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Sizing (kW & Amps) your Element & Controller

Updated: Sep 21, 2023




We all want to brew as much as we can and do it as quickly as possible however there is a limit to what we can achieve safely. Both batch size and speed are ultimately dictated by the maximum element power (kW) we can install and use, this has its limits. The article below is general advice, you must always seek professional electrical advice from a suitably qualified professional that knows and has viewed your installation. EINBREW cannot be held responsible for any direct or consequential damage caused by the exceeding of the current ratings on their products.


The first limit is the capacity of our electrical supply to the premises, and indeed the supply to the brewing room. While your property may have a capacity of 100 amps (100A) the circuit to your brewing room might only have a 16A capacity, limited by the wiring. So let’s assume the wiring of the brewing room does have a 16A capacity, what size of (single) element should we choose and what size of controller do we need?


The power output of the element is dictated by its electrical resistance (which is fixed) and the voltage supplied to it. The problem is, the voltage you receive from your power company varies throughout the day, this means for any heating element with a given (fixed) resistance, the power output will vary with the voltage supplied to it. As the voltage increases, the power output will go up, with the voltage decreases the power output will go down. Moreover, as the voltage increases the current through the element will increase and you can easily exceed your capacity, blow fuses and trip breakers and worse, lose a brew!


Elements are specified with a power output at a defined voltage, for example a good quality element WILL have a rating stamped on it, for example this could be "2.9kW @ 230V". This means this element will deliver 2.9kW at that voltage of 230V taking 12.6A, it will deliver less at lower voltages taking less current and deliver more at higher voltages taking more current. So as the voltage varies, the power AND current (amps) also vary!


Voltage on a 230V system can (legally) vary as much as +/-10%, the range can therefore be 207V to 253V. If we now consider a 3.6kW @ 230V element, this will draw 15.56A (but only at 230V). If you have a 16A limit, many people will choose a 3.6kW element, because at 230V this will take 15.65A, just under your 16A maximum but you must consider the normal supply voltage changes throughout the day, your voltage supply many never be 230V. This same 3.6kW element connected to the various voltages changes will give:-


At 207V, will deliver 2.914kW and draw a current of 14.0A (amps).

At 230V, will deliver 3.598kW and draw a current of 15.6A.

At 240V, will deliver 3.918kW and draw a current of 16.3A.

At 253V, will deliver 4.354kW and draw a current of 17.2A.

The above currents do not account for pump, controller and other ancillary loads!


So if you are on a 230V system and choose a 3.6kW (@230V) element you will almost certainly exceed the capacity of your 16A supply, and if you choose a 16A controller, you will blow fuses and damage both the controller and your property’s wiring system. Unfortunately many people with a 16A capacity do choose a 3.6kW (@230V) element, this will cause long term damage because while the element is ‘only’ 15.6A at 230V, the voltage will almost certainly rise above 230V on occasions and you will damage your wiring and controller.


It should be noted that even if your voltage does (impossibly) stay at 230V and you run at 15.6A on a 16A system, you will blow (thermal) fuses, simply due to long term heating and degrading of the fuse and fuse holder.


So how do we choose our maximum element power. Take your brewing room loads and add them up, Pump 50W ( 50W/230V = 0.3A), controller 5W (5W/230V = 0.03A). This leaves you with 16A minus 0.3A, minus 0.03A, resulting in 15.67A capacity left. Now multiply this by 90% (0.9) giving 14A capacity for the element. The kW power of the element is defined by Power = voltage (230V) x current (14A) giving an element power of 3.220kW @ 230V, this is the absolute maximum we would recommend for a 16A circuit with a 16A controller. This 3.220kW element would draw a current 14.6A if your supply voltage rises to 240V, and if it rises to 253V the current draw would be 15.4A.


We'd even recommend that you consider adding an extra margin of safety and round down from 3.220kW to 3.0kW. If you have information that your local voltage supply does not vary as high as 230V + 10%, you can use a slightly higher power element, but do the calcs! You can increase the element power if you 'know' your voltage never goes higher than a defined voltage, be warned, even if historically it has never gone higher that say 240V, with the increase of microgeneration in the community, this has often the consequence of pushing your local voltage higher than historical maximums.


Conclusion, on a 230V (+/-10%) system with a circuit capacity of 16A, you should consider a maximum element power of 3kW element, controlled by a 16A controller. ***It is important to consult a locally qualified electrical professional. ***

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