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: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Thursday, July 17, 2008 8:07 PM To: Repeater-Builder@yahoogroups.com 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: Repeater-Builder@yahoogroups.com <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: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> >[mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Wayne >Sent: Thursday, July 17, 2008 11:01 AM >To: Repeater-Builder@yahoogroups.com <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 >> > >-- >Using Opera's revolutionary e-mail client: http://www.opera.com/mail/ <http://www.opera.com/mail/> > >------------------------------------ > >Yahoo! Groups Links > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
