Getting power to my tiny house at a distance

Hello all! I’ve live in a yurt for the last four years and am upgrading to a tiny house! I should have my house in the next 2 months….here’s my dilemma ….I want to run power 200 ft from my friends breaker ….my house is a 30 amp 120 v service and I won’t be running a washer and dryer or anything that pulls a ton of power….I’m thinking to run 8/3 wire from a 30 amp breaker and just set up a 30 amp receptacle at my site for my tiny to plug into…my question is will this work? Has anyone else done something like this? Thanks in advance!

should work no problem your only running 120 volts you only need 8/2. hot/black, white/neutral, bare wire or green/ground. 8/3 would be for 240 volts, two hot leads a neutral and ground

Permies has an electrical forum.  You may want to post this question there.   That is a fairly long run.  Without checking codes (where are you located) as a guideline; I think 8 gauge would be sufficient for the extra resistance due to distance; but you will need to put that underground which is another ball of wax.  You will need to use appropriate conduit and rated wire.  I am not an electrician however.  If you have to do a trench, conduit, wire, etc... check to see what a second meter and pole would cost to install.  It will be more, but maybe not that much more.

you would probably want to get direct burial romex (UF-B), good for outdoor use much less costly than SJOOW OR SOOW cable

Added this to the electrical forum. Good idea Jack!  

Thanks all! Yes was thinking to get the direct burial and copper which from what I understand doesn’t require conduit? Thanks for your help !

I once did a 700' run hooked to a 70 amp breaker using #4 copper wire never pulling more than 50 amps at the end, never had any problem with anything heating up or anything starving for power. end power tested for amps and volts with full 50 amp draw,  there are charts used by electricians and engineers, I'm no expert but at 200 feet going one side larger on wire I would think this falls well within guidelines. for 30 amps #10 is good for at least 100 feet

Thanks for all the info Bruce! 8/2 wire will fit into a 30 amp breaker correct? It’s not too big?

I was just looking at a breaker in my box. The Square D QO breakers are rated for up to #8 solid copper wire; I think it is likely that other brands have the same capacity.

I looked up a calculator ( https://www.southwire.com/calculator-vdrop ) and found that for 30A 120V (direct burial or conduit) copper, #8 is good for 87 feet, #6 is good for 135', and #4 is good for 209'.
Aluminum in conduit takes #2 for 204'.

Depending on the insulation temperature rating, #8 can carry 40A to 55A.
I would run the wire for 240V even if you only set it up for 120V. That way you have the option of doing something different in the future without having to retrench or climbing poles.

Figure out if you need 200ft of wire or 250ft of wire when in doubt get the larger length of wire. Having to splice wire underground doesn't sound like fun.

Are we talking UF-B cable or THHN inside a Conduit

glenn, I'm not arguing with southwire chart, but, 100" extension cords rated for 30 amps are made with #10 wire.

The Southwire calculator results are for the recommended 3% maximum voltage drop; if you allow 7% drop, you can use #8 copper direct burial or in conduit for 202'.

At 3%, if the supply voltage is exactly 120V, you would get 116.4V at the end of the run. At 7% drop, you would get 112.9V at the end of the run if using the full 30 amps. Testing the voltage in the box might be useful. Actual supplied voltage from the pole can vary. At my wife's house, I measured something like 130V at an outlet.

like I say I'm no expert but these are pretty common

https://www.amazon.com/Ceptics-Generator-Extension-Industrial-GN-CD-3-100/dp/B07K7X7W61/ref=asc_df_B07K7X7W61/?tag=hyprod-20&linkCode=df0&hvadid=241942867107&hvpos=&hvnetw=g&hvrand=14933839095936267273&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9010320&hvtargid=pla-580315687890&psc=1

According to the calculator, #10 copper "overhead" can run 30 amps for 105' with 5.5% voltage drop. This sounds reasonable for a temporary use like an extension cord.

I think the final wire choice depends on the tradeoff between efficient electrical use (wasting as little as possible of the power in heating wires under load) and first cost - copper wire is expensive.

If the tiny house will seldom draw the full 30 amps or anything close to it, there will be little power loss most of the time, and 8 gauge may work fine. It can handle 13 amps at 3% voltage drop over 200'.

Thanks so much all for this very informative conversation! You can be rest assured that what you contribute to this discussion is directly helping make happen a real persons situation! I very much appreciate it ....Glenn and Bruce you are very much fleshing out the details of what I’d like to know ....Glenn thank you for addressing the possible 7% voltage drop ...I used a similar calculator and got a result of around 5.5 % voltage drop but that might have been for 8/3 wire as apposed to 8/2 which Bruce hipped me to....I guess the question is is a 7% voltage drop bad? I know it isn’t recommended

Sorry Glenn I didn’t see your last post before I posted this ....thanks so much this is one of the specific details I needed

If you have a 30a breaker in the source box and a 30a breaker in your house that's not quite right.  The breakers are supposed to be sized down, generally 80% of the load above.  Thus a 40a in the source and a 30a in your house, or a 30a in the source and 20 (25?) in your house.

It may not make a lot of sense at first, but you want to have the closest breaker be the one that trips in an overload.  B/C of the aforementioned drops in voltage with wire run its possible to surge your panel to just under 30a and not throw the breaker ... but the source one will go!  And now you've got to walk 200' in the rain & dark & cold....

A 40a breaker takes the same space as a 30a, but I think (without referring to a chart...) that you need 8g wire with the 40a (otherwise there's the risk that the wire melts before the breaker is triggered).  You're doing that gauge anyway, so consider spending an extra $10 or so on the breaker.

Electricians and municipalities seem to have differing opinions on the need for a local ground rod.  It may not be necessary, but you increase the safety of the system with a local ground rod.

Oh also ... some folks suggest that refrigerator compressors are particularly sensitive to voltage drops - its like a minor brown-out.  I don't know if its true (today or ever) but most electronics are designed to operate within a fairly tight voltage range.  Its not just safety nellies who say you shouldn't run appliances off an extension cord - I recall my refrigerator warranty being dependent on NOT using an extension cord.

So ... bigger gauge might be worth it!

Also, 8/3... with 8/3 instead of 8/2 you can choose to run 240v (as mentioned) or you can split the circuit and run two 30a circuits (assuming your box is a the "sub-panel" type without a main breaker).  That just gives you some options, such as powering everything in the house on one circuit and then having an exterior circuit to power saws, pumps, electric car chargers, etc.

The larger gauge also has the very real advantage of leaving options open for the future.

until recently speaking  to an electrician I thought it would be ok to split an x/3 wire 240 volt circuit into two 120v circuits but to be done properly and meet current national code each needs its own neutral and ground wire and a ground fault breaker should be used in there somewhere.
when my current house was wired, probably back in the 40's when the TVA came through with power, things were much different than they are now.

When sizing wire, on top of voltage drop consideration, you want to factor in the maximum current draw allowed by the breaker. If you undersize the conductor it could lead to a fire or damage to the wire insulation and cause an electrocution hazard. It's been a number of years since I was an electrician, but I'm fairly certain that hasn't changed. Also keep in mind that many electrical inspectors are not electricians, and as such will often err on the side of saying no to things they don't understand or are not comfortable with. Even doing everything 'by the book' and would otherwise be passed by most inspectors doesn't mean your local inspector will approve.

I would never recommend someone size a conductor for what they use 'most of the time' and then attach a larger breaker. The breaker size determines the maximum current by which conductor size is calculated (I believe the word in the code is 'shall', conductors shall be be sized larger than the maximum current of the breaker). Back when fuses were popular, some people would just install a larger fuse, or jam a penny under it, and many houses burned down or were on the verge of it. It's part of the reason the National Electrical Code book looks like a large novel compared the the children's book size of the first edition.

I read up on it and the formula for figuring out CSA (Cross Sectional Area, in circular mils) doesn't seem to have changed, nor the maximum 5% voltage drop for residential branch circuits. Doing the math for (KIL)2/Voltage Drop=CSA shows me the closest appropriate size wire for ~200 feet @ 30A would be 5 gauge (which would likely be hard to find locally) so you would need 4 gauge wire. This page goes over everything:

https://www.mikeholt.com/technnical-voltage-drop-calculations-part-one.php

The trick of using a 240V circuit as 2 x 120v circuits with a single neutral is referred to as an Edison circuit. If the neutral ever becomes disconnected, it tries to push 240V across when things are plugged in on both sides. If there isn't anything plugged in on both sides, there will be no power. Once you connect something to complete the circuit to both sides there will be a huge power spike, with varying results depending on the type (resistive, inductive) and size of load. My electric shop teacher had a sheet of plywood with this kind of setup and showed how to ruin things using an Edison circuit. They aren't allowed by code in residential wiring as far as I am aware.

Thanks to Bruce and Daniel for pointing out the error in my ways!

I agree that using a 3 wire cable for two 110/120 circuits is "iffy" and certainly "cheating" - and I'll take their word for it.  It works in a pinch, but its a clever solution not a smart solution.  I think the local ground mitigates some of the dangers but not all.

I retract my suggestion.

BUT you could run 240v power to the panel and then put the internal circuit on one phase (and thus get 120v) and the external circuit on the other phase.  Same result but within the code.  (... right?)

So if I use 4/2 wire what size breaker would you say I should put in at the main breaker panel?

Also, do you think 6/2 would most likely be adequate or is that pushing it ?

you know rather than taking advice from a hack like me it might be worth your while to hire a local electrician for an hour to figure out exactly what you need. all I know is what I've done in the past and what I'm able to learn as I go through this life.

The best bet would be to figure out the largest load you have, size the breaker to that, and calculate a wire size capable of handling that amperage with a maximum voltage drop of 5%. If you only have devices with standard plugs, it would be cheaper to replace the breaker with one rated at 15A like standard residential branch circuits. Following the formula shows you would need 8 gauge wire. If you need more than that it might be substantially cheaper and easier to run two circuits using two 8/2 direct burial cables. Beyond that would mean much heavier cables, likely need to be in PVC conduit, and greatly increase costs.

Depending on the electrical panel you might be able to add a double breaker that fits in a single breaker slot if no more slots are empty. It really depends on a number of things (brand, amperage of service, etc), so it might be worthwhile to find an electrician to go over everything. Never work on live circuits or expect that a circuit isn't live. I personally have been zapped from guys way more experienced than me telling me to work on something and then forgetting and turning power on.

Two circuits would probably be wise for the new tiny house, especially if you have any electric kitchen appliances. You could split the loads so neither line gets overburdened and avoid tripped breakers. Putting refrigeration and lights together would let you know that when the lights go out the fridge is also out, and a separate circuit for kitchen countertop loads or any other large 'continuous load'. A safety disconnect box should be more than sufficient for safety should you need to cut power in an emergency. Going to a full sub panel will greatly complicate things and increase costs. I would treat it like any outdoor load such as a detached shed, pool, or air conditioner unit. Safety disconnect, outdoor rated waterproof boxes and connectors, and GFCI. If GFCI breakers are overly expensive, what we used to do was run power from a normal breaker to a GFCI receptacle, and then wire appropriately from there so everything on the load side is protected.

bruce Fine wrote:you know rather than taking advice from a hack like me it might be worth your while to hire a local electrician for an hour to figure out exactly what you need. all I know is what I've done in the past and what I'm able to learn as I go through this life.

In any case, I'd recommend getting an electrician to validate your installation (even if you're doing the grunt work), because not doing so might compromise your friend's house insurance in case of fire. (Happened to my inlaws and it took years of court procedures and insurance hell to demonstrate that their electric installation was not at fault.)

What is the voltage at your friends panel? This seems to be pretty important. One panel here is high enough I would feel fine running an extension cord and cutting some corners. The other I wouldn’t.

It depends on how intermittently you load it and lots of other factors as mentioned.

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Thanks a lot all ya I will definitely talk to a electrician at this point and go from there ....I appreciate it!

Hello all! So to update, my tiny house builder spoke with a master electrician she works with and he said that I would be ok with either 6/2 or 8/2 at a 200 ft distance! He told me to go with a 30 amp breaker at the panel I’m connecting to....I bought a 2 pole 30 amp breaker and the largest wire size it says it’s rated for is 8 awg....so I went ahead and ordered 220 ft of 8/2....my question now is I noticed you can buy a single pole 30 amp breaker ...since I’m only doing 120v should I go with single pole as opposed to double pole? Thanks in advance!

My thought would be if I am going through all the other costs and effort, why not build in maximum flexibility.   I always try to plan for the future, even if I dont know what that is.

Peiro Mele wrote:my question now is I noticed you can buy a single pole 30 amp breaker ...since I’m only doing 120v should I go with single pole as opposed to double pole? Thanks in advance!

Yes, the single pole breaker is for 120v, and two pole breakers are for 240v.

On a side note referring to your original post above, and not having read every post after, the direct burial wire will work well if you're sure no vehicles or other heavy machines will be driving over it. If your wire needs to cross under a driveway for example, or if it is possible that a vehicle may drive over the wire in the future, may I suggest pulling it through some 1-inch pvc conduit, the grey kind. It's a fairly long run, and instead of pulling the wire through 200ft of conduit, may I suggest laying the wire out straight on the ground and sliding each piece of conduit, then gluing them all together. I've done this before, and it's much easier than pulling wire through such a distance as there will be a lot of friction. One risk of driving over direct burial wire laid bare in the soil is the weight of a vehicle could press the wire on a little stone or other object, puncturing the jacket (insulation) causing failure, which would be near impossible to isolate and locate for a repair.

I have almost the same question and I thought it might be better to post it here instead of a new thread. I hope that's ok.

Almost the same situation: I want to supply 30 amps to a small cabin 160ft from the panel on the side of a house. The supply from the panel on the house is through a 40A breaker. At the cabin I would like 2 separate 15A circuits. Do I need a 30A breaker at the subpanel in the cabin before the 15A breakers? Or is it ok to pigtail both 15A breakers together directly from the wire coming from the 40A breaker at the house?

So, Perio, what is the outcome?