Believe me, I've been reading. I'm terrified of this stuff, but also intrigued. I post these questions in the forums in hopes that someone more read than myself can guide me and ensure I'm reading the right stuff -because theres plenty of very wrong stuff. Fortunately, you guys are always friendly and helpful, and I appreciate it.
I am using 240v 30a 120v coil relays. I just got a little confused because P-Js diagrams always call for "contactors", but when I ordered his specified part number from Auber, I recieved a "relay" instead. I'd built and tested my first box before I noticed this, and the box operated perfectly. I just wanted a second opinion before I built another box with the same part number. Sooo... am I correct in understanding that the words "contactor" and "relay" are interchangeable?
The other issue I'm having is understanding the load on individual circuits. I understand that with the 5500w element pulling close to 25 and another 2 from each pump, my system can pull nearly 30 amps, and as such would require 10g wire.
I also understand that the fuses prevent the circuit from running greater amperage that it allows, but does that I mean I can run a lower guage wire after the fuse only, or is it safe to run a lower guage wire for that entire circuit?
I am also I bit unclear about advise that was given regarding running lower guage wire to the relays as it is "only powering on the relay, and not part of the circuit beyond the relay". Please advise.
Contactors are relays, but not all relays are contactors. The parts you have meet the definition of contactor.
To understand currents and loads you have to understand that current always flows in a loop, and the entire loop has the same current flowing throughout. However the voltage may vary at different locations in the loop, and the voltages at many points in a loop change depending on how much current is flowing.
The following drawing shows a simplified diagram of main load current flow in a two element, two pump, control panel.
The diagram shows current flowing in one direction, but with AC the direction of current flow switches 120 times/sec. Note that between branch points (called nodes) the current is constant, and the the sum of currents flowing into a node must equal the sum currents flowing out of a node. In almost all cases in typical designs, a node has one input and multiple outputs, or multiple inputs and one output. Multi input, multi output nodes are almost never used. Nodes can be physically implemented as bus bars, multiple connections to a component terminal, or multiple wires connected together (wire nut, crimp, soldered, etc.) The current in a load is determined by the voltage on either side of the load and the resistance (element) or impedance (coil, motor, etc.) of the load. In the example above, all the Hot 1 (black) lines are at +120V, Hot 2 (red) lines are at -120V, and the neutral (white) lines are at 0V. The polarity of the hot lines switches from plus to minus (and vice versa) 120 times/sec.
Lower gauge wire can be used on the load side of a fuse, or very short runs on the supply side (this is a judgement call.) For 240V loops, both hot lines need to be fused when transitioning to smaller wire. For 120V loops, only the hot line needs to be fused. The neutral does not need to be fused when going to finer wire. Likewise when wanting to disconnect voltage from a loop, all hots should go through a mechanical switch, but neutrals don't need to be switched. Note that SSR's do not disconnect voltage, they switch from high current to very low (mA's) current.
It may help you to think of current as analogous to water flowing in a pipe, and voltage as the water pressure which causes the water to flow. Our systems consist only of pipes and restrictions in pipes (the loads.) We don't usually have anything analogous to surge tanks. Mechanical switches are like blocking quick disconnects (they shut off flow, and physically disconnect the pipes.) SSR's are like valves that leak a little bit when closed.
This probably doesn't answer all your questions, but I hope it helps.
Brew on
