Overloads on fractional hoursepower three phase motors?

[olc]

Say a 1/2HP or 3/4HP 3 phase motor for a roof fan - would it typically have internal overloads or does it need a starter?

Follow up question - can a damper operator be tapped off the circuit on the load side of the starter?


Side note - we are replacing existing fans 3/4HP and 3HP. At some point the existing starters were removed and the box used as a junction box. The motors likely don't have thermal protection?

 

[Jraef]

Say a 1/2HP or 3/4HP 3 phase motor for a roof fan - would it typically have internal overloads or does it need a starter?

Follow up question - can a damper operator be tapped off the circuit on the load side of the starter?


Side note - we are replacing existing fans 3/4HP and 3HP. At some point the existing starters were removed and the box used as a junction box. The motors likely don't have thermal protection?

You cannot ASSume anything. Either the motor nameplates SPECIFICALLY state that they have internal thermal protection built-in, or you must act on it to supply an external relay (or other means). Sometimes the designation on the nameplate is a simple "TP" (Thermally Protected) or "TC" (Thermal Cutout) on the plate, sometimes they are explicit in the way they word it, so you have to be able to see it and read it. But UL requires that if they are, it MUST say so on the nameplate, so if it doesn't, you must provide it.

On simple roof fans that are controlled by a manual switch, don't forget that the manual switch might itself be the "OL relay". If it has the word "Reset' on it somewhere, it probably does.

 

[ptonsparky]

Damper motor should operate first, then the fan.

Typically we use a damper motor with position switch. Once the damper is open the fan starts.