Anyone have any good explenations that an MCC is better than a switch rack for about 15 different motors. I have a couple but engineers never listen unless you have about 20 reasons and then they will still just look at the cost. I may be way off but I can't even see that big of switch rack being cheaper than an MCC. I tried to explain how you have to turn the entire rack off to change out a starter.
Switch Rack or MCC
- Thread starter 69boss302
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- retired electrician
Why would you have to do that? You would need a disconnect on the line side of the starter. In general, it would be my opinion that compliance with the electrical safety rules would be much easier with a switch rack as opposed to a MCC.
That being said, I would expect the MCC to be much cheaper if you look at the labor required to install the switch rack.
(note that my first comment assumes individual enclosures for the disconnects and starters)
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Most switch racks I've seen and the one proposed does not have a disconnect for each starter, that is why they use switch racks, so they can save money, with another 15 disconnects there is no way you would save any money. They just put in combination starters and figure you can work on the starter with it turned off.
With a switch rack you have to turn off the entire rack to pull a starter or you will have exposed 480 Volt leads as you are pulling the starter off the rack. Unless you decide to change out just the guts, which normally on a switch rack when the starter goes bad you need to change the whole box.
On MCC you just pull the bucket, work on the bucket if can be or put in a new bucket.
Of course following all applicable safety precautions in each one. No matter what, with a switch rack you have 480V leads dangling in the air while your starter is removed.
With a switch rack you have to turn off the entire rack to pull a starter or you will have exposed 480 Volt leads as you are pulling the starter off the rack. Unless you decide to change out just the guts, which normally on a switch rack when the starter goes bad you need to change the whole box.
On MCC you just pull the bucket, work on the bucket if can be or put in a new bucket.
Of course following all applicable safety precautions in each one. No matter what, with a switch rack you have 480V leads dangling in the air while your starter is removed.
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- Location
- Illinois
- Occupation
- retired electrician
As far as the switch racks, the only ones I have seen have had either a group of combintation starters, or a group of disconnects and starters. If there is only a common disconnect, you are correct that you would have to turn off the complete rack to work on it. I question the ability of a single disconnect to provide the required short circuit and ground fault protection for the motor circuit and its controller (starter)
Does the proposed installation meet the requirements of Exception #2 to 430.102(A)? If not each starter needs its own means of disconnect.
Does the proposed installation meet the requirements of Exception #2 to 430.102(A)? If not each starter needs its own means of disconnect.
weressl
Esteemed Member
- MCC provides individual, isolated compartment for each motor.
- Each starter can be worked on without affecting the rest of the system.
- Entire starter can be removed without affecting the system.
- Arc resistant features, although not listed yet, available.
- MCC is listed as an assembly.
- Safer for many reasons.
- Can use MCP's while switchracks can only do that under special circumstances, like if the entire subassembly is listed as a combination starter.
- Unitized fault level management, can be built for systems with higher fault levels available than switchracks.
- Modular construction allows for highly automated asssembly in large volumes, whereas switchracks remain hand assembled and individually designed systems.
Thanks, you hit pretty much all my same points, next question, how to get people to listen.I just got an email that said they would look at an MCC and add $70,000 or $80,000. I'm not sure I'm dealing with people that have gotten these before. I would think the entire set up would cost more than 30 to 50K. I guess I'll have to put in the extra time to get things put together myself just like usuall.
weressl
Esteemed Member
You have to obtain actual comparative bids, then there can be an inteligent discussion. Add $70-80K? Try 1/3 or less for the COST of the MCC and haven't even deducted the price of the switchrack to come to the cost differential.
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