I'm breaking ground this weekend for my foundation and I'm really getting nervous about the electrical. I'm having problems getting my electrican out to the hous,e so I figured I would put a post out there. Does anyone know how to calculate voltage drop of a wire over a distance of 300 feet. I'd like to put 100 amps out to the garage. We have a 200 amp service in the house. The distance to the garage is about 300 feet. lets say 310 for good measure. WHat size wire will I have to run in order to not burn anything down? It has to be run in schedule 40 PVC, so I'll probably run a phone line out with it. Any ideas? Thanks Bob
Take the resistance per foot of whatever wire you're thinking of using, multiply that by the number of feet, and then by the max current you will draw. That will give you your voltage drop. I'd run the heaviest wire you can afford. There's no problem going too big. I would think 1/0 should be minimum to consider. At 100 amps, it would drop about 7 volts for your run. Interesting to consider that the wire would be dissipating 700 watts at that point! Good thing it's spread out over 300 feet. Going bigger would be better, but it gets more expensive. 4/0 would drop about half that voltage at 100 amps. ________ Expert insurance
Check code as to if you can put a phone wire in the same conduit as your 240. It might not be fun if those two rub together and you go to answer the phone. :laugh:
You should run seperate conduit for a phone and low voltage lines........it will likely pick up a 60 cycle hum that you will hear in the phone. :bglasses:
CEC Table D3 100A @ 120/240VAC Distance to Centre of Distribution for a 1% drop in Voltage on nominal 120V-2 conductor copper circuits. You can expect to see a 1% drop after 26 ft., using No.3 copper. You want to go about 310 ft., one way. Therefore you will see about a 12% drop, again using No.3. Try to keep voltage drops to within 5%. Equipment/tools/lighting will work & last longer. A 5% drop on that distance with breaker/fuses @ 100A would require 2/0 copper , at a minimum. For other types of conductors, aluminum or Nu-Al, a completely different set of tables must be applied. This is based on the Cdn. code. Voltage drop is the same no matter which side of the border. Only difference is that we base No.3 to carry 100A, loaded 80%.
Bob, Is this for a house or new service to a garage?. If so the best thing to do is call CL&P. Your electrician should have done this and should have requested a CRS. Before you get to involved with your project have CL&P tell you what is required, such as you already mentioned the schedule 40 conduit. If this a new service you will need to be 2 feet in a trench with a 1/4 nylon rope in the conduit. If this is a new service CL&P will take care of the cable. The number for electric service is 1-888-544-4826 and ask for a New Service Technician. Good Luck. :TU:
Hey Joe, I looked into getting a new service at the garage. I talked to a tech at CL&P and they came out to look and measure. They can splice the cable coming from the street at the garage which is going to be halfway down the driveway, but that would require a handhole, which is basically a 36 inch wide concrete cylinder in which they put the splice. Then, it has a fiberglass manhole cover on top. That would go to a new meter and I would get a seperate electric bill. The hanhole and associated parts are fairly pricey, and I really don't want a huge manhole cover next to my driveway, plus it will definitely fill with water as its a wet yard. The CL&P tech said if it was him, he would trench from the house to the garage 300 feet and run a line from my service in the house. Thats why I'm trying to get an idea for the size of the cable from the house to the garage. Bob
Bob by the formula that I use here at work, having a 3% drop and 100a load it figures between 2/0 and 3/0 aluminum. If you go with the smaller 2/0 aluminum it figures out to be about a 3.5% drop. Thats not bad at all. The 2/0 size would be plenty. You will probably never load it to 100a unless you have electric heat. Thats how I would figure wire sizing for a customer here. Hope this is helpful. Thanks Rick
I see a lot of problems here... There are local codes, utility guide lines, and national elect code (NEC). If this is from the utility pole to your garage, it is probably the utility that can dictate what you need to your new meter (at the garage). If this is the case, it will cost you the least amount of money because the utility does NOT care about the NEC. If the power is coming from your basement, it is local and you MUST follow NEC codes. Hint, NEC does not derate the cable with the same formula as the utility. I don't recall for sure, but 2' deep should be good enough (I'd check though). I would NOT put more than (2) 90* long radius elbows. One where the cables from the pole go into the ground, the other where the cables exit the ground at your garage. Use MUCH larger conduit than you need.By code you can use up to 4 elbows I think, but pulling the wire is going to be a major job (use cable rated lub too). Petroleum base oils will eat the insulation on the wire. My opinion, you better have somebody with experience help you. :Smarty:
bquick OHMS law watts divided by voltage=amperage 3kw is 3000w running on 240v will be 12.5a or running on 120v 25a. Thanks Rick
I understand what you mean by not wanting to use a handhole. You must have all direct buried service. There is some good information but you must also consider the voltage drop already from the transaformer to your house along with voltage drop from the house to the garage. There are some variables here that I don't know without seeing your application but you should be able to fill in the rest. If you use the formula of %VD = (A x L x kVA) of xmfr to house + (A x L x kVA) of house to garage you should get a good idea of the total voltage drop. A = Cable Voltage Drop Factor #2 cu = .00068 #2 AL = .00089 1/0 AL = .00062 4/0 Al = .00033 L = Cable Lenth kVA Voltag x Current If you have 100 amps to the garage, which I doubt you will ever use that much but for an example use 100 amps then you have: 1/0 AL voltage drop = .00062 x 300 feet x (.240volts x 100 amps) =4.46% That is from house to garage. You need to figure from the transformer to the house then add the two for a total drop. Keep in mind this is at max current levels and would most likely occur only at motor start ups. The main problem you will have is dim/flickering lights. Also 1/0 cable may be a bit of a challenge to get into your house circuit breaker. I hope this helps to explaine what your up against. 300 feet is a good distance and you will need to run a good size cable.
wire size If your talking about a 100 amp service and not a 100 amp load to your shop then your normal wire size would be only #3. Since you have a fair distance I recommend that you go with #2. Go with a panel brand Sqaure D. Our home depot has it or if you know a wholesaler that will sell it to you. My wholesale price for a Sqaure D, 32 circuit 100 amp combination panel is $36 CDN I would go with a 2 inch PVC for the conduit run and limit the total number of bends or sweeps to a total 360 degrees (which is equal to 4 90's but probably only will need 2). If you for some reason need to exceed that amount of bends then you will need a junction box or fitting through which you can pull through. There is approved wire pulling lubricant or foam you can probably find at home depot and don't use anything else. You will definately have to put your phone in a seperate run of pipe but it can be much smaller size. The depth of the buried pipe should be 2 feet for an area where you drive over and if not it can be down 18 inches. There are a few things you have not mentioned like the things you will need power for in your shop, the activity you will be doing in general.etc. The biggest concern would be your source of heat especially if it is electric. These things will have a direct effect on the size of you service and wire size. Your average 2 or 3 car shop will have plenty of power if you are doing it for hobby. And you won't get a 2/0 wire in a 100 amp breaker. Hope this helps. Marcel.
In an application like this, does an additional ground wire need to be run, or will a ground rod buried at the garage suffice? Any web site recommendations on this subject? Interesting thread, Thanks! :beer
I was wondering that also.....when I connected the gas line to my grounded heater, it sparked. :shock: I checked with a voltmeter, and there's around 3 volts AC between the actual ground on my garage fusebox and earth ground. My assumption is that since the ground wire runs alongside the hot wires underground inside the conduit for about 100 feet, inductance is taking over and creating voltage in the resistance of the ground wire and I need to drive a stake into the ground at the service entrance in my garage and connect it to the circuit breaker box........am I correct? o No:
Not sure about the NEC, but in Canada you need to install a "bond" conductor in the conduit. This will already be built into a cable. The bond will ensure a path to ground in the event of a short. Ground conductors are installed at the main incoming service only, directly to the neutral. Different tables for sizing between bonding & grounding. 100A breaker will accept 2/0 with a lug adaptor kit.Should you use a disconnect switch the lugs are available in a wide variety of conductor ranges.
Have bond connector yet get shocked Several years ago I ran 30 amp service to the garage with 4 - 10 gage conductors. The standard black wire, red wire, a neutral white wire and the bare bonding wire. Both the white insulated and bare conductors are bonding the respective electrical panels. The panel in the house is grounded to the copper pipe for the water service coming into the house. The trouble light with the metal cover connected to the ground conductor, has a slight voltage that you can feel. Have never measured it, but there is a voltage difference between the concrete floor and thit grounded cover. ou: Why would there be electrical potential? The garage is only about 80 ft from the garage.
Joe, Yes you need a ground rod at the garage. Loyd, You shouldn't have any voltage. Look for leaks. Sub panel should have seperate nuetral bus bar and ground bar - service panel shares these. try www.electrical-online.com
Been in the electrical profession 24 years. You will need to install one of three grounds, ground rods at the shop, a ground plate or a under footing ground. Up here it's 2 6 ft ones or 1 10ft. I would have to look up the size for you. I prefer under footing grounds my self. I would also have to look up the size, the lenght and the distance to the bottom of your footings. You need to remove the screw that bonds the neutral and the ground at you shop panel. You do not need a ground wire to the shop from the house with one of the grounding methods I gave you. To answer the measurement of voltage question or the spark one is that there is a difference in potential between the two grounds. All grounds are not eqaul. If you rely on the ground from the house you will most certainly have the same condition where the ground at the shop and the ground at the house will be different, a condition you do not want. You regularliy find the differnce between telephone, water pipe grounds. Your house should be bonded to the water pipe on the street side of the shut off. Now a days with plastic water pipes you have to pay closer attention to your grounds. Your gas lines are required to be bonded as well. All these rules are the Canadian code and you should check what your local codes are. But I think they will be similiar. Hope this helps. Marcel.
