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I found a great article on sizing circuit protection for transformers and their loads: http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1492-in001_-en-p.pdf In it, a helpful standard is listed: Circuit breaker protection for the primary side of the transformer can...

I need to modify a piece of equipment to include a circuit for an additional piece. The equipment is powered at 460VAC, 3-phase. The original equipment contains one step-down xfmr to 120VAC, and is protected by two primary and one secondary fuses. The add-on is 120VAC, nearly 10A max inrush...

Gents, I appreciate your time and input more than I can say. Have reached out to my customer/contact for more info. Will have a conversation and continue post with more details. Thank-you.

I have a report of two of the three motor phase terminals in a motor contactor being fused (shorted by melting) together. Twice in a row, same machine, same motor, same phases. This is on a machine in the field. I was thinking it could be a short in the motor windings. We are operating...

This is great, thanks. I will be well within bounds. I appreciate the assurance.

I am redoing a cabinet layout. We are using a different control transformer that is larger, and so the fuse holder that was formerly mounted on top of the transformer is being replaced by two DIN-rail mounted fuse holders (2P primary + 1P secondary). I am wondering what the proximity...

Gents, I have just returned from the job site. I waited for two days with test equipment set up. Finally a fault happened. My hand happened to be on the joystick at the time. As I Extended the machine, it began to drag for maybe 2 seconds, before stalling and faulting. Same fault: Phase...

Let me ask you this: what about the possibility of the contactor coil dropping out? To me this would more closely describe the fault: phase loss/open load. Is a contactor coil likely to drop out momentarily?

I appreciate your help. Please let me know what further info I can provide. I have a lot. Here, for one, is the sfst sequence of operation, attached.http://files.engineering.com/getfile.aspx?folder=053fd51f-cfa2-48ee-92d4-ce8ab4a1df08&file=SMC-3_sequence.pdf

wire 21 is +24VDC control power wire 22 is 24VDC common wire 31 is essentially 21 after the master control relay wire 32 is 31 after customer interlock relay.

On the sfst, A1-A2 is control power and is on all the time (+24VDC). START is initiated by sending IN1 high (24VDC).

Hi all. I have been working with a softstarter fault issue on my company's equipment for over a month now. The softstart is an Allen-Bradley SMC-3, and the fault is four-flash Phase-Loss/Open Load. I have initiated one fix so far, which initially reduced the faults entirely. What I suspected...

I feel truly enriched, can't thank you all enough. Plenty to go on (solve the problem), and plenty to look further into. Thanks again.

Ah! Thanks. The transformer I spec'd does say that it is suitable for "reverse wiring," which brings up a question I have had. What is it about transformers that would make them suitable for only one way? Would one need to look for a step-up vs a step-down transformer?

That is a great suggestion, thank-you! Any hangups I should look for in a step-up transformer? Interference issues stepping up from the 208V supply and then (for part of the equipment) stepping down to 120V inside the equipment, etc.?

Our machinery normally uses 460V, 3-phase supply. We have come across an instance where customer only has 208V, 3-phase, and not a hope of changing. I am in the process of converting the equipment. Someone suggested wiring the 460V motors in the delta configuration. Any advice?

I have a dumb question: In our control cabinet, we run several motors off the 3phase, 460V line. I need to add another branch circuit. I have the motor starter, reverser, motor, etc, but what do I do about the wiring? I've noticed that the terminals of the other motor starters use two wires...

Really good suggestion, thank-you.

I am designing a simple test setup with an Crouzet PLC. I am concerned about fusing and voltage spikes or bounce that would damage the PLC or other components, or give false reads on the PLC inputs. I have no control, at this point, over the PLC code. I would like to mimic as close as...