How to wire the systemUpdated 2 years ago
- How to wire the system
How NOT to wire the system
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Do not run wiring over sharp corners, use conduit:
Wiring was run over a corner and roofing contractors dragged roof sheets over the wiring causing a serious fire. Had the wiring been in conduit this may have been prevented. | |
Work neatly, tie your wires up with cable ties. Do not leave power supplies hanging and supported by their own wiring. Take pride in your work, imagine your boss or wife or children are going to be shown this – will you feel proud? Also shown here – avoid using red and black for mains wiring, this is a disaster waiting to happen as you might mix them up. | |
Do not use cheap, so-called, chocolate block connectors because there’s always the risk of missing the wires with the screws and connecting to the insulation instead resulting in intermittent connections. We will discuss this in more detail later. Saving a few Rand on connectors may come back to bite you and cost several thousand in re-fits. | |
Damage to the power supply due to the sub-standard wiring above – the switch mode transformer gets turned on perhaps hundreds of times a second due to arcing in the connector, leading to excessive inrush start-up currents. |
- Mains wiring to the power supply
- Choosing wire
When wiring mains, care must be taken as there is the risk of fire and shock. Use good quality new wire of the correct size. Avoid using red or black as you may confuse these with the DC output. If at all possible use conventional brown, blue and green wiring for mains. If multiple PSU’s are wired in parallel you must allow for the total current requirement.
2. Choosing wire size for mains wiring
Add up the total power requirement, assume full load case. Ie if you are wiring 2x 300W supplies in parallel, assume 600W. Divide this by the mains voltage eg 600/230 = 2.6A
Note: Wire size is usually given in the cross section area of the wire, not the diameter e.g. A 1mm diameter wire has an area of
There are many factors to be taken into account when working with mains wiring, the current, temperature, %volt drop, open/conduit runs, grouping and there are some easy calculators on the Internet (see references at the end) but for LED PSUs at normal temperatures, allowing a 3% volt drop and a maximum length of 20m the table below gives an idea
Wire size for mains (230V) wiring 3% volt drop | |||
Power W | Amps | Wire Diameter ( mm) | Area mm2 |
700 or less | 3 | 1.3 | 1.5 |
1200 | 5 | 1.8 | 2.5 |
2400 | 10 | 2.5 | 5 |
Mains (230V) wire sizes
3. Connectors & joints
If the 230Vmains needs to be joined or split, use good quality chocolate blocks as shown in C below. Never use the type shown in D as the screw often cuts the wires or contacts only a few strands. Type C has a pressure plate that pushes down on all the strands ensuring a much better connection. Cut and fold the wire as in A. Never fold back over the insulation as in B.
Figure 13 Chocolate block connectors
Figure 14 Suitable connectors
4. Fig 14 shows several suitable connector types: A and B are single wire connectors, B and C for multiple wires – D is good for mains or heavier wires, although do not use type D for currents in excess of 5A, E to H are custom connectors from wire to strip lights, a good supplier has many varieties, J is for joining 2 sections of strip together.
Always tightly twist wires together, solder, or use ferrules to prevent short circuits from stray strands as shown above. |
Be careful not to skin wires too short or push them too far in to connector blacks as they may not make proper connections |
5. If you have to take a wire through the side of a box or cabinet made of metal always use either a cable gland or grommets.
6. Earthing
Always earth the PSU and metal parts of the sign assembly in case they make inadvertent contact with any 230V wiring. Also, in certain situations e.g. signage on high buildings, proper earthing may save the system in the event of nearby lightning. Always use an adequate size wire (at least the same size as the mains wire you used) and the shortest possible route to a good, tested earth point.