New Cutler Hammer Motor Control Centers 2

[richanton]

Cutler Hammer now sells their "IT" smart MCC line which features 24VDC control as opposed to the historical 120VAC control via control transformer. Any opinion on this new direction. As far as I can find, they are only vendor offering 24VDC control.

 

[peebee]

I'm not familiar with this new line, but that's no reason to keep from throwing in my $0.02.

Are they IEC contactors? If so, beware that IEC contactors are rated for many fewer operations than NEMA contactors, it's like an order of magnitude less. I forget the exact numbers, but I want to say 10,000 (IEC) vs. 100,000 (NEMA).

Also, 24 VDC might cause voltage drop problems if your control wiring has to run long distances.

 

[pablo02]

I think all of the MCC manufacturers have already or are in the works of putting out "smart" MCC line-ups -- where the bucket has already been wired for RS-232 or other computer interfaces -- you just run the communication into the MCC rather than pulling in control wires to each bucket... you just pay more up front (and hopefully save on the field wiring)

These will be for NEMA style MCC panels as well...

 

[richanton]

The starters are available as NEMA rated. All the control switches and local lights on the MCC are soft. Each starter compartment has Devicenet capabilities. So there will almost be no control wiring. All the I/O in the field goes to local I/O racks and the outputs controlling starting and stopping will be outputted to the individual starter via the Devicenet link.

 

[peebee]

The IEC/NEMA information I gave above had the right idea, but the wrong numbers. I think the 10,000/100,000 numbers are for air power breakers, not motor contactors. Here's some corrected information on contactors.

From the Cutler Hammer 2003 Consulting Guide:

Contactor Performance
IEC Type:
Electrical life - 1 million AC3 operations; 30,000 AC4 operations when tested per IEC recommendations
NEMA Type:
Electrical life typically 2.5 to 4 times higher than equivalently rated IEC device on the same test.

Fault Withstandability
IEC Type:
Typically designed for use with fast acting, current limiting fuses.
NEMA Type:
Designed for use with common domestic fuses and circuit breakers.

 

[CHDean]

To expand on Richanton's comments about communications.
There are two communications methods. A.) individual devicenet to the starter or B.) QC port which daisey chains the starters together back to an I/O block that converts to devicenet. This allows you to use one node rather than a node per device.

 

[dpc]

There is a definite push in the US to move towards 24vdc for motor control circuits for safety reasons. There are other advantages and disadvantages, including ease of interface with PLC and other smart devices.

I think it is coming and C-H will not be the only manufacturer offering this.

 

[PUMPDESIGNER]

We looked hard at the CH DC 24 contactors 9 months ago.

1-They are being offered to reduce panel space (contactors are extremely small, probably 30-40 percent smaller than comparable IEC contactor. This size reduction is due primarily to the reduction in size of the coil.

2- They have potential but not necessarily advantages in remote control.
3- Safety perhaps but very little advantage by my thinking.
4- Larger power supply will be required if you already have one, if no DC power supply then you will have to add that into the cost.

We decided against (at this time) because we see no advantage in most of our products, and because we are making it difficult for a customer to get replacement for their equipment locally.


PUMPDESIGNER

 

[jraef]

My humble opinion, for what it is worth...

I think that there is a distinct disadvantage to the additional complexity of the 480VAC-24VDC switch mode power supply over a simple control power transformer. The additional risk of failure and additional heat is unwarranted for the benefits recieved.

Quando Omni Flunkus Moritati

 

[PUMPDESIGNER]

jraef - That is a very good point. If I had no power supply then adding one into that panel introduces more potential for failure.
We already have a power supply, and adding that contactor into our panel is still not desirable because we have to upsize our power supply.
Just one more component to have a problem.

PUMPDESIGNER

 

[jbartos]

Suggestion: The DC control circuits will not be affected by a low power supply quality, e.g. harmonics that affect the control transformers and propagate to the control transformer secondary thus negatively affecting the 120VAC control circuits and loads.

 

[uno]

24V DC Control voltages in MCC are very common in some European countries. We have just used it. We also found other suppliers like ABB, SChneider and Siemens offering this range with very compact power supply modules for each feeder. Also the voltage drop problems were solved by using some very low burden interposing relays.

Thanks