Combining two 15 amp circuit to get 30 amps

[wmtire]

The site team is reopening this thread to hopefully help.

One of my favorite links that I post a lot is below. It explains in very simple terms how 120/240 volt split phase electricity works (what most everyone has in their home). It also explains how 120/240 volt 50 amp RV service works and how the current carrying neutral wire will only carry the current imbalance between the L1 and L2 hot legs.

https://www.rvtechmag.com/electrical/chapter3.php


Now as juice5 pointed out earlier as a 'parallel feeder' which does sound like what the OP is attempting to accomplish, there are other caveats to insure against wires burning up/fire as in the article below about how the wires have to be the same size, length, and other.

https://www.ecmag.com/section/codes-...ame-electrical

This link below may also help with the following taken from it also explaining how the neutral wire(s) may be overloaded now:

https://inspectapedia.com/electric/M...l-Circuits.php

Case-1: both breakers placed on same panel bus:

Performing work on an electrical panel in which a multi-wire branch circuit was not wired using a double-pole common-trip circuit breaker, an electrician relocated one of the individual breakers such that both of the multi-wire feeds were on the same electrical bus.


In our sketch, using the narrow-width circuit breakers 10A and 10B, if wired as a multi-wired circuit, would both be connected to the same bus and same phase. This is an improper wiring hook-up because this placed both breakers on the same electrical phase in the electric panel.

When both circuits were in maximum use the result was a neutral wire current which exceeded the permitted rating.

------------------------------------------------
What this all means is that in a 120/240 volt configuration, the two OPPOSITE hot legs basically cancel out the current on the neutral wire so it really never gets overloaded.........but in the OP's scenario of using two hot feeds from the same 120 volt leg to double the amps, the neutral now has the potential to carry double what it was designed for, thus overloading it.

In short, it's just not worth the risk for the OP to attempt what they are trying (if I am understanding correct). It would be best to just use one 15 amp outlet as designed (and wire sized for) to connect the RV to, and limit your electric usage to 15 amps or less. Many people do this while connected at home via an adapter to let them connect their RV to the 15 amp outlet.

If you do want a full 30 amp capability, then it just makes sense to run a new circuit with the proper wire for such. Here is a great link we keep for just such:


https://www.forestriverforums.com/fo...let-27223.html



Hope all of this helps.

[Chuck_S]

The 30a "RV" outlet on the outside wall of my garage next to the house panel is on a single 30a breaker. Professionally installed. Just saying.

-- Chuck

[formerFR]

hmmmmm, the 'normal' 30amp RV outlet is simply a 120v 30amp outlet wired back to a 30amp single pole breaker - nothing terribly different than your 'normal' everyday household outlet, only larger wires and breaker.

if the original post owner has 'heard' that it is a 240v outlet, needing some kind of 'special' wiring, they are wrong.

[KyDan]

One final comment and I'm outta here---
IF you actually move forward with this scenario of 2 breakers to feed your #12 supply wire you could overload the neutral wire and burn down your house.
It's against the National Electrical Code
and might not be covered by your insurance due to the code violation.
Please hire an experienced licensed electrician and get it inspected- remembering you still want 30A 120V RV service.

[tgold]

It doesn’t meet current or past National Electrical Code. If the length of each run of romex isn’t exactly the same you could have an issue. Also illegal to place two small #14 AWG under the same lug of the receptacle. Play it safe and run # 10 AWG AND BUY A 30 amp breaker.

[nrightinhead]

Originally Posted by RVasylum

Hey guys, I did mess up my first post, I got the in phase and out of phase backwards. The two circuits need to be in phase for a shared 120v circuit. Other than than that please explain why it is okay to share circuits to create a 240 v circuit and it is not okay to share circuits to create a 120v circuit. Below is a explanation from another electrical engineer.


IF you use two different 15 amp branch circuits AND they are from the SAME PHASE you should get a maximum of 30 amps 110 VAC from the two legs. you would connect both black hots from the dual pigtail to the hot on your 30 amp RV socket and both white neutrals to the neutral on your 30 amp RV socket. Twist the copper ground wires together and connect to the ground lug on the 30 amp RV socket. The load (what ever it is) will be split equally between the two feed lines. For example if the camper is pulling 20 amps; 10 amps will come from each circuit breaker as long as the camper is the ONLY thing on both branches.

The phases on a panel ZIG ZAG down the panel and alternate every other breaker. Example: Left side: Breaker #1 phase A; Breaker #3 phase B; Breaker #5 phase A again.

So you would use Breakers #1 and Breaker #5 to tie together.

IF you make a mistake and use a circuit from the OTHER phase in the panel, when you throw the second breaker there will be a light show like you have never seen before. You will have a DEAD SHORT of 220 volts at the 30 amp RV socket which will cause quite a fire.

He is correct however the terminology he uses is not the best. He should not be calling it phase because it is all the same phase. That is why I refer to it as A & B, he did reference it but went to phase which is confusing.

He is correct on the panel configuration the left side will be B-A-B-A, and the right A-B-A-B as it goes down. So if both 15A breakers are on A what he stated is correct. However this is not Per code in most Places because you are combining two wires in a connector designed for one wire. Your trying to play with electricity in a way that can be dangerous. The 2 conductors with the 120V could come out of the connector and cause a short, it is just not a good practice. One breaker is actually cheaper then 2 and the cost difference in wire is not worth the damage it could cause.

I did make one mistake, I said the ground = bare copper, that is incorrect in a stranded cable. The ground will be a green or green with a yellow strip.

I hope this helps

[Chuck_S]

"Surprisingly" neither a 30 amp dryer cord nor 30 amp range will plug into my external RV outlet... Nor will my camper plug into a dryer or range outlet.

Hmmmmmmm, maybe because the "30a RV/Marine" outlet is 120vAC and not 240v?

(50a RV connections are 240vAC.)

[nrightinhead]

Originally Posted by Chuck_S

"Surprisingly" neither a 30 amp dryer cord nor 30 amp range will plug into my external RV outlet... Nor will my camper plug into a dryer or range outlet.

Hmmmmmmm, maybe because the "30a RV/Marine" outlet is 120vAC and not 240v?

(50a RV connections are 240vAC.)

That is correct and is done because of the use. In a dryer or range use the 240V, in an RV (most cases) they are used as two separate 120V circuits, each circuit can pull 50A. They wire RVs very differently then house hold appliances or other things that use 240V. Hence the different connector so you can not mix them up. It is all designed to keep people safe and to keep them from accidently burning down their house.

[llamb]

Originally Posted by wmtire

Case-1: both breakers placed on same panel bus:

Performing work on an electrical panel in which a multi-wire branch circuit was not wired using a double-pole common-trip circuit breaker, an electrician relocated one of the individual breakers such that both of the multi-wire feeds were on the same electrical bus.


In our sketch, using the narrow-width circuit breakers 10A and 10B, if wired as a multi-wired circuit, would both be connected to the same bus and same phase. This is an improper wiring hook-up because this placed both breakers on the same electrical phase in the electric panel.

When both circuits were in maximum use the result was a neutral wire current which exceeded the permitted rating.

------------------------------------------------
What this all means is that in a 120/240 volt configuration, the two OPPOSITE hot legs basically cancel out the current on the neutral wire so it really never gets overloaded.........but in the OP's scenario of using two hot feeds from the same 120 volt leg to double the amps, the neutral now has the potential to carry double what it was designed for, thus overloading it.

In short, it's just not worth the risk for the OP to attempt what they are trying (if I am understanding correct). It would be best to just use one 15 amp outlet as designed (and wire sized for) to connect the RV to, and limit your electric usage to 15 amps or less. Many people do this while connected at home via an adapter to let them connect their RV to the 15 amp outlet.

If you do want a full 30 amp capability, then it just makes sense to run a new circuit with the proper wire for such. Here is a great link we keep for just such:


https://www.forestriverforums.com/fo...let-27223.html



Hope all of this helps.

This is the same thing when it happens in an RV park pedestal (common phase or bootleg 50A service). But when it happens at the pedestal, it typically has a neutral large enough to handle it, but your RV wiring doesn't. Things like this why it's important to check the pedestal before hooking up your rig to it.

Mike Sokol from RVelectricity.com has a good video on things.

RV Power Pedestal discussion with electricity expert Mike Sokol

Apologies for being a little off the OPs topic.

[llamb]

Originally Posted by nrightinhead

That is correct and is done because of the use. In a dryer or range use the 240V, in an RV (most cases) they are used as two separate 120V circuits, each circuit can pull 50A. They wire RVs very differently then house hold appliances or other things that use 240V. Hence the different connector so you can not mix them up. It is all designed to keep people safe and to keep them from accidently burning down their house.

I'm not an electrician but this is my understanding.

Over the years, you've seen different types of connectors for 240v appliances in homes. They're typically 30A and thus you'd never want to be able to plug a 50A RV. You'd also run into a lot of issue with the 2 pole with ground connectors used in a lot of older homes. They have your L1 and L2 split phase hot lines and a ground. As the appliance pulls load from each phase equally, there wasn't a need for a neutral (split phase loads are subtractive).

In an RV, it's still split phase 240V, but loads only pull from one hot line. As that load can be pulled disproportionately from one phase, the neutral will only carry the difference between the two. Example, you're pulling 10A on L1 and 5A on L2. In a split phase system, the neutral only carries 5A at that point.

[RVasylum]

I want thank all the responders to my original post. I would like to add what got all of this started was the install of a LiFePO4 12v 100ah battery which included a new Progressive Dynamics Lithium capable power center and a Renogy 20Amp Dc to Dc charger. With this new setup my amp draw to the new battery was increased and after 5 to 10 minutes of charging from a 20Amp GFCI protected garage outlet with a 30 to 15amp pigtail, it would trip the GFCI which I concluded to be a false trips. That’s a whole other subject. My solution to that issue was to install a non GFCI protected outlet dedicated solely for my camper. If I was going to do that I might as well install a 30amp RV outlet after my sub panel and not use the pigtail. There is 12/3 Romex to my garage buried under my driveway and I didn’t feel like tearing up my driveway and sidewalk to rerun 10/3 which could then could power my new 30amp outlet off a single breaker. After all the responses and web searches on paralleling A/C Circuits and after I had successfully paralleled my new outlet I will be disconnecting one of the feeds to the outlet making it 20 amps and going back to using the pigtail.

[Bogieboy]

It really is not that difficult to put in the correct stuff... i am mostly done with wiring my house for a 30a rv plug, i am into the job about$140, 2 trips to lowes, and about 1 hr of labor... have about 30 more min of finishing the wiring pull and it will be done...

[5picker]

Originally Posted by RVasylum

I want thank all the responders to my original post. I would like to add what got all of this started was the install of a LiFePO4 12v 100ah battery which included a new Progressive Dynamics Lithium capable power center and a Renogy 20Amp Dc to Dc charger. With this new setup my amp draw to the new battery was increased and after 5 to 10 minutes of charging from a 20Amp GFCI protected garage outlet with a 30 to 15amp pigtail, it would trip the GFCI which I concluded to be a false trips. That’s a whole other subject. My solution to that issue was to install a non GFCI protected outlet dedicated solely for my camper. If I was going to do that I might as well install a 30amp RV outlet after my sub panel and not use the pigtail. There is 12/3 Romex to my garage buried under my driveway and I didn’t feel like tearing up my driveway and sidewalk to rerun 10/3 which could then could power my new 30amp outlet off a single breaker. After all the responses and web searches on paralleling A/C Circuits and after I had successfully paralleled my new outlet I will be disconnecting one of the feeds to the outlet making it 20 amps and going back to using the pigtail.

Good decision and should end this discussion.

[wmtire]

Originally Posted by RVasylum

After all the responses and web searches on paralleling A/C Circuits and after I had successfully paralleled my new outlet I will be disconnecting one of the feeds to the outlet making it 20 amps and going back to using the pigtail.

That sounds like the best and safest course of action. We will go ahead and close this thread as it has been solved.

[Herk7769]

Sorry Bobby, I opened the thread to add this:

So what I did in my garage was to dedicate a 20 amp circuit to a 30 amp RV socket from Home Depot.

I marked the socket 20 amps and it works just fine. I even plug my new 50 amp camper into it using an adapter.

I do have an ammeter installed on the camper that tracks the L1 and L2 current so I know how close to 20 amps I am getting.