Do I Need Greater Than 15 amp Circuit Breakers?

[d30gaijin]

I'm doing a cargo trailer conversion and am starting on the AC power circuit. I have a 30 amp inlet, 12-2 wiring from it to the breaker box. I will have two breakers one for each electrical plug in outlet inside the trailer. Each outlet will be wired with 12-2 wire from the circuit breakers. I was going to install a pair of 15 amp circuit breakers but then started to wonder if I should go with 20 amp, or possibly one 15 and one 20 amp. Appliances I will be running that would seem to consume the most are an 800 watt household microwave oven, a 5k btu window type air conditioner, an AC/DC power converter from a 1970's vintage motor-home, and occasionally a two burner electric counter-top stove. I would only envision the air conditioner, the microwave and the AC/DC converter running at the same time (I have a two burner propane stove that I will use externally for most of the cooking)

Any thoughts would be appreciated.

Don

[Engineer Guy]

Check out the Breaker Box on your House. The various Branch Breakers add up to more than the typical 150 Amp or 200 Amp Mains Breaker amperage.

You will have little Trailer surges that will trip a 15 Amp Breaker, and these events will be a PITA. When the A/C Compressor kicks on AND the Hot Plate cycles on/off, 15 Amp Breakers [as at our '87 Tract House] will open very occasionally. Microwaves also 'surge' as they cycle to cook.

Consider going with all 20 Amp Branch Breakers with 12 AWG Wire. If any combo of items exceeds 30 Amps, either your 30 Amp Breaker will open, or the 30 Amp RV Park Breaker will open safely. ~30 Amps is also about the max value trip point on 4 kW Generators, so you're covered regardless of any typical Shore Power input.

In the fine print, Breakers open at faster trip times depending on the overload current relative to their rating. So, at a typical 125% overload condition, any Breaker opens 'faster' than at 110% of rating. This Breaker characteristic will get you through some lil surge events, but not all.

This idea safely meets Housing Electrical Codes.

[d30gaijin]

Check out the Breaker Box on your House. The various Branch Breakers add up to more than the typical 150 Amp or 200 Amp Mains Breaker amperage.

You will have little Trailer surges that will trip a 15 Amp Breaker, and these events will be a PITA. When the A/C Compressor kicks on AND the Hot Plate cycles on/off, 15 Amp Breakers [as at our '87 Tract House] will open very occasionally. Microwaves also 'surge' as they cycle to cook.

Consider going with all 20 Amp Branch Breakers with 12 AWG Wire. If any combo of items exceeds 30 Amps, either your 30 Amp Breaker will open, or the 30 Amp RV Park Breaker will open safely. ~30 Amps is also about the max value trip point on 4 kW Generators, so you're covered regardless of any typical Shore Power input.

In the fine print, Breakers open at faster trip times depending on the overload current relative to their rating. So, at a typical 125% overload condition, any Breaker opens 'faster' than at 110% of rating. This Breaker characteristic will get you through some lil surge events, but not all.

This idea safely meets Housing Electrical Codes.

Engineer Guy,

Thank you for the excellent information. It is somewhat as I suspected.

One additional question; is there a difference between a "Branch breaker" and a regular circuit breaker? I did a Google and what little I could find showed a branch breaker at $184 (http://tinyurl.com/25bvx7s) as opposed to a regular QO breaker at about $6. Not trying to cheap out here, in terms of safety there can be no cheaping out, but I don't want to spend the money if I don't need to. By your reference to a branch circuit breaker are you simply referring to the breaker on the incoming side i.e., before the outlets inside the trailer or the specific breaker type in the url above?

Thank you so much for your help. It is truly appreciated.

Don

[Engineer Guy]

Sorry for any lack of clarity. Too many Int'l Training Sessions, I'm afraid, and language like 'Branch Breaker' and 'Mains' has crept into my speech.

I meant to refer to the ordinary, $6-, QO Breaker before your Trailer Outlets when I wrote 'Branch Breaker'. I happened to use 'Homeline' Breakers since a pal with his own Electrical Contracting Biz correctly advised me of their widespread use here in CO. It's what's available that's most important.

QOU Breakers also sense DC Voltage, according to the Square D Site. I haven't used them.

http://www.schneider-electric.us/produc ... -breakers/

Circuit Breaker Boxes are not interchangeable between Manfs, BTW. I am told - but have not confirmed - that even 'very old' and new Boxes from the same Manf. are not interchangeable. Breakers won't snap in securely and enjoy good electrical contact. Some sloppy Breakers Homeowner-retrofitted into a Box my Sister inherited via House purchase just about brought her House down with a Box fire.

The very exacting Electrical Code guy who signed off on my House told me he doesn't like to see one GFI 'daisy chained' after another. They too often trip falsely, in his experience. So, while you would certainly want reliable GFI protection somewhere in the electrical path, many RV Park Boxes have them already on their 20 Amp Breakers. Just an FYI... Me, I'd want GFI protection on my CT that I had wired in.

[Chuckles2153]

I'm doing a cargo trailer conversion and am starting on the AC power circuit. I have a 30 amp inlet, 12-2 wiring from it to the breaker box. I will have two breakers one for each electrical plug in outlet inside the trailer. Each outlet will be wired with 12-2 wire from the circuit breakers. I was going to install a pair of 15 amp circuit breakers but then started to wonder if I should go with 20 amp, or possibly one 15 and one 20 amp. Appliances I will be running that would seem to consume the most are an 800 watt household microwave oven, a 5k btu window type air conditioner, an AC/DC power converter from a 1970's vintage motor-home, and occasionally a two burner electric counter-top stove. I would only envision the air conditioner, the microwave and the AC/DC converter running at the same time (I have a two burner propane stove that I will use externally for most of the cooking)

Any thoughts would be appreciated.

Don

Hey there Don,
I've done alot of my own wiring on my house and i would go with 20 amp breakers. the microwave at 800 watts could be ran off of a 15 amp if you don't run any of the other listed things at the same time so just go with standard 20 amp breakers and you should be fine.
And as engineer guy said use the same name breakers as the name of your box.

[madjack]

...there is an old saying..."fuse the wire, not the appliance"...since 12ga wire is good for 20A, that is what you should use...IMO anyway......
madjack

[d30gaijin]

Engineer Guy, Chuckles2153, & MadJack,

I want to thank each of you for your input. It is a tremendous help!

I went with a 2 breaker 2 circuit 30 amp box as shown in this thread http://www.tnttt.com/viewtopic.php?t=20164 about 1/4 of the way down the page, the post by Miriam C. I will go with QO 20 amp breakers. I want to get it roughed in from the inlet to the breaker box and two 12-2 wires out of the breaker box and will deal with the rest of the wiring later. I'm going what seems like six different direction on my project i.e., still working on finishing up interior insulation, getting a start on AC wiring while considering DC wiring and what is existing, building the cabinets that will go in the nose section, installing a sink, and some rudimentary plumbing to/from it, getting the existing plywood floor ready for installation of Linoleum, etc.

Again, your help is truly appreciated (I will also repost this in the CT Conversion forum if that's OK?... just in case you didn't see it in the ES forum).

Don

[Chuckles2153]

Engineer Guy, Chuckles2153, & MadJack,

I want to thank each of you for your input. It is a tremendous help!

I went with a 2 breaker 2 circuit 30 amp box as shown in this thread http://www.tnttt.com/viewtopic.php?t=20164 about 1/4 of the way down the page, the post by Miriam C. I will go with QO 20 amp breakers. I want to get it roughed in from the inlet to the breaker box and two 12-2 wires out of the breaker box and will deal with the rest of the wiring later. I'm going what seems like six different direction on my project i.e., still working on finishing up interior insulation, getting a start on AC wiring while considering DC wiring and what is existing, building the cabinets that will go in the nose section, installing a sink, and some rudimentary plumbing to/from it, getting the existing plywood floor ready for installation of Linoleum, etc.

Again, your help is truly appreciated (I will also repost this in the CT Conversion forum if that's OK?... just in case you didn't see it in the ES forum).

Don

You are very welcome Don and i know what you mean about going in too many directions, I'm feeling the same way myself.

Anything else you need help with just ask.
Chuck

[BPFox]

[quote="d30gaijin"]I'm doing a cargo trailer conversion and am starting on the AC power circuit. I have a 30 amp inlet, 12-2 wiring from it to the breaker box. I will have two breakers one for each electrical plug in outlet inside the trailer. Each outlet will be wired with 12-2 wire from the circuit breakers. I was going to install a pair of 15 amp circuit breakers but then started to wonder if I should go with 20 amp, or possibly one 15 and one 20 amp. Appliances I will be running that would seem to consume the most are an 800 watt household microwave oven, a 5k btu window type air conditioner, an AC/DC power converter from a 1970's vintage motor-home, and occasionally a two burner electric counter-top stove. I would only envision the air conditioner, the microwave and the AC/DC converter running at the same time (I have a two burner propane stove that I will use externally for most of the cooking)

Any thoughts would be appreciated.

Don[/quote

You might want to consider up grading your wiring from the 30 amp inlet to the breaker box to 10 gauge wire. While I understand it's a pretty short run, it is the "weak link" in your system at 12 guage. You will also want a 10 guage extension cord to the power supply pole and use the 30amp recepticle plug at the pole not the 20 amp recepticle. If you prepare your system for maximum usage, you should not have a problem.

[bobhenry]

Our full electric outings are all in the state parks.

Useing a 1500 watt heater flat out to stay warm and toasty at these January Indiana shivarees has taught me a little trick.

I have finally gotten wise and use 2 feeds from the parks power head. Each park site has a 20 and a 50 amp feed. I plug the heating and cooling appliances in the biggen with an adapter into my 10 -3 grounded extention cord and the trailer plugs into the 20 amp power port on a seperate drop cord. I have finally trained ol' what's her name to not piggy back heating appliances but use them one at a time.
A Toaster oven OR a coffeepot OR a crock pot OR a microwave but ONE AT A TIME ! Perhaps a seperate power inlet circuit on the conversion dedicated to HVAC might be an answer! It is the one item that need to run uninterupted the other items can be cycled as needed.

P.S. a good well insulated coffee caraf is nice to have. It helps to keep the coffee warm without electrics.

[BPFox]

Our full electric outings are all in the state parks.

Useing a 1500 watt heater flat out to stay warm and toasty at these January Indiana shivarees has taught me a little trick.

I have finally gotten wise and use 2 feeds from the parks power head. Each park site has a 20 and a 50 amp feed. I plug the heating and cooling appliances in the biggen with an adapter into my 10 -3 grounded extention cord and the trailer plugs into the 20 amp power port on a seperate drop cord. I have finally trained ol' what's her name to not piggy back heating appliances but use them one at a time.
A Toaster oven OR a coffeepot OR a crock pot OR a microwave but ONE AT A TIME ! Perhaps a seperate power inlet circuit on the conversion dedicated to HVAC might be an answer! It is the one item that need to run uninterupted the other items can be cycled as needed.

P.S. a good well insulated coffee caraf is nice to have. It helps to keep the coffee warm without electrics.

Just curious, if you have a 50 amp 220 v receptacle, why not just plug into that with one cord and run everything you got. More power there than you will ever need or use. Just sayin'. Peace.

[StPatron]

I am told - but have not confirmed - that even 'very old' and new Boxes from the same Manf. are not interchangeable. Breakers won't snap in securely and enjoy good electrical contact.

I can confirm an old/new compatibility issue with Square D breaker boxes. Older "QO" boxes will not accept recent model tandem breakers.

The single breakers are unchanged but the company changed the base on the tandems and they will not snap in, even loosely. The old-style tandems are still available if you're willing to search a bit and pay a premium.

(I know,, not an answer to original question but thought the info. might be helpful.)