Query on DOL Starter

[sirilkt]

we have got 2 Fan motors of 0.5 HP Each. Our service engineer says that we need not provide any seperate starter for motor capacities till 1 HP. But in my career all through out I have ran fan motors of even 0.1 HP also with starter only.

Can you please advise if for motors less than 1 HP we don't need any starters ?

 

[waross]

This is a code requirement and depends where in the world you are and what code you work to.
In addition to electrical codes there may be safety codes that require a disconnecting means for each motor.
In Canada:

28-200 Branch circuit overcurrent protection (see Appendix B)
Each ungrounded conductor of a motor branch circuit shall be protected by an overcurrent device complying
with the following:
(a) a branch circuit supplying a single motor shall be protected, except as permitted by Item (c), by using an
overcurrent device of rating not to exceed the values in Table 29 using the rated full load current of the
motor;
(b) notwithstanding Item (a), an overcurrent device having a minimum rating or setting of 15 A shall be
permitted even though it exceeds the values specified in Table 29;

And

28-206 Grouping of motors on a single branch circuit
Two or more motors shall be permitted to be grouped under the protection of a single set of branch circuit
overcurrent devices having a rating or setting calculated in accordance with Rule 28-204(1), provided that the
protection conforms to one of the following:
(a) the rating or setting of the overcurrent devices does not exceed 15 A;

Safety codes often require a disconnect adjacent or near a motor. A manual motor starter is often use to meet this safety requirement.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

His point may be based on the commonality of motors in that size range often having integral thermal protection in them. That is however not universally true. The motor nameplate must CLEARLY STATE* that it has integral thermal protection and if not stated, you must assume it does not have it, meaning it needs an external means of protection. That could be a DOL starter, but there are other ways to attain the needed protection and on-off control.

* the term "clearly" is open to interpretation. I've seen some simply have a code on the nameplate that says "TP", meaning "Thermally Protected" in English, which may be completely useless to someone in Sweden or Malaysia...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[GroovyGuy]

We routinely install motor starters into MCCs down to 1/3 to 1/4 hp. This is dependent upon a number of factors, ie;
1) is the motor single-phase and provided with integral thermal-protection (ie Klixon)?
2) what means of disconnect is required? ie local or centrally located in a MCC?
3) is the motor 3-phase?
4) what is the availability of 1-phase and 3-phase power?
5) how far is the voltage source from the motor? ie is voltage drop an issue?
6) what type of control is required, or can the motor run continuously?
7) what is required reliability? a single-phase motor is not as reliable as a 3-phase motor.
8) what industry are we talking about here? or is this a commercial installation where initial cost is the only concern.
9) etc, etc, etc