240 V receptacle wiring diagram

Light: on

Both legs are live — the load sees the voltage between them, and the breaker opens both at once. There is no neutral in this three-wire load. The copper highlight is the live loop, not a wire colour.

A 240 V load sits across two live legs, not between a hot and a neutral. Each leg is an ungrounded conductor; the load sees the voltage between them. A bonding conductor is there for safety, and a two-pole breaker opens both legs at once. In this three-wire arrangement there is no neutral at all.

Trace it yourself

Do this one twice: once from line 1, once from line 2. Both traces should reach the load, because both are live.

Find the panel on the left. Two conductors leave it through the two-pole breaker, one at the top and one at the bottom. Both blades are closed. Finger on line 1.
Through the upper blade, along line 1 to the receptacle's upper terminal, into the load. Cross the load.
Out of the load onto line 2, back along it, through the lower blade, to the panel. Loop closed — and you never touched a neutral. There is none.
Now look at the bond, the thin line along the bottom. It runs from the panel to the receptacle's metal and stops. It does not enter the load. In a healthy circuit it carries nothing.
Open the breaker. Both blades lift together, because the handle is ganged. Your finger stops at the panel on either leg. Now the whole run is dead — both terminals at the receptacle, not just one.

How this circuit works

Current leaves on one leg, passes through the load, and returns on the other leg. There is no third current-carrying wire to make it work — the two legs are the whole circuit. Because both are live, both have to be switched, which is what the ganged two-pole breaker is for. Open it and watch the entire loop go cold in the diagram.

Where a neutral does appear on a 240 V circuit, it is because the appliance has 120 V controls or accessories inside it, and that is the four-wire case. The pure heating or motor load shown here needs only the two legs and the bond.

What goes wrong

1. Only one leg opens

Symptom: the appliance is off, the breaker looks tripped, and one terminal at the receptacle is still live.

Two single-pole breakers side by side with no tie, or a two-pole with one pole gone bad: open just the upper blade in your head. Line 1 is dead, so the loop is broken and the load stops. But line 2 is still fed straight from the panel to the receptacle — its terminal sits at line potential with the appliance apparently off. The load is off; the outlet is not dead. That is the whole reason the breaker is ganged: on a load with two live legs, "off" has to mean both.

2. Metering it like a 120 V circuit

Symptom: you read from one terminal to the bond, get half the number you expected, and report the circuit as wrong.

On a hot-and-neutral circuit, hot to ground tells you the supply voltage. Here there is no neutral, and each leg is a hot: leg to bond reads each leg's own voltage to ground, which is half of what the load sees. The load sees the voltage between the legs, and that is the only place to measure it. Trace the loop again — the bond is not part of it. A reading that is half of what the nameplate says is usually the meter on the wrong pair of points, not a bad supply.

3. The bond used as a neutral

Symptom: the appliance's controls work, and the bonding conductor is carrying current all the time.

Some appliances have 120 V parts inside — a clock, a light, a control board — that need a neutral. That is the four-wire case. Land those parts on the bond instead and trace it: their return current now flows along the bonding conductor, through the receptacle's metal, through every bonded box and the panel on the way home. The bond was drawn as a conductor that carries nothing until a fault; now it carries load current by design, and every piece of bonded metal in the path is part of a working circuit. Physics does not object. Everything about safety does.

Sur le chantier

Two live legs changes your habits, not just your wiring. Everything you do on a 120 V circuit by reflex — test one conductor, open one breaker, measure to the bond — has to be done twice here, and the meter has to go between the legs rather than from a leg to anything else.

Common mistakes

Two single-pole breakers with no tie. One handle leaves the other leg fed straight from the panel to the receptacle. The load is off; the outlet is not dead.
Carrying an old arrangement over to a new circuit by habit. Three-wire and four-wire arrangements are not interchangeable, and what is permitted for a new circuit versus an existing one is a question for the book, not for what the last one looked like.
Matching the receptacle to what is in the van instead of to the appliance's plug and its nameplate. The configuration is how the two agree on what circuit they are on.
Tightening a large terminal by wrist. Big conductors want the torque printed on the device's own label, applied with a torque driver, and a re-check after they have been carrying load.
Working one leg at a time. Prove both dead, and prove leg-to-leg dead as well. A single leg reading nothing to the bond tells you almost nothing here.

What the inspector looks for

That both legs open together — a genuine two-pole device or an approved handle tie, not two breakers and good intentions.
The conductor and the overcurrent device paired against the appliance's nameplate figures. You read those figures off the plate and out of the book; nobody should be guessing them.
The bond, and neutral and bond kept apart everywhere downstream of the panel.
The receptacle configuration matching the circuit it is on, not just the plug that happens to be nearby.
Box, support and — where a cord is used — the strain relief and the fitting the book calls for.

Check it before you call it done

Breaker off. Live-dead-live on leg 1, on leg 2, and between the two.
Land the two legs, the neutral if it is a four-wire circuit, and the bond. Torque every terminal to the device's own label.
Energise. Read leg to leg — that is the voltage the appliance actually sees, and it should match what the nameplate expects.
Read each leg to the bond, and expect the answer to belong to the supply rather than to the receptacle. A centre-tapped 120/240 service reads half the leg-to-leg figure on each leg. A wye system reads 120 V on each leg against 208 V leg to leg. A high-leg (centre-tapped) delta reads about 120 V on two legs and about 208 V on the high leg — that is the one with a high leg. A corner-grounded delta reads nothing at all on the bonded leg and full line voltage on the other. So neither the ratio nor both legs reading the same is a check that travels: on two of those systems a healthy circuit fails it, and on a corner-grounded delta a leg that reads zero to the bond is the normal one. What proves both legs are landed and fed is the leg-to-leg reading in step 3 together with the figures the supply you are on is supposed to give. If you do not know which system you are on, find that out before you judge the meter.
Read neutral to bond: nothing. Anything there means the return is carrying what it should not.
Open the breaker and re-read both legs. Both dead, on one handle movement. Only then plug the appliance in.

Questions fréquentes

Where is the neutral on a 240 V receptacle?

In a straight three-wire 240 V load there is no neutral — the load sits across two live legs, with a bonding conductor for safety. Some appliances also want a neutral for their 120 V controls, and those use a four-wire arrangement. The diagram shows the three-wire case: two legs and a bond.

Are both legs really hot?

Yes. Both legs are ungrounded conductors, each live with respect to ground. The load sees the voltage between them. That is why the diagram lights the whole loop in copper and why a two-pole breaker is used — you have to open both legs to make the load safe.

Why a two-pole breaker?

Because there are two hot legs feeding the load, and both must be disconnected together. A two-pole breaker ties its handles so throwing one throws both. Open it in the diagram and both legs go dead at once.

Voir aussi

Glossary: bonding vs grounding — what that third conductor does.
Contactor wiring diagram — switching larger loads with a coil.
All wiring diagrams

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