Wiring on mhemeryck

Electrical cabinet

Tue, 13 Jul 2021 00:00:00 +0000

In earlier posts, I did provide an overview of the architecture of my custom-made home automation system. I also did describe some specificities related to a wired home automation setup. For my system, I decide on wiring everything in a star-configuration, meaning all wiring around the house for lights, push buttons, … all converges in a centralized electrical cabinet. The focus of this post is to show you some details of what this cabinet looks like and some pointers for practical issues I had run into.

This post is a part of a larger series of posts on my home automation setup. See the home automation overview post, to learn about the rationale and a description of the other posts!

Inside the cabinet

Given the star-configuration for all of the lights, the amount of wiring in the central electricity cabinet quickly adds up. The following picture shows a work-in-progress view while laying out the cables:

Be sure you have a consistent labelling scheme while pulling all of the cable. Looking back at these pictures, I think it is a bit of miracle I did not miss anything …

Terminal clamps

Besides from labelling the cables during the pulling of the cables, I also did use terminal clamps, like the WAGO rail-mount terminal blocks. On one end of such a block, you have one or more terminals where you can connect your wires. The other end on this block can then later be used to connect whatever you need.

The next figure details the terminal clamps I did use, the WAGO TOPJOB S 2003-7642.

The details include the nominal voltage and current ratings, wire gauges, the physical width of the clamp itself, etc. The lines next to the clamp indicate the different clamp variants available. The first 2 variants are 2 “stories” high (2 electrical connections on a single clamp) whereas the bottom 2 feature 3 “stories”.

Each story represents a single electrical connection, isolated from the other stories. The number of stories all have to do with saving space inside the cabinet: 2 stories really mean you need only half the amount of clamps. Additionally, since most mains voltage wiring is for single phase electrical connection, you can group the phase and neutral wire in one such clamp.

Aside from the first row indicating the details about the terminal clamp, the figure also details many different variants of jumpers available. These jumpers can be placed in the middle ends of the clamps and provide a connection between the different clamps, which facilitates making electrical parallel connections.

Functionally, these terminal clamps does not do all that much. In terms of costs, a single block is not that expensive but since the amount of blocks you need quickly adds up, so do the costs. Nonetheless, I would still highly recommend it to keep a clear overview while inside of your cabinet.

Relays

The next picture shows 2 DIN-rails with all of the terminal blocks for my lights.

top row: termination of phase (brown) and neutral (blue) wires.
bottom row: termination of 2 more wires which I intend to use as a [DALI] bus¹; DALI+ (grey) and DALI- (black).
jumpers: middle of terminal blocks
orange spacers: each set of blocks between these spacers represent a single electric circuit. This makes it easier to map the one-wire diagram to the actual wiring inside the cabinet.
green / yellow wires: these are terminated separately on the copper bar (visible between the two DIN rails) and directly connected to the main earth wire.
two-level terminal blocks: the terminal blocks used here have 2 levels, i.e. the outer 2 terminals are connected as well as the inner 2. A multitude of such terminal blocks exists, ranging for single to multiple levels as well as different functionalities (built-in diodes, resistors, …). Here, two-level terminal blocks were used mostly because of space constraints.

Note that at this point that the wires from the light fixtures in the house were just connected to these terminal blocks: having these blocks there means you can later still have all flexibility for connecting them elsewhere.

The next part is connecting them to the unit that contains the relays themselves. The unipi relay outputs KB lists all of the details for connecting a single relay:

This connection in itself is not all that complex for a single relay. Since multiple lights on the same circuit are connected to the same circuit breaker, there is the practical concern of how to ensure these are all properly connected in parallel while still maintaining again a good overview. The following picture shows another set of terminal blocks that I did use for this (orange blocks on the left of the unipi unit):

phase wire (brown): the terminal block holders (orange, left from the unipi module) hold a set of terminal blocks which have one end connected to the circuit breaker, the other ends serve to distribute the voltage to multiple relays.
neutral wire (blue): since all neutral wires of a single circuit are placed next to each other, these can just be connected in parallel using a jumper.
relay: each of the lights are connected to “RO” connections coming from the unipi module.

Push buttons

Next to the series of clamps for terminating the cables for the lights, I also did use the same type of clamps for terminating the SVV analog signaling cable:

At the top, the incoming signaling cable is terminated. Spacers are placed series of clamps which belong to the same signaling cable run. The bottom part then connects each of the signaling wires to a digital input somewhere lower in the cabinet. In the middle of the clamps, you can see a number of overlapping jumpers. These jumpers have been set up such that they only make an electrical contact in a fixed number of slots, in this case for connecting one of the wires for each cable run to 24V.

As before, the following image shows the electrical connection from the signaling cable to the unipi digital input unit. The DIGND corresponds to the ground level of your 24VDC power source. The DI level is the signaling cable to one of the push buttons. Pushing a button means the 24V level gets connected to the signal cable and thus giving a DI level of 24V. For more technical details, consult the unipi digital input KB.

As can be seen from the following picture, making the physical connection between the incoming signal wires and the unipi units is easier than for the relay unit, shown earlier.

There is no need to have dedicated circuit breakers for the different signal wire cable runs; all of them can run on the same 24VDC power source. Also, since the wire diameter is much lower, the screw connectors can just be used directly to terminate multiple wires and effectively provide electrical parallel connections. Since each of the green screw connectors could have up to 4 signal wire connections and 1 ground level, I did use 4-wire SVV cable to connect them to terminal clamps higher up in the cabinet. Note that I also did use my color coding again here (red / yellow / blue / white).

Closing thoughts

I started this post with some scary pictures of electrical wiring spaghetti.

However, it turns out that with proper planning, schematics and some determination, it was actually quite doable to wire the full cabinet together. Terminal blocks also help a lot in this process: it makes it easier to visually separate everything, removes the need to do all of the wiring in the beginning and enables rewiring at some later point in time.

As before in the series, I did try to explain how to make the connection for push buttons (inputs) and relays (outputs). The connections for the inputs were a bit simpler in the sense that the wiring runs on a safer lower voltage of 24VDC. For the relays, as it runs on mains voltage, there are the additional constraints of the need to add in a circuit breaker for each electrical circuit as well as a higher wire gauge. Consequently, I did some extra clamps to ensure the proper connections.

I did opt for this approach at the time, since it seemed the most simple to me (comes closest to a “classical” setup), the most flexible in terms of rewiring (all wires are within reach) and does not depend on some proprietary, more expensive closed-off bus system. In hindsight, the main disadvantage of such a central star-configuration is the excessive amount of wiring you need to deal with. For costs, you have the additional costs of the wiring material itself. In terms of work, I did do all of the connections myself, so even though I did not lose any money on that, it surely was a very long, laborious process I might rather avoid in the future. With that in mind, at some point in the future I will surely have a closer look at bus-based systems.

DALI is a bus system for digital light control. In theory, you could do full light control with DALI only (removing the need for relay-based control), but this means all of your light fixtures need to be DALI-aware. ↩︎

Wiring

Tue, 29 Jun 2021 00:00:00 +0000

In this post, I will take a deeper dive into the bottom layer, the wiring. Different kinds of inputs and outputs can be discussed, but for the sake of simplicity, I will focus on a push button operating a lamp. These components will also come back later on in the series.

This post is a part of a larger series of posts on my home automation setup. See the home automation overview post, to learn about the rationale and a description of the other posts!

I will cover:

caution: safety first
principle: operating principle behind a light push button and relay
conductors: the physical wires and cables themselves

A mandatory word of caution (!)

This post will touch a number of points where working with mains voltage is required. If you do not have any background in working with electricity, please be sure you get help from a qualified electrician. Also, some of the details really only apply to my local regulations (Belgium), so make sure you are well aware of your local regulations. Related to this, some of the terminology used might be a poor translation of some term which would have been straightforward in my native language (Dutch). Even though I had a background as an electrical engineer, I still got a local professional electrician involved to ensure the overall safety …

Principle

Relays

A relay is an electrically operated switch. The voltage over two of its terminals can then control (switch) the voltage over the two other terminals. The control voltage will typically be on a safe, low voltage, whereas the other terminals can carry higher (mains) voltage. You can use it to control any other electrically switched device, e.g. lights or motors.

Push buttons

Where the relay serves as the output, the push button, together with a digital input sensor, serves as the input. The push button itself is actually a simple mechanical contact. Pushing the button results in the internal mechanical contact making an electrical contact.

There are two types of contacts: a normally open (NO) contact or a normally closed (NC) contact. Normally open means that the mechanical contact maintains an open electrical contact for the majority of the time, unless the button is pressed. Normally closed is then the opposite situation, meaning a closed electrical contact whenever the button is not pressed. For push buttons, such as those to operate lamps, an NO contact would typically be used. NC contacts make sense for situations where you want to be sure that the electrical contact is always guaranteed, e.g. a sensor for an alarm system. Loss of signal for an NC contact might indicate the sensor has been tampered with.

The voltage used for a push button is typically not mains voltage (240VAC), but rather a lower, safer voltage like 24VDC. Typical digital input sensors such as those found on DIY devices like the arduino or raspberry pi would operate on 5V or 3.3V, respectively. For wiring a house, this is not an option because of the longer line runs and the resulting voltage drop related to the resistance of the wiring itself.

An important thing to consider in the push button - lamp constellation is that the way the push button is used is stateless. Considering the lamp is off, one push would switch the light on. Another push would switch it back off again. Based on the position of the push button itself, you would not be able to tell the state of the light. It differs from a rocker switch in that it only maintains the contact for the duration of the push of the button. While these observations might be rather trivial, for the purposes of modeling them higher up on the stack, they are relevant.

Conductors (Belgium only)

Relays

The following image shows a typical tube containing 3 wires with diameters of 1.5mm², fit for lights.

For the cables carrying mains voltage, the following rules are relevant (non-exhaustive see e.g. ¹, ², project huisinstallatie naslagwerk):

for circuits up to 16A (typically lights), a min 1.5 mm² cross-section wire is to be used
for circuits up to 20A (lights and / or others like power sockets), a min 2.5 mm² cross-section wire is to be used
each of the circuits need to have proper matching circuit breakers
all cables consist of neutral wire, live wire and an earth wire
color coding:
- neutral: blue
- live: brown
- earth wire: green / yellow
max 8 consumers (lights, power sockets) per circuit

Keep in mind:

circuit breakers protect your wires from burning up
residual-current devices protect living things!

Note that this is only a subset of the rules and pointers to keep into account while doing the physical wiring. Other things to consider are the type of cable (in a plastic tube or as a cable), solid vs stranded wire, stiff vs flexible wire, etc. …

Push buttons

Contrary to the cabling for the lights, the push buttons run on the lower, safer voltage of 24VDC. Consequently, the wire diameter can be a lot smaller and there is no strict requirement on the use of circuit breakers. An additional advantage in terms of safety compared to a more “traditional” installation is that the push button itself is never connected to the consumer on the higher mains voltage.

The following image shows an SVV signal cable, which is typically used in Belgium for analog signaling applications. I did some online research into the international naming for this type of cable, but there does not seem to be any. For the sake of the discussion here however, the characteristics are actually more important:

small diameters, on the order of 0.8mm²
solid core, as this makes connecting to the push buttons easier as they mostly have screw connectors
multiple wires in 1 cable (as shown in the picture). These cables mostly come with either 4, 8, 12 or 16 wires.
visually clearly differing wires, i.e. highly contrasting colors for the wires

The idea of having this multitude of wires in one signal cable is that you would ideally need one cable run for e.g. the push buttons for one floor. Each push button contact then uses one of the wires of the signal cable. Apart from the push button contacts, you also need to reserve one of the wires for the positive level. Essentially, the push buttons thus internally connect 1 signal wire (on ground level) to the common positive level – which can be detected by your digital input readout.

As a side note, some manufacturers also have push buttons with a built-in LED light. If you want to provide power to that LED, you would also need to reserve an extra wire for that feature.

Concerning the various colors available in the signal cable, I did find it useful to have a fixed order in which to assign them to the different inputs. I would always use the red wire for the positive (24V) level. The remainder of the wires would then be assigned according to the colors on the visible electromagnetic spectrum. For example, you could go from black, grey, brown, orange, green, blue, … all the way to white.

The following image shows the wiring diagram for a simple NO push button from Niko, a Belgian manufacturer of electrical switches and sockets.

The diagram indicates the push button can be used to switch voltages up the 230VAC, but since we’re only interested in for the signaling application, it might just as well be a lower voltage. Also visible is the optional LED light.

Closing thoughts

The focus of this post was first to describe the basic principle of some key components, the relay and the push button. I did want to highlight what exactly they are and also how the operating principle relates to the modelling higher up in the stack, e.g. the fact that I mostly consider the push button to be stateless.

The second part of the post dealt with the details of the physical electrical conductors connecting to and from these components. Relays, for lights, use 3 x 1.5mm², whereas higher loads require a higher wire gauge of 3 x 2.5mm². The push buttons can use a lower wire gauge of e.g. 0.8mm² since you would run these on a safer, lower voltage of 24VDC. While the regulations pertaining to the wiring are specific to my country’s regulations, I still hope someone else might learn from it!

Finally, always keep safety into account! Even you feel you are really knowledgeable, I still think it was an added value for me to involve a local professional electrician to get proper hands-on advice.

ISBN/EAN 9789030142942 ↩︎
the official Belgian regulation is the AREI ↩︎