Electrical, current capacity

[Anonymous-0]

I need to install new system for my 7000 watt ONAN generator to my camp. I will need to bring in a 6 conductor underground cable ( in conduit) for the remote starting with an extra pair of wires to supply 12V from the generator battery to a power outlet in the camp. Is 14ga stranded copper sufficient? The new service location is approx 120 feet from the camp.

 

[JDemaris]

You need #4 gauge wire for just 10 amps for 12 volt power at 120 feet. That is, unless you can live with a 10% voltage drop. Then, you can squeak by with #8 gauge wire. If you wanted 15 amps with a standard 2% drop, you'd need 3/0 cable.

You need to be more specific. Wires running power to activate remote-start relays are often low-amp draw. But, if you want to run 12 volt battery power 120 feet for a 12 volt outlet? It will be useless. Good for 1 amp max. You need 4 gauge wire for a 120 foot run for 10 amps of 12 volt power. For 15 amps, you need #2 gauge.

14 gauge wire can carry 1 amp about 45 feet with a 2% volt drop, or 120 feet with a 5% drop.

I've wired many DC systems at remote sites with solar and battery banks. For long wire runs, often step-up transformers are used to raise voltage.

 

[buickanddeere]

Are you trying to keep the starting battery in camp 120ft away from the generator?
Three #6 copper conductors for the 120/240 plus a bare #6 for ground is ok. A 10ft ground rod at the generator and a 10ft ground rod driven at the camp electrical panel.
The generator will likely use a bonded neutral neutral so isolate the ground to neutral bond in the camp breaker panel.

 

[da-bees]

The short version is,yes 14ga is fine "if it is fused/breakered 15 amp at the gen set". However,the best advise is get someone who understands the installation to help you. There are to many considerations besides conductor size. You could dig&cover the ditch and help pull wire if cost is a factor.

 

[JDemaris]

14 gauge wire run 120 feet at 12 volts is basically useless. Fine for what? 1 amp (12 watts) isn't much good for anything I can think of. And, if you draw a whopping 2 amps on the 14 gauge wire, voltage drops below 10 volts.

 

[JDemaris]

Here are some charts so you can figure what you need. Read closely before you following some bad advice. Just go by whatever your max wattage or amps need is. 12 volt is pretty useless for long wire runs and I've had to wire many. That's why many solar panels now are hooked in series and run at 200-400 volts DC.

You said you want a 12 volt power outlet, so I assume you want it to power something of use.

Even a small 12 volt TV that draws 36 watts needs 8 gauge wire for a 120 foot run. And remember, once you've got over a 10% loss, you don't have 12 volts anymore.

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[MarkB_MI]

Easiest solution if 12VDC is needed at the campsite would be to run a battery & charger at the campsite. You could buy a very nice charger for what 240 feet of 8 gauge wire will cost.

Dunno why someone would want 12 volts if they've got 120/240, though.

 

[JDemaris]

I agree for the most part. But most portable AC generators do not run battery chargers correctly. A DC to AC inverter generator, yes.

Easiest solution for long 12 volt runs is not to have any. It's always been a headache and I've had to work with many. Many small off-grid campsites have a few solar panels and 12 volt battery banks. With many now, the trend is to run at least 48 volts, and use step-down transformers to run 12 volt appliances. Also, many DC appliances now run on mutiple voltage inputs.
My refrigerater runs on 12 - 36 volts DC.

The cost of wire to run 12 volts any distance over 40 feet is usually much more then the alternatives.

But the guy asked specifically, so an answer was in order.

 

[John T]

Wire gauge ampacities can get a bit tricky to the untrained eye, for example, are the conductors in free air?,,,,,,how may conductors in the same raceway?,,,,,,inside enclosed conduit?,,,,,,in free air or buried?,,,,,,,etc etc and then there are differences for the insulation and ambient temp etc etc BUT REGARDLESS if youre talking about any long runs and if youre only starting with 12 volts anyway THERES JUST NOT MUCH TO SPARE ....Which is why its not a preferred method.

John T

 

[bill b va]

DC step down transformer ????

 

[Ecnerwal]

Well, for one thing you should have at least 2 if not 3 conduits - one for the 120/240V power, one for the low-voltage control circuits, and perhaps one more for the 12V power circuit, though you could run that with the control circuits. Its a violation of both code and common sense to run low voltage circuits and 120/240 in the same conduit. "Code" is often not an issue at camps, but common sense surely is. Usually the fire truck can't get there, and if it can, it's just to damp down the embers after the building is gone.

Depending on exactly what you want to run off 12V, aside from suggestions made already, you could put a 12V battery at the camp and charge it (at relatively low amperage) with the wires from the generator - that will provide some issues on the charging side, but limits the overall amperage in the wires. But if it's just a very low draw LED night-light, that may not matter much. Running a 120V charger from the generator as already suggested makes more sense for any heavier loads.

 

[John T]

You cant step up /step down transform pure DC !!!!!!!!!!!!!!!!! Transformers need AC or chopped/pulsed DC

John T

 

[Anonymous-0]

I am replacing my existing utility bldg. where my present 4500 watt generator is located with new building which is additional 50 feet further from camp. This makes the run approx. 100 feet from the camp. The buried wiring will be in separate PVC conduit runs. My inquiry is about the whether I can use the generator onboard starting system when I add 50 plus feet to the run to the new generator location. The existing system has worked fine for many years which is 12 ga. Rather than splicing onto the existing wire I think I would run new wire since I need to trench for the service wire.

 

[JDemaris]

There are many DC step-up units available. I've installed many, pure DC in and pure DC out. They are not pure wire-wound transformers inside the box. There are more sophisticated components inside along with the wire-windings.

CV12/24-6 converts 12 volt DC input to 24 volt DC output 6 amps maximum.

CV12/48-3 converts 12 volt DC input to 48 volt DC output 3 amps maximum.

CV24/48-6 converts 24 volts DC input to 48 volt DC output 6 amps maximum

PPT12/24-20/R12 will take 24 volts DC and produce 12 volts DC 20 amps max

PPT48-10/R12 will take 48 volts DC and produce 12 volts DC 10 amps max

O-SOL DOWN-2A/12: 12 volts DC in, output adjusts from 6-12 volts DC

O-SOL DOWN-2A/24: 24 volts DC in, output adjusts from 6-22 volts DC

O-SOL DOUBLER: 12 volts DC in, 24 volts DC out

 

[JDemaris]

Remote starting relays/controllers usually use very little current. Usually less than 1 ampif 12 volts. Just read the specs that are on it. Just remember that you have to figure for two way, not one way. If the battery is 120 feet away, you are carrying 12 volt to your remote switch and then back to the relay. So, the 120 foot run is actually 240 feet. All depends on the demands of the on-board relays.
Keep in mind that things like TV antenna rotators have similar amp draws and are often wired with 18 gauge wire at 250 feet.

But, you also mentioned a 12 volt power outlet at your camp, and that is a different issue. Even something limited to 10 amps would require extremely large wire if run at 12 volts.

 

[John T]

Good point JD, youre exactly right, they make "devices" "black boxes" (or whatever they are called lol) that will step up DC to DC its just that if its a regular straight passive transformer and theres no chopping or pulsing or electronics or anything else whatsoever, just pure DC in, TRANSFORMER ACTION WILL NOTTTTTTTTTTTTTTT WORK........Take say a door bell transformer or some other simple passive AC transformer and apply steady non pulsing non chopped DC across its input and measure the DC voltage across its output !!!!!!!!!!!!!!!!

While this is pretty simple basic transformer theory if one has knowledge of basic electricity, to lay persons it may be all Greek lol. An inductor stores energy in the magnetic field surrounding it and if that field collapses/changes due to the current flow changing or reversing direction or just stopping, the field collapses and if theres another inductor/coil wound close by or around the first one and theres a changing magnetic field in its vicinity, such can induce a voltage in the second coil/winding. Thats how and why a transformer works at AC (household AC reverses 60 times per second) and how an auto coil steps up 12 VDC because the points open and close to chop/pulse the DC into something like AC to get an expanding and collapsing magnetic field.

SORRY this can not be explained here in a paragrapgh what takes books and time to fully comprehend and such is beyond this board but this may help and its fun as I as an electrical enginner LOVE this sparky chat. The FACT REMAINS and you are sure right you can make a device to step up or down DC but a basic passive in/out transformer CAN NOT step up or down pure steady state non chopped non pulsed DC....

I dont usually put so much deep hard core technical info in a short answer because such may just confuse the poster but just wanted people to know a transformer DOES NOT WORK AT PURE DC and am glad you pointed out they can still buy a "device" to do that (they can call it a transformer if they like lol)

Thanks for the fun discussion even if we bore the others grrrrrrrrrr

God Bless yourself and all here and have a Merry and Blessed Christmas, hope we can meet and chat at the next New York Expo

John T

 

[bill b va]

units and devices huh . must not be transformers . maybe magnetic amplifiers ?

 

[Anonymous-0]

Thanks for the additional info. Actually the 12V power plug (separate pair of wires) is used to plug in the cell phones and also powers a automotive dome lite at the beer tap. If that will not work because of the distance thats O.K. I have talked to the Onan people as the later units now have an optional remote battery powered starter like offerd in automtive applications, however it is not adaptable to my unit.

 

[KF]

Maybe I am seeing this all wrong, but could one not run a 120V control circuit from the remote start location to a small relay that would have twelve volts on the contact side to operate a regular starter solenoid?

 

[John T]

Youre exacxtly right, they can make something (device, unit, widget lol) to step up DC to more or less DC volts BUT (as was the intent of my original comment) ITS SURE NOTTTTTTTTTT ONLY A TRANSFORMER BECAUSE A PASSIVE TRANSFORMER ALONE CAN NOTTTTTTTTTTT STEP UP OR DOWN PURE STRAIGHT STEADY STATE NON CHANGING DC.....

Fun discussuion for us sparkies at least

John T

 

[buickanddeere]

Where is the 120V's source in order to activate the generator starting circuit?

 

[JDemaris]

AC and DC can use the same ground. You don't need totally separate wires for Neg and Pos of the DC circuit. You're allowed to use the common ground that the AC is using, for one of the DC legs (negative I assume). For the power outlet, it's a one-way distance. For the remote start, it's a two-way distance, so 120 feet for the oulet and a 240 foot run for the remote start.

If all you want is power for a cell phone charger or a single dome-lite of some sort, you're probably talking in the max. 5 amps range. For that, you could squeak by with a single 8 gauge wire. If you already have something that is two-wire, tie the conductors together to get more carry capacity. Two 10 gauge wires tied together will equal one 8 gauge wire.

 

[Anonymous-0]

Thanks to all. Lots of thing to consider.