Boring a wire under a driveway, or multiple conductor pairing

[four-thirteen]

I am considering going with off-peak electric heat for the detached shop. Last year we installed a geothermal heat pump for the house which involved installing the off-peak equipment (meter, breaker box, cut out switch). Oddly, the monthly fee for the extra meter and off-peak service is more than the cost of the electricity they sell us for the heat pump.

So, seeing as how we already have a slick 100 amp load center that only serves the house heat pump, it seems like a great idea to use it to power electric heaters in the shop to replace the propane heater that totally *****. We had a kick-*** woodstove in there but the insurance company required it's removal.

Currently the electrical service to the shop is through two direct burial cables, each with 15x 12 gauge stranded conductors inside. The guy who built the shop 20 years ago swears that the electric code allows the pairing of these multiple 12 gauge wires for the combined capacity. I looked at the NEC codebook for 2008, and can't find anything that allows this for 12 gauge wires, it states that multiple conductors can be paired for conductors larger than 1/0 wire. If this sounds really hokey, I totally agree and can't see how it would pass code. If you have some insight as to why this does in fact pass code, please tell me why, because it would be great to be able to steal a few conductors out of the bunch to power the electric heat.

I assume that the service conductors I am talking about above aren't up to code and thus the whole setup needs to be reworked. This is all well and good, not something I have a serious problem with, but between the shop and the house is a concrete paved driveway. No ordinary driveway, it was an quarry road in the 1940s built on a very thick bed of heavy packed class 5 that is more like concrete than dirt. Is there an economical way to get wires under this that doesn't involve tearing up the driveway? I am sure $5000 would get a horizontal boring machine out to my place, but that would kill all the savings I am trying to get out of my heating retrofit. Ideas?

 

[hidollartoys]

I believe the code only allows pairing of 1/0 and bigger wire and only for service cable and not branch circuits. If you are going to use the new wire only for the heating it could be considered as a branch circuit.

 

[Dman]

Buy some PVC pipe that is as wide as your drive. Also buy the fitting so you can hook up a water hose from your house to the pipe. Dig a trench on the side that your house is on as deep as need to get into the softer area. You will have to dig the trench back aways so that you can put the pipe in there and go straight. Turn on the water and start pushing the pipe through the ground under the drive. It may take a couple of you pushing to get it through. This will work as my brother just did this under the road at his house as he wanted to run power to land he owned on the other side of the road. The pipe he used was probably about 1.5". He then finished digging in the trench and ran his wire. Hope that helps.

 

[bimmer1980]

Check out my thread on this topic....

http://www.garagejournal.com/forum/showthread.php?t=48027

this was a real PITA!!!!

If i had to do it over again, here's what I would do.....
I would recommend using a chunk of steel pipe and use a large sledge hammer to drive it in. If you can get a rotary hammer drill or a chipping hammer would be even better. A mini excavator can help to support the pipe and put some added driving force on it....

 

[mhm993]

My neighbor has a buddy who's business is to, literally, shoot a hole with a shaped charge, under your drive at the necessary depth. He told me the guy estimates the direction, geology, and length of the cut, and loads just the right amount of explosive and shoots it like an underground cannon. And that it costs much less than the boring maching. I'll admit I can't imagine what happens if it hits a boulder, but this is what he tells me.

I have no personal knowledge, and have never seen it done, but maybe.....?