If you're a GC and you ask clients what they would like to have
in their newly remodeled home, they'll probably mention things
like additional windows, granite counters, and new hardwood
floors. One item they are unlikely to ask for is a new
electrical service. But that doesn't mean they're not going to
notice if you fail to advise them to replace obsolete or
They might not notice right away, but eventually they will
— if breakers are always tripping, if there's
insufficient capacity to add a spa or major appliance, or if
their computer gets fried because the surge protector was
plugged into an improperly grounded circuit.
And they will definitely notice if someone gets electrocuted or
the house burns down.
Need to Replace
As an electrical contractor, my company works mostly on
existing buildings, and we never do anything without first
checking the service panel.
The existing service could be so old it's completely unsafe, or
it could be so close to capacity that adding any new loads
— even small ones — could push it over the brink.
Either condition would require a service change (see sidebar),
which nearly always means increasing the capacity of the
service in amperes, and if the house is really old, taking it
from 120 volts to 240 volts.
When to Change The
At the beginning of every job, the GC should consider
whether the service needs to be upgraded.
Adding loads. A major remodeling project
is likely to increase the loads on the electrical
system. If you add any heating or motor loads, you
should get the electrician to do a load calculation to
see if the existing service has sufficient
Outdated equipment. Old
three-wire (240-volt) 30-amp services are still around,
and we've run into a few two-wire (120-volt) ones, too.
We also encounter main disconnects with pull-out fuse
blocks in the main/range configuration. Many people
don't realize both fuse blocks must be removed to kill
all the power to the house.
By code, you must be able to kill the power with no
more than six movements of the hand — flipping
six breakers or switches, or pulling out six blocks. A
service with no main disconnect and six or more
breakers will need an upgrade if you add any new
circuits as part of the remodel — and all
remodels should add circuits.
Sometimes the existing service has plenty of capacity,
but the branch circuits are fused. There's nothing
inherently unsafe about screw-in fuses; the problem is
that homeowners or tenants can create a hazard by
installing oversized fuses.
Faulty equipment. Another
reason for a service change can be the three letters on
the existing service: FPE, or Federal Pacific Electric.
This company used to produce Stab-Lok panels, which are
often found in homes built in the 1950s and '60s. The
breakers that fit these panels (both the original and
the aftermarket breakers) frequently fail, which can
result in house fires or electrical shock.
The "service" refers to all of the equipment between the
utility splice and the main means of disconnecting power to the
house — including the neutral bus and the grounding
electrode system (see illustration).
Changing the service involves removing the old meter socket,
the main disconnect, and often some distribution equipment,
such as a fuse or breaker panel. This is followed by the
installation of a new meter-main, which is a single metal
enclosure containing a utility pull section, a meter socket, a
main disconnect, and — in most cases — a
In areas with above-ground power lines, the service drop is a
twisted triplex cable that runs between the power lines and the
house. It ends in a utility splice at the weatherhead, a
helmetlike cover on top of a conduit. The wires on the house
side of the splice — called service conductors —
travel through a service conduit to the meter socket.
On older homes, the meter socket is in a separate enclosure,
but on newer homes it's usually in the main panel.
In areas where the power lines are buried, there is a service
lateral — an underground feed — running to the pull
section of the meter-main.
The Local Utility
The NEC (National Electric Code) has a very specific set of
requirements for the service. But strict as those requirements
are, the utility's rules are often even more stringent.
For example, whereas the NEC allows the use of exposed service
entrance cable and EMT for the service conductors, our utility
requires 1 1/4-inch or larger rigid metallic conduit.
Utilities also have rules governing allowable distances from
doors, operable windows, metal gutters, communications drops,
gas service, and metal railings. In addition, they prescribe
the height of the service drop above walkways, stair landings,
and other areas of pedestrian access; higher clearances are
required over driveways and streets.
It's important to understand what the utility expects. If
there's anything unusual about the installation, we get a
service rep to come out and approve the plan in advance.
The last thing we want is to complete an installation and have
the utility people refuse to hook it up because they interpret
the regulations differently than we do.
A Case in Point
Most of the photos in this story are from a project in which
we replaced the original service on a house built in the 1920s.
The drop contained three wires, but only two (a neutral and a
hot) were connected, so the service was 120 volts rather than
the usual 240 volts (a neutral and two hots).
This type of service is archaic but not uncommon in the older
homes in our area. We replaced it because it was of
insufficient capacity and was clearly unsafe (see Figure 1):
Live metal parts were exposed in a ground-level outdoor wooden
enclosure. A curious child could have opened the door and
touched something live, and even an adult would risk
electrocution by changing a fuse in the rain.
Figure 1.The author's company
was hired to replace this original 1920s electrical service; it
posed a hazard because it was old, undersized, not grounded,
and in an outdoor ground-level wooden enclosure next to the
driveway (top). The service drop was connected to knob-and-tube
wiring, which entered the building through holes in the wall.
One of the hots was bent back and not connected (bottom), so
the house had only two-wire 120-volt service.
Most of the wiring was knob-and-tube. The entire house ran on
two 20-amp circuits that, given the age of the wiring, should
have been fused at 15 amps. They were actually fused at 30
amps; it's a wonder the house hadn't burned down.
Locating the New Service
The old service was on the side of the house next to a narrow
driveway, but we couldn't put the new service there because
there wasn't room to install protective bollards (3-inch steel
pipes set in concrete) in front of the equipment, as required
by the utility.
Instead, we decided to install the new service on the opposite
side of the house; a utility pole was nearby and the exterior
wall was far enough in from the property line to give us 36
inches (the code minimum) of clearance in front of the
equipment (Figure 2).
Figure 2. An electrician verifies that
there will be the required 36 inches of clearance in front of
the new panel within the property line.
Also, there was enough room under an existing window for us to
install the panel and still comply with the utility's
requirement that the centerline of the meter be no lower than
36 inches and no higher than 75 inches above grade.
We used a standard meter-main with distribution — a
metal enclosure containing a meter socket, a main disconnect,
and buses for branch circuit breakers. The plan was to bring
the service conduit in from above and take conduit for the
branch circuits out the bottom and into the crawlspace.
Mounting the panel. Since the equipment is heavy and supports
a length of steel conduit, it's critical that the panel be
solidly attached to framing members — not just siding. We
typically fasten panels with 3/8-inch-by-3-inch lags or Simpson
SDS structural screws. If the holes in the panel don't line up
with framing, we drill new ones.
To prevent water intrusion, we run a bead of quality caulk
across the top of the enclosure and down both sides.
Service Conduit Clearance
The service drop for this particular project could not hang
over the neighbor's yard, so the periscope (the part of the
mast above the roof) had to be at the front corner of the
building (Figure 3).
Figure 3. With the new meter-main firmly
bolted to framing, the electrician installs a vertical section
of the service conduit (top). To avoid running the service drop
over the neighbor's property, it was necessary to run the
conduit to the front corner of the building before turning it
up and passing it through the roof overhang
To get the conduit there, we ran it up from the panel, turned
it 90 degrees toward the street, then turned it 90 degrees up
before passing it through the eaves. We extended the conduit 24
inches above the roof; if we had needed more clearance for the
drop, we'd have made it higher.
In areas of pedestrian-only access, the NEC requires 10 feet
of clearance between the drip loop and grade; our local utility
requires 12 feet. If it's possible to meet this height
requirement without penetrating the eaves, we extend the
horizontal run of the service conduit about 18 inches past the
building corner and install the weatherhead there.
In this case, we needed the height, so we penetrated the eaves
and installed a roof jack over the conduit to prevent the hole
from leaking. The utility required us to fasten the conduit to
the wall within 3 feet of the hub at the top of the enclosure,
once every 10 feet after that, and twice where it left the
building wall. To clear a piece of trim, we spaced the service
mast — conduit — off the wall by installing it over
pieces of Unistrut.
Once the panel and service conduit were in, we pulled the
service conductors into the conduit. Since this was a 125-amp
service, we used 1 1/4-inch conduit and #2 THHN (thermoplastic
high-heat-resistant nylon-coated) copper conductors.
Copper vs. aluminum. The electrical code allows us to use
aluminum service conductors, but we always use copper because
it's more reliable.
Aluminum has more resistance than copper, and it also tends to
oxidize, which creates even more resistance at connections.
When the flow of current encounters resistance, the wire heats
up and expands. When the flow drops, the wire cools and
contracts. Over time, this activity stresses the connections
between the service conductors and the lugs on the panel
— sometimes enough to loosen them.
Applying an antioxidant compound to the connections can
mitigate the problem, but in my view the added cost of using
copper service conductors is a small price to pay to avoid
Color-coding. Before pulling the wires, we typically mark them
at each end with color-coded tape.
In a single-phase service, the phase legs are black and red;
the neutral is always white. And when we install the wire, we
leave enough extra at the weatherhead for the utility to form a
drip loop and make the service splice.
Inside the panel, the hots terminate at the upper — or
line side — lugs of the meter socket, and the neutral at
its own lug (Figure 4).
Figure 4. Gravity makes it easier to
"pull" service conductors (top) by pushing them into the
conduit from above. The electrician uses colored tape to
color-code conductors so the utility knows which two to connect
to the hots and which one to connect to the neutral (bottom
left). Once the conductors are in the meter-main, the
electrician connects the hots (red/black) to the line-side
lugs, and the neutral (white) to a lug that ties to the neutral
bus in the distribution section (bottom right).
Our next step was to build the grounding electrode system,
which consisted of a copper ground rod wired to the service
main and water line (Figure 5). Although we're allowed to use
1/2-inch rod, we use 5/8-inch rod because it's less likely to
bend when we drive it.
Figure 5. The electrician uses a rotary
hammer with a ground-rod-driving attachment to drive a
grounding rod into the soil (first). He then runs a single
grounding wire that connects to a clamp on the water main
(second), an acorn clamp on the ground rod (third), a lay-in
lug on the grounding bushing on the conduit to the loads (not
shown), and the neutral bus in the main service
The rod is driven into the earth near the panel and is
supposed to go 8 feet deep. In some jurisdictions we're
required to drive two rods 6 feet apart. We always add a second
rod if we hit something and have to drive the first one at an
The grounding electrode conductor is #6 bare copper wire. It
should run as a continuous single piece (no splices), and it
should connect to the following items:
• the neutral bus in the panel;
• a lay-in lug on the grounding bushing on the conduit
that goes to loads;
• an acorn clamp on the ground rod;
• a ground clamp on the water main located within 5 feet
of where the pipe enters the house.
By code we're required to bond the water pipes in the house to
the gas pipe. This creates a larger grounding system and
ensures that any existing circuits mistakenly "grounded" to a
gas pipe are connected to something that actually is grounded
Figure 6. If the house has a gas line,
the water pipes must be bonded to it. This is usually done at
the water heater because both pipes are accessible there. A
single length of grounding wire is connected to clamps on the
water lines into and out of the heater (left), then to a clamp
on the gas line. The electrician installs a grounding clamp on
the gas line (right) after scraping off paint to ensure
We normally bond the gas and water pipes at the water heater
(if it's gas) because all of the pipes are accessible
The wire runs between the gas line and the water lines at the
heater; it's necessary to connect to both the cold-water inlet
and the hot-water outlet, because if dielectric unions were
used, the pipes downstream from the water heater might not be
Before shutting down power, transferring loads, and demoing
the old service, it's critical to check the existing circuits.
If something isn't working, we want to know about it before
making any changes; that way, it's clear we didn't cause the
We also want to find out which wires are neutrals. Wires often
aren't color-coded in old knob-and-tube systems, so when we
find the neutrals, we mark them white. If we forget to identify
them and accidentally hook up a hot and a white (120-volt) as
two hots (240-volt), we could fry whatever is plugged into that
When changing out an old 240-volt service, we mark the phases
black and red, based on testing before we shut off the power.
Never rely on somebody else's colors. That person could have
run a black to a red phase on a multiwire circuit. If, at the
new panel, you connect both of them to the black phase, you
could be loading the shared neutral with twice as much current
as it can handle — which could torch the house.
Transferring Existing Loads
This house had only a couple of circuits, so when we removed
the original service we were able to reroute the wires from the
existing loads to a junction box inside the crawlspace. There
we connected them to Romex, then ran the Romex to the other
side of the house and fed it through a conduit into the service
panel (Figure 7).
Figure 7. The electrician transfers the existing
loads by disconnecting the knob-and-tube wiring from the fuse
"panel" and running it to a junction box in the crawlspace,
where it's connected to Romex (top). From there, the Romex runs
to the other side of the house, exits the wall through a piece
of conduit, and enters the bottom of the service panel
Since both circuits served more than one room and included
bedrooms, we wired them to AFCI (arc fault circuit interrupter)
breakers, which we then installed in the distribution section
of the panel. Eventually, more circuits will be added, and only
the bedroom circuits will be on AFCI breakers.
If we had been replacing a newer service — one with a
metal enclosure — we would have stripped out the interior
and treated it like a giant junction box. We would have run
Romex between breakers in the new panel and existing loads in
the old enclosure.
Once the old loads were transferred to the new panel and we'd
labeled the panel to indicate which rooms the circuits served,
we reinstalled the cover and called for an inspection.
Sometimes, if we're lucky, we can get the utility people to
show up, install the meter, and reconnect the house on the day
we call (Figure 8).
Figure 8. Once the loads have been
transferred to the new panel, the electrician labels the
circuits (top) and installs the cover. Since the house was
occupied and it was going to be some time before the utility
could show up and make the final connection, the author's crew
supplied temporary power by running Romex between the existing
service drop and the new service conductors (middle). Later,
the utility came out, removed the jumpers and existing service
drop, and connected the new service drop (bottom).
But often it's difficult to make this happen, so if the home
is occupied and the homeowners need the power interruption to
be short — they work from home, say, or have medical
equipment — we may leave the old service connected and
temporarily heat up the new one with a jumper. That way, we can
move branch circuits one at a time, which means the only one
that's off is the one we're working on.
We also might use a jumper to power the house until the
utility is able to show up and make the permanent connection.
Keep in mind, though, that not every utility will allow you to
install jumpers, because doing so requires connecting to a live
service drop.Peitsa Hirvonenis a licensed electrical
contractor and the owner of SESCO Electrical in Berkeley,