Hello all. I am running power to detached shop on a hobby farm in rural
Missouri. For the work, permits and inspecions are not required.
Power will come from 200 Amp meter box. Straight run to breaker box will
be 130'. Trench will have to be moved over some to avoid corner of double
wide. I am figuring 160' wire length from meter, through trench, and up
to breaker box. Breaker box has 100 amp main that will accept 1/0 wire.
Will be using 230 volt 50amp lincoln 225 arc welder on occasion for
equipment repairs. There will be a 3HP 110v air compressor there also.
Other electric items will be drills or circular saws on occasion and in
the winter we will have a block heater for the tractor plugged in
To figure wire size, can I just add up the amps from all the items that I
might be using at the same time, or is it supposed to be rated for the
The guy at the local supply store suggested 2-2-4 bury grade cable. Can
this be put in conduit?
Voltage at the meter box is 125v. If I have a voltage drop of 10 volts in
the wire, does this mean I will have 115v at the shop? Is this enough to
keep the motors in the tools happy?
On grounding, can I run a ground wire from the breaker box to a nearby
freeze proof water hydrant, or should I still plan on puting in a
grounding rod? Should the ground and neutral in the breaker box be bonded?
I know this is a lot of questions, but the more I try to read, the more
confused I get.
Thank you for your time.
Short answer? No.
Wire size is based on the size of the main breaker size coming in, not
the loads (which can, and will, change over time). If your sub panel
has a 100 amp breaker, that's what determines the minimum size wire
coming into the sub panel.
1. 2-2-4 What? AL or CU? If AL no, too small for 100 amps.
2. How big is the conduit? 4"?
Standard USA voltage is 120/240, not 125 volts. (Not saying you
measured 125 volts, but you work from the standard...) 10 volts drop
is too much, wire is too small... Most equipment will work OK on 115
volts, but in fact you must work from 110 volts (120 - 10).
Is this a main panel from the meter, or a sub panel from another
panel? Big difference. No you don't ground to a water hydrant... You
put in the required number of ground rods (minimum of 2, often more).
If the building's floor is cement, and has rebar, you must tie the
rebar into the building ground too...
Prepare to be even more confused, you will get a lot of advice, some
of it not correct, on Usenet. Go to garagejournal.com, and setup an
account. Then post in the right forum (electrical and lighting) and
you will get good advice--the guys there are great at this, do it all
Sorry aobut that, the 2-2-4 is aluminum and I was thinking 1-1/2" conduit.
If I go to 1/0, 1/0, 2 aluminum, what conduit do you suggest? I will be
laying the wire in the trench and sliding the conduit on the wire one
piece at a time.
Double wide is not there yet. Will be running the wire for the trailer
and the shop into the 200 amp service at meter pole. It has a main 200
amp breaker and place for 3 feeders to attach on each leg. The guy doing
the wiring only does trailers and he only deals with 4/0 aluminum. That
just costs too much for my use not to mention it won't fit into the
breaker in the breaker box in the shop.
Will also be putting pvc water pipe in the same trench and maybe a 3/4" or
1" conduit for bringing phone or ethernet cable to building.
Floor is currently gravel in the shop, The guy that quoted putting
concrete said there would only be rebar near the entrance. I will tie it
in if I get a chance. What size ground wire is needed?
No, and no. #2 Al won't do 100 amps. No way you'll pull that stuff
through a 1 1/2" conduit. Technically AWG 1 AL would work for 100
amps, but you probably won't be able to find it, instead you will have
to go to #1/0 which is rated at 120 amps.
The 2x1/0 + 1x#2 will work in AL.
I'd go with 3" miniimum, and 4" is more realistic. That stuff is stiff
and difficult to work with. Also make 100% sure you get cable rated
for direct burial, as even with it in a conduit that is necessary to
prevent insulation failure in the future.
4/0 SE would work for the other service (shop/garage) well. But that's
big stuff! Normally 4/0 is used with 200 amp boxes. 1/0 is used with
100 amp boxes. That's why your breaker is rated for 1/0 wire! <g>
True, cost is not the main issue, but it won't fit a 100A breaker.
Make sure you have proper spacing between power and communications
Personally, I use as big as possible, but for a 4/0 feed, a 2/0
neutral. For a 1/0, use of a smaller neutral is acceptable. That third
wire is not a ground, it is the neutral, and is a current carrying
Thank you for the input. I believe I will go with the 2x1/0 1x2 aluminum.
I took some pics of the breaker box and meter box if you are interested,
they are at http://www.pcassistant.net/land.html
To use 4/0 Al for a feeder protected at 200 amps, you need to meet one
of a few conditions: (a) the feeder is the main power feeder of a
dwelling unit (carrying all the loads and only the loads of the
dwelling unit), (b) you do a load calculation for the feeder and it
comes out below 180 amps, or (c) you use a wire with a 90C insulation
and you take extra measures to allow the use of the 90C rating.
Otherwise, you need to use 250 kcmil Al.
I think the OP was asking about the Grounding Electrode Conductor
(GEC) to the Ufer ground (the rebar), not the neutral conductor. The
GEC is sized based on the largest ungrounded conductor. For Al, 1/0
or smaller requires a #8 Cu GEC, 2/0 or 3/0 requires a #6 Cu GEC, and
4/0 or 250kcmil requires a #4 Cu GEC. For an Al GEC, go up 2 sizes on
the GEC. Regardless, connections to a ground rod need not exceed a #6
Cu, and connections to a Ufer ground need not exceed #4 Cu.
I'll not make a recommendation, because if i do I'll get flamed. But i
will tell you this:
We ran a detached garage, with the following equipment and at times a
very busy "fab" shop.
Lights, overhead gas unit heater, grinders, 110v air compressor, drop
lights, fans, and a Hobart beta mig 200A welder.
The detached garage was fed by a 10/3 wire UNDERGROUND, and hooked to a
30 A breaker in the house panel. NEVER, in the 35 years of being at
that location with that setup, did we pop the breaker in the house. So
read that as you will. I am currently fixin' to run a wire to my barn
which will have similar stuff as mentioned above and i'm gonna run a 6/3
with ground to the pole box. (about 400 feet).
remove the "not" from my address to email
welders don't pull anything NEAR what people think they do. That's why
there's special provision for their wiring requirements. We ran a 200A
mig in that detached garage (sometimes nearly wide open) with never a
problem with it being fed with a 10ga.
remove the "not" from my address to email
receptacle. Many large residences have a three phase supply (like my
sister's). 230 V Schuko receptacles go up to 16 A, with a 2,5 mm^2 conductor
(#16). A water heater is 20 A (4 kW) #14. A usual service is #10 (35 A).
Code says that in all installations a GFCI breaker must be installed, 30mA
major in electrical engineering
In US terminology, a GFCI trips at 5 mA differential current. A
device that trips at 30 mA differential current would be called GFPE,
ground fault protection for equipment. Almost all US AFCI breakers
also incorporate GFPE as part of their propietary AFCI technology.
panel, so if it would be 5mA we would have lots of nuisance trips. There are
a few times when we get nuisance trips with 30 mA and I have to play
detective to find the leakage (usually humidity or bad insulation). I know
that in USA you have GFCI receptacles, but you also have 120 V. IMHO the
best brand for breakers is ABB, closely followed by Geyer and Siemens (first
Swedish-British, second and third german).
major in electrical engineering
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