Some control panel wiring questions - Wire sizing & grounding

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Sean_SA

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Hi guys

I have some questions regarding wiring sizing and grounding my control panel correctly. I'm going to be running a 63A control panel 230v... 2 x 5500w elements running at a time.

The electric brewery recommends 10 gauge wire for wiring the element components(relays, contactors, fuses) for 5500w elements. 10 gauge wire is the equivalent of 6mm² in my country. 6mm² is rated at 41 amps here and 4mm² is rated at 32 amps... so seeing as each element only pulls around 23 amps can I not use 4mm² instead of 6mm²? Each element will have its own 32A contactor, 40A relay and 32A fuse.

Then regarding grounding my control panel below. There is a grounding post in the door (top left of image) but nothing in the main enclosure besides the threaded bolts used to fasten the back plate. How do I then ground the main enclosure? Should I fit a grounding bar or can I simply use the threaded bolts for the backplate as a ground post as well?

20210920_230944.jpg


Finally, and this is wire size related again. In the diagram below they show 10 gauge (6mm²) grounding wire going to the pump receptacles. In my situation I have chosen to go with 10 amp kettle plug connections for the pumps. Would I really need to use such thick wire for the grounding or could I just use 2.5mm² (14 gauge) wire?

ground50A1BBL240V_728.jpg


Thanks guys
 

doug293cz

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Hi guys

I have some questions regarding wiring sizing and grounding my control panel correctly. I'm going to be running a 63A control panel 230v... 2 x 5500w elements running at a time.

The electric brewery recommends 10 gauge wire for wiring the element components(relays, contactors, fuses) for 5500w elements. 10 gauge wire is the equivalent of 6mm² in my country. 6mm² is rated at 41 amps here and 4mm² is rated at 32 amps... so seeing as each element only pulls around 23 amps can I not use 4mm² instead of 6mm²? Each element will have its own 32A contactor, 40A relay and 32A fuse.

If code in your country allows 32A thru 4mm2 wire, and you fuse before that wire with a 32A (or less) fuse/breaker, then you are good to go.

Then regarding grounding my control panel below. There is a grounding post in the door (top left of image) but nothing in the main enclosure besides the threaded bolts used to fasten the back plate. How do I then ground the main enclosure? Should I fit a grounding bar or can I simply use the threaded bolts for the backplate as a ground post as well?

View attachment 743102

You can use the threaded bolts/screws that mount the back panel for grounding. You need to make sure that you get good electrical contact between the ground wires and all the metal structures. Make sure there is no paint in the area where you do the grounding, and use star washers.

Finally, and this is wire size related again. In the diagram below they show 10 gauge (6mm²) grounding wire going to the pump receptacles. In my situation I have chosen to go with 10 amp kettle plug connections for the pumps. Would I really need to use such thick wire for the grounding or could I just use 2.5mm² (14 gauge) wire?

Ground wiring is designed to carry temporary fault currents (just till the GFCI, or your equivalent, or the upstream overcurrent protection blows/trips), so doesn't need to be as heavy as for continuous current. US code allows for ground wires to be one size finer than the current carrying wires it is associated with in most cases. So 2.5mm2 ground wires associated with 4mm2 current carrying wires seems appropriate.

View attachment 743103

I would use more daisy chain wiring for grounding, and less star wiring than shown above.

Thanks guys
I am not a licensed electrician, but I am fairly expert at control panel design for homebrew systems. There are some electricians on HBT, and I hope they will (gently please) correct any mistakes I may have made above.

My answers embedded in blue text above.

Brew on :mug:
 

RufusBrewer

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If you want to play it safe, size your wires to match the circuit breaker rating, not the devices you plan to connect to the breaker.

The idea is during a failure status, you want the breaker to trip due to excessive current draw before the wire heats up and starts a fire.

You can avoid big fat wires by putting a breaker on a branch that is downstream of a higher rated breaker. E.g. 2 ea 30 amp breakers, each dedicated to one 5,500 element.

For ground, use the supplied ground post on the door. For a braces and belt design, sand/scrape some paint off a place to expose bare metal and create a second ground point.
 

RufusBrewer

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Also for the ground, true, the star ground is optimum design.

When you are talking inside a control panel, you can do some daisy chain design ground connections. As long as you are making sound and reliable connections, you will be fine.

You can relax the wire gauge requirements for ground wires, inside the control panel. This is especially true if reducing the wire gauge allows you to make a more solid, robust connection.

I have seen design where people oversized cables that force the designer to make fragile unreliable connections.
 

Mad Mann

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One additional note: In my 50A system there was a lot of internal heat generated when using both elements, to the point where the PID was providing false readings! Recommend you install a fan and you will need some air hole for movement. The holes should be covered to protect against contact from outside the panel.
 

maddjaxx

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I am a master electrician here in the US and have designed and wired both of my systems (1/2 bbl then 1 bbl). To reduce heat I mounted a heat sink to the side of the panel and cut a hole out so my SSR ‘s for the elements are mounted directly to it. I have never had a heat problem and my cabinet remains watertight this way. I am assuming you are using SSR’s (solid state relay ) along with a contactors to control the boil and the hlt elements as a contactor alone will burn out from the constant cycling of the pid.
 

maddjaxx

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One more thing - I added a switch so I could run one or two elements in each tank so once I reached temp I switch to one element to maintain as both are not necessary at this point
 

RufusBrewer

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I do believe Kal, aka the Electric Brewery, is using a thicker wire to the receptacle to handle any grounding problems from the other ground wires (elements, pumps, etc). Always, want a larger sized wire to handle an overload.
In the case of a ground wire, during normal operation, (or "overload") no current passes through the ground wire. If current is passing through your ground wire, literally in less than second, the GFCI should trip and kill all current in the circuit.

Even if current flows through the ground wire, the relatively short length of a conductor inside a typical control panel the conductor gauge is much more forgiving when compared to wiring in the wall or on an extension cord.

Let's look at 10 amps going through 20 feet of 10 gauge ground wire against 16 gauge ground wire.

10 gauge = 1.02 ohms/1,000 feet = 0.0204 ohms per 20 feet
16 gauge = 4.09 ohms/1,000 feet = 0.0818 ohms per 20 feet

At 10 amps
10 gauge = 0.0204 voltage drop & 2.04 watts
16 gauge = 0.8185 voltage drop & 8.18 watts

Under what conditions is the above going to make a difference?

Keep in mind, my comment was that you are best served making good, solid, robust and reliable connections inside your control panel. This true even if you make the trade off of using a smaller sized conductor to get there. Why do I make this proposition? All you have to do is review the quantity of threads in this forum that the topic is bad/failed connection points and the problems that they bring.

Over my years I have seen DIY builders go through all kinds machinations to satisfy the "bigger is better" mantra. I have seen crummy crimp connectors that do not really fit the larger cable, the stiffer cable is bent awkwardly, messy combination and layers of shrink tube and electrical tape, wire sort of jammed into spaces where not so neat and clean.

In these cases, go with a smaller cable to allow for proper connection points. Why? Because connection points are important too. It is also possible that that a hanky connection point can introduce as much resistance as the smaller gauge cable does.
 
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