30 amp cord??

[maxx1963]

I have a 15,000 air conditioner and a 50 amp cord on my trailer. I hate toting around that heavy 50amp cord. Can i make a 30 amp with a twistlock that fits my trailer and be ok to use the a/c on the 30 amp?

[Bean]

If you are not running too many other things...AND the cord is connected to a 30 amp breaker (not a 50 amp)...I'd say you will be alright.

But connecting a 30 amp cord to a 50 amp breaker is just asking for trouble.

P.S. It might not work anyway. I think a 50 amp cord actually has two separate 25 amp feeds. Where a 30 amp cord just has one 30 amp feed.

Bean

[maxx1963]

I have heard that you can just tie those to 25 amp terminals to the single power wire coming in from the 30. the thing is, if i have to use my 50 amp cord then i have a 30 amp cord for a extention right now, what is the difference??

[Quad]

No, a 4 prong 50 amp plug has two 120 volt 50 amp wires. So a combined total of 100 amps. That's why they have a double 50 amp breaker. You should be ok running the camper on a 30 amp cord so long as you don't run any other amp hogging items. Just remember both circuits in your camper will now be on 30 amps instead of 100 amps total.

[allmi01]

Quad, a correct here. A 50 amp cordset has 2 50 amp circuits however, the total amperage you can draw is 50 amps. 50 amps on each leg as 120 volts or 50 amps as 240 acroos both together. Since nothing the in the RV is 240 volts, you get 50 amps to play with accross 2 seperate circuits. But that is not really 100 amps.

If you do not have 2 A/C units, then you might be OK with a 30 amp cordset (and yes they are commercially available but not cheap) as long as you don't try to draw more than 30 amps total. The plugs on 30 amp and 50 amp are different as the 30 amp ony carries 1 circuit and the 50 amp carries 2 circuits.

I hope this helps some. Not trying to be critical but.. this is important as overloading electrical cords will cause fires.

Mike

[byrdr1]

Marinco 124ARV-25 RV Electrical Power Cordset (50-amp 125/250-Volt Receptacle with 30-Amp 125-Volt RV Straight Blade Plug, 25-Feet) its on Amazon.
This is what I use at home. I had the 30amp box already wired up from the popup and TT days.
So i found this cord set and it keeps my heavy 50 amp cord in the camper safe and sound. I run the 15K main AC but have never run both. I dont use anything other than the frig as cold place for can goods.
randy

[maxx1963]

I was going to use the 50 amp twistlock plug with the 30 amp on the other end. I have 8/4 and 10/4 wire at home to make my own length. i was thinking like 50 or 60 ft to minimize extention cords.

my 8/4 wire says it is good for 55amps, so I should be safe with that even if i get to a 50amp service campground.

all 4 wires will go on the twistlock and at the 30amp end, the 2 hot wires will join into one, correct?

[byrdr1]

Originally Posted by maxx1963

I was going to use the 50 amp twistlock plug with the 30 amp on the other end. I have 8/4 and 10/4 wire at home to make my own length. i was thinking like 50 or 60 ft to minimize extension cords.

my 8/4 wire says it is good for 55amps, so I should be safe with that even if i get to a 50amp service campground.

all 4 wires will go on the twistlock and at the 30amp end, the 2 hot wires will join into one, correct?

8/4 for the 50 ft Plus length.
10/3 for 30ft or less. my opinion only..
randy

[Bob Landry]

There is a considerable amount of misinformation here pertaining to 50A service. 50A service consists of two 115V, 50A sources, 180 degrees out of phase and referenced to a common neutral. It will feed two sets of circuit breakers with 115V and 50A per side, so there is actually 100A available at the panel on each leg. You are not splitting 50A between two legs, you are splitting 100A between two legs because each leg has 50A available.

My concern with what the OP wants to do is that he will still be plugging into a 50A inlet at the trailer. If he plugs into a 30A outlet at the pedestal, it can work, but if he is intending to plug into a 50A outlet and use only one leg, he still has a trailer with a power leg that can accept 50A service, a power source that can provide it, joined with a 30A(10g a) cable connecting them. Unless he has a way to monitor and insure that he is only drawing 30A max, that's potentially a fire waiting to happen.

I've been in the marine service business for 15 years and I've seen firsthand the problems introduced by owners wanting to modify existing electrical systems, so my advice is that unless he is versed in 30A/50A service, he would do well to pick up a Marinco catalogue and start looking for a commercially made adapter for both ends of that 30A power cord.

Truthfully, how much hassle can it be to use a power cord that is designed to provide all of the power you would need in a travel trailer?

[Bob Landry]

Originally Posted by maxx1963

I was going to use the 50 amp twistlock plug with the 30 amp on the other end. I have 8/4 and 10/4 wire at home to make my own length. i was thinking like 50 or 60 ft to minimize extention cords.

my 8/4 wire says it is good for 55amps, so I should be safe with that even if i get to a 50amp service campground.

all 4 wires will go on the twistlock and at the 30amp end, the 2 hot wires will join into one, correct?

Your 8/4 wire is labeled incorrectly or it is refering to DC. #6 is only rated for 50A. #8 is smaller and is capable of carrying less current. If you are going to have a 50-60' run. you really need to increase a size. That would put you at 8Ga, so at that point, a 50A cable isn't that much heavier and you are assured of having all of the power you might need.

[maxx1963]

I have the wire and the twist lock plug, all I would heve to buy is the 30amp plug, so I was trying to save some money and make my own length.

I see all the adapters they make and it can not be complex. And how can they go from a 50amp twist lock to a regular 110v plug?

I can buy the cord I want to make, I was just trying to save money, and I have never been to a campground that has 50amp service.

[EricLynnAllison]

Another option is to install a cord real. If you look for my post "utility mods" you see how I added one.

[PND]

If you have a 50 amp circuit, you should ONLY be using a 2 pole 50 amp breaker. NEVER use two single pole 50 amp breakers. The circuit is rated for 50 amp max.. Also larger wire are multi strand and extension cords use a larger number of strands per wire size to add flexability to it. The more strands also helps increase (slightly) the current carrying capacity since it reduces the "skin effect" of AC current flow.
Now, a single phase 240 volt system with neutal is 2 120 volt circuits IN PHASE with each other. This is called a split-phase system and is the norm. in the US utility system for single phase usage. If you have 5 amps on one and 4 amps on the other, since they are in phase, the neutral has 1 amp on it. They cancel out eachother and the resultant is what is on the neutral. This why your neutral wire (in your panel) is half the size of the main conductors. A 30 amp circuit (RV) is a single pole 120 volt circuit only. The 30 to 50 amp adapters connect the 2 "hot legs" of the 50 amp plug together so the 30 amp circuit will supply power to the unit HOWEVER you will need to reduce your power draw. Hope this helps.

PND
45 years in electrical
Marine and High Voltage Jouneymen cards
Utility Relay Electrican

[Bob Landry]

Originally Posted by PND

If you have a 50 amp circuit, you should ONLY be using a 2 pole 50 amp breaker. NEVER use two single pole 50 amp breakers. The circuit is rated for 50 amp max.. Also larger wire are multi strand and extension cords use a larger number of strands per wire size to add flexability to it. The more strands also helps increase (slightly) the current carrying capacity since it reduces the "skin effect" of AC current flow.
Now, a single phase 240 volt system with neutal is 2 120 volt circuits IN PHASE with each other. This is called a split-phase system and is the norm. in the US utility system for single phase usage. If you have 5 amps on one and 4 amps on the other, since they are in phase, the neutral has 1 amp on it. They cancel out eachother and the resultant is what is on the neutral. This why your neutral wire (in your panel) is half the size of the main conductors. A 30 amp circuit (RV) is a single pole 120 volt circuit only. The 30 to 50 amp adapters connect the 2 "hot legs" of the 50 amp plug together so the 30 amp circuit will supply power to the unit HOWEVER you will need to reduce your power draw. Hope this helps.


PND
45 years in electrical
Marine and High Voltage Jouneymen cards
Utility Relay Electrican

Single phase 240V/50A service is comprised of two 120V legs 180 degrees out of phase with each other. It is still single phase because current and voltage are in phase with each other as opposed to a 2 or 3 phase power as would be used in commercial applications to operate high output motors that require a lot of torque. In a RV or marine application, there is nothing to shift the two components of the signal out f phase with each other.

You are correct, however, in that a double pole breaker needs to be used so that both current carrying legs of the circuit are broken. We are required to do that in marine applications also as per ABYC.

[SAD]

Originally Posted by PND

...If you have 5 amps on one and 4 amps on the other, since they are in phase, the neutral has 1 amp on it. They cancel out eachother and the resultant is what is on the neutral. This why your neutral wire (in your panel) is half the size of the main conductors....

you are correct that the neutral generally carries the delta....

however, the neutral wire must be the same size as either hot leg wire... (or more correctly, capable of carrying the breakers rated load)

In the event that no load is on L1, and L2 is fully utilized, the neutral has the potential to carry 50 amps.

To wire it any other way is wrong.

[Bob Landry]

Originally Posted by SAD

you are correct that the neutral generally carries the delta....

however, the neutral wire must be the same size as either hot leg wire... (or more correctly, capable of carrying the breakers rated load)

In the event that no load is on L1, and L2 is fully utilized, the neutral has the potential to carry 50 amps.

To wire it any other way is wrong.

That is correct. Neutral is a current carrying leg and has to be the same size as the hots. I've seen a lot of shore power problems at marinas where the neutrals to the pedestals were wire with undersized wire and they will definitely burn up under load..

[PND]

I am continuing this in an effort for all to understand an electrical (single phase) system. Please understand I am not trying to slam anyone, just give everyone information that everyone can understand in their own way. As I have stated, I do work for a power utility, so electrical is my field.

That being said here goes! Short of putting in drawings, if you want to follow on paper what I will describe. If you draw a transformer secondary winding (over lapping vertical circles), on the top, connect a horizontal line and next to that is a dot (polarity mark), on the bottom, connect another horizontal line. This is a simple single phase 240 volt system. Now, next to the polarity mark put a "+" sign (we call this relative polarity) and on the bottom put a "-" sign. Above the upper horizontal line draw an arrow pointing to the transformer winding, and on the bottom horizontal line draw an arrow pointing away from the transformer winding. The upper and lower horizontal lines are 120 Volts and across them is 240 Volts. What we have is two 120 volt lines in SERIES with each other and is a SINGLE phase. As pointed out by others the arrows are 180 degrees out from each other HOWEVER they are still only one phase. Yes, many of you call this out of phase, but remember this is only a single sine wave. Now let's make a 120/240 system (your house). Draw a line parallel to the upper and lower horizontal lines, coming out of the center of the transformer winding. Now we have our "neutral". Remember our "relative" polarity dot and the + mark on top, now next to the "neutral" line (above the line) put a "-", and below the line put a "+". You see that on the "neutral" line there is both a "+" and a "-". Now many have said that the "neutral" wire MUST be the same size as the "hot" wires. I will explain this shortly. What we have here is a "split-phase" system, still only one phase. The wires from your KWH meter to your breaker panel has three wires, the two "hot" wires (running through the meter) and a wire AT LEAST 1/2 the size of the two "hot" wires. If you ever see your panel cover off it is apparent. I don't recommend you take your cover off unless you have some experience with electricity. Now, remember the "+" and "-" signs on your "neutral", and noticing that the arrows on the "hot" wires are pointed in opposite directions, draw a load from each "hot" wire to the "neutral". Your upper "120 volt" circuit (following your arrows) runs to the transformer, down to your "neutral", OUT (arrow away from the transformer) to your upper"120 volt" load. If you follow the this arrow from the top, not turning at the "neutral" going OUT the bottom "120 volt" circuit to your load (note this arrow matches direction of the first arrow you drew) and if you put a load across the upper and lower lines (hot wires), you have a 240 volt circuit, but if you turn at the "neutral" ( on the lower 120 volt load), your arrow now points BACK towards the transformer, this is your other (lower)"120 volt" circuit. NOW, as to what is happening on the neutral, REMEMBER, this is a single phase circuit and because of that the two opposing currents in the neutral, they CANCEL each other. If you have EQUAL loads on EACH 120 volt circuits, you would have zero current flow in your neutral. However, there is never a real "balanced" condition in reality, so there will be some current in the neutral.

Now let's move to your RV system. If you have a 50 amp system, it will be like the "split-phase" system described above (two 120 volt systems in series). If your RV has a 30 amp system, you have only ONE side of the above system (one 120 volt circuit). On 30 amp RV systems the "hot" and "neutral" MUST be the same size, since all current is running through both wires. 50 amp systems have the "neutral" current load being "cancelled", just like a normal 120/240 split phase system. BUT!!!! If you don't have a true 50 amp system to plug into - only a 30 amp, there is a problem. 50 to 30 amp adapters parallel the two "hot" legs, so you only now have one true 30 amp circuit and the neutral now has to carry full current. Your 50 amp (two 120 volt circuits) RV is now a 30 amp (single 120 volt circuit). Your wiring is installed with ALL wires to your RV panel (from the receptacle) the same size (someone pointed that out) AND ALL your wires in your shore power cable are the same size (also much easier to manufacture with all conductors the same size). Now, you can plug into 50 amp (if you have a 50 amp system) or into a 30 amp plug and everything works (with current limitations). Note, that when you are on a 30 amp circuit, the "hot "legs "share" the current (parallel circuits, current divides), but the "neutral" carries the entire current.

I truly hope I haven't offended anyone and that this makes sense to all. The terms of "in phase" and "out of phase" are apparently understood differently by different people. I work with three phase systems, from generating plants, to substation, down to single phase loads. Happy Camping to all!!!

PND