Jury-rigging shore power at the house

[Belegedhel]

Thanks all for your feedback. I had another look at my breaker box last night, and it turns out that both breakers for the two circuits going to the garage are located on the same breaker "block" (ie., there is a single breaker unit that has two breaker switches on it), so there should be no worries about phases, etc.. I thought it was two 15A breakers, but in fact they are 20A each. I thought about it some more, and think I have found the real danger in the plan.

As a thought experiment, lets take the jury rigged pigtail arrangement out of the equation and imagine just hard-wiring a female 30 amp plug where the two sets of wires for the two circuits enter the garage, combining the inputs as described earlier. If I plug my trailer into this plug, theoretically the two circuits will share the 30A load, roughly equally assuming wire lengths are the same and overall resistances are the same. The problem is that those circuits will continue out of the 30A plug (where they are joined), one of them supplying lights, and the other supplying outlets in the garage. If I plug my mal-functioning circular saw into an outlet and the motor windings are in a dead short, it will try and pull all the current it can through the circuit. Since the outlet circuit combines with the light circuit at the 30A plug, the breakers won't pop until they see a combined 40A load. This 40A dead-short max load will be seen by the 20A max capacity wiring that goes from the 30A plug to the outlet that the saw is plugged into, and here is where the fire danger lies, when that wiring melts. I could defeat this by installing a secondary set of breakers within the garage, in between the 30A plug and the two garage circuits, but it is still a jury rig, definitely wouldn't meet code.

Another option might be to replace my garage circuit breaker with a 50A breaker, wire that to a sub-breaker box, and then put the two 20A circuits and the 30A circuit breakers in that box. This would still require running the additional 30A wiring out to the garage, though. I guess I'll see if I can find an electrician with a more creative/cost effective solution than the first one I consulted.

[HowieE]

Originally Posted by Belegedhel

Thanks all for your feedback. I had another look at my breaker box last night, and it turns out that both breakers for the two circuits going to the garage are located on the same breaker "block" (ie., there is a single breaker unit that has two breaker switches on it), so there should be no worries about phases, etc.. I thought it was two 15A breakers, but in fact they are 20A each. I thought about it some more, and think I have found the real danger in the plan.

As a thought experiment, lets take the jury rigged pigtail arrangement out of the equation and imagine just hard-wiring a female 30 amp plug where the two sets of wires for the two circuits enter the garage, combining the inputs as described earlier. If I plug my trailer into this plug, theoretically the two circuits will share the 30A load, roughly equally assuming wire lengths are the same and overall resistances are the same. The problem is that those circuits will continue out of the 30A plug (where they are joined), one of them supplying lights, and the other supplying outlets in the garage. If I plug my mal-functioning circular saw into an outlet and the motor windings are in a dead short, it will try and pull all the current it can through the circuit. Since the outlet circuit combines with the light circuit at the 30A plug, the breakers won't pop until they see a combined 40A load. This 40A dead-short max load will be seen by the 20A max capacity wiring that goes from the 30A plug to the outlet that the saw is plugged into, and here is where the fire danger lies, when that wiring melts. I could defeat this by installing a secondary set of breakers within the garage, in between the 30A plug and the two garage circuits, but it is still a jury rig, definitely wouldn't meet code.

Another option might be to replace my garage circuit breaker with a 50A breaker, wire that to a sub-breaker box, and then put the two 20A circuits and the 30A circuit breakers in that box. This would still require running the additional 30A wiring out to the garage, though. I guess I'll see if I can find an electrician with a more creative/cost effective solution than the first one I consulted.

I am going to assume you are attempting to create a fictional episode for a comedy TV show here. If so please sign your comments with a disclaimer, or as Rube Goldberg, as there may be some readers that may see this as possible and follow suit.

[markdoane]

The option in your last paragraph may be feasible, but you should get an electrician to calculate the wire size for the 30a run out to the garage.
Also check with your local building inspector. You will need a permit and they will be able to tell you any local requirements and maybe a cheaper alternative.

[splyb]

BTW, jerry-rigging is an approach. Jury-rigging is a crime.

I'm just saying'...

Jay and Lisa

[ijustlee]

I always say living in a trailer is life at the end of an extension cord. Getting enough power for me to stay comfortable is a bit of an art form as the 15A to 30A adapters melt if you look at them hard. It's hard to say much about your situation without knowing exactly what is there because details count when dealing with electricity. From what you have shared so far it seems like you have 2 hots and maybe 2 neutrals running to the garage. How do the wires enter the garage, is there a junction box that you can look into? What do you see in there? How much would you spend to have AC? Breakers are sized to protect the wires and usually 20A breakers go with # 12 wire and for a long run like you have I wouldn't try to pull more than 15A per hot wire. There is hope but meeting code could be tricky so you need an electrician that knows what they are doing. Maybe send 220 to a transformer and sub panel in the garage? A sub panel with breakers for the garage circuits? There is probably a way to get the job done safely.

[C21Tiger]

I had the same problem and fixed it with adjusting the breakers in the box so that I could open up 30 amp service. I had the installer put an outside 30 amp plug just below the box and then bought a 50ft male to female 30amp extension to go to my RV which has to be in the street (driveway to short). This has worked very well except for 1 day when the outside weather was at 120deg (AZ). The cord got so hot in the sun it tripped the coach breaker for the ac unit. I kill the breaker at the box when not in use (I have an outside box so it is a weather protected outlet). This was a lot cheaper than having the installer run conduit. Just a note, I also looked at trying to use something makeshift and was quickly talked out of it. If you can move some loads around in your box and not create a fire hazard I think this is a great solution.

[jdalrymple]

A quick wire calculation says 30 amps of single phase 120 volt AC at 150' requires 4 gauge wire.

150' seems like a long measurement, even for a long, skinny home.

Measure and make sure that the 50 yard estimate is correct. The re-arrangement of breakers and/or the addition of a sub panel are acceptable methods to add circuits.

The combining of receptacles via extension cords is not.


Regards,

JD

[J. Morgan]

http://www.ecmag.com/section/systems...ected-parallel


Superat stultitia.

[J. Morgan]

If my understanding of the above article is correct, you could combine the wires of the two current 20 amp circuits via a single 30 (or 40?) amp breaker, and install a sub panel in the garage with three breaker circuits, one for a 30 amp trailer plug, and one each 20 amp circuit to serve your two existing garage circuits.

This would be a lot cheaper than changing out the main panel.


Superat stultitia.

[J. Morgan]

Revision, it seems that this is NOT allowed for smaller wires.

http://www.jade1.com/jadecc/courses/...p?imDif=2580.1


Superat stultitia.

[wcrockett]

Originally Posted by jdalrymple

A quick wire calculation says 30 amps of single phase 120 volt AC at 150' requires 4 gauge wire.

150' seems like a long measurement, even for a long, skinny home.

Measure and make sure that the 50 yard estimate is correct. The re-arrangement of breakers and/or the addition of a sub panel are acceptable methods to add circuits.

The combining of receptacles via extension cords is not.


Regards,

JD

Rivet Master can you show us the calculation that says he needs 4 gauge wire? I put a 30AMP breaker in an available spot in my panel. Ran a few inches of size 8 wire from the box to a 30AMP RV plug in. Then ran 100' of 8 to the AS. The 100' of wire has RV plugs so it is essentially an RV extension cord. We have been using it to power a 30' International for the last 2 months. Now that summer is here the AC runs everyday.

[joemikeb]

Originally Posted by Belegedhel

I did start this consideration by calling an electrician. His recommendation, which I would imagine may be the "best" way to do the job (though not the mmost affordable) was to replace the entire breaker box with one that has greater capacity, and then to run the additional 30A circuit back to the garage and so on. The cost of the job was well over $1000 with other potential inflation involved in hiring out the necessary trenching associated with running the 30A circuit.

Look at it this way, in order of out potential of pocket expense, what will it cost when...

1. The A/C in the trailer burns out because it is running under low power (brown out) conditions
2. The improperly provisioned load causes the electrical panel to burn out and you have to replace it under emergency conditions and live in a hotel for a few days while it is replaced.
3. Your house burns to the ground and takes the trailer along with it.

My advice would be to take the $1,000 and buy lottery tickets. Your odds of a successful outcome are much better.

[alantbird]

Find a 20amp plug like for your washer and get a long 10 gauge cord to run out to the trailer. I plug my 40' motorhome with 50 amp service into an outlet on the porch of our vacation house and can run one A/c with no problems. most outlets by code should be 20 amp but that don't mean they are. And that rig job your considering may just tap into a 220 volt circuit and then your done!

[Belegedhel]

Originally Posted by splyb

BTW, jerry-rigging is an approach. Jury-rigging is a crime.

I'm just saying'...

Jay and Lisa

Actually, "jury rigging" is what I was going for--but in this case it may still be illegal (at least for building code):

http://www.dictionary.com/browse/jury-rig

[Belegedhel]

Originally Posted by J. Morgan

Revision, it seems that this is NOT allowed for smaller wires.

http://www.jade1.com/jadecc/courses/...p?imDif=2580.1


Superat stultitia.

Good find! Yep, this paralleling approach is what I was going for, but alas, the article indicates that the approach is not supported for smaller gauge wires.

[markdoane]

Maybe they meant jerry-built?

[Debit]

Originally Posted by J. Morgan

If my understanding of the above article is correct, you could combine the wires of the two current 20 amp circuits via a single 30 (or 40?) amp breaker, and install a sub panel in the garage with three breaker circuits, one for a 30 amp trailer plug, and one each 20 amp circuit to serve your two existing garage circuits.

This would be a lot cheaper than changing out the main panel.


Superat stultitia.

Here's an option to consider and one that at least has built-in breakers - just in case...

http://www.streambrite.com/images/in...r-power-I6.jpg

[JimGolden]

Why not simply change a few of his regular sized breakers to slim line breakers? Then you free up room in the main panel to install a 30amp or 50amp breaker and run the appropriate sized wire to the new outlet.

Sub panel is nice, but I'd look at slim lines before I went to that trouble.

[Debit]

Steambrite.com has this interesting converter box that might be considered. At least it has built-in breakers for each phase of the 240. Perhaps a temporary solution until a licensed electrician can find a dedicated circuit solution.

[jdalrymple]

Originally Posted by wcrockett

Rivet Master can you show us the calculation that says he needs 4 gauge wire? I put a 30AMP breaker in an available spot in my panel. Ran a few inches of size 8 wire from the box to a 30AMP RV plug in. Then ran 100' of 8 to the AS. The 100' of wire has RV plugs so it is essentially an RV extension cord. We have been using it to power a 30' International for the last 2 months. Now that summer is here the AC runs everyday.

Mr. Two Rivet:

Any one of a number of online calculators will render the same result.



The use of 4 ga wire keeps voltage loss to 3%.

One can certainly use smaller wire, but voltage drop will be greater.





Regards,

JD