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Old 12-08-2017, 02:35 PM   #1
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THOR #7741
30 vs 20 Amp Circuit Breaker for AC unit

So... during a trip over the summer we had issues with our AC unit keeping up with the 117 degree weather. As noted in a different post, our unit died all together and had a new unit installed.

The tech who did the work, according to him, was told by Coleman that since the extreme heat conditions was also causing the 20amp circuit breaker to trip, to switch the AC unit over to the 30amp breaker and move the main for the coach to the 20amp breaker...

I am going to switch the breakers back to the way they originally were, but my question is, if what the tech/Coleman said is true, would it make sense to replace the 20amp AC breaker with a 30amp one? Or am I just asking for trouble...

2009 Thor Hurricane 31D w/ a Coleman Mach 15, BTU Level: 15000 BTU, Voltage Rating: 115 Volt AC, Ampere Rating: 14.8 Amp
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Old 12-08-2017, 02:43 PM   #2
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THOR #2601
30 amp for the A/C would probably be OK, but I would not have the main for the coach on a 20 amp.

If the A/C is running, and the electric water heater comes on, while making a TV dinner in the microwave, with the TV on, and the coffee maker brewing a cup of coffee -- well you know where this scenario is heading.
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Old 12-08-2017, 02:48 PM   #3
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THOR #7741
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Originally Posted by bevedfelker View Post
30 amp for the A/C would probably be OK, but I would not have the main for the coach on a 20 amp.

If the A/C is running, and the electric water heater comes on, while making a TV dinner in the microwave, with the TV on, and the coffee maker brewing a cup of coffee -- well you know where this scenario is heading.
Most definitely, I am moving the coach back to the 30 amp breaker!
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Old 12-08-2017, 02:52 PM   #4
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THOR #6582
Ed's right, 20 amp for the Main won't work (stupid tech!) Buy an additional 30. A/C units draw a gawdaful amount of current to start the compressor. The code allows oversizing the breaker but I think the issue was with your original unit.
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Old 12-08-2017, 03:05 PM   #5
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THOR #7741
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Originally Posted by gnach View Post
Ed's right, 20 amp for the Main won't work (stupid tech!) Buy an additional 30. A/C units draw a gawdaful amount of current to start the compressor. The code allows oversizing the breaker but I think the issue was with your original unit.
Are the breakers fairly standard? Or should I see what type I have first and replace with same?
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Old 12-08-2017, 03:25 PM   #6
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Yes, anymore, mostly. (big help, right?) With shore power off, remove the 20a and take it to your hardware store to match up a 2pole 30a (2/30a). That should do it.
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Old 12-08-2017, 03:28 PM   #7
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Yes, anymore, mostly. (big help, right?) With shore power off, remove the 20a and take it to your hardware store to match up a 2pole 30a (2/30a). That should do it.
Much appreciated!
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Old 12-08-2017, 03:28 PM   #8
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THOR #7035
NO! Leave the AC on 20 amp breaker. It should not pull 20 amps long enough to trip the breaker if it is operating correctly and the wiring, etc is not rated for 30 amps. The breaker is there to trip and protect your coach from burning to the ground in the case of a fault.
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Old 12-08-2017, 07:47 PM   #9
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Couple of things, first, though the AC compressor is an inductance motor, it will draw a lot of amps on startup, but that should be for such a short period of time that even a 20 amp breaker should not trip. You could in all likelihood safely put a 30 amp breaker on the AC line, because the only time it would draw over 30 amps would be if there was a short on the motor feed line, or if the motor (compressor) froze, and then it would try to draw hundreds of amps, so the 30 amp breaker would trip. I don't know what your Colemans current draw specs are, but my Dometic 13500 AC draws 15.01 amps, but will draw less in cooler weather. That, of course, is not the start up current, which my guess would be 30 to 35 amps, but not positive on that one. Just for reference, my home AC which is a 4 ton, or 48000 BTU unit is on a 40 amp circuit.
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Old 12-08-2017, 08:11 PM   #10
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Couple of things, first, though the AC compressor is an inductance motor, it will draw a lot of amps on startup, but that should be for such a short period of time that even a 20 amp breaker should not trip. You could in all likelihood safely put a 30 amp breaker on the AC line, because the only time it would draw over 30 amps would be if there was a short on the motor feed line, or if the motor (compressor) froze, and then it would try to draw hundreds of amps, so the 30 amp breaker would trip. I don't know what your Colemans current draw specs are, but my Dometic 13500 AC draws 15.01 amps, but will draw less in cooler weather. That, of course, is not the start up current, which my guess would be 30 to 35 amps, but not positive on that one. Just for reference, my home AC which is a 4 ton, or 48000 BTU unit is on a 40 amp circuit.
There is a lot of "in-between" between the motors in the AC running normally and the unit drawing less than 20 amps; and one of the motors stalling and drawing a large surge of current to trip a 30 amp breaker. If either the compressor or the fan motors load up due to failing bearings, high head pressure, or any other reason or you have a high resistance connection, the unit could pull 25 to 30 amps long enough to heat up the supply cable and connections and cause a major issue.

This is akin to replacing a fuse with a penny. I'm certainly not a card carrying member of the Internet Safety Patrol, but I would never advocate replacing a 20 amp circuit breaker with a 30 amp breaker without upgrading the circuit.
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Old 12-08-2017, 08:52 PM   #11
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There is a lot of "in-between" between the motors in the AC running normally and the unit drawing less than 20 amps; and one of the motors stalling and drawing a large surge of current to trip a 30 amp breaker. If either the compressor or the fan motors load up due to failing bearings, high head pressure, or any other reason or you have a high resistance connection, the unit could pull 25 to 30 amps long enough to heat up the supply cable and connections and cause a major issue.

This is akin to replacing a fuse with a penny. I'm certainly not a card carrying member of the Internet Safety Patrol, but I would never advocate replacing a 20 amp circuit breaker with a 30 amp breaker without upgrading the circuit.
The scenario you describe, is not a highly probable event, but it certainly could happen, so as you say, the safest way to go would be to stay with the 20 amp breaker, which would meet any code requirements. The other consideration is, if there was a fire, and the ignition point was traced to a modified electrical system, there could and probably would be a problem getting insurance to pay damages. Just something else to consider.
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Old 12-08-2017, 10:00 PM   #12
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THOR #7035
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The scenario you describe, is not a highly probable event, but it certainly could happen, so as you say, the safest way to go would be to stay with the 20 amp breaker, which would meet any code requirements. The other consideration is, if there was a fire, and the ignition point was traced to a modified electrical system, there could and probably would be a problem getting insurance to pay damages. Just something else to consider.
Old wives tale: Insurance coverage has no exemptions for stupidity or mistakes.

You would also think that a poor electrical connection turning into a burning situation would be a rare event in these motorhomes, but there are multitude documented cases on this forum especially with water heaters and transfer switches.
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Old 12-08-2017, 11:05 PM   #13
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THOR #6582
Coming back to my suggestion of keeping the 30a in place... the 15kw A/C specs call out Running Watts Desert: 2025 and Locked Rotor Amps: 61. 2025 watts / 115vac = 17.6 amps. Sizing the breaker at 125% (Natl Code) would be 22 amps. Since a 25 amp breaker isn't available the 30 amp would be my choice for the extreme load. Yes, not perfect, but not going to overheat the breaker either. -2cents worth
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Old 12-09-2017, 12:31 AM   #14
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THOR #2053
25 amp breakers are readily available, but that is not the answer to your problem.
1. Switching the breakers around is stupid. Now you have a 20a breaker for your main. It will not allow more than 20a so the 30 on the a/c will never see more than 20a anyway.
2. The wire to the a/c is rated for 20a, not 30. The breaker is sized to protect the wire AMONG THINGS. The bi-metal breaker can operate at 165% of it's rated capacity for 8 minutes before it trips, and this is from the heat generated by current flow according to design standards set by the NFPA and NEMA. It will trip immediately on a short circuit. This is all by design and testing. These breakers are inverse time trip, not instantaneous trip-which you cannot afford.
3. The comment about 125% is somewhat correct but it is limited to wire sizing and over current protection. The actual correct answer is the name plate on your unit. It will have a comment such as 'max. over current protection allowed'. That will account for everything allowed, plain and simple. NEC allows for NO deviation. As stated earlier 25 a breakers are easy to come by. Use the same brand as the rest of the breakers in your panel. They have been tested and labeled for use in that particular panel. Bad practice to mix brands or styles among brands. Your panel will have a label listing what is allowed.
4. The last place you want electrical advice from is an rv tech. If you need electrical advice ask an electrician.
Remember that your rv was not wired by a professional electrician but some guy on an assembly line to start with. I don't mean to run him down, but facts are facts. This is allowed by fed and Indiana state law because of the assembly line process. Is allowed in most all manufacturing processes. Still is supposed to be designed and installed to the relevant part of the NEC, but very little oversight as to workmanship, such as proper splices which cause a lot of electrical problems, especially fires.

The comment about we should not see fires due to bad connections is totally wrong. I'm amazed we don't see more. It happens in the 'outside world' every day. And to professionals. Humans make mistakes, especially untrained people.We should see more of it in rv's in my opinion.
Why take a chance of a fire and a death in the family over advice from a rv tech that tells you the way to fix your problem is to put a smaller main breaker in? FIND AND FIX THE PROBLEM CORRECTLY!!

Bill= retired EE with 40 yrs expereince
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Old 12-09-2017, 05:06 AM   #15
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THOR #9748
You are misunderstanding what that 30 Amp breaker is.

It is a main which protects the the wire and circuit you plug it into. In other words the wire that runs to the plug will not melt if 30 amps is drawn. Draw more than 30 amps and the breaker pops. It also represents the maximum current that can be distributed inside the breaker box installed in the coach. Means the Bus Bar that connects all the breakers can handle 30 Amps.

Now from the Bus Bar there are a number of circuits of lower current typically 15-20 amps for standard plugs and more for high current devices like the AC unit. The breaker designed for the AC unit must not be changed to a different rating. That breaker and the wire to the AC unit must all meet certain rating rules. This means if the AC fails and shorts out the wires all the way to the breaker will not melt or catch fire. If you increase the breaker the wire is no longer protected, it may glow like a light bulb until it melts.

In a coach there are power limits. Running the AC, hot water heater and the microwave all at the same time might exceed the 30 amp limit. This is a good reason why 50 amp circuits are advisable when available.

There is a reason why in a home a 200+ Amp breaker panel is used. Your never going to exceed that rating if you turned on every device in your home.

One more thing - Sockets wear out when plugs are installed and removed over and over again. The weakest part of your connection is at the campground connection box. When you plug in, make sure the connection is tight, if not, get the campground to replace the socket. A loose connection will get hot and you will have a voltage drop that can hurt your devices.
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Old 12-09-2017, 12:22 PM   #16
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Coming back to my suggestion of keeping the 30a in place... the 15kw A/C specs call out Running Watts Desert: 2025 and Locked Rotor Amps: 61. 2025 watts / 115vac = 17.6 amps. Sizing the breaker at 125% (Natl Code) would be 22 amps. Since a 25 amp breaker isn't available the 30 amp would be my choice for the extreme load. Yes, not perfect, but not going to overheat the breaker either. -2cents worth

Current rating for desert conditions are even higher than your estimate because they are based on lower voltage and also include a power factor correction.

Having said that, Tfryman and Porkchop are absolutely correct. A/C breaker should remain at 20 Amps not only to protect the wiring from the panel to the A/C, but also to protect the A/C itself. Even if the wires don't start a fire, I'm not sure I'd want my A/C running at higher currents for long periods. Even a 25 Amp breaker could lead to A/C early failure. I'm aware they have other built-in protection, but I wouldn't oversized the breaker at all.

It's too late in this case, but a future solution is to install higher efficiency A/Cs that draw significantly less power. I'm not sure if Coleman has a 15,000 BTU/hr Power Saver A/C, but their 13,500 only pulls just above 10 Amps under standard conditions.
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