Motor Controls 1

[Reesh14]

I am replacing four 20HP hot water pumps that are fed by an MCC. Each pump has a 60A/3p heavy duty safety switch. The MCC compartments for each pump has the H-O-A controls and a 50A/3P breaker. I want to put in the new pumps and keep the existing pump alternating controls through DDC. I am not sure if I can replace not only the pump, disconnect, but also the compartment in the MCC. Normally I would provide a combination starter and disconnect for the pump if it was fed by a panelboard. I am unclear how it works with the MCC and the general idea of motor controllers.

 

[bklauba]

What is your 3 ph voltage?

BK

 

[Reesh14]

the voltage is 480V.

 

[jraef]

So if I understand what you are saying, you don't see a starter in each pump circuit? Only a circuit breaker at the MCC and a disconnect at the motor? If so, what is the HOA switch controlling then? There must be a motor starter somewhere already, because that would be what he HOA is controlling, and that is what is providing the Overload protection for the motor. Is there another control panel associated with each pump (or all 4)?

You have left something out here.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Reesh14]

I was not sure how the HOA switch on the MCC is involved. I guess this means that the enclosure at each pump contains both the 60A disconnect and motor starter? I am confused as to how it all relates: the disconnect, the motor starter, the HOA and 50A/3P circuit breaker inside the MCC compartment. I am not familiar witht he components inside of the MCC compartment. Can I just replace the disconnect/motor starter, and just the circuit breaker inside of the MCC compartment? Please advise.

 

[jraef]

I'm just guessing here, and assuming that you already opened the MCC bucket door to see that there is no motor starter inside with the circuit breaker. If so, I would say that you have a feeder breaker and HOA switch in the MCC bucket, which is feeding a combination motor starter near the pump that has a non-fused safety disconnect included, because the MCC bucket is not within sight of the pump. You can tell by turning off power and opening the disconnect enclosure to see if there is a motor starter inside. If on the other hand you have not yet opened the MCC bucket, it is more likely that the starter is inside WITH the breaker and HOA switch, that is the most common setup.

Either way, if the starter has a rating plate that says it is rated for 20HP or more (or NEMA Size 2), then you don't need to replace anything other than the pump. You must however check the nameplates on the new pump motors and make sure the overload relay in the starter is sized correctly for the new pump motor. Depending on how old the MCC is, the relay may be adjustable within a small range, or you may need to replace the heater elements that provide OL protection.

Eng-Tips: Help for your job, not for your homework Read faq731-376