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Old 07-23-2006, 09:25 PM   #1
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Someone kindly posted the actual amps that can be drawn on 20 & 30 amp supplies as 16 & 24. How about from a 50 amp plug in? Someone else put up a list of typical power needs of various appliances. I'm building our chart of what we can use in combination.
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Old 07-23-2006, 09:25 PM   #2
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Someone kindly posted the actual amps that can be drawn on 20 & 30 amp supplies as 16 & 24. How about from a 50 amp plug in? Someone else put up a list of typical power needs of various appliances. I'm building our chart of what we can use in combination.
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Old 07-24-2006, 12:15 AM   #3
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National Electrical Code dictates that a circuit should only be loaded to 80% of overcurrent protection device for constant use. Each leg should only be loaded to about 46 amps maximum, however the circuit is protected to hold to 50 amps and if eveything is balanced the neutral will carry the difference of the two legs.
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Old 07-24-2006, 10:40 AM   #4
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RV Wizard, I'm elec challenged. What's that in English? While I'm speaking to the Wiz, how many watts = 1 amp? my conversion prog doesn't do elec. Ask Jeeves says 120 be that doesn't agree with some appliance suppliers.
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Old 07-24-2006, 11:39 AM   #5
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by eandy:
While I'm speaking to the Wiz, how many watts = 1 amp? </div></BLOCKQUOTE>Here is the formula for Watts: P=IE Where Power in Watts is equal to the voltage (110 volts) (X times X) the Amperage (46 amps). Therfore, you can expect the total watts to be equivalent or close to 5060 Watts per leg OR 10,120 Watts total from a 50 Amp shore power receptacle.

Ya sure can cook up a bag of pop corn with that much juice for sure.
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Old 07-24-2006, 11:41 AM   #6
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eandy. volts times amps = watts.

Therefore, 1 volt times 1 amp = 1 watt.

120 volts times times 50 amps = 6000 watts, which is 1 leg of the 59 amp service. Total max watts from both legs would be 12,000.

A 50 amp service, loaded to 80% of overcurrent protection, or as Mike posted, 46 amps "should" be safe to 46 times 240 = 11,040 watts, or 92 times 120 = 11,040 watts. A "perfectly" balanced 50 amp service could/should, have as high as 12,000 +/- watts available.
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Old 07-24-2006, 12:15 PM   #7
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OK, I'll bite. How does 80% of a 50A circuit breaker yield a sustained capacity of 46 amps? .80 x 50 = 40, doesn't it?
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Old 07-24-2006, 05:51 PM   #8
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">actual amps that can be drawn on 20 & 30 amp supplies as 16 & 24 </div></BLOCKQUOTE>
So how is it that my power mgt system tells me I routinely draw 28 amps from a 30 amp service when running both ac compressors??? It's 30 amp service ...not 24 amp service!
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Old 07-24-2006, 06:11 PM   #9
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Paul,

As stated above, 80% of overcurrent protection device for constant use.
80% of 20 amp ciruit is 16 amps, 80% of 30 amp circuit is 24 amps.

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Old 07-24-2006, 06:52 PM   #10
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With all said open your service load box and check to see if you have both AC's on same leg of ckt panel. Some have found such and it causes problems with surge protector and EMS panels. Try to balance loads on both sides of load panel.
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Old 07-24-2006, 07:21 PM   #11
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AFChamp,

The 80% load limitation(the 16 out of 20, or 24 out of 30), is a "Design" safety factor used in the circuit component sizing. the point being to assure the circuit breaker/fuse pops before the wire melts and starts a fire, when an overload occurs. so its not the actual amps that can be drawn, its the code required design & sizing limit.
ie. an engineer or licensed electrician should not use a 30 amp breaker and its corresponding #10 wire size on any circuit where the expected load is more than the 80% of 30 amp brkr rating. the actual limit on the circuit current in use is the circuit breaker itself. if the end user plugs more than the expected load into that circuit, the circuit will carry the load up to the point the circuit breaker/fuse trips. a 30 amp breaker will usually trip between 28-32 amps, depending on the type of breaker, type of load and ambient temp.

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Old 07-25-2006, 11:04 AM   #12
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">o how is it that my power mgt system tells me I routinely draw 28 amps from a 30 amp service when running both ac compressors??? </div></BLOCKQUOTE>


The key word here is "sustained". If you are in a climate where both a/c's run much of the time (all afternoon on a hot day), you are indeed overloaded at a continuous 28 amps on a 30A circuit. But if it is occasionally reaching 28 amps for short (undefined) periods when both a/c's happen to be cycling at the same time, you are not. Obviously the designer considered there would not be any "sustained" loads above 24 amps, cause he would be violating the NEC if he did.

In practice, it depends on how other parameters of the NEC were employed in the wiring. Heat is the main problem and if the junction boxes and cable runs do not have the max allowed conductors crowded together in a small airless space, there is no reason the circuits cannot safely run at the full 30 amps.
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Old 07-25-2006, 11:51 AM   #13
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Had the ans long ago but glad you kept it up. JRP & Roamer added the heat stuff, thanks. This will help when I do the elec layout on my res deisgns. There are places I like to have junction boxes accessable. That also explains the radical power available at Salton Sea state park. We were the only rig there when reported temp was 106, not in the sun. Another rig came in and power probs came on. No idea how they managed a full park. Thanks for the lesson
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