Sizing Wires

Heating Element Current

There is a lot of discussion in the electric brewing community about the correct wire sizes for a electric home brewery. To understand wire sizes you need to understand that the power in your house has two parts - voltage and current. Also, you need to understand that current, not voltage or wattage determines your wire sizes.

Household water heater elements come in voltage and wattage ratings, and to come up with current you divide watts by volts:

120 Volt, 1500 Watt = 12.5 Amps
120 Volt, 1650 Watt = 13.8 Amps
120 Volt, 2000 Watt = 16.7 Amps
240 Volt, 3500 Watt = 14.6 Amps
240 Volt, 4500 Watt = 18.8 Amps
240 Volt, 5500 Watt = 22.9 Amps

Brewery Power

Once you know the current required for your heating element (or elements) add the current drawn by everything else, which usually isn't much - usually less than 2 Amps including a pump motor, to come up with the total current drawn by your electric brewery.

Next you step the current up to the next standard breaker and wire size to feed your electric brewery.

Two 18.8 Amp or 22.9 Amp elements that will be on at the same time need a 50 Amp breaker and #6 copper, or #4 aluminum wire.
18.8 Amps & 22.9 Amp elements need a 30 Amp breaker and #10 copper, or #8 aluminum wire.
14.6 Amp & 16.7 Amp elements need a 20 Amp breaker and #12 copper wire.
12.5 Amp & 13.75 Amp elements need a 15 Amp breaker and #14 copper wire.

Heater Element Wiring

To choose the correct wire size for your heater element or elements you need to know the current rating of the flexible cord you will be running to your heating element. And these ratings are not the same as the NEC Code ratings for your house wiring.

 Comparing NEC House Wiring ratings to SJOOW cable (the most common extension cord type cable used in home breweries):

NEC #14 copper house wire = 15 Amps
SJOOW #14, 300V, 3 wire extension cord = 18 Amps.
SJOOW #14, 300V, 4 wire extension cord = 15 Amps.

NEC #12 copper house wire = 20 Amps
SJOOW #12, 300V, 3 wire extension cord = 25 Amps.
SJOOW #12, 300V, 4 wire extension cord = 20 Amps.

NEC #10 copper house wire = 30 Amps
SJOOW #10, 300V, 3 wire extension cord = 30 Amps.
SJOOW #10, 300V, 4 wire extension cord = 25 Amps.

Many homebrewers believe that #10 SJOOW cable is needed for their 4500 and 5500 watt elements when they really only need 3 wire #12 SJOOW cable.

Internal Controller Wiring

To choose the correct wire size for your brew panel you need to understand the maximum ampacity for chassis wiring, and this is also not the same as the NEC Code ratings for the romex cable in your house walls. These ratings come from The Handbook of Electronic Tables and Formulas for American Wire Gauge. This data is also in NEC Table 310-16.

#14 THHN copper wire is good for up to 25 Amps
#12 THHN copper wire is good for up to 30 Amps
#10 THHN copper wire is good for up to 40 Amps

 For comparison, here are the Romex house wire capacities that are often mis-quoted for chassis wiring.

Romex #14 house wire is rated for 15 Amps
Romex #12 house wire is rated for 20 Amps
Romex #10 house wire is rated for 30 Amps

Accessory Wiring

Because the only heavy current carrying conductors are the wires feeding power to your heating elements, these are the only wires that need to be rated for high current. Other cables like the wiring to your PID, indicator lamps, etc. are perfectly safe if run with a smaller wire like #22 gauge.

Wiring for accessories that plug into your panel like pumps, etc. needs to be sized correctly and protected with a fuse or breaker to protect the internal wiring.

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