A Guide to LED installation Safety and the Importance of Fusing
Here at UltraLEDs the safety surrounding LED installations is paramount, we have assembled this useful guide to highlight with the safety aspects surrounding Low Voltage LED Circuit installations to help you with safely installing your LED circuit, efficient and reliable as possible.
There are 3 areas of safety in this guide we shall be looking into, these areas are:
- The Importance of fusing
- The Importance of Wire Selection
- Conservative Low Voltage Design
- Cable Management
- Circuit Voltage
- Driver Quality
- Surface Mounting
The Importance of Fusing
The primary function of using a fuse in a circuit is to protect the conductors in the downstream of the current by providing short circuit protection and over-load protection against any over currents that may occur within the circuit.
An overcurrent is any current running through a circuit that exceeds the ampere (Amp) rating of any wiring or componentry in the circuit.
An Introduction to Overcurrents?
There are two types of over current to be aware of when building a circuit.
- An overload occurs when the the current exceeds the amp rating of the wiring or components in the circuit. This can happen when there are too many components connected to the circuit, or a component malfunctions and causes a higher than normal current to flow.
- A short circuit occurs when an accident or malfunction causes the current to flow on an unintended path bypassing the circuit components.
- In this situation a very high current will flow causing components to heat up quickly.
- Purpose of a Fuse
- These sustained overloads can eventually overheat circuit components and create potential fire risks. A fuse is designed to blow when the current flowing through it exceeds a precise amount.
- Including a fuse in your design means the circuit will break when the too much current flows through it, protecting the wiring and components.
Overcurrent Reaction Time Explained
All overcurrent protective devices have a "reaction time" from when a circuit fault occurs and the fuse blows. Throughout the time it takes for the fuse to blow, there will be a constant stream energy flowing through the fuse and that energy is measured in I²t.
There two elements to the fuse’s "reaction time".
1)The time taken for the fuse element to melt, this is known as melting time (Tm).
2) The time taken stem the electrical arc, this is known as arcing time (Ta).
The total time taken for the fuse to blow from to an overcurrent until the fuse stops the current flow is known as the total clearing time. Tc + Tm + Ta, During this clearing time, there is energy is being "let-thru" the fuse.
The downstream components are then subjected to this extreme energy as it passes through the fuse (if only for a few milliseconds).
In order to specify the correct fuse to be used in a circuit, the engineer must understand the pulse cycle withstand capabilities of the downstream circuit components and select a fuse that has a let-thru energy below that of the components in the circuit.
You can calculate the size of the fuse required by looking at the smallest conductor to be connected after it and choosing the next fuse rating below it’s capacity.
More than one fuse can be used on a circuit, for example if there are a number of smaller wires connected to a high power driver, multiple fuses can be used to protect each branch of the circuit.
Here are four things to take into consideration when wiring fuses into circuits:
- Connect the fuse on the positive wire as close to the power source as possible
- Differentiate fuses
- where one fuse is connected after the other, typically where a circuit branches, ensure that the fuses are of different sizes so that it's clear which one will blow for a given fault. This will make future fault finding much easier.
- The BS7671 regulation requires the reaction time of the fuse to be 300 milliseconds or less.
The Importance of Wire Selection
As current passing through a wire it generates heat. If a wire gets too hot its insulation will begin to soften, exposing the conductors and allowing them to touch. This short allows more current to flow through the wire creating yet more heat. The circuit is now at increased risk of causing a fire or burns if touched. At the very least, the installation will no longer work, requiring a maintenance visit incurring inconvenience and cost for the end user.
Wiring and Current Handling
There are several factors that affect how much current a wire can safely carry, but as a general rule the thicker it is, the lower its resistance, the less it heats and the more load it can take.
The quality of the conductor and material used for insulation also makes a difference, standard PVC insulation is made from PVC with a maximum temperature of around 80°C. More specialised cables are also available with hardened insulation with a higher melting point allowing them to run at increased temperature. The thinner insulation also allows better dissipation of heat meaning that their current rating is significantly higher than a standard cable of the same thickness.
Unlike mains cable, there isn’t a single standard to which low voltage wire must adhere. It’s therefore important to understand how the manufacturer has rated the cable, and to buy from a reliable source.
Cables are sized according to the cross sectional area of the conductor in mm² or AWG – American Wire Gauge. Remember when using AWG that the bigger the number, the smaller the conductor!
The table below gives a useful indication of how much current a cable might be expected to carry.
You can calculate the size of a cable to use by adding up the current in a circuit and selecting the wire that is capable of handling the required load. It is advisable to select a wire that can handle at least 20% more than it’s required load. This has the added benefit of reducing voltage drop – the amount of voltage lost between the power source and a luminaire.
Advantages of Ultra Cable
Large LED installations can draw a lot of current. Ultra LEDs have developed a range of Ultra Cable specifically for these demanding applications. British made with hardened insulation and high quality copper conductors, our 0.5mm² cable is rated to 11A - up to 3.5x more than a standard equivalent.
Ultra Cable simplifies installation design because the lightweight cable is easier to handle and route and can be used throughout an installation. Choosing Ultra Cable often results in overall cost savings in an installation project and maintains efficiency and reliability.
The new Ultra Cable is available in 4 core and 5 core versions for RGB and RGBW circuits respectively.
Conservative Low Voltage Design
It's important to be conservative when installing low voltage lighting. Backup statement. Ambient temperature, heat dissipation. Following some simple guidelines will help ensure the efficiency and safety of your circuit.
Avoid bundling cables together, as this can cause them to trap heat and increases the chance of on the wire insulation. Always keep cables separate and clip the cables to a secure surface to help with heat dissipation. Where cables pass through a hole, ensure the hole is adequately protected to help avoid any tearing to the insulation of the wiring.
Consider Circuit Voltage
Where you can, use a higher voltage system, as a 24-volt system will deliver the same power of a 12-volt system with half the current running through it, reducing the risk of over-current conditions as mentioned in the Importance of Fusing section. A higher will also allow the use of thinner cabling which is easier to manage.
Choosing a High Quality Driver
A high-quality driver will usually be better tested than a low-quality version and will run at a cooler temperature. It may also offer better protection against fault conditions, such as over-current, high temperatures and short circuit.
Therefore, you should make sure you buy your driver from a reputable seller. However, this should not be relied upon as the only protection method, so a driver should be used alongside a fuse, rather than in place of one.
High quality drivers from a reputable source will also be more thoroughly tested and safer in general.
Using the right surface
LEDs can get hot even in normal operation, so it’s important that they’re installed on a surface that can help to dissipate some of that warmth. A metal surface is great for this, as the material is a good conductor of heat, which can help prevent over-heating and lower the risk of fire. Ideally, LED light strips will be installed in an aluminium profile or extrusion that is designed for this purpose.
This information is intended for guidance only and any electrical installation should always be designed and verified by suitably qualified personnel.