Reason for Motor Circuit Protector with Upstream OCPD?
Reason for Motor Circuit Protector with Upstream OCPD?
(OP)
I tried to find a previous post that answered this question but had no luck. Please feel free to steer me in the correct direction if there is a previous post that covers this question:
I am failing to see the reason for having a Motor Starter with a Motor Circuit Protector (MCP) when there is a single motor on a feeder and a CB in the upstream panel?
Does the MCCB in the upstream panel not have the sensitivity to protect the motor if there is a fault at the motor?
As always, thanks for the help all!
DJR
I am failing to see the reason for having a Motor Starter with a Motor Circuit Protector (MCP) when there is a single motor on a feeder and a CB in the upstream panel?
Does the MCCB in the upstream panel not have the sensitivity to protect the motor if there is a fault at the motor?
As always, thanks for the help all!
DJR





RE: Reason for Motor Circuit Protector with Upstream OCPD?
If the upstream MCCB is within sight of the starter, then a second overcurrent device is not required by the NEC. However, an MCP (instantaneous trip only MCCB) does over some advantages over a standard thermal magnetic breaker for motor short circuit protection. The MCP has a wider range of trip ranges and adjustments than a thermal-mag breaker, so could provide better protection in some situations.
RE: Reason for Motor Circuit Protector with Upstream OCPD?
Now go out and try to buy one... What you will discover is that nobody stocks them and even if they offer them at all, they are generally made to order so long lead times compared to an off-the-shelf combo starter with an MCP, and virtually no difference in price. Sometimes it's all about volume and convenience.
"Will work for (the memory of) salami"
RE: Reason for Motor Circuit Protector with Upstream OCPD?
I have seen a lot where they have the non fusible disconnect switch, control power transformer, and non combination starter all in the same disconnect enclosure next to the motor.
Do the combination motors on the shelf come already with a disconnect switch/enclosure and the MCP, CPT, Contactors, and OL already mounted inside the disconnect? So you just purchase the whole unit off the shelf?
I guess my confusion started with the fact that I thought whether it was a combination motor starter or non fused disconnect switch, that they were both composed of discrete parts that were field installed and wired. I need more exposure in the field....
DJR
RE: Reason for Motor Circuit Protector with Upstream OCPD?
RE: Reason for Motor Circuit Protector with Upstream OCPD?
You should put the idea of using a NON-FUSED disconnect switch (for anything) out of your mind. They have very limited short circuit withstand capability unless protected by an upstream fuse. Always use fused disconnects at 480 V - it will save a lot of hassle.
The "combination" in combination motor starter means it includes both the motor starter and its short circuit protection/disconnecting means. This can be either a fused disconnect or an MCP. And yes you can purchase it as an assembly complete with all of the auxiliary devices such as CPT, indicating lights, pushbuttons, etc.
RE: Reason for Motor Circuit Protector with Upstream OCPD?