Does a bigger meter raise the price per unit?

No — the per-unit rate depends on your customer class and units used, not meter size or phase count (MEA notes billing follows the amount of energy used; the “no separate 3-phase rate” point is on our 3-phase page). What changes is the one-off application fee and possibly the main-cable work — except that a 5(15) home on the free-50-units right should check the impact with 1129 first.

Can a 5(15) meter run a water heater?

Not advisable — a single 3,500 W heater draws about 15.9 A, which already hits a 5(15)'s whole-house 15 A ceiling; 4,500 W and up needs a 15(45) with the manufacturer-specified breaker and cable — the model-by-model table is on our water-heater page.

Can I install an EV charger on my existing 15(45)?

Light portable-cable charging of a small battery works (MEA cites ~6–8 h on 1-phase), but a 16–32 A continuous wall charger on top of house load usually outgrows a 15(45) — the options are a 30(100) single-phase upsize, a 3-phase switch, or a separate second meter for the EV, with the main cable recalculated by an electrician in every case.

Is electricity cheaper on 3-phase?

No — Thailand has no separate 3-phase tariff; the per-unit price is set by customer class and units. Three-phase buys you load capacity, load balancing and support for 3-phase equipment or larger solar — not a discount. Details are on our 3-phase cost page.

What documents, timeline and fee does a size change take?

The same document set as a new-meter application (ID card, house registration, proof of rights to the premises); the fee follows the new meter size, and timelines vary by area and outside-line work — the per-size fee table, full document list and official day counts are on our meter application page, or call 1130 (MEA) / 1129 (PEA).

Home Electricity Meters · MEA / PEA

Which Electricity Meter Size Do You Need? 5(15) / 15(45) / 30(100) A — How Much They Really Carry

Name: CapSolar
Address: 429/44 Sukhonthasawat Rd, Lat Phrao, Bangkok, 10230, TH
Telephone: +66 2 124 5414
Price range: $$$$

MEA/PEA home meters come in only a few standard sizes, but the questions people actually ask are “is 15(45) enough for three air-cons?”, “which main cable does it take?” and “does an EV charger mean 30(100) or 3-phase?”. This page answers with a size-vs-load table, a step-by-step way to sum your own load, the signals that it is time to upsize, and a short how-to (the full fees and paperwork live on the meter-application page).

8 min readLast updated: August 2026As of: Aug 2026 — sizes/rules per PEA-MEA manuals · loads are computed guidance

Almost every Thai home runs a single-phase 15(45) A meter — MEA calls it the standard residential size, upgradable to 30(100) as the load grows. The first number is the rated (normal) current and the bracketed number the maximum the meter carries — so 15(45) handles about 45 A ≈ 9.9 kW of simultaneous load at ~220 V, enough for 3–4 air-cons plus one water heater that are not all on at once. 5(15) suits a small room or house with no water heater, while 30(100) or 3-phase is the answer for a wall-mounted EV charger, a large house, many air-cons or 3-phase equipment (MEA guidance). Any size choice or change must be paired with a main cable and main breaker calculated by a licensed electrician to the EIT (วสท.) standard — the utility inspects the wiring before fitting the meter, every time.

How Many Air-Cons Can a 15(45) A Meter Carry?

Short answer: a home with 3–4 air-cons runs fine on 15(45) — as long as everything is not on at once. The limit is not the number of air-cons but the total current of what runs simultaneously, which must stay under the meter's 45 A ceiling. Approximate currents of the big loads (watts ÷ ~220 V; check each nameplate): 9,000 BTU AC ≈ 900 W ≈ 4.1 A · 12,000 BTU ≈ 1,200 W ≈ 5.5 A · 18,000 BTU ≈ 1,800 W ≈ 8.2 A (full AC table) · water heaters 3,500/4,500/6,000 W = 15.9/20.5/27.2 A per manufacturer specs (details).

Worked example (15(45) home, 3 air-cons): two 12,000 BTU + one 18,000 BTU running together = 5.5 + 5.5 + 8.2 ≈ 19 A, leaving ~26 A of headroom. Add a 4,500 W shower (+20.5 A) while all three run = ~40 A — close to the 45 A ceiling but workable; add a second heater or a high-power hob at the same time and you are over. That is why “three air-cons” is fine while “three air-cons + two simultaneous showers” is the point to think about upsizing.

Electricians' practice is to keep simultaneous load under roughly 80 % of the maximum (about 36 A on a 15(45)) to avoid nuisance breaker trips and heat build-up — that figure is a trade rule of thumb, not a utility rule, and a properly sized main breaker always trips before the meter's ceiling.

Which Main Cable Does a 15(45) A Meter Need?

The commonly used answer: copper THW/IEC01 main of at least 10 sq.mm (most trade tables use 10–16 sq.mm) with a matching standard main breaker. That figure comes from the main-cable preparation tables electricians use under Thailand's EIT (วสท.) electrical installation standard — it is not a utility announcement. The real size depends on the wiring method (open-air, conduit, buried), the distance from the pole to the house, and voltage drop — long runs need a step up. Common ranges for the other sizes: 5(15) ≈ 4–6 sq.mm copper · 30(100) ≈ 35–50 sq.mm (aluminium mains run one to two sizes larger than copper).

Two non-skippable points: (1) have a licensed electrician size and run the cable to the latest EIT tables — PEA's citizen manual states plainly that the applicant runs the main cable from the house to the pole, and indoor wiring must “follow the EIT standard or PEA's requirements”. (2) The utility inspects before energising, every case — if the main cable or main switch is under-sized for the requested meter, the inspection fails until it is fixed, so a meter-upsize budget must include the main cable and switchboard you may need to replace.

5(15) vs 15(45) vs 30(100): What the Numbers Mean

The A(B) format: A = rated (normal) current · B = the maximum current the meter carries. Standard home sizes per PEA's manual are 5(15), 15(45) and 30(100) A in both single- and three-phase (MEA also lists 50(150) and larger sizes for buildings). Approximate power is P = V × I at ~220 V per phase:

Home meter sizes, currents and approximate loads
Meter size	Rated / max current	Max load ≈ (kW)	Typical fit
5(15) A · 1-phase	5 / 15 A	≈ 3.3	Rooms/small houses, a few lights, one small AC — not suited to a water heater
15(45) A · 1-phase	15 / 45 A	≈ 9.9	The standard home size (MEA) — 3–4 ACs + one heater, not all on at once
30(100) A · 1-phase	30 / 100 A	≈ 22	Large/high-load homes, several heaters, or a wall-mounted EV charger
3-phase 15(45)–30(100) A	per phase 15–30 / 45–100 A	≈ 29.7+ (all three phases)	Very large homes, many ACs, multiple EV points or 3-phase equipment (MEA guidance)

Meter size does not change the price per unit — the tariff depends on your customer class and units (residential rate structure), and there is no separate “3-phase rate” (the 3-phase cost explainer). The kW column is P = V × I arithmetic for intuition, not an official utility spec — the size is printed on the meter's faceplate; see how to read your meter.

How to Sum Your Own Load and Know If the Meter Is Enough (4 Steps)

Use the same watt-summing method electricians use for a first pass — the result is your home's worst-case simultaneous current, ready to compare against the size table above:

List every high-power appliance
Write down the wattage from each nameplate: every AC, every water heater, hob/oven, microwave, kettle, washer-dryer, water pump, and the EV charger if any — small loads (lights, TV, fridge, fans) can be lumped at roughly 500–1,000 W.
Keep only what genuinely runs at once
Picture your real peak — early evening, say: 3 ACs + 1 shower + one kitchen appliance. Do not add every device in the house (no home runs them all at once), but be honest about habits: an EV charging overnight overlaps with bedroom ACs running all night.
Sum the watts, divide by ~220
Total current (A) ≈ simultaneous watts ÷ 220. Example: 2×1,200 + 1,800 + 4,500 + 1,000 (misc.) = 9,700 W ÷ 220 ≈ 44 A.
Compare with the meter's max — and leave headroom
If the result sits at the ceiling (say 44 of 45 A) or a big purchase is coming next year, plan the upsize now — and have an electrician confirm the existing main breaker and cable can carry it, since those two heat up or trip before the meter ever does.

When to Move Up to 30(100) — or to 3-Phase

The main breaker trips at peak times (early evening/morning) even though an electrician found no leak — the classic sign that simultaneous load hits the system's ceiling.

A wall-mounted EV charger is coming — home chargers draw a continuous 16–32 A per their spec, instantly claiming a big slice of a 15(45) (see the EV section below).

Adding another water heater or high-power appliance — one 4,500–6,000 W shower is 20–27 A; two at once nearly fill a 15(45) before a single AC is counted.

A big house/renovation with many ACs, or 3-phase equipment — MEA's guidance: large, high-demand homes and multi-EV households suit 3-phase (380–400 V, 4 wires), which spreads load across three phases and charges EVs faster (MEA cites ~6–8 h on 1-phase vs ~2–3 h on 3-phase) and carries rooftop solar beyond 10 kW versus ~5 kW on single-phase.

The per-unit rate gets neither cheaper nor dearer with meter size or phase count — what differs is the one-off fee and the main-cable work. The full “there is no 3-phase rate” explainer is at 3-phase electricity cost.

Does Home EV Charging Need a Bigger Meter?

It depends on how you charge: trickle-charging a small battery through a portable cable works on single-phase, MEA says, at roughly 6–8 hours. A real wall charger (typically 16–32 A continuous ≈ 3.7–7.4 kW per its spec) added to the existing house load usually outgrows a 15(45) — the common routes are upsizing to 30(100) single-phase or switching to 3-phase 15(45) (the same logic as MEA's 1-phase/3-phase guidance). MEA runs a dedicated “EV home supply” channel in MEA e-Service, and the other option is a separate second meter for the EV at the same house number (two-meters rules).

Overnight charging can get cheaper still with a TOU meter — whether it pays and how fast is worked out in is a TOU meter worth it for home EV charging (that page owns the TOU question; this one covers only meter size).

How a Meter Size Change Works (In Brief)

File a “meter size increase/decrease” with your utility: MEA via MEA e-Service or 1130 · PEA via the PEA Smart Plus app (its online-services menu explicitly lists meter size changes), the e-Service site or a local office. The sequence: request + documents → pay the fee for the new size → your electrician brings the main cable/switchboard up to the new size's standard → the utility inspects and swaps the meter. Documents, the per-size fee table and processing days are all on the meter application guide — and if your meter was just swapped to a digital one and the bill looks odd, read does a digital meter make bills higher.

Homes still on a 5(15) meter that enjoy the free-50-units right should know PEA's FAQ guideline ties that right to rate 1115, which it describes as “meter size 5(15) A” plus usage under 50 units for three straight months — confirm the impact with 1129 before upsizing (the full free-50-units conditions).

About the Author

Compiled by the CapSolar team under Frank Lee (Founder). CapSolar is a commercial & industrial solar EPC/PPA provider in Thailand that condenses meter, electrical-system and utility rules from official sources so households and businesses can make confident energy decisions.

FAQ

The 15 is the rated (normal) current, not a cap — a 15(45) is built to carry up to 45 A, so exceeding 15 A is normal use. What matters is not to park simultaneous load at the 45 A ceiling for long periods (electricians allow ~80 %), and to have a standard-sized main breaker and cable, which always trip before anything dangerous.

Meter Application: Cost & Steps

Per-size fees, documents and timelines.

3-Phase Electricity Cost

Why there is no 3-phase rate, and the fees.

Home EV Charging & TOU Meters

Cost per charge and the TOU payback.

Digital & Smart Meters

Is the bill really higher after the swap?

Factory-Scale Load? That Is Where Solar Starts to Pay

Homes think in amps; factories think in hundreds of kilowatts. If your building or factory pays tens or hundreds of thousands of baht a month, CapSolar assesses free from your actual bill how much an EPC or PPA system cuts your unit cost.

Free Consultationor call +66 2 124 5414