Control Cabinet Review - Opinions?

[Jieve]

Hey guys,

I posted about this a while ago but am coming back to it now. We were donated a conveyor system that was used in an automated PCB soldering station and we are using parts of it as assignments for our automation course. The setup has a conveyor driven by a 3-Phase ¼ HP motor and a control cabinet. The system is controlled by a Siemens S7-1200 1214C CPU. An extension of the project as a second assignment will be a second conveyor that is connected to one end, driven by a second motor (same size). It will be controlled via the same CPU through a distributed I/O profinet interface module. A co-worker of mine is working on building the control cabinet and we have most of the parts laid out, but neither of us nor our interns who are also participating are totally versed in industrial electronics (I’m a mech E, two of the other guys are mechatronics). The components and wiring we have laid out works, but I wanted to ask the experts (that’s you guys) if there are any extra components needed or if there is anything we have laid out that we don’t necessarily need, and if they need to be in a specific order, etc. for this to be a “realistic” setup. The parts we have are not all necessarily sized exactly correctly, most were spare parts we have laying around and seem to be working for the application. There are a number of inductive sensors on each conveyor, as well as a light barrier, a 3-Lamp (RYG) post with Siren, and a single phase 230V fan. The programming will be relatively simple.

The following components are planned to be included in the first control cabinet:

1) 3x ABB S261 B10 Circuit Breakers, one for each phase.
2) Terminal Blocks for 3-Phase Distribution
3) 2x Mechanically Interlocked Contactors, Fuji Electric SC-E02/G
4) 1x Siemens Sirius Motor Protection Device 3RV1011-1FA15 (Not Sure if necessary)
5) 5A PS307 Siemens Power Supply
6) Simatic S7-1214C DC/DC/DC CPU
7) 2x Siemens Sirius 24V Contactors 3RH1122-1BB40 (1 for E-Stop, and one for Single Phase 230V Fan Motor)
8) +24V and 0V Terminal Blocks
9) Terminal Blocks for Input/Outputs to PLC
10) Main Power Switch

The motors have the following nameplate specs:
50Hz 0.18kW, Delta/Wye 230/400V 1.2A/0.7A (We’re in Europe)

They are not being controlled by any variable frequency drives, just straight 3-Phase in, no starters either. We are also doing our best to keep the 230V wires separate from 24V in the cabinet to avoid interference.

The second control cabinet will take 3-Phase out from the distribution block of the first cabinet. In the second cabinet there are a few solenoid valves as well, controlling pneumatic stoppers on the conveyors.

So after that long winded description, I am posting a pic of what we were sorta envisioning the cabinet to look like. The size of the cabinet will be 380x600mm, if that matters. I would really really appreciate if you guys could give me your opinions on anything we are missing hardware-wise, or anything we else should consider (wire-routing, size, etc.) while building this.

BTW I could only find a German datasheet for the Sirius Motor Protection Device and even after reading it, I am still not certain what it actually does (I think it is a type of overcurrent device?) Is this necessary? Or should we have a residual current device in there instead? Or additionally?

Thanks so much for any input!

 

[Andy6]

The following components are planned to be included in the first control cabinet:

1) 3x ABB S261 B10 Circuit Breakers, one for each phase.
2) Terminal Blocks for 3-Phase Distribution
3) 2x Mechanically Interlocked Contactors, Fuji Electric SC-E02/G
4) 1x Siemens Sirius Motor Protection Device 3RV1011-1FA15 (Not Sure if necessary)
5) 5A PS307 Siemens Power Supply
6) Simatic S7-1214C DC/DC/DC CPU
7) 2x Siemens Sirius 24V Contactors 3RH1122-1BB40 (1 for E-Stop, and one for Single Phase 230V Fan Motor)
8) +24V and 0V Terminal Blocks
9) Terminal Blocks for Input/Outputs to PLC
10) Main Power Switch

Here's a couple things.
1-2) Do not use 3 individual circuit breakers for a 3 phase load. Unless they are all pinned together. Use a 3 pole circuit breaker. You can also get distribution blocks for many 3 pole circuit breakers that mount right to the circuit breaker.

3)Is there a reason you have 2 mechanically interlocked motor contactors? Will the belt be running in reverse?

4) I would not use this, I would use the proper overload relays that fit the Fuji contactors. http://www.fujielectric.co.jp/fcs/eng/product/control/pdf/DEC2001_P001-077.pdf


7)Unless you already have these I would go for something a little less heavy duty, and alot cheaper. Many cheap cube relays can handle up to 15 amps.

10) What kind of main power switch are you talking about? A lever style disconnect? If you get a proper 3 pole circuit breaker, there are many brands that have a disconnect lever as well.

 

[GeoffC]

You need to consider segregation of power supplies - should not have 415V and 24V in the same duct. Put all the power control and cabling on one side and all the low voltage control on the other side

 

[johnnysparks24]

speaking of control cabinets

I was told that there was a min and max amont of communication cable permitted in a power cabinet. I can't seem to find a code rule in the CEC or my old Ontario code book.
Any ideas...

 

[Jieve]

Guys thanks for the responses.

Andy6: ok cool, we have the breakers already so I'll see if they can be pinned together. In terms of the application, does it sound like they are about the right size? Also, what are the downsides to having One of the breakers trip and the others not? I could imagine a number of things depending On which phase powers the PLC and motor, but Maybe a more detailed explanation would be good for my understanding.

Both belts run backwards and forwards, hence the interlocked contactors.

As I understand the breakers are supposed to protect the wiring and the overload relay with adjustable current setting protects the motor, but how and what exactly does it do? Would having a residual current device here also make sense? Or is it unnecessary?

We already have all these components laying around to play with, so if we can use them without buying anything else it would be great, but for students to learn i would like this to be realistic. We already have the contactors.

The mains switch is a switch you turn 90 degrees to switch On the power from the 3 phase supply.

All 230V cabling is in a separate duct from 24V.

Not sure about the communication cable length.

Thanks for the input!

 

[Andy6]

Take a look at the lever of the breakers. There is probably a small hole on the side, near the end of the lever. This is where a small metal rod goes so that if one breaker trips, it will pull down the breaker next to it, and so on.

The problem with having only one breaker trip is that you could, under certain circumstances, have the motor running on only 2 phases. And combined with a lack of overload protection, the motor would continue to run until it burnt out, or you shut it down. The only way you could tell it was running on 2 phases, would be that the motor will probably sound different, and it will get really hot. If you were away for a few minutes you could easily lose the motor.

Circuit breakers do protect wiring. But they are designed for very high current ratings compared to overload protection. Your motor only requires 1.2 amps. That circuit breaker will protect your motor leads from short circuits. But should your motor be overloaded, have a locked rotor, be fed with only 2 phases, or stall. The circuit breaker will probably not trip until the motor windings have been burnt.

* After reviewing the current rating for that circuit breaker you are talking about, you should disregard my previous post about not using it and using only overload relays. You SHOULD use both the circuit breaker and the overload relays.

I dont know what the German electrical code is like, but Canadian code demands both circuit breaker (or fuse) protection and overload protection for 3 phase motors.

A residual current device is unnecessary, unless you are planning on installing a power outlet (wall socket).

As for keeping the 240V seperate from the 24V, it is good practice, but not against the rules if they need to be run together for short distances.

 

[Jieve]

Andy6,

Thanks again for the excellent tips. There is a screw On the overload device for adjusting the current rating, i'm not at work and Cant access the data sheet but if you Google the part number, it should say something like 2.5 to 5 Amps, maybe even lower. What would you recommend I set it at?

Also, are these thermally triggered devices or are they the electromagnetic trip type, and what about inrush current for the motor? Does that need to be taken into account in sizing overload protection devices generally?

Should the overload protection be wired in after the contactors or before, or does it even make a difference?

Thanks!!

 

[Jieve]

Ok, just found the datasheet, the adjustment is between 3.5-5A for overload and 65A for short circuit protection. The overload device is rated S00, i read from another post that this is for motors drawing up to 1.5 Amps or something. 65 Amps seems really high considering that the max continuous allowed current coming from the building power outlets is max 16A.

 

[Saffa]

Hi Jieve, Normal sequence for wiring is power to circuit breakers, then contactor, then motor overload, then isolation switch, then motor. Can whip up a quick sketch if you need. The motor overload should be set for the full load rated current of the motor, from the nameplate. Your one might be a bit big then if it's lowest rating is 3.5A and your motor is only +-1A. Thermal overloads are pretty cheap, I'd just pick up another one at your local electrical wholesaler. thermal overloads are normally just that - heat up a bimetal strip, it closes a contact. You need to use the clean contacts on the overload to interrupt power to your contactor's coil. They make fancy electronic ones these days but I've had mixed results with those. circuit breakers are normally electromagnetic. The 65A rating is probably the rated current for the overload before it burns out, i.e. the max current the internal wiring could withstand. it's certainly not going to be expected to carry that amount of current for any length of time as your circuit breakers will trip well before then. As for the RCD discussion - if this machine is going to be worked on by students, I'd personally run the whole thing through a 3 phase RCD or at the very least have the control related single phase on RCD.

 

[Jieve]

Hi Saffa,

Thanks so much for the reply. Looks like we may have to pick-up some lower current rated motor overload protection devices. The specific info from the data sheet for the ones we have says:

Continuous Current 5A
Instantaneous Short-Circuit Trip 65A
Current Dependent Overload Trip 3.5A-5A

I just read a really simple to understand article on sizing motor protection devices and I'm starting to wonder if the motors don't already have built in overload protection. There's nothing on the nameplate that says anything like this, but there were a couple extra wiring terminals on the motor itself that one of my co-workers mentioned may be related to internal overload protection. I took some pictures but I don't have them available at the moment. Is there some way to tell if they already have internal overload protection? If so, do we still need the external device?

I know that the ABB Breakers we have are both thermal and electromagnetic. At high current they trip via an instant electromagnetic trip or some sort, and at lower overloads they trip after a period of time via a thermal mechanism. It sounds sorta like the overload device we have is similar, judging from the 65A Short Circuit and 3.5-5A Overload. Does this sound reasonable, or are they generally just thermal devices?

Thanks again so much for the help, you guys are awesome!

 

[Jieve]

Ahhh, also forgot to ask, what is the isolation switch used for, and is it necessary in this case?

 

[Steve Etter]

Jieve - It hasn't been specifically said yet, but there is a reason for having both over current and overload devices and it is simply this; the over current situation is typically one that instantaneously spikes the current well above normal and the overload situation is one that happens slowly over time where devices heat up and insulation breaks down.

An instantaneous over current - like a direct short to ground - won't typically give devices time to heat-up before damage occurs. This is where fuses or circuit breakers are used.

A sustained overload, as others have already described, occur when motors are over truly over loaded, a phase has been lost, loose connections exist, or when wiring insulation breaks down and small amounts of current begin to pass between conductors or ground. In these cases, the current draw can build slowly and not be enough to trigger your over current device but still be enough to cause damage.

I looked up the specifications for the Siemens 3RV1011-1FA15 and it appears to be nothing more than an adjustable circuit breaker. If so, you have two things here to consider. First, you don't need both fuses and a circuit breaker - they serve the same purposes. However, the fuses you have are rated for 10 amps which is probably too high for your application. The circuit breaker, on the other hand, is closer to right for this application and if you use it, I would set it for its lowest setting. Second, it look like you have no overload protection devices on your list.

As for your motor, I seriously doubt there is any built-in overload protection within, rather I suspect you simply have a thermostat. Even if the motor does have its own overload protection built in, I wouldn't rely on it - not when purchasing an external device is so inexpensive.

Finally, the disconnecting device just before the motor is primarily used to isolate the motor for maintenance purposes. For safety it gives anyone who needs to work on the conveyor or change the motor a guaranteed method for locking out the motor to prevent any opportunity for injury. Obviously it is possible to build a system without one, but from where I stand its a cheap insurance policy and, since you are in a teaching environment, it would be best to teach doing it the right way. I highly recommend the disconnect.

Steve

 

[kamenges]

I would disagree with Steve about the Siemens 3RV1 device. It looks to me from the specs like it is a motor protection circuit breaker, similar to an Allen-Bradley 140M device. I'm not sure about Europe, but in the US this device can be used as free-standing short circuit and motor overload protection as well as a motor disconnecting device, all in a single device, assuming that Class 10 protection is what you are looking for. However, as Steve said, you want to have a separate motor disconnect by the motor for safety reasons.

Keith

 

[Jieve]

Hi Steve, thanks for that info, you're right it is an adjustable circuit breaker and not an overload device. I will look tomorrow to see if we have any small overload devices and isolation switches. If not we can purchase them no problem.

Regarding the 10 amp ABB breakers, the idea was to use them at the mains, right where the wires from the 3 phase wall plug come into the cabinet, meaning that ALL power is running through them, to the motor, plc, 24V supply, actuators, etc. Plus the extension of this project is a second conveyor, Powered by a second motor also fed from those breakers. I am assuming 10 Amps should be somewhere in the ballpark, but not totally sure to be honest. How should i go about figuring this out properly?

The main task for the students will be programming the PLC so they shouldnt be sticking their hands into the control cabinet, but they will have to work from the wiring diagram and i will be giving them a detailed run-through of the cabinet as well as a detailed description of how each of the components works and why.

Thanks!

 

[Jieve]

Sorry Keith, missed your message, in German the data sheet says "Leistungsschalter" which translates to cirrcuit breaker in English. So you're saying its a specifically designed motor circuit breaker?