Why can't 15A + 15A = 30A?

[rkresge]

Originally Posted by nothermark

It is not a smart move. That said you have not shown why it would not work if properly done.

[ Snip ]

FWIW2 - the neutrals in a split phase 240 VAC circuit are already combined. No problem there.

Here's the heart of the problem, and you stated it: "if properly done". Consider that one may build a working/workable 'cheater' adapter that could be plugged into properly-wired outlets. But what happens if you encounter an outlet that is not wired properly???? It only takes one. The results will be both spectacular and dangerous to say the least. This is NOT a good idea.

Roger

[ladagobago]

Originally Posted by mel s

Sweetbria
Methinks the "baddest" thing that will happen if/when you plug the 2 extension cords into 2 "in phase" 15A outlets is that you will only have 15A usable in the coach.
Mel
'96 Safari

in reality he will have 30 amps.

[sflabrkr]

Originally Posted by jporietis

with a meter check the two hot wires from the two outlets. If you have 220v you could combine them into a 220v 30 amp service similar to a 50amp. Not sure if its worth it.

This would work and it's not illegal

[twinboat]

Originally Posted by sflabrkr

This would work and it's not illegal

Where would this be used ?

30 amp RVs are 120 volts.

[rgvtexan]

Originally Posted by ladagobago

in reality he will have 30 amps.

Maybe in a perfect world! But ANY imbalance in the circuit will cause one of the breakers to open first, then you only have 15 amps. Breakers and fuses in parallel just doesn't work for double the current.

[nothermark]

Originally Posted by twinboat

So by the time we gather all of the relays, contactors, phase sensors, pigtails, plugs, recepticals and enclosure we could have picked up 50 ft of 10-2 with ground, a 30 amp RV receptical and breaker.

Now it's there for ever.

To sell it to the public.

I could do it with a couple of cords and a meter but I do not see any point in doing it. ;-)

I don't know about the rest of you but I see it mostly as a mental exercise about how well I understand the system. OTOH I can see why somebody might be in a bind trying to run an AC in the driveway while getting the RV packed. A much better answer is just to put in a 30 Amp service.

[twinboat]

Originally Posted by nothermark

To sell it to the public.

I could do it with a couple of cords and a meter but I do not see any point in doing it. ;-)

I don't know about the rest of you but I see it mostly as a mental exercise about how well I understand the system. OTOH I can see why somebody might be in a bind trying to run an AC in the driveway while getting the RV packed. A much better answer is just to put in a 30 Amp service.

Still not sure how your going to detect if your on the same branch circuit or not.


But your right ! Everybody needs another gadget in the electrical bay.

If you make it, we will buy.

[Dr4Film]

Originally Posted by F4Gary

How come there isn't a converter that I could plug two 15A power cords into and get 30A capability out the other side? Seems like with computerization these days, some one would sell a box that I could make 30A for my motorhome at home from two 15A extension cords coming from two different outlets.

Just wondering, I know there is a reason.

For the life of me I don't understand why people will not take 2 minutes to edit their signature specifying what their RV is so people can better answer their questions.

First off, you don't specify whether your coach is powered from 50 amp or 30 amp. That would have helped.

Second, there is some really bad information posted here especially mixing water with electricity. LOL

nothermark and ladagobago have posted the best information for the OP from what I can gleam from this thread.

However, here is my 2 cents with the disclaimer that I am not an electrician. I come from the school of common sense.

Let's say that your home electrical supply service is 240 VAC with 200 amps of power coming into the house. The main panel will have 2 hot leads (out of phase), one neutral lead and one ground lead that is attached to a ground rod buried deep into the ground.

In the main panel there could be numerous single pole 15 amp, single pole 20 amp, single pole 30 amp, double pole 40 amp and double pole 50 amp circuit breakers placed into the panel for power distribution throughout the house. The 15 amp, 20 amp and 30 amp single pole circuit breakers will come from either side of the 2 HOT leads depending on what side of the panel the circuit breaker is mounted into. Whereas all of the double pole circuit breakers will use both sides of the 2 hot leads because they require 240 VAC.

You cannot put in more circuit breakers than you have AMPS available from the power pole. Meaning if your service is 200 amps then when you add up all of the circuit breakers you have placed into the panel they cannot be more than 200 amps.

Now to try and answer the OP's question with the assumption that his coach is a 30 amp RV, with 30 amps you have 3600 watts available to use throughout the coach. This all comes from ONE hot line of the main panel through a single pole 30 amp circuit breaker with wire that is sized to handle the 30 amps. If you have two 15 amp circuits that are NOT being used anywhere else in the house for ANYTHING, you could use those two circuits provided that they both come from the same side of one incoming HOT lead. If by chance you accidentally use one from each side now you have 240 VAC when you combine them at your coach and as a result you will have LOTS of sparks and fireworks after you have fried all of the 120 VAC stuff in your coach.

Personally, it would be much easier just to run 30 amp wiring sized correctly for the length of run from the house to the RV and be done with it instead of trying to jump through hoops with using two different 15 amp circuits.

Dr4Film ----- Richard

[HHIDan]

Originally Posted by Dr4Film

You cannot put in more circuit breakers than you have AMPS available from the power pole. Meaning if your service is 200 amps then when you add up all of the circuit breakers you have placed into the panel they cannot be more than 200 amps.


Dr4Film ----- Richard

You can not draw more than 200 amps from the pole as the main breaker would trip but typically if you add up all the breakers you would get more than 200. Typically they don't all draw max at the same time, it's a distribution panel.

[HHIDan]

If the OP has a 30 amp coach then there is only one buss, all the 120 has to be same phase. You do not ever connect two sources of 120 (two black wires) together no matter what the phase (RV or house). Out of phase will cause sparks. In-phase, one breaker trips and you still have power. It's totally against code.

IF the OP has a 50 amp coach then there are two 'busses' in the panel, two Legs and these two 120 volts can be supplied in phase or out of phase. IT DOES NOT MATTER, no sparks... However, as some have posted, if you supply the two legs with out of phase (typical) then the return current is current Leg1 minus current Leg2 (or vice versa). If you feed Leg1 and Leg2 with in phase then the current coming back on white Neutral is the current on Leg1 + current on Leg2 and in a 50 amp coach the neutral will handle up to 60; so if you feed 50 on L1 and 50 on L2 you might get up to 100 amps coming back which is where the danger is, wire starts to melt. You can however feed up to 30 amps in phase (or out) on each Leg.

[Dr4Film]

Originally Posted by HHIDan

You can not draw more than 200 amps from the pole as the main breaker would trip but typically if you add up all the breakers you would get more than 200. Typically they don't all draw max at the same time, it's a distribution panel.

Yup, that's correct now that I think more about the situation.

Thanks for the clarification!

If all circuits were drawing the maximum which usually they seldom do is the only time you will get into trouble.

The important point is that you will only have the total number of amps available to use that your house is supplied with, 100 amps, 200 amps, 300 amps, etc.

Dr4Film ----- Richard

[mel s]

Originally Posted by rkresge

Here's the heart of the problem, and you stated it: "if properly done". Consider that one may build a working/workable 'cheater' adapter that could be plugged into properly-wired outlets. But what happens if you encounter an outlet that is not wired properly???? It only takes one. The results will be both spectacular and dangerous to say the least. This is NOT a good idea.
Roger

rkresge
While I agree that adding a permanent 30A or a 50A RV receptacle is the "best" option it is not always possible or practical.

We often stay at the homes of friends and family where adding a receptacle is not an option.

On those occasions I sometimes use a cheater box, (and a 30A to 15A adapter), to connect my 50A coach to 2 different out of phase 15A receptacles with 2 14/3 extension cords.
See: Progressive Industries RV Surge and Electrical Protection industry lea

However if/when I "encounter an outlet that's not wired properly", (whether 15A, 20A, 30A or 50A), I simply do not/will not plug anything into it.

Mel
'96 Safari

[rkresge]

Originally Posted by mel s

rkresge
While I agree that adding a permanent 30A or a 50A RV receptacle is the "best" option it is not always possible or practical.

We often stay at the homes of friends and family where adding a receptacle is not an option.

On those occasions I sometimes use a cheater box, (and a 30A to 15A adapter), to connect my 50A coach to 2 different out of phase 15A receptacles with 2 14/3 extension cords.
See: Progressive Industries RV Surge and Electrical Protection industry lea

However if/when I "encounter an outlet that's not wired properly", (whether 15A, 20A, 30A or 50A), I simply do not/will not plug anything into it.

Mel
'96 Safari

Mel, it's up to you. This is one of those things that will work until the day it doesn't work, and when it doesn't work I would much prefer not to be nearby.

Good luck,

Roger

P.S. I notice the lack of a UL certification on the "cheater box". For me that triggers alarms, flashing lights and sirens.

[F4Gary]

Originally Posted by twinboat

So by the time we gather all of the relays, contactors, phase sensors, pigtails, plugs, recepticals and enclosure we could have picked up 50 ft of 10-2 with ground, a 30 amp RV receptical and breaker.

Now it's there for ever.

Thank you Captain Obvious. I was just curious as to why 2 15A couldn't be combined. I'm not actually trying to do it. I run a 15A cord to keep my batteries charged and run my fridge when loading up.