I purchased an electric heater for my garage that requires 240V and about 25
amps. I'm looking for a little advice on how to wire up an outlet to go
Right now I have a box with the wiring pretty much ready to be routed out.
The main wiring from the house has black, white and red, with the black and
white each going through a 40 amp fuse. The outlet I need says NEMA 6-30,
it's rated for 30 amps and has two horizontal prongs plus ground. I believe
the correct way to wire it is with the black and red to the horizontal
prongs (the ground is just for safety). My question is about the ground.
There is no ground currently wired into the garage, should I connect the
white wire, leave it disconnected, or what? Is there some relatively easy
way to make a good ground? I wouldn't mind switching over my 110 outlets to
3-prong as well.
This is Turtle.
In the modern world we have everything grounded and feel safe by doing it. I
would not have a electric heat in my home , if it was not grounded. Run
ground wires for everything. The putting on the ground prong of the
receptical and plugs was the single best thing that stopped a lot of fires
and people getting killed by the electricity.
Please fill in some details.
Is the garage detached?
What wiring method is used to supply the garage? i.e. rigid metallic
conduit, triplex, rigid nonmetallic (PVC).
Is there a bare or green insulated wire run with the black red and white?
Is the box you already have in the garage a junction box or a panel
I will need this information to provide you with good answers to your
I will try to answer the best I can, hopefully it'll be enough. The garage
is detached and there are actually two metal boxes in the garage. The main
fuse-box inside the house has two 40 amp fuses going to the garage. In the
garage, in the big box, I see the wiring coming from the house. I'm not
sure what guage, but it is a very large cable with three insulated, stranded
wires inside: red, white and black. That's all, there is no green or bare.
The wiring goes underground from the house, all I can see is a metal conduit
coming up from the garage slab into a junction box and then wire to the big
box described above.
Inside the big box the white is wired to a lug on the side of the box, and
the black and red are wired to fuses. At present the output side of these
fuses go noplace. This is where I intend to wire from. The white, red and
black are also wired out (unfused) to a smaller box where four 15 amp
circuits of 110 are made and the fuses are in this box. The larger box has
a large on/off lever switch on the side which currently does nothing, but
will be a nice emergency off for the heater.
Now that you made me look, I see that my solution is probably to derive
ground from the metal condiuit between the house and the garage. Do you
agree? I could just clamp maybe some 10 guage wire to the conduit and run
it into the boxes as a ground source.
Is the wiring underground run in a continuos rigid metal conduit? If it
is continuous and has not rusted away it can indeed be used as the
Equipment Grounding Conductor.
What kind of cable is in the raceway? The presence of cable suggest
that the rigid metal conduit is only risers to provide protection from
the bottom of the trench to the first enclosure.
To test for continuity of the feeder raceway you need to pull the two
forty ampere fuses at the house and isolate the white wire from the lug
in the garage and from the neutral buss bar in the house panel cabinet.
Use an ohm meter to check the white wire to make sure it is clear of
faults to the raceway. Then reconnect it to the neutral buss in the
house panel cabinet. Then check for continuity between the neutral
that remains isolated at the garage and the cabinet of the garage Over
Current Protective Devices (OCPDs). If continuity is found it will
indicate a conductive loop via the white neutral wire through the
neutral bar of the house panel, the main bonding jumper, the house
panel's cabinet, to the raceway, and back to the garage. Then you can
separate the grounded current carrying conductor of the feeder from the
garage OCPD enclosure cabinet. Do that test and let us know what you
Is the large switch you spoke of in the cabinet or is it a separate
enclosed switch? Are the two unused fuses you spoke of part of an
enclosed switch assembly? Are the conductors from the house and the
conductors to the separate fuse panel terminated in the same terminals?
Well, let me first state that I am providing suggestions based on the
information you provided, and it is your discretion to take or discard the
information I give you.
May I also say that I graduated from a technical vocational high school with
Electrical being my major and I have over three thousand hours of
residential and commercial electrical work under my belt... Anyway.. I think
I should have been a lawyer. 8-)
I assume the box is in your garage with the wires from the main panel.
I have to assume you have mistyped the " with the black and WHITE each going
through a 40 amp fuse "
If you are mistaken, the black and RED wires should be the ones going thru
the "fuses". If you were correct, change the wires a.s.a.p
I have to assume you have actual fuses and not circuit breakers.
First things first - You have to verify the wires are capable of carrying
the amperage you require. Wire sizes are measured in AWG, or American Wire
Gauge (Used in the United States and other countries as a standard method of
denoting wire diameter. The HIGHER the number the THINNER the wire)
You have to verify the wires in your garage are #10 AWG or heavier. #14 AWG
is rated for 15 amps, #12 AWG is rated for 20 amps and #10 AWG is rated for
30 amps. Very long runs of wire require you to increase the wire size
because of the resistance applied over long runs. If it is not very far away
from the panel, you have nothing to worry about. The wire size should be
printed on the insulation, if not, use a tool that has a wire gauge to
determine the size. You are looking for #10,8,6 and better or so on.. I
assume the wire is at least #10 AWG.
The fuses in the panels should be reduced to 30 amp fuses. If you have
breakers, they should be changed to a 30 amp double pole breaker, as this is
the maximum amperage of the new three prong outlet you have for the heater
and #10 AWG wire. NOTE - If you have fuses, the 30 amp fuses should be side
by side in one removable carrier in your fuse panel. If the black and red
wires go to mounting screws leading to separate "screw" in type fuses like
other 110volt circuits in your house, you must change this by adding a
separate sub-panel that contains a 30 amp double pole breaker. If you do not
know how to do this, call an electrician. The purpose of a modern double
pole breaker with the little metal bar connecting the individual breakers
together is in case only one hot leg trips because of a short, the other
intertwined leg is pulled to the off position rendering both hot wires of
the circuit dead..with fuses, if only one hot leg trips, the other hot leg
may very well be live and a danger to anyone working on the circuit. The
fuses being in the same carrier allows someone to pull both fuses at the
same time and work on the circuit safely.
The two spades of the outlet should be wired to the black and red
wires.These are the discolored or brass screws on the outlet. The white wire
should be wired to the ground of the outlet, which should be the green
screw, AND you should put a few wraps of green electrical tape around the
white wire. The green tape now designates that you are using the white wire
as a ground wire. Back in the panel, the black and red wires should go the
30 amp fuses or 30 amp double pole breaker. Once again, wrap this end of the
white wire with green tape. Now... Where to put your designated ground wire?
Older panels have both the white (neutral) and green or bare (ground) wires
going to the same bar in the panel.
Modern panels have the neutral and ground wires going to separate bars in
the panel with, in essence, the neutrals going back to the street service
and the green or bare wires going to a grounding rod. A grounding rod is a
copper rod pounded into the ground with a wire clamped to it leading to the
grounding bar in the panel. In some cases, the neutral bar and grounding bar
in the panel are both connected to each other and then the ground rod, as
this is the safest. The simple fact both bars are attached to the same metal
with one of them connected to a rod offers protection with out a jumper
also. There is an extremely rare chance of certain situations happening
outside of your house where the neutral wire of the grid may become
electrified and backfeed electricity into your home thru the neutral system.
If you do not have a ground rod and your grounds and neutrals are on the
same bar in the panel, there is no where for this electricity to go,
backfeed your house, and may seriously injure or kill someone and/or damage
electric devices... It's a slim chance to none, but as the government says,
Anything that is a statistical probability at some point becomes a
certainty. If you have both these bars connected to a ground rod,
electricity will take the path of least resistance and discharge safely thru
the ground rod. Your current panel configuration will dictate what you have
If you have a grounding bar in your panel, put your newly designated white
wire with green indicating tape to the ground bar.
If all the grounds and neutrals go to the same bar and you do not see
anything going to a bona fide grounding rod, you have two options -
1. Find out what the local code requirements are for grounding rods in your
neck of the woods, drill the concrete floor if applicable, and pound the
required length and diameter grounding rod into the ground. Note - Put the
clamp you are going to use to clamp the wire to the rod leading back to the
panel on before you smash the end with a sledge hammer.. the copper rod will
form a nice mushroom on the end and if you can't split the wire clamp in
half, you will have to cut off the end of the rod to get it on.
2. Cross your fingers and hope you do not hit any rocks with the rod.
Many areas allow the use of the cold water pipe entering your house as a
suitable ground. The catch - It must be copper, municipal water supplies are
a go, personal wells may require approval to ensure the pipe is long and
deep enough, and in the case of municipal water supplies the clamp must be
on the street side of the meter, that is the clamp must be attached before
your water meter.
As for your outlets in the rest of the house - For many years, a ground wire
has been part of all wiring, it just has not been wired to the outlet plug.
If you remove an outlet and look at the back of the box, you may see a
ground wire attached to the box. If it is there, all you have to is pull out
the extra ground and attach it to the green screw on a new 3 prong outlet.
If the wire is too short, attach a pigtail to the wire with one ground wire
going to the box and one going to your new outlet. The only problem you may
encounter is aluminum wire in older houses. If the wiring is aluminum, you
can never splice aluminum and copper together. The differences between the
two metals will cause a "deleterious" effect and erode the aluminum causing
a dangerous situation where electricity will arc across the joint creating a
fire hazard. If the wiring is aluminum, you must use split connecters that
never allow the two metals to touch, or simply drill a hole in the back of
the box and drive in a self threading green grounding screw to secure your
new copper grounding wire to a metal box leaving the aluminum ground wire in
it's current attachment to the same metal box.
I hope I did not overwhelm you, as I aim to educate along with help. I hope
many other people will learn from this post..Wishful thinking on my part? I
Good Luck. Anymore questions you may have, just reply to this same thread
and I will try to help you out.
Aint No Stinkin Viruses Here!
Checked by AVG anti-virus system (http://www.grisoft.com ).
Tom and Grim, thanks for the informative help.
This house was built in 1969 and for whatever reason, there is no ground
going anywhere. There was one grounded outlet in the basement, grounded to
the city water pipe. I have followed suit and grounded a few outlets
upstairs by running separate ground wire to this same pipe. This is
probably not strictly code, but I think it's safe.
As for the garage, I can see no definite ground out there at all. Only a
very large three conductor cable has been routed out there. I did typo, the
red and black go to the fuses and the white just goes to a lug from which
other connections are made. The white is "grounded" to the box itself, but
the box is completely isolated (mounted on wood, no conductive connections
other than the three wires) so I think this is pointless.
My plan of attack then is to wire the black and red to the spades
(horizontal looking connections) of the outlet and the white to the ground.
Then at the box, ground the white wire somehow. I will check to see if the
conduit from the floor of the garage is continuous to the ground in the
house, but now that I think about it, I really doubt this is the case. The
cable looks like a kind that would just be run through bare ground (looks
like the kind I'd buy at Home Depot, only much bigger).
I'll try to answer Tom's questions about the two boxes in the garage. The
larger box is where the 3-conductor cable enters from the conduit in the
floor. Inside, the cable splits apart so that the white goes to a lug on
the side of the box and the red and black go to two large fuses (cylindrical
shaped fuses). The large lever switch is external to the box and disables
the fuses when in the off position. The smaller box works from the white
wire connection at the lug and from the "input" side of the two fuses,
unaffected by the fuses or the switch (it's as if the larger box doesn't
exist to the smaller box, except to reduce the wire guage to a manageable
size). All you really see when you open the larger box is the dual fuse
arrangement right in the center. It looks to me like it's made to make 220.
Back to work...
Here is how I suggest you proceed at your garage providing that there
are no metallic pathways such as water, sewer, fuel gas, or other
piping; and no other wiring such as video, intercom, alarm, or telephone
between the two buildings. Wiring that comes to each building
separately from the utility owned lines does not count. This also
assumes that the interior wiring in the garage is cable rather than
As long as the two cartridge fuses in the large box are larger than
thirty amps I suggest you use the enclosed switch as the code required
building disconnecting means. Replace the single terminal lug in the
enclosed switch that the white wire form the house connects to with a
multi terminal lug. The new lug should have four terminals and be
connected directly to the enclosure of the switch by its mounting
screws. Use the new lug to terminate all of the white and green/bare
conductors that start or end in that switch. Install two driven ground
rods at least six feet apart. The two rods are the required building
grounding electrode system. Make sure you do not drive them through your
feeder cable or any other underground utility. Call the local miss
utility service at least one week in advance so they can mark the
location of any utilities for you. In most cases they will not mark the
location of the feeders or other utilities you own. From the farthest
rod's acorn clamp run a bare solid number six copper conductor, that
will serve as your Grounding Electrode Conductor (EGC), through the
acorn clamp on the nearest rod to the enclosed switch and terminate it
on the multi terminal lug in the switch enclosure. The EGC will be run
in a trench that you dig between the two rods and the wall outside the
enclosed switch. The trench should be deep enough to make later
disturbance to the EGC unlikely.
Install a main lug only (MLO) panel of the 100 ampere or so variety and
supply it from the load terminals of the enclosed switch. The panel you
buy should have six to twelve slots in it for single pole breakers
depending on what you anticipate your future electrical needs to be in
the garage. Remove the wires that go from the line terminals of the
switch to the other fuse panel. Demolish that panel and install your
new MLO panel in it's place. Remove the green bonding screw or metal
strap that came with the new panel. The white wire from the enclosed
switch will terminate on the neutral buss of the new panel. Install an
Equipment Grounding Conductor (EGC) buss bar in the new panel. Run a
green insulated or bare EGC from the enclosed switch to the new panel
and terminate it on the EGC buss bar. Since the supply feeder to the
garage is fused at forty amperes you can use a number ten wire as the
EGC. Rewire the existing circuits to your new panel. If the existing
circuits have EGCs than terminate them on the EGC buss bar.
Install a thirty ampere double pole breaker in your new panel. Run a 10
gauge, two conductor plus ground cable to an outlet box near the
location of the new heater. Terminate the cables two insulated
conductors that are not green to the dark or brass colored terminals of
the receptacle. Terminate the green or bare wire to the hexagonal
and/or green screw of the receptacle.
Actually the US NEC does permit the connection of an Equipment Grounding
Conductor (EGC) to a grounding electrode such as the first five feet
within the structure of an underground water pipe that has ten or more
feet in contact with the earth. The applicable section is quoted below.
VII. Methods of Equipment Grounding
250.130 Equipment Grounding Conductor Connections.
Equipment grounding conductor connections at the source of separately
derived systems shall be made in accordance with 250.30(A)(1). Equipment
grounding conductor connections at service equipment shall be made as
indicated in 250.130(A) or (B). For replacement of non-grounding-type
receptacles with grounding-type receptacles and for branch-circuit
extensions only in existing installations that do not have an equipment
grounding conductor in the branch circuit, connections shall be
permitted as indicated in 250.130(C).
(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions.
The equipment grounding conductor of a grounding-type receptacle or a
branch-circuit extension shall be permitted to be connected to any of
(1) Any accessible point on the grounding electrode system as described
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the
branch circuit for the receptacle or branch circuit originates
(4) For grounded systems, the grounded service conductor within the
service equipment enclosure
(5) For ungrounded systems, the grounding terminal bar within the
service equipment enclosure
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