Overload relay symbol: one device, two places on the print

Most overload calls I get start the same way. Somebody has the print open, the motor won't start, and they've found the overload relay symbol on the power page: three little curls under the contactor. What they can't find is the part that actually stops the motor. They're looking at the wrong half.

An overload relay symbol is never one picture. The relay is one device in the panel, but the print splits it in two. The thermal elements go in the power circuit with the motor leads, and the trip contact goes in the control circuit with the contactor coil, usually on another rung, sometimes on another sheet. Below is how both halves look on NEMA and IEC prints, where they tend to land, and the lookalikes that send people after the wrong part.

Where the overload relay symbol shows up on a motor print

Start on the power side. Three phases come down through the fuses or breaker, through the contactor's main contacts, then through the overload relay before they leave as T1, T2 and T3. That's where the thermal elements sit, one per phase, each in series with a motor lead and carrying full motor current. On a NEMA print each one is a curl or a step in the conductor. IEC boxes all three poles in one rectangle and runs a stepped line through each.

The control circuit is where the overload relay symbol actually does something. There it's just a normally closed contact, 95-96, in series with the contactor coil. The thermal elements never open the motor circuit themselves. They heat up, the mechanism trips, 95-96 opens, the coil drops out, and the contactor takes the motor off the line.

Then there's 97-98. Normally open, closes on a trip, and goes to a pilot light or a PLC input, so on a PLC panel the same relay turns up a third time, on the I/O sheet. They're separate contacts, which means they can serve two different circuits: the coil circuit on one, a PLC input on the other. Setting the dial, trip classes and the H/A reset switch are their own topic, I went through them in a separate article on thermal overload relays.

The overload relay symbol in all three places it lands: thermal elements in the motor leads, 95-96 in the coil rung, 97-98 on a PLC input.

 

Nothing on paper connects those pieces except the device tag and the terminal numbers. Inside the relay it's one mechanism. IEC even has a name for drawing a contact away from whatever operates it, detached representation, and practically every control circuit is drawn that way. Put the coil rung next to the motor leads and nobody could read the print.

Overload relay symbol shapes: NEMA vs IEC

NEMA prints use two shapes for a thermal element, a curl in the line or a squared step that looks like a sideways bracket. Same meaning either way. IEC goes with a rectangle crossed by a stepped line. The stepped line is IEC's general mark for thermal effect. It isn't reserved for overloads, and that comes back later.

Watch the zigzag. A zigzag across the line on a NEMA print is a magnetic overload element, not a heater at all. IEC writes that one as a box with I> inside.

Part of the relay	NEMA print	IEC print	Where it sits
Thermal element (heater, bimetal)	A curl in the conductor, or a squared step, one per phase	Rectangle with a stepped line, one step per pole (IEC 60617 S00325)	Power circuit, between the contactor and the motor
Magnetic overload element	Zigzag across the conductor	Rectangle with I> inside	Power circuit
Trip contact	Normally closed contact tagged OL	Normally closed contact marked 95-96, small stepped mark beside it	Control circuit, in series with the contactor coil
Signal contact	Normally open contact, same tag	Normally open contact marked 97-98	Pilot light or PLC input
Main poles	Usually just T1, T2, T3 on the motor side	1/L1-2/T1, 3/L2-4/T2, 5/L3-6/T3	Power circuit
Electronic overload	Can be drawn with the same curls as a thermal relay, with both contacts inside one dashed outline	Same layout. IEC 60617 also has a separate symbol for a static thermal overload relay (S00381)	Same places

The overload relay symbol by drawing standard: what each part looks like and where it sits.

Overload relay symbol shapes side by side. On a NEMA print the zigzag is a magnetic element, not a heater.

 

Manufacturer internal diagrams add one more layer. A Siemens 3RU21 is drawn as three stepped elements in a box, a dashed line running from them to 95-96 and 97-98, and short dashed stubs for TEST, RESET and STOP. Dashed means mechanical. No current flows along that line. Electronic overloads like an Allen-Bradley E1 Plus or a Siemens 3RB30 get nearly the same picture, which is fine. On the print they do the same job.

Which side of the coil the OL contact goes on

On a NEMA ladder the OL contact usually ends up at the right end of the rung, after the coil, right before the L2 rail. An IEC control circuit drawn top to bottom tends to flip it: 95-96 near the top, straight off the supply, then STOP (21-22), START (13-14) with the M1 seal-in beside it, and the coil, A1-A2, at the bottom.

Neither one is a rule. What matters is that 95-96 is in series with the coil. Which side it sits on is just how that particular print got drawn, so go by the print in front of you, not by a picture of somebody else's. I've traced plenty of panels with the contact on the "wrong" side that worked exactly as designed.

Say the contactor won't pull in. Find the coil on the print, follow the rung both ways until you hit the overload relay symbol, and meter across 95-96 while START is held or the PLC is calling for the motor. Full control voltage across it means it's open: the relay tripped, or the contact itself is bad. Close to zero, and your problem is somewhere else in the rung.

How a PLC print shows the overload relay symbol

On a PLC panel the overload relay symbol often appears that third time, on the input card page, as 97-98 feeding an input. Same tag as the heaters and the coil contact.

What I check on those prints is which contact actually comes back to the PLC. A lot of panels only wire an auxiliary contact off the contactor, 13-14 or similar. That tells the PLC the contactor is pulled in. Why it dropped out, or whether the motor is really running on three phases, it can't say.

Situation	Contactor auxiliary (13-14)	Overload 97-98
Running normally	Closed	Open
Stopped by command	Open	Open
Overload tripped	Open	Closed
One power fuse blown, contactor still in	Closed	Open, unless the overload trips on the lost phase

What the PLC sees from each contact.

The overload row is why I want 97-98 on an input. Without it, a trip, a failed coil and a blown control fuse all look the same to the program: command on, feedback off. The last row is the nasty one. Contactor in, auxiliary says running, motor single-phasing. Feedback from the contactor is not feedback from the motor.

Lookalikes that aren't overloads

Symbol	NEMA	IEC	How to tell it from an overload
Fuse	Rectangle with the conductor running straight through	Rectangle with the line running through it	Straight line inside, no step, no curl
Resistor	Empty rectangle	Empty rectangle	Nothing inside the box
Contactor coil	Circle with the tag inside	Rectangle marked A1 and A2	Control circuit only. It's the coil 95-96 drops out
Current transformer	Loops drawn beside a straight conductor	Circle with the conductor running through it	The loops sit next to the line. A heater curl is the line itself
Thermal-magnetic breaker	Arc on each pole plus a squared step	Contact with an x on each pole	The step belongs to the breaker. Look for the arc
Temperature or thermal switch	Contact with a stepped actuator under it	Contact linked by a dashed line to a box with Θ, or, for a self-operating bimetal switch, a contact with the thermal step attached	A contact worked by temperature, with nothing in the motor leads

Symbols that get mistaken for an overload relay symbol, and how to tell them apart.

Two of these cost real money. The breaker first: a thermal-magnetic breaker on a NEMA print already carries its own step on every pole. Read that step as heaters and you'll go hunting for an overload relay the panel never had.

The other is the thermal switch, the bimetal that opens from its own heat inside a motor winding or a small control transformer. It's only a contact. IEC gives that self-operating thermal switch its own symbol, S00265, separate from the overload contact, but both can carry the same thermal-effect step, which is exactly why they get mixed up. Quick test: an overload contact has a matching element in the motor leads with the same tag. A thermal switch doesn't.

Prints that look wrong but aren't

A single-phase motor on a three-pole overload is drawn with the motor current run through all three elements in series, with a jumper carrying it from one pole into the next. That's on purpose. Don't "fix" it.

Mixed prints are the other one. A machine built in Europe and serviced in the US ends up with IEC terminal numbers next to NEMA curls, or a European relay redrawn in NEMA symbols. If the print gives you 95-96 and 97-98, trust the numbers over the shapes. Plenty of NEMA prints skip numbers and just tag the contact OL, and then the tag is all you get.

One check I run on every print I don't know: find both halves of the overload relay symbol, heaters first, then the contact. If either half is missing, the print is incomplete or the protection was never wired. I want to know which one before that motor runs again.

Overload relay symbol questions

What is the overload relay symbol?

Two symbols for one device. Thermal elements sit in the power circuit, one per motor lead, and a normally closed contact, 95-96, sits in the control circuit in series with the contactor coil. NEMA draws the element as a curl or a squared step, IEC as a rectangle with a stepped line.

Is the zigzag in an overload relay symbol the heater?

No. On a NEMA print a zigzag is a magnetic overload element. The thermal element is the curl or the squared step.

What is the symbol of a relay, and how is an overload relay different?

A control relay shows up as a coil, a circle on NEMA prints or a rectangle on IEC, plus the contacts it operates. A thermal overload relay has no coil on the print. Its thermal elements in the motor leads do the operating, so look for them in the power circuit.

Why is the OL contact after the coil on my print?

Because that's how NEMA ladders are usually drawn. The contact has to be in series with the coil, and which side it lands on depends on the print. IEC drawings often put 95-96 at the top instead.

How do I reset an overload relay?

Let it cool first. A thermal relay won't reset until its bimetals have cooled down. On manual, press the reset button, usually the blue one. On automatic it resets by itself, and with a maintained run command the motor can restart right away, so check the mode before anyone goes near the machine.

Ordering the relay behind the overload relay symbol

Once the overload relay symbol on the print is matched to the part in the panel, read the catalog number off the side of the relay and send it over. IQElectro keeps surplus overloads in stock: Schneider TeSys D LRD08 (2.5-4 A), LRD10 (4-6 A) and LRD16 (9-13 A), TeSys K LR2K0312 (3.7-5.5 A) and LR2K0314 (5.5-8 A), the Eaton C306DN3B, and for older Allen-Bradley NEMA starters the 42185-800-01 for Size 0-1, plus Type W heater elements like the W68 (38.5-51 A), which is the actual part that NEMA curl stands for. Everything ships with a two-year warranty, and we'll confirm the match before you order.