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Old 04-30-2017, 09:05 AM   #1
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50 amp Electrical per Line

A quick discussion. I have the typical 50 amp camper, which technically means (I assume) designed for a maximum of 50 amps per hot lead (2 Hots).
The largest breaker I have is a 20 amp on both leads.
Configuring gauge for a 4 wire direct burial to feed my camper, should we really assume it possible to actually hit (even peak when the A/C compressor kicks on) 50 amps per line! That's an awful lot of current.
The energy hogs in my camper are definitely the converter and A/C's...but only for peak load when the compressor cycles.
Note: I do know I peak at least 30 amps because if I try to run the converter and only 1 A/C on a 30 amp generator (which dogbones the 2 hots into 1 lead) it will trip the 30 amp breaker momentarily. So, with the generator, I can either run 1 A/C or my converter to charge the batteries, but not both at the same time.
The run will be approximately 160 feet, and I really am trying to stay away from 4/0 cable.
Gauge calculators with a 30 amp load suggest a #1 wire (aluminum) this I can handle cost wise and weight wise...4 wire 4/0 cable is a monster.
Thoughts?
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Old 04-30-2017, 09:20 AM   #2
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The distance, amps, and weight versus cost seem you be your limiting factors so why not move the Rig closer to the source. Not sure I understand the weight issue wouldn't the cable be buried.
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Old 04-30-2017, 09:31 AM   #3
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a number #4 aluminum wire has the capacity of 65 amps,a number #2 has the capacity of 90 amps at 75 degree Celsius at that distance I doubt you will have more than a 3% voltage loss,

you can find ampacity charts and voltage drop calculators online, if it was me I would use copper, but to each his own, if you are going to run one ac, I would run a 50 amp circuit and use a pipe with copper and use A 220 breaker, but thats me,
and by the way a 4/0 aluminum wire is good for 180 amps

http://www.cerrowire.com/ampacity-charts

Quote:
Originally Posted by 2nd House View Post
A quick discussion. I have the typical 50 amp camper, which technically means (I assume) designed for a maximum of 50 amps per hot lead (2 Hots).
The largest breaker I have is a 20 amp on both leads.
Configuring gauge for a 4 wire direct burial to feed my camper, should we really assume it possible to actually hit (even peak when the A/C compressor kicks on) 50 amps per line! That's an awful lot of current.
The energy hogs in my camper are definitely the converter and A/C's...but only for peak load when the compressor cycles.
Note: I do know I peak at least 30 amps because if I try to run the converter and only 1 A/C on a 30 amp generator (which dogbones the 2 hots into 1 lead) it will trip the 30 amp breaker momentarily. So, with the generator, I can either run 1 A/C or my converter to charge the batteries, but not both at the same time.
The run will be approximately 160 feet, and I really am trying to stay away from 4/0 cable.
Gauge calculators with a 30 amp load suggest a #1 wire (aluminum) this I can handle cost wise and weight wise...4 wire 4/0 cable is a monster.
Thoughts?
2014 PDEK 2 A/C's
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Old 04-30-2017, 09:32 AM   #4
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According to my voltage drop calculator (I'm a commercial electrical contractor) #6 copper or #3 aluminum will result in a 3% or less voltage drop for 160' at 50 amps. We recently completed a state park campground electrification project and there were two of 6 feeders in that project that each supplied 3 50/30/20 pedestals on a 100 amp feeder breaker using #2 copper for the direct burial conductors. These feeders were much longer than 160'.

If you were my customer, I would recommend #2 direct burial aluminum triplex for the phases and neutral and #8 copper for the ground. This is the most cost effective solution using the most common materials that I keep in my inventory.
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Old 04-30-2017, 09:43 AM   #5
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I am not an electrician and do not know the codes so do not take this as allowable. but i'm wondering... it seems like you want to install a cable smaller than what would be required for 50 amps. what if you installed 4 wire cable rated for 30 amps over the distance you have. you could terminate it on a receptacle typically used for 50 amp so you could plug into it. YOU WOULD HAVE TO INSTALL A 30 AMP DOUBLE CIRCUIT BREAKER as you could not rely upon the 50 amp in your trailer to trip in time. this would give you two 30 amp legs which would run the a/c and converter as long as they were wired on different legs. again, I think it would conceptually work but I do not know if it would be legal, etc. there are others that know a ton more than me who might comment.
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Old 04-30-2017, 09:44 AM   #6
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, last statement very true, I just do not personally like aluminum wire, seen to many problems over the past 38 years, but all is good,
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Old 04-30-2017, 09:47 AM   #7
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Quote:
Originally Posted by CHICKDOE View Post
I am not an electrician and do not know the codes so do not take this as allowable. but i'm wondering... it seems like you want to install a cable smaller than what would be required for 50 amps. what if you installed 4 wire cable rated for 30 amps over the distance you have. you could terminate it on a receptacle typically used for 50 amp so you could plug into it. YOU WOULD HAVE TO INSTALL A 30 AMP DOUBLE CIRCUIT BREAKER as you could not rely upon the 50 amp in your trailer to trip in time. this would give you two 30 amp legs which would run the a/c and converter as long as they were wired on different legs. again, I think it would conceptually work but I do not know if it would be legal, etc. there are others that know a ton more than me who might comment.
a number 10 wire is good for 35 amps, but the code requires it can only be installed on a thirty amp breaker, dual or single pole breaker, not seeing the point I guess,
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Old 04-30-2017, 09:48 AM   #8
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The highest loads usually come from the Air Cond units when starting.

There are RV devices made that will assure 2 units will not start at once.

Wiring one Air on one leg and the other on the second leg also works.
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Old 04-30-2017, 09:51 AM   #9
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50 amp Electrical per Line

Keep in mind:

1. To trip the 50 amp breaker, you only have to exceed 50 amps on one leg.

2. Distance affects voltage drop, not current capacity of wire. Although current is a factor for voltage drop calc.

3. Doing it right the first time is always the best choice. In the big scheme of things, 50 amps isn't that much... so the proper wire size isn't that expensive.

#3 copper would suffice for both current carrying capacity and voltage drop issues at 160 feet. At 160 feet and 50 amps, the voltage drop for 120 volts is 3.15 or 2.63%. The goal being 3% or less drop.

For aluminum, #1 would be required to stay under 3%.

Considering the likelihood of actually pulling 50 amps on either leg, you can use smaller wire. For example, if you were, in reality, only going to pull 30 amps on a leg, you could go down to #5 copper.

Pulling the same load on both legs does not change anything here. Meaning, you could draw the amps listed on both legs at the same time and it wouldn't change anything.

Whichever route you choose, you will need two hots and a neutral with the same current carrying capacity... and a ground ran. The ground would be smaller wire. This means 480 feet of #3 wire (or whichever size you choose based on above).

Unless you are wanting to run all your stuff at the same time, a 30 amp pedestal would be MUCH cheaper. Smaller wire size due to current needs and one less wire.
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Old 04-30-2017, 01:16 PM   #10
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50 amp line

Why are you even considering aluminum wire?
That was tried in housing in the 70's and it was a disaster.
I had some in 60 amp line from my house to garage and I had to replace it.
I know copper prices are up, but i would never use aluminum wire.

See link for a good wire size calculator.
Wire Size Calculator

You will never see a 50 Amp continuous load so you could calculate wire size for 30 or 40 amps, but then you must have a main circuit breaker for 30 or 40 amps at the source breaker box. You can't run wire for 30 amps and then put a higher current CB in.
You already know you will trip the 30 amp CB on the generator, but those generator CB's are probably a "B" or "C" curve which will trip faster for short current spikes.
A 30 amp "D" curve CB will not trip that fast. It will allow spikes 20 times longer spike than "B" curve CB's.
The wire size tables are all assuming 100% continuous loads. Startup currents for 100's of msec's will not be an issue for the wire size.
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Old 04-30-2017, 01:25 PM   #11
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Circuit breakers are rated at 80 percent continuous current.
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Old 04-30-2017, 02:01 PM   #12
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50 amp line

Circuit breakers are de-rated by a % depending on the thermal environment.
80% is a general rule that assumes temperatures of trip coil up to 60C.
There is a de-rating curve based on CB temperature.
I was referring to the load current being continuous for 100% of the time.
Not the CB current trip value de-rating.

Either way... I would never use aluminum wire and the wire gauge tables consider 3% voltage drop and also need to be de-rated for higher temperatures.

Thanks

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Old 04-30-2017, 02:41 PM   #13
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For the money you have invested in your rv and the cost of ac replacement, I would not cut corners on the wiring which should be a one time investments. Al wire has cost folks a lot of headaches under heavy loads! Go with correct copper wire size and proper breakers. If you had an issue, insurance claim could be an issue with substandard wiring.
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Old 04-30-2017, 02:53 PM   #14
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If you were my customer, I would recommend #2 direct burial aluminum triplex for the phases and neutral and #8 copper for the ground. This is the most cost effective solution using the most common materials that I keep in my inventory.
So this is all good stuff...I prefer aluminum simply because of the cost. Copper is definitely the way to go, Many people have told me at that distance, to be safe and simply go to a 4/0 wire, this would be expensive not only for copper (hence the aluminum) but also shipping weight and getting the wire in place where I need it.
A little bit about the camper placement: moving the camper closer is not an option as it is parked under a nice RV Port. The meter-loop on property is the 160' distance, and at over $5,000 per pole drop, I definitely do not want to move the transformer pole closer.
So we can assume each hot lead to carry a max of 50 amps momentary peak (I can not believe I would ever have a continuous 50 amp load) If I were to put in a sub panel for expansion, at the camper RV port, and run the 50 amp plug off the sub panel, and lets say I assume a rating of 80 amps per hot to the sub panel for expansion, a #1 copper should be allowed to carry the load, with an acceptable voltage drop, especially considering I simply can't imagine pulling a continuous 80 amp load...that's a lot of current.

To WY Husker Fan's point, I initially was thinking a 4-wire direct burial, simply because it is one cable, instead of a triplex, and an additional cable for ground...I'll have to think on that concept. I'm leaning towards a 1/0 aluminum for cost savings, which should offer me plenty of expansion should I choose. The aluminum should last 20+ years, which will put me at close to 80...I'll probably be in the Geezer home by then!
So, it looks like we have the wire size (with no 4/0 suggestion!), now to decide copper or aluminum...copper is so darn expensive.
Thanks everybody!
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Old 04-30-2017, 03:04 PM   #15
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Unfortunately this turned into a copper vs aluminum argument, well afield from the original conversation. I have been installing aluminum feeders for decades with no issues if done correctly. The disaster of trying to use aluminum for small branch circuits in the 70's has tainted "aluminum" as a wiring method. We are completing a $24MM hospital project that utilized aluminum conductors for all of the panel feeders. I stand by my original suggestion if the soil is not rocky and you terminate the wire correctly. If the soil is rocky then either copper in conduit or sand bedding for the aluminum would be the preferred method. Another option is to use direct burial copper "tray" cable. That is what we used for the campground project I mentioned earlier but it is pricy though cheaper than individual direct burial wires.
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Old 04-30-2017, 03:13 PM   #16
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Thanks to WY Husker Fan. You are definitely making a strong point for aluminum, especially the "terminating correctly" part, which I assume you are speaking about the grease for anti-corrosion, which I can't remember the name of it.
The ground that will be trenched is in a good soil valley, so it is not rocky, and I'll trench at 2', county code is 18". I have read it best to keep direct burial out of conduit so as not to collect moisture...thoughts on that?
Thank you
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Old 04-30-2017, 03:54 PM   #17
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These recommendations for #1 and higher are a waste of money. #3 copper is the proper size for 50 amps at that distance.

The continuous vs non-continuous discussions are not relevant and just cloud the issue. Ampacities for conductors are for continuous use. In this case, due to the distance involved, conductor size is being increased for voltage drop. If voltage drop was not an issue, #8 THHN copper would suffice.
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Old 04-30-2017, 05:37 PM   #18
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There is a lot of good information in this thread so I'll just add, regardless of the conductor (copper or aluminium) follow the code. Do it right or don't do it at all.
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Old 04-30-2017, 05:55 PM   #19
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why not just run a 30a line to the RV? why would you need 50a/100a when it's just parked there?
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Old 04-30-2017, 06:20 PM   #20
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why not just run a 30a line to the RV? why would you need 50a/100a when it's just parked there?
I actually go out to property on the weekends and live in it. Thanks
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