cannot have any
load greater than 12 amperes plugged into it. An outlet rated at 20 amperes
cannot have any load greater than 16 amperes plugged into it. This is
clearly stated in Article 210.21(B)(2) of the National Electrical Code. A
device that actually draws 20 amperes at 120 VAC must be plugged into an
outlet and branch circuit rated at 30 amperes.
When load currents exceed 16 amperes at 120 VAC, it's time to consider a
branch circuit rated at 208 or 240 VAC. Most repeaters and high-power PAs
have optional connections to enable operation on 208 or 240 VAC. Keep in
mind that there is no such voltage as "220" although that obsolete figure
is
still in common usage. The nominal single-phase voltage supplied to
residences is 120/240 VAC, while the electrical supply to light commercial,
apartment complexes, and condos is usually 120/208 VAC derived from two
phases of a three-phase distribution system. I mention this because a
fellow Ham who now lives in a large apartment complex mentioned to me that
his 500 watt rig that worked fine in his former home was not putting out
full power at his new location. The cause was revealed when he measured his
line-to-line voltage as close to 208 VAC. His power amplifier was rated for
240 VAC, but was "starving" when fed 87% of its design voltage. A
commercially-available "boost" transformer was installed to give him a true
240 VAC supply. Problem solved.
73, Eric Lemmon WB6FLY
-----Original Message-----
From: [email protected]
<mailto:Repeater-Builder%40yahoogroups.com>
[mailto:[email protected]
<mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Wayne
Sent: Thursday, July 17, 2008 11:01 AM
To: [email protected]
<mailto:Repeater-Builder%40yahoogroups.com>
Subject: Re: [Repeater-Builder] Re: RadioShack Recalls Power Supplies
To properly plug in an item that is a 20 amp draw. etc., one should
install a 20 amp outlet.
This can be single or duplex, and is readily spotted (if dual purpose) by
the fact that one side will be flat instead of vertical, or have both
horizontal and vertical on that side.
the flat/horizontal is on the neutral side.
Not to be confused with a similar looking outlet for 250 volts, which has
two flats , and one has vertical as well on the left side, looking at the
front with the ground hole down.
Anyway, there are oulets made for 20 or more amps, which are different
than the 15 amp common outlets.
local ordinances can often be more stringent than even the NEC codes.
of course, if you are running a high power repeater, you would probably
wish to put it on a circuit breaker by itself.
But ordinary house wiring normally has several outlets wired in series
from one breaker, and is NEC approved that way.
Shop and Industrial become another matter, ha ha ha...
Wayne WA2YNE
On Sun, 06 Jul 2008 20:08:33 -0500, Bruce Bagwell <[EMAIL PROTECTED]
<mailto:bbagwell%40swbell.net> >
wrote:
I figured that was A local code, not NEC. The only reason I can think
of for that requirement is the ampacity of the 12 or 14 ga wires. While
we all know, in actual use, 2 or more outlets strung along will not all
have 15 amp or higher loads in EACH outlet. However, theoretically, each
outlet could have A 20 amp load plugged into it.That is probably why
some pencil pusher decided each outlet needs its own wire. (Never mind
the fact the breaker would trip regardless of what is plugged into each
outlet or the number of wires leading to said outlets, but that's
another crazy thread) As for the Breaker Box, I would assume each also
has its own breaker. Trying to stuff more than one wire into A breaker
would more fun than I care to have.
Bruce
KE5TPN
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