Rerlay amps setting for Star delta motor

ask the manufacturer regarding the allowable limits and consult with a experienced commissioning engineer. dont go just like that bcoz it may damage the motor if proper settings are not adopted. Or refer the relay manual , you may find some information.

Set the overload to the same setting as the full load current on the motor plate.

If the relay is in the main circuit, you need to set it to 51A. If it is within the delta (see diagram), you need to set it to 51÷√3 = 30A

Here we go again!

Where to put the overloads

see http://cr4.globalspec.com/thread/63668

As TonyS and kvsridhar have pointed out, there are several ways to configure the motor Over Load Relay when using a Star (Wye) Delta motor starter. Their illustrations show 3 different valid connection diagrams. Depending on how yours is set up, the selection of the OLR settings will either be 100% of the motor FLC or 58% of the motor FLA. Only you can determine which one you have, and to do so you will need to observe and understand the OLR location in your connection pattern. If this is beyond your capabilities, please consult a professional in your area who can understand it. The ramifications of getting it wrong could be disastrous.

u have not mentioned the application of motor

i suggest to set the relay setting greater than 4 or 5 amps of it normal running ampers

i.e., if normal running ampers is 35A it is beter to set relay at 40A

Relay must be set to actual current, not higher ! Please do not give wrong advice, it can be dangerous.

i have explained it taking the condation that the motor is drawing current less than the rated current while running on load. if it is running by drawing full load current in normal load condation it is good to set relay setting to rated current setting of motor

The main thing is ... a 10HP motor can indefinitely take the appropriate current, say 16A. Any overcurrent beyond 16A is detrimental to the motor, but any current upto and including 16A is not. So, even if the load is 7.5HP, you can set it to to 10HP (16A). NOT higher than this.

Having had to tackle a motor fire after some fool upped the O/L's I will always set the relay to the motor rated current.

If you need to raise the O/L settings the motor isn't big enough!

It's only common sense!

TonyS,

Methinks, after parsing the statemenst in post 6 & 7 (and applying my experiences in this forum) that they are under this very common mistaken belief that motor OL protection should be set for the LOAD current, not the motor FLC from the nameplate, which hopefully also meant "as long as the load current is blow the FLC rating of the motor".

You and I know differently, but I have discovered that this is an all too common practice. I guess people think it provides closer protection? I don't really know why they do it though. Personally I would never do that because it just sets the system up for nuisance tripping, and repeated nuisances like that cause people (fools) to do things like set them TOO high and smoke the motors, as you experienced.

It keeps motor rewind shops in business though, maybe they are the ones surreptitiously planting that information!