Motor fed from breakerpanel no need for seperate fusing/mccb?

I have (or will be getting) a 250A motor that I am building a starter for. The starter will be in 36x36NEMA enclosure with a disconnect. This will be fed directly from switchgear breaker with nothing else on it. This should mean that my panel only needs a non-fused disconnect correct? I believe that should be correct since the switchgear breaker would be the branch ocpd.

The switch gear MCB is there to protect the cable after it and nothing else. You need additional provisions to protect the motor.

janner_10 said:

The switch gear MCB is there to protect the cable after it and nothing else. You need additional provisions to protect the motor.

Click to expand...

The switch gear breaker will act as the OCPD for the wiring/motor circuit.
My starter will have an overload to protect the motor.
My panel will have disconnect -> contactor -> overload

janner_10 is correct.

the switchgear is designed to protect the wiring to the enclosure.
you then have a fused disconnect to protect the main power wiring in the panel.
you then have a fuseblock to the motor starter.
after the motor starter, you have fuses/ circuit breaker to protect the wiring to the motor.
the overloads are for the motor.

i'm doing this rather quickly, I have to goto into the plant.

look at nec 70.
fusing, circuit protection, branch circuits and motor protection.

james

No, technically you are correct, so long as the breaker in the switchgear meets the criteria for Article 430.52 regarding the OCPD for the motor circuit.

HOWEVER...

If this could be considered an "industrial control panel", then it falls under Article 409 as well, and that means you will need to be able to show an SCCR (Short Circuit Current Rating) for the ASSEMBLY that is equal to or greater than the Available Fault Current at the line terminals.

The problem then becomes that you will find out that the OVERLOAD relay in that starter is only going to be rated for 5kA SCCR all by itself and the way SCCRs work, the overall rating is the LOWEST rating of any power device in the assembly. It CAN however be used in a listed series circuit with fuses or a circuit breaker, but not with a non-fused disconnect. Then, those will be SPECIFIC fuses or circuit breakers that have been TESTED AND LISTED by the mfr of the OL relay. Next you will find out that in most cases, the mfr of the OL relay will ONLY list it in series with THEIR OWN circuit breaker. So if for example you have a Square D panelboard with the breaker in it, and you use an Eaton starter in your box, that Eaton OL relay will not have a series listing with a Square D breaker, only with an Eaton breaker.

As a general rule, it's just easier to use a combination starter now so that you can show an SCCR that meets or exceeds your Available Fault Current. If you do insist on "rolling your own", do so with components that match up with your mfrs Series Listings for SCCR.

Thank you for the help. If i go this route (though now boss man is talking VFD like I wanted to originally) I will add a breaker or fused disconnect to my combination starter