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RollingHome
07-06-2010, 05:24 PM
Does anyone know what is the lowest AC voltage (120 VAC) our units AC will run on and not trip the breaker ? I just installed a 120 VAC 30 AMP receptacle for my BH. I plugged in, turned on the AC and it tripped the breaker in under 15 minutes. I think it's because of low voltage. Tomorrow I will put a digital VOM on the circuit. I had to stop today because I was getting heat goofy ! We are experiencing a terrific heat wave in the northest corrider of the US that is standard Texas weather. It hit 115 F in Newark NJ, 107 in NYC and 105 in NE Philly. The mezzanine over my shop in the barn pegged the T Mometer at 120 F ! We had 8 feet of snow last winter and a super heat wave now, so on the average we're just right... Anyway, if you know the voltage that will trip the 20 amp panel breaker for the AC it would help me tomorrow. Before I get heat goofy... :o Tom

Rickhansen
07-06-2010, 05:40 PM
Hi Tom,
While your question is straightforward, the answer can be a bit more elusive.

There is a direct relationship (Ohm's Law) between the voltage and the current - http://www.the12volt.com/ohm/ohmslaw.asp

You need to consider also that a circuit breaker is a thermal device - it trips by heat. It's rated trip point is also based on ambient temperature and must be derated when the ambient temp increases above that.

branson4020
07-06-2010, 06:04 PM
Tom,

Not sure what voltage would cause the breaker to trip, but you should be glad it does. It's certain death to the compressor to run it at low voltage for any length of time. I'd bet it's the single biggest cause of premature failures in these units.

cookie
07-06-2010, 06:26 PM
Tom, what size wire did you run to your new 30 amp receptacle? And how long of a run is it?
That 20 amp breaker is there to protect the #12 wire that feeds the AC. Not to protect the AC.
If your wire feed is not heavy enough or is too long, you will have a voltage drop. The AC will struggle to run.

Peace
Dave

Ray LeTourneau
07-06-2010, 06:37 PM
Tom, is the breaker tripping the 30 AMP one recently installed? Check all connection to see that they are tight. As Dave says and you probably know, long wire runs require heavier wire. I know there's a chart somewhere but... also, I've seen it done in manufacturing places but never in a home environment but you could direct a fan on the breaker box to help reduce the ambient temps at the breaker.
On edit, I just re read your post and see it's the 20 amp in the RV's panel. I'd still check the connections on the breaker. Easy to pull the panel. 4 screws on the panel cover and 2 for the inside if needed.

RollingHome
07-06-2010, 09:00 PM
You guys are very technical... and smart ! The toy barn circuit is 30 amp (120VAC) breaker, twist lock outlet ... and you also zeroed right in on it ! I'm impressed, so here goes... I put a 30 amp twist lock recept in. Then I pulled out 100' of 10/3 cord. I pulled ALL the 50 amp way too heavy BH cord and plugged in (140' total) ... The 30 amp barn panel stayed in but the RV 20 amp tripped inside the RV (you were sharp Ray !) . Tomorrow I will put a digital VOM into the BH outlet but today I overheated, man it's HOT here in PA. ... Anyway, your actual experience and input will help me more then ya think ! At what voltage will our units take a powder ? Tom

cookie
07-06-2010, 09:22 PM
Tom, I think that for 100 feet of #10 wire you are way under sized. That number 10 is good for about 25 feet at 30 amps.
You really should have #6 for 100 feet. And realistically you are at 140 feet.
This is assuming you use all 30 amps.

Peace
Dave

porthole
07-06-2010, 09:23 PM
Tom, is the breaker tripping the 30 AMP one recently installed? Check all connection to see that they are tight. As Dave says and you probably know, long wire runs require heavier wire. I know there's a chart somewhere but... also, I've seen it done in manufacturing places but never in a home environment but you could direct a fan on the breaker box to help reduce the ambient temps at the breaker.
On edit, I just re read your post and see it's the 20 amp in the RV's panel. I'd still check the connections on the breaker. Easy to pull the panel. 4 screws on the panel cover and 2 for the inside if needed.

If the breaker is new - maybe it is bad.

Bob&Patty
07-06-2010, 11:19 PM
Tom, use #6 wire at the least. My 30amp is using #6 wire and it is only a 20' run.

RollingHome
07-07-2010, 12:06 AM
I can't wait to test the voltage tomorrow ! I'll bet that is the problem ! Thanks for yer input ! Tom

RollingHome
07-07-2010, 11:22 AM
It is low voltage. We are in the middle of a heat wave wth temps around 100F. The power company has done a great job thus far... but, the supplied voltage is lower then normal. I checked my mains on my house panel lugs and I got 110 volts hot to neutral both legs with 220 volts leg to leg (normal is 120 VAC leg to neutral). I checked the RV and got 108 at a duplex. It dropped to 105 when I turned on the AC (fan only) and dropped to 96 to 99 volts when the compressor kicked in. The amp draw was about 15 Amps. +/-. A 20 amp breaker will carry 80% or 16 Amps. at ambient (68 - 72 F). It's over 100F at the RV panel so, you all were right, it's voltage drop and high temps causing the tripping. So I don't toast my AC compressor I am not going to run it.

I have conduit and boxes installed from the panel to the RV area and plan on pulling # 8 AWG to compensate for voltage drop. However, this heat wave put everything on hold. In the interim I put a 30 Amp. receptable below the barn breaker panel 100 feet from the RV. I then used 1 - 15' - 6/3 cord (twist loc to 30 Amp. RV receptable) 2 - 30 Amp. (#10 AWG) 30' RV extension cords + the BH 50' - 50 Amp. cord = About 125' of # 6, 8 & 10 AWG rubber cord... I'll see what happens when we return to normal voltage and temps. Thanks for your input & help everyone. Tom

JohnDar
07-07-2010, 12:30 PM
Not sure if it relates to your problem, but my Progressive EMS-HW50C surge suppressor is designed to shut down if voltage falls below 104 volts, or rises above 132 volts. Those might be the points that damage may occur if lower or higher, with some safety margin perhaps.

branson4020
07-07-2010, 02:01 PM
Dometic says a minimum of 103.5V. Coleman says exactly the same number, which corresponds to the Surge Guard and EMS low-voltage cutoff point. My buddy the commercial HVAC guy and fellow RVer says if your running it for very long at less than 110V, your shortening it's life.

wdk450
07-07-2010, 03:14 PM
Tom:
If you really,really need the AC on NOW in the trailer, you could rent a 4KW or better generator. I would probably turn off the electric heating on the refrig and water heater, and maybe even the converter, to lessen the overall load.

RollingHome
07-07-2010, 06:39 PM
I was trying to get the AC working for packing and I wanted to try the tent mod... But the heat here is terrible. Hate to sound like a whiner, but it really is HOT. I know we have to put up with weather, but us yankees ain't used to this 100+ temps. I actually feel for my southern neighbors who face this stuff year in year out, Wow how do you guys do it ? Here's 2 pics to illustrate what this toasted yankee is going thru. The first one is temp in the shade at 101.3 F, the second, my shop mezzanine is 112F, yesterday it was 120 it pegged the Tractor Supply T mometer. Keep in mind this is "cool" Pennsylvania ! Tom

9304

9305

RollingHome
07-10-2010, 10:01 PM
OK, it finally cooled off and rained here. Man I never would have thought rain would be welcomed so much, but we needed it. Anyway, I pulled the wire into the conduit and here's the result. First I measured with a FLUKE DVM, during the heat wave I read 98 VAC to the AC unit, using 100' of 10/3 RV extension cords. Today in "normal" temps I read the same circuit at 108 VAC ! 10 volts difference, but, it's mid 70's not 100+. Then I switched to the new circuit with # 8 AWG and got 118 VAC. The AC is happy. In reality, Dave is correct, I should have run # 6 AWG wire. But I had already bought #8 AWG THHN (into the conduit) and I wanted to get it done. I share this info, so you guys can learn from my errors. Tom

jmgratz
07-10-2010, 11:35 PM
Don't be embarassed as many folks do not realize there is a voltage drop with the distance wire is run. There is a formula to figure it out but I can't remember it off the top of my head. Has to do with Ohms law or something like that.