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Posted By Topic: Control Panel Wiring Help

5char
Nov 16 2013 11:28

I have been designing a control panel for a brewery, and I would like to get someone to double check my wiring to make sure everything will be safe.

As my circuit breaker panel is not RCD protected, I have decided to install a PDL Domae 63A RCCB (RCD), which supplies the breakers. The 25A breakers are for each element (labelled 3500W and 4500W at the top) as they draw 14.6A and and 18.8A respectively. The 16A breaker is for supplying the temperature controllers (labelled \\\"Auberin PID\\\") and the 240V out for a couple of pumps (they use less than 20W each).

I apologise for the wrong colour wire being used in the diagram, as I edited an existing schematic in Paint. This also had the American outlets down the bottom, which I did not bother to change. You get the idea, though. I have added a .gif version of the drawing, which is low quality. Here is a higher quality version - http://i.imgur.com/8ALYwrM.png

Thanks!
   

BrianW
Nov 16 2013 14:02

Unless you\'ve been specifically asked for it, Why are you adding the RCD? Its not required in that application, and given that youre going to be plugging in immersion elements, its likely that youre setting yourself up for nuisance tripping. I\'m also not sure i\'d be using the EM Stop in that method. Introducing a short to trip the RCD might work okay, but what happens if your 1 amp fuse is blown, and you try to stop your system? Personally, i would be using the EM stop across a contactor/relay coil for a slightly more fail safe setup. JMO
   

DougP
Nov 16 2013 16:44

I’m with Brian. I wouldn’t use an RCD in this at all unless it has been specified for some reason which you haven’t explained. I also definitely would have an “emergency stop” wired the way you have shown. Change the 16A MCB to 10A and put a N/C locking stop switch in the active supplying the controllers and pumps.

Assuming this will be a fixed control panel supplied by a 32A or 40A circuit, I would also have an accessible & lockable isolator, so there isn’t any need for a main CB inside the panel.

The elements you have shown plugged in, will require 25A wiring and plug/sockets if you are using the 25A MCBs on those circuits. Maybe better to change to 20A if you think it will be reliable on the 4500W element. Maybe a “D” curve may prove more reliable for cold inrush current?

In addition to not using the correct colours on the drawing, you’ve also shown the sockets wired with the polarity incorrect. Usually, a control diagram would be kept with the equipment for future maintenance so eventually you should produce an accurate diagram using the correct symbols, rather than pictures.

You may also want to clarify on the diagram what is contained within the control panel, and what is connected by external wiring, as well as any connectors in the panel for connecting the external wiring.

Lastly, have a think about how you will be identifying the ELV wiring within the cabinet for clarity – and use a different colour for them on your diagram.

   

DougP
Nov 16 2013 16:56

If you really want to have the emergency stop tripping the RCD, don\'t connect it to the earth, connect it to the neutral on the incoming side of the RCD.

You don\'t need a separate fuse in that part of the circuit.
   

DougP
Nov 16 2013 17:23

My first post should have said:
\" I also definitely WOULDN\'T have an “emergency stop” wired the way you have shown\"
   

DougP
Nov 16 2013 18:31

You\'ll also have to keep in mind about your cabinet design so they don\'t have to open a cabinet with live parts to reset the RCD.
   

Davei
Nov 16 2013 21:35

I agree with above comments about your emergency stop circuit. The emergency stop circuit you have is unsafe. What would happen if the fuse was blown and you pushed the e-stop? That\'s right - nothing!!!!

It needs to be failsafe, maybe something like a normally closed switch holding in a main power contactor.
   

mralarms
Nov 16 2013 22:26

Put your latching open stop button in the 230v line to the PID\'s and pump and it also depends upon where physically you want the stop. A contactor arrangement is probably the best situation.

Also check on the american outlets. They are usually 110Vac rated and not too sure if they are legal to have in NZ
   

mralarms
Nov 16 2013 23:02

So what is the point for the emergency stop button, is it actually needed for safety?
   

5char
Nov 16 2013 23:46

@Brian W - I added the RCD, as it is the norm for brewers to use one in their control panels. I thought it would just be added protection in an environment with electricity and liquids involved. Is there any issues with this other than possible nuisance tripping?

I have taken your advice about the E-stop on board, and will be making changes accordingly.

@DougP - The way you have suggested that I wire the E-stop will only cut power to the temp controllers and pumps. If an SSR fails closed, the E-stop will do nothing.

The supply to the panel is a 32A circuit with an externally accessible isolator. I have added the breakers in the panel for convenience, and so I can isolate each circuit in the panel.

I am using 4mm^2 flex cable to supply the panel and elements, and using NEMA L6-30 plugs and receptacles. Both of these are rated to at least 30A.

Again, I apologise for incorrect polarities and colours, it was because I modified an existing diagram and got lazy. I have rectified the polarity issues in the new diagram. I will produce a neater diagram with correct symbols once I build the panel for future reference.

@mralarms - Sorry for the American outlets. I modified an existing diagram and got lazy. Maybe an E-stop is not necessary, as I won\'t be able to react fast enough to prevent electrocution (what the RCD is for), and I can cut the power to the elements with the element selector switch and contactors.

Here is the new digram, with suggested changes - http://i.imgur.com/DMDUAx8.jpg - I may not use an E-stop after thinking about it.
   

mralarms
Nov 17 2013 00:18

Dont forget the protection on your stop circuit if you use it.
   

DougP
Nov 17 2013 10:46

So you have fixed the problem with the element selector switch not selecting the correct controller, but I don’t see any reason for adding the two extra contactors for the elements. The only reason I can think of, is that you want to disconnect the neutral to the elements, but the SSRs aren’t disconnecting the neutral anyway.

You’ve also got active and neutral reversed across one of the contactors.

You could do away with those contactors and use a 2 pole changeover switch for the element select back in the original position on the SSR control side.

   

5char
Nov 17 2013 11:48

Oops, I forgot to mention the reason for the contactors on each element. I was going to switch the DC common on the SSR inputs for selecting which element can be used, but it has been brought to my attention that SSRs will leak a small amount of current when open. Not a huge deal, but not something I want. This way, I am switching the power to the contactors, which means I can mechanically disconnect each element from the supply. If an SSR fails closed, I can disconnect that element without hassle.

Sorry for the polarity error, I had just got back from work and was a bit tired.
   

BrianW
Nov 17 2013 12:48

With having two elements, 1 for boil, and one for hot liquor, im assuming that these will be in the same tank and one is used to bring the mash to the boil, and the other is used to hold it once hot? If so, then why would you have a manual selector switch? I havent read the full spec, but im guessing that your SYL-2352 will have a latching relay that you could use to have the changeover occur automatically, it also appears that you could use the alarm outputs (terminals 13,14) to power the second SSR for Hot Liquor, eliminating the need for the second PID controller.

That said, personally, I would have written all that into a small PLC with two temp inputs, powering a couple of contactors for the elements, and some relays for the pumps and fitted it all into a gewiss box.
   

5char
Nov 17 2013 13:13

The \"Hot Liquor\" element is for a vessel that just heats water. This water is used for mashing and sparging (washing the mashed grain). There is also a copper coil inside this vessel that you can run the mash water through to maintain the correct temperature, hence the need for a pump.

The boil element in a separate vessel, used for boiling the wort (mash and sparge runnings), and this is where the hops are added.
   

justsuppose
Nov 17 2013 17:54

I presume your 63A rccb is also to act as an isolator for the panel?? in which case the contactor should be after the isolator to ensure all items of equiptment in the panel are isolated when its operated..
   

justsuppose
Nov 17 2013 18:00

also as an aside.... what about putting the element selector switch in their relavant control phase conductor not the neutrals..