# MCC Question



## 51360 (Jun 9, 2014)

Babster said:


> Hello to everyone
> Can the fuses inside an MCC be higher than the disconect?
> Example I have an MCC bucket with a Disconnect, Fuses, Contactor and O/L. All parts are rated at 30Amps except the fuses which are at 40amps and O/L is turn down to 22amps. This seems wrong to me does anyone have a code rule that could shed some light on this?
> 
> Thanks in advance


Are you sure about the ratings?  What size of starter is it? I would guess size 1, but it's been awhile.

If that bucket is designed for that MCC, and for that starter, ( usually all one unit ), I would say it is rated accordingly. 

Borgi


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## JRaef (Mar 23, 2009)

Babster said:


> Hello to everyone
> Can the fuses inside an MCC be higher than the disconect?
> Example I have an MCC bucket with a Disconnect, Fuses, Contactor and O/L. All parts are rated at 30Amps except the fuses which are at 40amps and O/L is turn down to 22amps. This seems wrong to me does anyone have a code rule that could shed some light on this?
> 
> Thanks in advance


There are several areas of concern here, you are right to question it.

So 22A would technically be a NEMA Size 2 starter. Most NEMA Size 2 MCC starter buckets will have a 60A disconnect switch, which is what you would need to hold 40A fuses. 40A fuses will not fit into a 30A disconnect switch, they are designed that way on purpose. If someone hacked it to force them to fit, that needs to be replaced.

A NEMA Size 2 starter will have a contactor rated for 45A. If your contactor says 30A, it is not a NEMA starter. That means it is either an IEC starter or it is a Furnas / Siemens, who sells "1/2 size" starters, so it would be a "Size 1-1/2", which is something they made up, NEMA doesn't really recognize that sizing convention. 

So assuming it is an IEC starter, an OL relay set for 22A means it is either a 15HP 460V motor, or a 7.5HP 230V motor. Most recommendations show 30A as the proper fuse for that motor, either voltage. Table 430.52 of the the NEC allows for the fuses, assuming time delay, to be 175% of the NEC FLA table FLC (21A), which means 38.5A maximum. 40A exceeds the NEC rules. If it is a non-time delay fuse, it can be 300%, in which case the 40A is OK, but I would never use a non-time delay fuse on a motor. If for some odd reason it is a Class CC time-delay fuse, which is very rare in an MCC format, then you can use the 300% rule as well, but that too would indicate it is a hack, because I don't know of anyone who uses Class CC fuses in MCC buckets.

The devil is going to be in the details here.


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## JRaef (Mar 23, 2009)

Ammendment:
Can't be a Class CC fuse, they stop at 30A, you said it is a 40A fuse. 40A would be a Class CD, and the NEC rule exception allowing 300% only applies to Class CC. So forget that part.


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## 51360 (Jun 9, 2014)

Babster said:


> Hello to everyone
> Can the fuses inside an MCC be higher than the disconect?
> Example I have an MCC bucket with a Disconnect, Fuses, Contactor and O/L. All *parts are rated at 30Amps* except the fuses which are at *40amps and O/L is turn down to 22amps*. This seems wrong to me does anyone have a code rule that could shed some light on this?
> 
> Thanks in advance


I checked NEMA charts on an Eaton site, and others, and this sure sounds like a size 1 starter.

But, I agree with " JRaef " that it sounds like they have somehow put 40 amp fuses in! 

Would be nice to get some feedback from the original poster. 

Borgi


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