Do all conduits need a bushing?

NEC 300.4(G) requires an insulating bushing or equivalent protection only where the raceway contains 4 AWG or larger insulated conductors, but many contractors install them on every raceway as standard practice.

Does a bonding bushing count as an insulating bushing?

Only if it has an insulated throat. A bare metal bonding bushing satisfies NEC 250.92(B) for bonding but not 300.4(G) for insulation protection.

Does the service mast require a bushing where it enters the meter socket?

Q: Can I attach a communications drop to the service mast?

No. NEC 230.28(A) permits only power service drop or overhead service conductors to be attached to a service mast.

Yes, in almost every case. Section 300.4(G) requires that where raceways contain 4 AWG or larger insulated circuit conductors and those conductors enter a cabinet, box, enclosure, or raceway, the conductors shall be protected by an identified fitting providing a smoothly rounded insulating surface, unless the raceway is provided with a fitting that gives equivalent protection. Service entrance conductors on a 100, 200, or 400 ampere residential service are 2 AWG or larger, so the rule applies.

The mast is a raceway like any other

People sometimes treat the service mast as a special case because it is on the line side of the service disconnect. It is not exempt. The mast is rigid metal conduit or intermediate metal conduit, the conductors are 4 AWG or larger, and they enter the meter socket enclosure. That is precisely the condition 300.4(G) describes. Install a plastic or metallic insulating bushing on the mast thread inside the meter can.

The purpose of the rule is mechanical. A cut conduit end or a bare thread will shave insulation off a conductor as it is pulled and will keep cutting into it every time the conductors move with thermal cycling or wind load on the mast. On a service, a failure there is a phase to enclosure fault with no upstream overcurrent protection.

Insulating bushing versus grounding bushing

Do not confuse the two rules. Section 300.4(G) is about protecting the conductor insulation and requires a smoothly rounded insulating surface. Section 250.92(B) is about bonding service raceways and enclosures, and requires bonding by one of the methods in 250.92(B)(1) through (4), which include threaded couplings and hubs made up wrenchtight, threadless couplings and connectors made up tight, and other listed devices such as bonding type locknuts and bushings.

A service mast threaded wrenchtight into a meter socket hub satisfies the bonding requirement through the threaded connection. It does not satisfy the insulating bushing requirement. You still need the bushing on the conduit end inside the can, and where a bonding bushing is used it must have an insulated throat or a separate insulating bushing must be installed.

The other mast rules worth checking

Section 230.28(A) requires service masts used as supports to have raceway and fittings identified for use as a service mast, and prohibits hubs intended for use with a conduit that serves as a mast from having holes for anything other than the mast raceway. Only power service drop or overhead service conductors may be attached to a service mast.

Section 230.24(A) sets the clearance above roofs, generally 2.4 m, or 8 feet, with reductions to 900 mm, or 3 feet, for roofs with a slope of at least 100 mm in 300 mm, and a 450 mm, or 18 inch, allowance where not more than 1.8 m, or 6 feet, of overhead conductors pass over not more than 1.2 m, or 4 feet, of roof. Section 230.24(B) sets the vertical clearances above grade, from 3.0 m to 5.5 m depending on what is below.

Field takeaway

Put an insulating bushing on the mast inside the meter socket, and on every raceway carrying 4 AWG or larger into any enclosure. Bond the service raceway separately per 250.92(B). A wrenchtight hub handles bonding but never substitutes for the bushing.