Setting up a motor protection relay for a medium voltage motor. 1

[bdn2004]

I'm looking through the classic book "Protective Relaying and Theory and Applications" (attached article). The attached chart is from that book. It says to set the required overload for 90% of the full load amps for a motor with a service factor of 1.0.?? This appears to me to violate the National Electric Code section 430-32 that requires it to be set at 115% FLA...

Can someone explain this?

 

[wroggent]

430-32 says "...shall be rated at no more than..."

You should be looking at 430-225 for medium voltage.

 

[bdn2004]

430.221 says this section on medium voltage "adds to or amends the other provisions of this article" (NEC 430). I take that to mean 430.32 still applies to all motors installations.

 

[JG2828]

I believe that 90% setting is specific to the ABB/Westinghouse BL-1 thermal overload relay, function 49.
It was written a little differently in the attached 1978 Silent Sentinels publication.

 

[bdn2004]

Thanks,

What does the term IT-2 mean? I'm looking at Eaton EMR-4000 MPR. It has this function 49/50. There's no other hardware needed
to sense this thermal condition besides the CT? This is the overload protection. The 50/51 relay apparently is for locked rotor protection.
This is what I gather from a similar example in the IEEE Red Book (attached). Seems like some conflicting info here.

 

[JG2828]

Here is the manual for the Westinghouse BL-1 relay.
IT-2 is short for Instantaneous Trip unit. The 2 means that the relay has 2 of them. They are separate from the thermal overload part of the relay which uses a Heater Unit within the relay to simulate motor temperature based on current previously applied to the relay.

https://library.e.abb.com/public/ee82e62302f68ec0c1256e61006dc122/41-553.1G.pdf