Motor starter needed.

[maplecherry]

Setting up a new system and wondering if a motor starter is needed for the vacuum pump. Unit is 1phs, 7.5 hp, 230 v, 31 amp and will be turned on/off manually. Had differing opinions so far - wondering what some of you out there have for their set up.

[Flat Lander Sugaring]

I would use one make sure there are heaters(overload) in it
for a few hundred dollar investment they well worth it

[BAP]

Single Phase 7.5hp motor you would need one.

[Flat Lander Sugaring]

Single Phase 7.5hp motor you would need one.
Hey Bap just in Walpole today at the agway store.
Yea should really have a motor starter with overload but I know one guy who use breaker to turn his 7.5 on. I dont recommend it but will work

[ToadHill]

I'm not an electrician and don't pretend to be one. I have the same motor you're using and I called CDL. I asked their technician and he said I didn't need one. I'm using a fused knife switch.

[Flat Lander Sugaring]

[QUOTE=ToadHill;239710] . I asked their technician and he said I didn't need one. I'm using a fused knife switch.[/QUOTE
And they aren't electricians either

First off, realize that Circuit breakers and Fuses perform the task of protecting the CIRCUIT, i.e. the wires, from fast acting short circuits such as a wire going to ground or one motor winding melting into another one. For this reason, CBs and fuses collectively are referred to as SCPDs, Short Circuit Protective Devices.

The Overload Relay protects the MOTOR from a long-term running overload. It does not see the current from a short or ground fault until long after a fire will have started. It also does not interrupt current, it just senses it and trips a little relay contact. You would then wire that relay contact into the coil circuit of a magnetic contactor to drop out the magnetic coil power if the Overload Relay trips, and it is the contactor that interrupts the current flow to the motor. The Overload Relay works by sensing the heat produced by the current flowing through the circuit and uses the I^2t (Inverse Current / Time) calculation method to determine that heat. So an overload Relay is referred to as a Thermal Over Load (TOL) device.

According to the NEC every motor circuit, however it is used, must contain a SCPD, a TOL and a switching / controlling device, as well as a means of safely disconnecting the motor from power and locking it off.

Technically fuses can theoretically only be used as the TOL on motors 1HP and below, but only if they are specifically sized to a narrow range of the motor FLA, 115% max. I believe. The problem is, fuses only come in certain sizes so it is not really practical to find the exact right size, plus you have the problem of what happens when only 1 fuse blows.

[ToadHill]

Flats, Where does a motor starter fit into what you just explained? Is it considered a TOL device?

[Flat Lander Sugaring]

Flats, Where does a motor starter fit into what you just explained? Is it considered a TOL device?

Motor starter is a magnetic coil unit that once all your starting points, safety switches etc are satisfied it is pulled in at which time the power is let through to the TOL and then off to the motor.

Like the ones I'm ling for my RO power comes in to motor starter box I'm going to grab control power off of one leg fuse it at 5 amps and take that to my low pressure cut out and hi temp cut out bring it back theI get home the aux coil on side of motor starter. One power goes through both of those safety devices and they are satisfied the coil will pull in allowing power to pass through the motor starter. Once through that it will go through the TOL and then off to motor. Will load pic when i get home to computer cant load pic off of phone

[lpakiz]

I have seen motors that have a re-set button right on the motor. Will this built-in device be a substitute for the heater/interrupt system?

[Flat Lander Sugaring]

I have seen motors that have a re-set button right on the motor. Will this built-in device be a substitute for the heater/interrupt system?
Yes I believe so