The 125 percent rule says the breaker for an EV charger is rated at 125% of the current the charger is set to deliver — because charging is a continuous load. On a written quote, the rule becomes a check any homeowner can run: compare the charger’s current with the breaker size the installer wrote down. If the pair does not fit, either the charger will be configured lower than its headline number, or the quote is wrong. Either is worth knowing before you sign.
Key Takeaways
- Your quote’s breaker should be 125% of the configured current: 32 A → 40 A, 40 A → 50 A, 48 A → 60 A.
- The installed setting is the current that counts — ask for it in writing.
- A smaller breaker is legitimate if the lower setting is disclosed — a problem when it is silent.
- Final sizing is the electrician’s call — the rule is for reading quotes.
The Rule in the Form You Need It
The pairings below are the whole tool; column three reads the rule backwards.
| Charger set to deliver | Breaker the rule requires | Reading it backwards |
|---|---|---|
| 32 A | 40 A | A 40 A breaker supports at most 32 A of charging |
| 40 A | 50 A | A 50 A breaker supports at most 40 A of charging |
| 48 A | 60 A | A 60 A breaker supports at most 48 A of charging |
Two details matter. First, the current that counts is the configured current: chargers are set to their circuit at installation, so a unit badged “up to 48 A” may be quoted, quite properly, at a lower setting. Second, the pairing says nothing about panel capacity — that check sits behind our panel capacity explainer.
Running the Check on a Real Quote
- Find the charger line: the model, and the current it will be set to. A model with no setting named is your first question — the headline maximum is not the installed figure.
- Find the breaker line. A complete quote names the new breaker size; none written down is itself a finding.
- Compare the pair: set current × 1.25 against the breaker, or breaker ÷ 1.25 against the setting. Either takes seconds.
- Get the delivered current in writing — the number you will actually charge at belongs on the quote, not in a conversation.
The Three Mismatch Patterns
| What the quote shows | What it usually means | What to ask |
|---|---|---|
| Breaker smaller than 125% of the charger’s headline current | The design fails the rule as drawn — or the charger will be set down to fit the breaker, and you will charge slower than the badge suggests | “What current will it be configured to — and can that go on the quote?” |
| Pairing matches, but the price is far below other quotes | The saving may sit in the setting — a smaller circuit, charger dialled down. Legitimate, if disclosed | “Is the lower price a smaller circuit and setting? What speed do I get?” |
| No breaker size or no setting stated | The line that decides the design is left vague, so quotes cannot be compared like for like | “Please itemise breaker size and configured current so I can compare quotes.” |
The electrician sizes the installation under the locally adopted code. The rule is a reading tool — it spots the quote that does not add up.
Chargers That Make the Setting the Story
The EVDANCE EV-ACS4005T 40A NACS portable charger offers 16, 24, 32 and 40 A settings at 9.6 kW, pairing with 20, 30, 40 and 50 A breakers under the rule — four circuits, four quotes, one charger. The EVDANCE EV-ACT5006T 48A Level 2 wall charger tops the table: at its full 48 A setting the quote should show a 60 A breaker. If it shows 50 A, the installed setting will be 40 A — the number to get in writing. Full range: our products page.
Frequently Asked Questions
My quote pairs a 40 A charger with a 40 A breaker. Problem?
As drawn, yes: 40 A of charging requires a 50 A breaker, or the charger set to 32 A on the 40 A breaker. Ask which the price assumes — both are legitimate, but they deliver different speeds.
Can a 48 A charger legitimately appear with a 50 A breaker?
Yes — with the charger configured to 40 A, sometimes the right call where panel capacity is tight. It is a problem only if you thought you were buying 48 A charging; hence the configured current on the quote.
Does a bigger breaker than the rule requires mean a better quote?
Not by itself: breaker, conductor and setting are designed as a set, and a larger breaker is sometimes future-proofing. Ask what the circuit is designed to carry, not which number is biggest.
Related Reading
- What Size Breaker Do I Need for an EV Charger?
- How Many Amps Does an EV Charger Need?
- What Size Wire Do You Need for an EV Charger?
- Can I Install a Level 2 Charger Myself?
