Looking into installing 30 TT outlet on my detached garage

[Boomerweps]

Problem is that it is about 90-100 feet from the home circuit breaker box. Voltage drop calculator has about a 5% voltage drop for that distance using 10awg and about 3.5% using 8awg (not allowing for the TT shore power cord).
I'm thinking I'll need to use 8awg.
Copper gets expensive, plus added components, outside jack, ditchwitch rental, etc.
Any thoughts?
I'm looking at Direct Burial wire or interior grade that would be routed through sealed plastic pipe. I've only checked Home Depot pricing so far and not the local electrical supply house.
Garage has 12awg run to it and is a good 110-120 feet run through the house and ground from the CB box.

[DrewE]

Dusty R wrote:


I also don't like those adaptors.
I put 30a RV recital on a 20a circuit where I plug my mh during storage and while loading for our next trip.
Someone once told me that was a code violation, but I don's see a problem with it.

(I hope I untangled who wrote what properly...)

I think that is not a code violation, but that part of the electric code is not the clearest (even by electric code clarity standards). Basically, the requirement is that the receptacle(s) be rated for at least as much current as the circuit, except for multiple 15A receptacles being permitted on a 20A circuit. For one practical example, it is not uncommon to have a 40A range circuit that is equipped with a 50A receptacle. It's also not unheard of for industrial or similar machinery to use a larger plug and socket than required, perhaps because it is more robust.

Needless to say, it would be a code violation (and potential safety hazard) to increase the circuit breaker or fuse size to 30A for your 20A circuit.

Please do be aware that I'm not a licensed electrician, and definitely not an inspector or agency having jurisdiction over your installation.

[Dusty_R]

DrewE wrote:

Bobbo wrote:

DrewE wrote:
Edit:

I'm also not a big fan of the 30A male to 15A female adapters that are available, partly because I've seen at least one case where one of those adapters, and the reverse 15A male to 30A female, were used with an ordinary (probably 16 gauge?) extension cord to power a 30A RV.

I also don't like those adaptors.
I put 30a RV recital on a 20a circuit where I plug my mh during storage and while loading for our next trip.
Someone once told me that was a code violation, but I don's see a problem with it.

[DrewE]

Bobbo wrote:

DrewE wrote:
Edit: Just noticed the 20A outlet there. Is that on the same 30A circuit (without a 15 or 20A breaker protecting it)? If so, that's definitely not up to code and a bit of a concern; the receptacle is underrated for the circuit's ampacity.

My S&B house has a bunch of 15 amp outlets on a 20 amp breaker. The receptacles are undersized for the circuit's ampacity too. As long as the wires going to the 20 amp outlet are sized for 30 amps, I wouldn't loose sleep over it.

Code specifically permits multiple 15A receptacles on a 20A circuit as an exception to the otherwise inflexible rule that the receptacle can't be rated for less than the circuit's overcurrent protection (for general-purpose circuits--there are probably some other exceptions for odd industrial sorts of things). I presume one reason why this is permitted is because the contacts for 15A and 20A plugs and sockets are internally the same size, with the 20A having one prong rotated 90 degrees. Most 20A sockets are 15A/20A combo sockets (with a T shaped slot), and 20A plugs are pretty uncommon.

The wires to the socket may be 10 gauge (sized for 30A loads), but the wires on the cords plugged into it are almost certainly not sized for that load. It's not as though it's going to explode imminently, but there is the potential for accidentally creating a hazardous situation if one isn't careful and plugs too much in at once (particularly using undersized extension cords or similar).

I'm also not a big fan of the 30A male to 15A female adapters that are available, partly because I've seen at least one case where one of those adapters, and the reverse 15A male to 30A female, were used with an ordinary (probably 16 gauge?) extension cord to power a 30A RV.

[Bobbo]

DrewE wrote:
Edit: Just noticed the 20A outlet there. Is that on the same 30A circuit (without a 15 or 20A breaker protecting it)? If so, that's definitely not up to code and a bit of a concern; the receptacle is underrated for the circuit's ampacity.

My S&B house has a bunch of 15 amp outlets on a 20 amp breaker. The receptacles are undersized for the circuit's ampacity too. As long as the wires going to the 20 amp outlet are sized for 30 amps, I wouldn't loose sleep over it.

[George3037]

DrewE wrote:

George3037 wrote:

I just installed a 30A plug for my TT about 3 weeks ago. I used 10 ga. direct burial underground wire inside 3/4" PVC conduit. Ran 50' from post to house and 50' through basement to a 30A breaker in the breaker box in garage. Voltage drop is acceptable.
I measured 121.5 at the breaker and 120.4 at the plug with no load. That's less than the 5% drop I expected.
Measured 119.9 at the trailer end with fridge running, some lights and a TV on. Kicked on the A/C with the above and it measured 113.6V which is about 8% drop under load but acceptable to me.
Total cost was about $450. All materials were bought at HD.

Under no load, the expected voltage drop is zero. (Recall Ohm's law: V = I * R. No load means that the current I is zero, and so the voltage across the resistance--the voltage drop--is also zero.) Maybe the line voltage fluctuated while you were making your measurements, or maybe there was a load you weren't considering such as the converter charging batteries.

At any rate, it seems to be okayish for what you need, so there's no need to speculate on what was going on.

I suspect you are correct that the house line voltage changed 1.1V in the time it took to walk from the garage out to the plug. I had nothing plugged in when I took those two readings.

The 20A GFI is on its own circuit.

[DrewE]

George3037 wrote:

I just installed a 30A plug for my TT about 3 weeks ago. I used 10 ga. direct burial underground wire inside 3/4" PVC conduit. Ran 50' from post to house and 50' through basement to a 30A breaker in the breaker box in garage. Voltage drop is acceptable.
I measured 121.5 at the breaker and 120.4 at the plug with no load. That's less than the 5% drop I expected.
Measured 119.9 at the trailer end with fridge running, some lights and a TV on. Kicked on the A/C with the above and it measured 113.6V which is about 8% drop under load but acceptable to me.
Total cost was about $450. All materials were bought at HD.

Under no load, the expected voltage drop is zero. (Recall Ohm's law: V = I * R. No load means that the current I is zero, and so the voltage across the resistance--the voltage drop--is also zero.) Maybe the line voltage fluctuated while you were making your measurements, or maybe there was a load you weren't considering such as the converter charging batteries.

At any rate, it seems to be okayish for what you need, so there's no need to speculate on what was going on.

Edit: Just noticed the 20A outlet there. Is that on the same 30A circuit (without a 15 or 20A breaker protecting it)? If so, that's definitely not up to code and a bit of a concern; the receptacle is underrated for the circuit's ampacity.

[George3037]

Boomerweps wrote:
Problem is that it is about 90-100 feet from the home circuit breaker box. Voltage drop calculator has about a 5% voltage drop for that distance using 10awg and about 3.5% using 8awg (not allowing for the TT shore power cord).
I'm thinking I'll need to use 8awg.
Copper gets expensive, plus added components, outside jack, ditchwitch rental, etc.
Any thoughts?
I'm looking at Direct Burial wire or interior grade that would be routed through sealed plastic pipe. I've only checked Home Depot pricing so far and not the local electrical supply house.
Garage has 12awg run to it and is a good 110-120 feet run through the house and ground from the CB box.

I just installed a 30A plug for my TT about 3 weeks ago. I used 10 ga. direct burial underground wire inside 3/4" PVC conduit. Ran 50' from post to house and 50' through basement to a 30A breaker in the breaker box in garage. Voltage drop is acceptable.
I measured 121.5 at the breaker and 120.4 at the plug with no load. That's less than the 5% drop I expected.
Measured 119.9 at the trailer end with fridge running, some lights and a TV on. Kicked on the A/C with the above and it measured 113.6V which is about 8% drop under load but acceptable to me.
Total cost was about $450. All materials were bought at HD.

[D_E_Bishop]

I liked the idea of using the existing conduit and upgrading the wire size and installing a sub panel until you mentioned a non-conforming garage and someone suggested solar.

It doesn't seem like you are interested in building a new garage closer or attached to your home, so I would consider pulling some #10s and a disconnect at the garage and CB in the main panel. Then as I could, I'd purchase 300 or 400 watts of solar panels and controller, add batteries as needed.

You could put the panels either on the garage or the RV. Unless someone was going to be sleeping in the RV, run off the solar. When someone is using the RV, the new wires would carry at least the AC or the MW and the batteries could carry the house 12 volt system.


A full upgrade will never give you a return, the solar will, especially if you can add the batteries to the RV and you want to dry camp.

[myredracer]

Go wireless? Just about everything is wireless these days. :C

I've usually gone with 1" PVC for underground when 1/2" or 3/4" would work. Small cost difference from 3/4". Makes pulling longer distances easier and allows for future pulling in of more or larger wire. You'll want max. 4 x 90 degree bends overall. Poly water pipe can be used providing you use the correct wire/cable.

Another option would be aluminum mobile home feeder cable. Min. size is #2 (4 conductor) and good for 100 amps. The stuff is cheap, like a dollar a foot and faster to install. I'd go with above suggestion and install a small sub-panel in the garage and a circuit for the RV outlet. That will give you a breaker you can shut off when plugging in. Can use a smaller breaker in the house panel like maybe 60 amps or larger up to 100. Would give more available power for other stuff/tools/equipment/heater in the garage. You could also use a junction box to reduce the wire size to something smaller if wanted.

I've used armored teck cable for direct burial a few times but is expensive unless you can find a smoking deal on it somewhere. Perhaps you could check CL to see what cable might be for sale.

But why not use the existing 1" conduit which is good for 3 x #3 (code burial depth requirement notwithstanding), pull in larger wire and install a sub-panel.

On voltage drop, start with the actual voltage at your house panel, not a nominal 120 volts unless you know it stays at or close to 120. Could be lower during the summer heat or other peak periods. Use a voltmeter and leave it there for 24 hours and see what it's like. But do you really need a full 30 amps available for your RV?

Instead of a ditch witch I'd go with a mini excavator from a rental shop. Or just dig it by hand depending on soil condition. Check the Code for min. burial depth, backfill material & protection.

[DrewE]

valhalla360 wrote:

wnjj wrote:

valhalla360 wrote:
Go big on the conduit...as you learned with the old conduit...If you want to run communications or 50amp line later, it's much easier if you have a 2" or even larger conduit to work with and the cost difference is negligible.

You’ll want communications in a separate conduit above the electrical in the same trench.

It's fine to put comms in the conduit. The only issue is anyone working on it needs to be qualified to work around electricity...assuming you farm out the work.

We did it all the time on signal systems...finally had to change and run independent conduits for power and comms because as we added more high tech devices needing comms, we were getting a lot of technicians who weren't licensed electricians working on the systems, so technically, they were not allowed to go into any part of the system that had live electrical wires. If they were combined, they had to drag an electrician along to watch...by splitting it out, they could go do work by themselves.

If the comms wiring is in the same conduit as power, the wire and wiring devices and terminations used need to be rated for those voltage levels. Typical cat 5, phone wire, coax, etc. is low voltage only and not so listed.

On a more practical level, it's not particularly good practice to run comms wire in parallel with power wiring for long distances due to capacitive and inductive coupling causing noise in the comms wiring. (Yes, twisted pairs and shielding and so forth do help cut down on this a lot, but it's still not best practice.) Also, it's just generally going to be a pretty bad day and make a potentially quite hazardous situation if your AC power cable somehow crosses to your comms cable, legal per code or not.

Fiber optic cable may well be a different matter since it's inherently non-conductive.

[valhalla360]

wnjj wrote:

valhalla360 wrote:
Go big on the conduit...as you learned with the old conduit...If you want to run communications or 50amp line later, it's much easier if you have a 2" or even larger conduit to work with and the cost difference is negligible.

You’ll want communications in a separate conduit above the electrical in the same trench.

It's fine to put comms in the conduit. The only issue is anyone working on it needs to be qualified to work around electricity...assuming you farm out the work.

We did it all the time on signal systems...finally had to change and run independent conduits for power and comms because as we added more high tech devices needing comms, we were getting a lot of technicians who weren't licensed electricians working on the systems, so technically, they were not allowed to go into any part of the system that had live electrical wires. If they were combined, they had to drag an electrician along to watch...by splitting it out, they could go do work by themselves.

[kellertx5er]

Macrosill wrote:
I just did this last week. I trenched and laid 1" pvc. I had lots of 10 awg thhn on hand so I ran 2 parallel sets of it to minimize the voltage drop. Paralleled 10s came in with less voltage drop then 8 awg did and the copper was free.

Now before anyone gets their pants in a twist I know I am using smaller than 1/0 conductors but there is an exception in the NEC provided all the conductors are in the same conduit and the condcutors are sized than any one of them can carry the full load should you lose one. They are all in the same conduit and they are all 10 awg.

Sorry Mac, but the NEC exception to which you refer only applies to "control power to indicating instruments, contactors, relays, solenoids, and similar control devices ..."

Quotes were used intentionally, as I was typing while reading directly from my code book. Don't have my pants in a twist, just see too many misquotes from the NEC in here.

[wnjj]

valhalla360 wrote:
Go big on the conduit...as you learned with the old conduit...If you want to run communications or 50amp line later, it's much easier if you have a 2" or even larger conduit to work with and the cost difference is negligible.

You’ll want communications in a separate conduit above the electrical in the same trench.

[enblethen]

You should be able to get 2 #8 and one # 10 in your existing 1 inch PVC.

Edit, fixed wire size