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Old 01-21-2012, 05:00 AM   #1
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Maximum extension length for shore power?

Hi All,

I'm wondering what the maximum length of 30-amp extension cord should be? Particularly when running the air conditioner

I know there is a voltage drop across the length of wire; with out current trailer (17' Casita), they said 30' of extension cord + the shore power cord is the max they would recommend for running the air conditioner.

Is 30' of extension cord also true for an Airstream (25FB if that matters)?

Living in Texas, AC in the summer is not an option! I am planning on have a 30-amp plug installed at our house (for loading & unloading for trips), but wonder how close I need to get it to the street (we can't get an 25FB into our driveway).

Thanks in advance,
Jeff
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Old 01-21-2012, 05:56 AM   #2
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Wire Size Calculator

It will be the amperage loss over the length that is an issue. Use this calculator to ssist you in determining the max lenght you can use. You know your wire size in the cord(s), you just need the amp draw of Airstream while loading to get your answer.

Your new outlet for the RV should be a dedicated outlet - the only one on the curcuit to the breaker box - prevents someone from plugging in something in the house on the same circuit.

The more connections the more loss. Use as few as possible to connect.
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Old 01-21-2012, 07:03 AM   #3
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What about using a 50 amp box at the house?? Then use the 50 amp extension to your plug.
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Old 01-21-2012, 07:07 AM   #4
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What about using a 50 amp box at the house?? Then use the 50 amp extension to your plug.
An RV 50 amp extension has two branches, both have the same size wire. So, putting in 50 amp and a 50 amp extension wouldn't do anything except add tot he complexity and expense.
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Old 01-21-2012, 07:21 AM   #5
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I was thinking for the size wiring, but you are right. Here is a link he could use.
Wire Size Calculator
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Old 01-21-2012, 07:45 AM   #6
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I have never had an issue using the standard extension available at RV stores....what are they....25' I think. And the one on the AS is 25'????

Anyway one standard RV 30 amp extension is fine IMO.
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Old 01-21-2012, 07:58 AM   #7
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I would not go over 50ft (total) and I would measure the voltage inside at max load. Anything below 110V is pushing it. I have thought of a 220V, 30A system which would put the air conditioner on one circuit and the rest of the trailer on the other circuit. You would need knowledge of wiring and a new breaker box. You can run your trailer off of a 50A 220V circuit then.

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Old 01-21-2012, 08:16 AM   #8
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Originally Posted by barrettjl View Post
Hi All,

I'm wondering what the maximum length of 30-amp extension cord should be? Particularly when running the air conditioner

I know there is a voltage drop across the length of wire; with out current trailer (17' Casita), they said 30' of extension cord + the shore power cord is the max they would recommend for running the air conditioner.

Is 30' of extension cord also true for an Airstream (25FB if that matters)?

Living in Texas, AC in the summer is not an option! I am planning on have a 30-amp plug installed at our house (for loading & unloading for trips), but wonder how close I need to get it to the street (we can't get an 25FB into our driveway).

Thanks in advance,
Jeff
Quite simply, the size of the wire for the extension cord, dictates how long it can be.

You could go 1,000 feet, if needed, as long as the wire size was adequate.

I used years ago, a 200 foot extension cord, and had less than one volt drop, "with the AC running".

A pain in the neck to haul around, absolutely.

But the performce was top shelf.

Andy
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Old 01-21-2012, 09:08 AM   #9
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Long AC Electrical Cord

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Originally Posted by barrettjl View Post
Hi All,

I'm wondering what the maximum length of 30-amp extension cord should be? Particularly when running the air conditioner ...
When preparing our Airstream for a trip, I routinely use two shore power cords (with a combined length of about 55 feet) to go from the 30 amp service I installed on the outside wall of our house to the trailer. One cord is a standard 30 amp shore power cord and the other cord is one that I built.

During this time, the refrigerator, the converter, and the air conditioner may be running. The voltage drop is not excessive, and everything works as advertised.
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Old 01-21-2012, 09:16 AM   #10
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We routinely use our regular 30 foot power cord with another 30 foot 30 amp R extension cord. We have probably used this configuration for over 200 nights. We have never experienced any voltage drop problem,s even in out Florida summers.

Brian
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Old 01-21-2012, 09:47 AM   #11
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Originally Posted by barrettjl View Post
Hi All,

I'm wondering what the maximum length of 30-amp extension cord should be? Particularly when running the air conditioner

Jeff
The actual answer is: "there is no maximum, as long as it is rated for 30 amps".

The question should be not how many feet, but how many cords.

A 100 ft extension cord rated for 30 amps is not the same, at all, as two 50 foot 30 amp extension cords. In fact two 50 foot 30 amp cables hooked together should be considered to have less capacity than one 100 foot 15 amp cable due to the extra connectors. So as long as the extension cord is rated for thirty amps, just buy one that is long enough. Then you don't have to guess and you are following safe electrical practices.

The wire size calculators are fine for estimates, but they don't take into consideration the voltage drop at each connector, which can be considerable at max current. The connector voltage drop can also varying considerably with the condition of the connectors. So use as few as possible.

The posts above of what others do while experiencing no problems, do not necessarily mean that they are good practice or will work for anyone else. Just buy one 30 amp cord as long as you need.

That is my advice.

Ken
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Old 01-21-2012, 11:35 AM   #12
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Originally Posted by w7ts View Post
The actual answer is: "there is no maximum, as long as it is rated for 30 amps".

The question should be not how many feet, but how many cords.

A 100 ft extension cord rated for 30 amps is not the same, at all, as two 50 foot 30 amp extension cords. In fact two 50 foot 30 amp cables hooked together should be considered to have less capacity than one 100 foot 15 amp cable due to the extra connectors. So as long as the extension cord is rated for thirty amps, just buy one that is long enough. Then you don't have to guess and you are following safe electrical practices.

The wire size calculators are fine for estimates, but they don't take into consideration the voltage drop at each connector, which can be considerable at max current. The connector voltage drop can also varying considerably with the condition of the connectors. So use as few as possible.

The posts above of what others do while experiencing no problems, do not necessarily mean that they are good practice or will work for anyone else. Just buy one 30 amp cord as long as you need.

That is my advice.

Ken
Agreed! Before I connect the connectors, I take some emery paper and clean any corrosion from the male and female ends, and then plug them in and out several time to assure as good a contact area as possible. If the connectors are not clean then you can get electrical arcing which can heat the connectors and actually melt them.
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Old 01-21-2012, 12:42 PM   #13
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The best way to know what to use is to test various combinations in use under load. Of course, to do that, you have to buy an extension and test it; if there's too much voltage drop, you have an expensive cord you won't use.

If you buy a 50' or 100' cord instead of using an extension cord, you will find it is very heavy and bulky to store. And two cords in the bumper storage compartment will inevitably get tangled. I agree that bad connections are bad electrical practice, but testing will show just how bad.

I don't know how old a cord has to be before you have to replace it. The conductors in these cords are braided wire (solid cores would be impossible to coil) and eventually the thin wires in the braid break down. Lamp cord after many years does that and then a household lamp stops working. Has anyone had the OEM cords fail that way and after how many years?

I note that Brian uses an extension cord and reports no problems (post #10). Brian is pretty careful about what he does, so I tend to believe him. We just stay close to the electrical connections at campgrounds and don't have an extension cord.

But the OP is not about campgrounds, but about parking on the street. One solution is installing a receptacle at the curb with underground wiring from your household breaker box. This would mean more expense that a 25' or 30' extension cord, but would, if installed properly, be safer (no wire to trip over, no chance of water in the connection on the lawn, no chance of voltage drop) and convenient. You'd save a lot of money if you do it yourself, but digging a trench is no fun (underground cable used to be at least 18" down by code, but that may have changed since I have checked in many years). And the municipality may not like a 30 amp receptacle at the curb, but 25' back from the curb may be fine.

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Old 01-22-2012, 05:01 AM   #14
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Thanks for all the replies.

Ideally I would like to put a 30amp plug near the street, but am trying to keep cost down. If I can get an outlet installed near the breaker box and run an extension cord to the street instead, then I imagine that will be much cheaper.

It looks like that would be just under 60'. I didn't realize that the number of connections causes an issue; I currently have two 25' cords, but it sounds like a single extension would be better. Once we get the trailer here and I can measure more accurately based on where we can park it, I'll get a single extension that is long enough.

Thanks,
Jeff
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