Meter Socket Guide: 4-Jaw vs 13-Terminal, Ringless Bases and NEMA 3R
The socket is the part the utility will not let you get wrong
Distribution equipment is usually chosen by the contractor, but the meter socket sits in the middle of a handover: you install and wire it, the utility seals it, and from that day the enclosure belongs to a metering system someone else owns. That is why a socket is bought on compatibility and shape rather than on price alone — a mismatch is discovered at the connection appointment, with the service already pulled.
What a socket actually does
A meter socket — often called a meter base — is a sheet-steel enclosure holding a set of spring jaws that the meter's blades plug into, and terminals where the service and load conductors land. It provides mechanical support, the electrical interface, and a sealed volume the utility can lock. Everything else is configuration.
It is not a meter box. An enclosure protects a meter that is mounted inside it; a socket is the mounting and connection interface the meter plugs into directly.
Jaw and terminal configurations
| Configuration | Typical service | What it gives you |
|---|---|---|
| 4-jaw | Single-phase three-wire | Two line terminals and a neutral; the standard residential and light-commercial interface |
| 13-terminal | Single-phase with additional terminations | Extra terminal positions for a fifth terminal / neutral arrangement and easier landing of multiple conductors |
The YOMIN range publishes both ends of that split: YM-20-13J-RL as a 125 A, 600 V, 13-terminal ringless socket with a plunger-type auto-close mechanism, and YM-320-4J as a 320 A, 600 V AC, 4-jaw ringless socket with a heavy-duty tinned lever.
Ring, ringless and the operating mechanism
"Ringless" describes the cover: the meter plugs straight into the jaws through an opening in the cover with no separate retaining ring. It is quicker for the utility to work on and one less loose part on site. The mechanism matters just as much:
- Plunger type (auto-close) — the jaws close as the meter is inserted, so there is nothing to set by hand. This is the published arrangement on the 125 A socket.
- Heavy-duty lever — a lever is thrown to open or close the connection, which is easier to operate with gloves on and better suited to heavier conductors. This is the published arrangement on the 320 A socket.
Choosing 125 A or 320 A
The rating follows the service, not the panel. A 125 A socket suits a typical single-family or small commercial service where the utility fuse or breaker upstream matches it. A 320 A socket is used on larger single-phase services — larger dwellings, small commercial units, multi-panel installations on one service — where the utility is metering a heavier service through one socket. Never pick a socket above the upstream protection simply because it is available; the socket rating and the service protection have to be coordinated.
NEMA 3R and enclosure construction
NEMA 3R is an outdoor enclosure rating: rain, sleet and snow, with the enclosure arranged to drain. Both YOMIN sockets publish NEMA 3R and are built from galvanised steel to AISI G90 — 1.2 / 1.5 mm on the 125 A unit and 1.5 mm on the 320 A unit — with an epoxy-baked grey powder finish. In practice that means:
- Mount it with the hub or openings down so water cannot track in.
- Use the correct hub for the mast or conduit, and seal it.
- Do not drill additional openings in the enclosure — every hole is a new water path.
Dimensions and feed direction
| Model | Rating | Jaws / terminals | Dimensions (mm) |
|---|---|---|---|
| YM-20-13J-RL | 125 A, 600 V | 13-terminal, ringless, self-grounding | 355 × 203 × 84 |
| YM-320-4J | 320 A, 600 V AC | 4-jaw, ringless, tinned lever | 716 × 332 × 132 |
The 320 A unit publishes both overhead and underground feed, which is the practical difference on site: an overhead feed enters through a mast hub on top, while an underground feed arrives through the base and the enclosure has to be set out to take it without stressing the conductors.
Installation checks that prevent call-backs
- Bending space. Service conductors are stiff. Leave enough conductor length inside the enclosure to land cleanly without forcing the termination.
- Grounding. Self-grounding construction on the 125 A unit means the enclosure ground path is provided as part of the assembly; still verify continuity before the utility arrives.
- Sealing. The utility seals the cover. Anything you need to check inside has to be checked before that seal goes on.
- Clearance. The socket has to be accessible for meter reading and replacement, with the working space an inspector expects.
Frequently asked questions
What is the difference between a meter socket and a meter box?
The socket is the mounting and connection interface the meter plugs into; the box is an enclosure that houses a meter and its associated equipment.
Ring or ringless — which do I order?
Because the utility will be working on it, follow the local utility's accepted configuration. Both YOMIN sockets are published as ringless.
Can a 125 A socket be used on a 200 A service?
No. Match the socket rating to the service and its upstream protection.
Specifying meter sockets for a service upgrade?
Send us the service rating, the feed direction and your utility’s accepted configuration. YOMIN builds 125 A and 320 A NEMA 3R meter sockets in galvanised steel to AISI G90.
Request a quote