O/L Relays

No, not continuously. The heater element is designed to handle the max. range, that's t. It is DESIGNED to trip at that level, so why the heck would a manufacturer think it is going to see more? The fuse rating is based on the fuse clearing time for an instantaneous short circuit, NOT a continuous overload.

By the way, a 10% increase in your motor current will cut your motor life in half! Why the heck do you even bother having an OL relay if you are going to jump out the contacts? Find out why your motor is drawing too much current, or if the motor nameplate FLA is higher than 5A, get the right overload relay. In one way or another, you are setting yourself up for a fire!

Hi JRaef,

Thank you.

I am interested to know that whether the maximum current flow alllowed through main circuit of O/L relay is equal to its max. setting or more than that?

Also if single phasing happened inside the relay,if we reset it (within few seconds)will the NC and NO contacts of relay get reset or not?

By the way, in all these statements, I am referring only to bimetal thermal OL relays. Solid state OL relays are different.

_{"I am interested to know that whether the maximum current flow alllowed through main circuit of O/L relay is equal to its max. setting or more than that?"}

It is equal to its max. setting. The relay itself is usually sized for a particular range of contactor attachment so the power path components, other than the heater elements, may be sized for the maximum of that range, but in each size of trip range, the heater elements are ALSO part of the power path, so they will only be sized to carry the maximum of that particular setting.

_{"Also if single phasing happened inside the relay,if we reset it (within few seconds)will the NC and NO contacts of relay get reset or not?"}

OL relays are specifically required to NOT be capable of being reset until sufficient time has passed (dwell time) for the motor to cool down. Tripping on single phase is something that only bimetal IEC OL relays will do, but in the background, it is still a thermal trip function so the reset time dwell will be the same regardless of what caused the trip.

Thank you very much Mr. JRaef.

I have sent you the detailed problem happened to your mailbox.

Good answer JRaef

Also keep in mind that if a thermal overload is protecting a motor, it should be sized so that it can be adjusted (if the adjustable type is used) to 125% of the FLA.

OK dumb question here. Normally, the OL relay is sized for the motor starter (e.g., a size 1 contactor uses a size 1 OL relay) which is for a current range. The heaters are then purchased to work with the motor current, so that if it is exceeded, the heater coils trip the NC contact which trips off the motor starter contactor coil and stops the motor. You are not protecting the relay but the motor. Now the dumb question; were the correct heater coils purchased for the motor?

Or, I meant to add, are the motor bearings failing? This will cause an increase in motor current as will a mis-alignment with the driven load.

OK:

• Why is the <...5A...O/L relay/siemens bimetallic relay...> still there?
• If <...damage the relay...> is a concern, then why hasn't it been changed in favour of a replacement that has <...5.5A...> in its adjustment range?
• Why was the wrong relay installed in the first place?