||11-04-2009 12:17 AM
Electrical Primer for Brewers
I've seen a lot of electrical questions pop up lately, many of them frequently asked. So I am going to share what I know and hopefully compile a reference that will answer 99% of the questions out there.
My background is in industrial control systems and system integration. Basically electrical controls for large industrial equipment. I am not an expert on residential power but I am comfortable working with it and understand it's principals. Local building codes may vary so if you are running a new service from your breaker, consult with local codes first.
*I am not going to go through all of the blanket disclaimer mumbo jumbo other than this;
Electricity will kill you dead
QUICK! So respect it.
You and you alone are responsible for burning your house down or causing yourself or others great bodily/mortal harm. So please be careful.
If you have any doubts or questions, put the wire strippers and screw driver down and seek an expert opinion.
Here is a list of important things to understand, know, and apply when working with house hold power and various electrical components of the brewery.
Volts= the potential to do work. Think of it as electrical pressure/psi.
Amps=The amount of electrons flowing through an electrical circuit. Think of it as an electrical gallons per minute.
Watts = Volts * Amps. This is the actual power a system uses.
A few terms:
Service/Supply- Where electricity is coming from
Load Where electricity is being used/sent to
Line/Leg one side of a 240 Volt system is usually called a Line or Leg, since there are two separate 120V services one is called Leg/Line 1 and the other Leg/Line 2.
A primer on Residential AC power:
I am going to over simplify this and omit the differences between AC and DC power for the sake of ease of understanding. It is important to note that the two are very different creatures and are not compatible.
Also 240/220 and 120/110 are interchangeable, the actual reading in your home is usually somewhere between those.
Most Residential is what is called a split 240v single phase. By the time it comes into your house from the transformer it is split into three wires and then goes into the circuit breaker.
One wire is 120V(A), another 120v(B), and Neutral. Each of these is attached to its own Bus or Bus bar. A Bus is a piece of metal where you can attach wires and devices (breakers). A fourth wire is brought in and is called Ground. There will be a rod buried in the ground close to the residence with a wire attached to it. This wire is brought into the main panel and attached to the Neutral bus and to its own bus. THIS IS THE ONLY PLACE NEUTRAL AND GROUND SHOULD BE BONDED, from that point on the twain never should meet again.
If you take a volt meter and measure from 120v(A) and Neutral, as well as 120v(B) and Neutral you will read 120 Volts. Now if you measure between 120v(A) and 120v(B) you get 240 Volts. The 120 Volt receptacles in your house are divided up into circuits and then attached to either one of the 120V A/B and Neutral.
For larger appliances like a water heater, dryer, or stove, have both 120v(A) and 120v(B) as well as ground and sometimes Neutral. These are the 240 Volt appliances.
As far as we are concerned, the ground is provided for safety. It provides a path for electricity to flow through in case of emergency. The metal shells of appliances are attached to ground so that in case a wire comes loose and touches the metal. Without this, the next person who touches the shell could have the crap shocked out of them because electricity is sitting there waiting to go somewhere. So, metal rigs and pots need to be well grounded. Plastic containers holding liquid and a heating element should have some kind of ground touching the liquid.
With the metal casing bonded to ground electricity will start to flow causing the circuit breaker to trip turning off the circuit.
This is why we dont bond Neutral and Ground anywhere else in the house. Since Neutral is used to carry current for 110 Volt circuits you dont want that current to be attached to anything you may touch.
Hopefully this has demystified the difference between 120V and 240V power, Neutral, and Ground.
Current Ratings and Circuit Protection:
The electrons flowing through a wire or subject to the same laws of physics just like everything else. As the electrons move the encounter friction which creates heat. The amount of friction created is subject to the size wire you use. Imagine two pieces of pipe, one is 1 inch wide and another is 6 inches wide. It is easier to push 1000 gallons a minute out of the 6 inch pipe than the 1 inch pipe because there is less friction. A wires AWG or Gauge is the width of a wire and the smaller the number, the larger the wire.
The reason why this relationship is important is that if too many Amps travel through a wire it starts to build heat and could get hot enough to melt/burn the protective insulation off leaving a bare wire. Worse still, the wire could get hot enough to cause whatever it may be touching to catch fire. Here is a table showing the maximum current ratings for the most common sized wires.
14 AWG/15 Amps
12 AWG/20 Amps
10 AWG /30 Amps
8 AWG / 40 Amps
6 AWG/55 Amps
To prevent a wire from getting too hot circuit breakers and fuses are used. These guys sense how much current is passing through a wire and if the current is greater than the fuse/breakers rating it will open up, essentially disconnecting the over drawn circuit from power. The size of the circuit breaker or fuse is determined by the size of wire attached to it. So if 14 AWG is used, nothing larger than a 15 Amps breaker/fuse can be used. If 10 AWG were used then anything up to and including a 30 Amp breaker/fuse may be used.
Breakers and fuses are meant to save property NOT LIFE! 1 Amp is more than enough to kill you.
Once the service wire makes it to the brew rig it can be redistributed using smaller wires. The important thing to remember is every time the wire size gets smaller, it needs a fuse or breaker rated no larger than the wires maximum rating.
For example, if a 30 amp services is brought to the brew rig and a circuit for the March pumps needs no more than 15 amps then 14 AWG wire may be used. To do this though, a 15 amp fuse/breaker must be installed between the two. So the 10 AWG wire providing power will go into the supply side of a 15 Amp breaker/fuse and the 14 AWG wire going to the march pumps goes into the load side of the breaker/fuse. The 14 AWG wire is now adequately protected.
GFCI breakers are designed to control a maximum amount of current like regular breakers but they are also designed to monitor if current is leaking outside of the circuit. Ideally, all current leaving the breaker should return to the breaker after it has been used. When the GFCI breaker sees less current returning than going out, it assumes that current has found an alternate path to ground and trips. The thresh hold for the breaker to trip varies but it is only a few milliamps (0.001 Amps) difference.
DO NOT DEPEND ON A GFCI TO SAVE YOUR ASS! Good workmanship and clean wiring should be your primary means of safety.
Yes, a 240 Volt 2 pole breaker can be used and will maintain GFCI protection if you split the 110. Follow the directions, it will show you how.
Water Heater Elements:
Water Heater elements have 2 parts to their rating. One is Wattage and the other is Voltage.
From these two numbers, you can determine the amount of current (Amps).
Amps = Wattage rating / Voltage rating
Example: A 5500 Watt element at 240Volts will draw 22.92 Amps.
It is okay to run a 240 Volt element at 120 Volts but not vice versa.
Halving the voltage does not halve the Wattage. When halving the voltage the Watt output is divided by 4.
Example: An element rated for 5500 Watts at 240 Volts used at 120 Volts has an actual Wattage rating of 1375 Watts. To determine the current draw, divide 1375 Watts/ 120 Volts = 11.46 Amps.
To run an element at 240 Volts, one terminal is wired to 120v(A) and the other to 120v(B).
To run an element at 120 Volts, one terminal is wired to 120v(A) or 120v(B) and the other to Neutral.
Device Protection: (Added 11/4)
To protect a device, (ie PID Controller, March Pump, Panel Lamp, etc, etc) it needs a dedicated fuse.
There are two main types of fuses, Fast Acting and Slow Blow.
Fast Acting fuses respond very quickly to over currents and should be used on devices that are very sensitive and easily damaged.
Slow Blow Fuses - Have a bit of forgiveness in them when it comes to over currents. They are designed for devices like pumps that have short periods surge current. It takes a sustained over current to cause a Slow Blow to pop.
Fuses should be rated for 125% to 150% of the rated current draw for a device.
Example: March pumps draw 1.4Amps at 120V. A proper sized slow blow fuse would fall some where between 1.4*1.25 = 1.75A and 1.4 * 1.5= 2.1A. So a 1.75 Amp or 2 Amp Slow Blow fuse would be acceptable per pump. Start on the small end and if there are nuisance blows (fuse burns for no real reason) then goto the next size.
Suggested fuse sizes:
PID Controllers - 0.25A Fast Acting (Auber suggests 1A Slow Blow but that is way too much in my opinion.)
March Pumps - 1.75 to 2 Amp Slow Blow.
SSR - For the supply side of the SSR use a Fast Acting fuse equal to or less than the rating of the SSR. Devices being switched by the SSR will need individual fuses should they be protected.
The next installment will be on components used for controlling elements and pumps. If there is any interest that is. Hope it helps.