Electricity reaches a house one of two ways, and which one is largely determined by when the neighbourhood was built.
Overhead
A service drop from a utility pole to a weatherhead at the top of a mast or riser on the house, down to the meter and into the panel.
Advantages: cheapest to install and to repair, faults are visible, and restoration after storm damage is quick.
Disadvantages: exposed to trees, ice and wind; visible; and the drop imposes clearance requirements over roofs, driveways and walkways that constrain where the mast can be.
Underground
Conductors in conduit from a transformer or a pole to the meter, buried at a required depth.
Advantages: not exposed to weather or vegetation, and not visible.
Disadvantages: expensive to install, harder and more expensive to locate and repair a fault, and vulnerable to excavation damage.
Where the responsibility divides
This varies by utility and it is worth establishing at the outset.
On an overhead service, the utility typically owns the drop up to the connection at the weatherhead. The mast, weatherhead, meter base and everything after are the homeowner's.
On an underground service, the split varies more. Some utilities own and maintain the buried conductors; others require the homeowner to provide and own the conduit and sometimes the conductors, with the utility making the connection at each end.
Converting overhead to underground
A substantial project: trenching from the pole or transformer to the house, conduit, conductors, a new meter location if required, restoration of whatever the trench crossed, and a utility agreement and often a charge.
Utilities frequently have a defined process and a published fee for it, and in some areas there is a queue.
It is not required by a service capacity upgrade. A 100 to 200 amp upgrade on an overhead service stays overhead, with a larger mast, weatherhead and conductors. Where a quote bundles a conversion with an upgrade, they are two decisions.
The mast on an upgrade
A larger service needs larger conductors, and a mast rated to carry the mechanical load of the drop.
Where the existing mast is undersized, corroded, or where the clearances no longer meet current requirements — over a roof, a driveway or a deck built since — the mast is replaced and sometimes relocated.
Mast height is set by the clearance the drop must maintain, and a mast extending well above the roof needs bracing.
Clearances that catch people
The drop has required clearances above roofs, above driveways and parking areas, above walkways, and horizontally from windows, doors, porches and decks.
Structures built after the service was installed are the usual cause of a violation: a deck added under a drop, a driveway regraded, a dormer built out toward it.
These are found at inspection and they can change the scope of an upgrade substantially.
Storm damage
If a drop is pulled off a house, the utility's part and the homeowner's part are usually damaged together.
The utility restores the drop; an electrician repairs the mast, weatherhead and meter base, and the utility will not reconnect until that work is inspected. Knowing the split in advance shortens the outage, because both calls can be made at once.
Which to choose on a new build
Underground where the developer or the lot arrangement provides for it, since the cost is far lower when the trench is open and nothing has been landscaped.
Retrofitting it later is the expensive version of the same decision.
Locating before digging
Any excavation near an underground service means calling the national locating service before work begins, and that applies to fence posts and tree planting as much as to trenching.
An underground service struck by a shovel is a serious hazard and an expensive repair, and the locate is free.