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Old 02-03-2016, 10:57 AM   #101
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Originally Posted by tkarper14 View Post
As much as everyone would like to believe, the 50 amp breaker is NOT there to protect your RV. It is there to protect the camp ground wiring.
Wrong! A breaker, or fuse, provides protection downstream from it only! No wiring before that breaker is protected by that breaker. The 30 or 50 amp breaker on the power pole supplies protection for the trailer power cord and plugs, the power plug on the trailer and any internal wiring fromtthe trailer plug and the main breaker on the trailers converter box only.

Why do so many think those breakers provide protection for the CG feed wiring? Think of those breakers as your kitchen faucet. If you pipes feeding that faucet what does that sink faucet do? Nothing!

My problem wit routinely using a dogbone connected to the 50 amp circuit is you are protecting trailer power cord and plugs, the power plug on the trailer and any internal wiring from the trailer plug and to the 30 amp main breaker in the converter at 50 amps and it is designed to operate at 30 amps only. As an emergency fix that is fine but I don't recommend it as an everyday thing.

Jim
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Old 02-03-2016, 11:08 AM   #102
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Originally Posted by oldtool2 View Post
Wrong! A breaker, or fuse, provides protection downstream from it only! No wiring before that breaker is protected by that breaker. The 30 or 50 amp breaker on the power pole supplies protection for the trailer power cord and plugs, the power plug on the trailer and any internal wiring fromtthe trailer plug and the main breaker on the trailers converter box only.

Why do so many think those breakers provide protection for the CG feed wiring? Think of those breakers as your kitchen faucet. If you pipes feeding that faucet what does that sink faucet do? Nothing!

My problem wit routinely using a dogbone connected to the 50 amp circuit is you are protecting trailer power cord and plugs, the power plug on the trailer and any internal wiring from the trailer plug and to the 30 amp main breaker in the converter at 50 amps and it is designed to operate at 30 amps only. As an emergency fix that is fine but I don't recommend it as an everyday thing.

Jim
Think you missed something, and this is a BIG something. If there was NO breaker on the pole and your system suddenly short circuited, what would that do to the power in the campground? How would that short on the campground wiring affect it if no breaker could blow? You would have instantly hot melting wiring and no voltage to speak of anywhere near that pole in other camp sites. Lots of damage. It's a 2 way street.
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Old 02-03-2016, 11:31 AM   #103
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Think you missed something, and this is a BIG something. If there was NO breaker on the pole and your system suddenly short circuited, what would that do to the power in the campground? How would that short on the campground wiring affect it if no breaker could blow? You would have instantly hot melting wiring and no voltage to speak of anywhere near that pole in other camp sites. Lots of damage. It's a 2 way street.
First off, a short circuit and an overload are two different things and react differently. I am not concerned about a short. A short will trip any size breaker.

The 30 and 50 amp breakers are there to protect anything pluged into them, not the wiring before them. That is what they are designed to do. This iis why they give us two different size breakers to work with. They could use any size breaker to protect against a short circuit. More than once I have read about a loose plug on the trailer getting hot. I want my 30 amp plug protected at 30 amps, not 50 amps.

Jim
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Old 02-03-2016, 12:10 PM   #104
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I have installed a lot of fuses and circuit breakers and have never selected and installed either to protect line side wiring, only load side wiring.
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Old 02-03-2016, 12:55 PM   #105
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I'm not an electrician but I think that oldtool2 and bubbles have the logic correct. A breaker or fuse protects the downstream wiring. The campground's wiring upstream from the power post (the feed line) is protected by another breaker upstream of that, likely in a distribution panel at utility feed into the campground.
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Old 02-03-2016, 02:48 PM   #106
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I'm not an electrician but I think that oldtool2 and bubbles have the logic correct. A breaker or fuse protects the downstream wiring. The campground's wiring upstream from the power post (the feed line) is protected by another breaker upstream of that, likely in a distribution panel at utility feed into the campground.
itat, you are correct! There is a main circuit breaker or fuse at the utility service entrance. That breaker/fuse protects the CG main bus and likely there is a distribution panel below the main that protects the CG wiring itself. On the utility side, if the main CG breaker/fuse fails to open, either the service drop wire overloads and burns down eliminating the short, or the transformer is overloaded about 225% andf it blows a fuse to protect the rest of the opwerlines from the low voltage short circuit. If there is no fuse on the utility transformer, then there is likely an up-line fuse or recloser(type of circuit breaker that automatically resets itself) that should clear the fault and keep the remaining HV wiring intact.

I think this thread is much ado about something that would likely never happen!

FYI, I am a Lead Electrical Engineer with the local electric company (36 years) as well as a licensed electrician. ........... Swampy
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Old 02-03-2016, 08:14 PM   #107
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I have installed a lot of fuses and circuit breakers and have never selected and installed either to protect line side wiring, only load side wiring.
Yes you have, you just haven't thought of it that way way you need to think. You are able (and should) select the breaker based off the load and use the appropriate size wiring. You are only able to do this because the upstream wiring can handle it. Now imagine a 200 amp panel box with 30 breakers. Plug 30 ten amp vacuum cleaners in each circuit and turn them on all at once. 10 times 30 is 300 amps. The full 300 amps is flowing through the feeder wires which is probably 4/0 AWG aluminum wire. Which according to the charts is too much current and the 200 amp breaker will trip and protect the feeder wires.

CG is the same logic. If the pole is fed with 2/0 AWG aluminum wire or 4 AWG copper wire it would probably handle about 100 amps depending on length (Don't beat me up if I am a few amps off. I didn't check the electrical calculator.) if those feeder wires went to 2 different camp sites and both sites pulled over 50 amps. The feeder wires would be overloaded. The 50 amp breakers would trip. Not the larger breaker at the main panel. Therefore the upstream wires are protected.

Your power cord connected to your 30 amp RV is 10 AWG wire. Any shorts in the power cord will trip the 50 amp CG breaker and stop the flow of current. An open neutral has nothing to do with current and needs protected with an EMS. An open will just stop the flow of current. I am not sure what other power cord fault could occur. Any overload of 30 amps in the RV will be protected by the RV breakers.
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Old 02-03-2016, 09:00 PM   #108
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I will add to above that only events down stream will trip a breaker, but because the breaker is in series, it protects the entire branch circuit.
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