For Wiring Diagram details
Handrail Wiring
Handrail Wiring, calculating cable losses, and establishing the right cable size.
We provide this design service free of charge with all Projectors purchased.
Please contact us for more information.
When planning an Illuminated Handrail installation there are many factors to consider. Light intensity, light uniformity, power, installation on site and more.
An often overlooked aspect is cable loss.
The high efficacy of our Projectors results in the AC supply cable to the driver being quite small.
This is due to the high voltage supply and low power consumption.
However , power transmission through the internal handrail wiring is the opposite – low voltage with relatively higher amperage.
What is Cable Loss and what effect does it have on the installation?
credit: unknown
Handrail Wiring and Cable Losses
Everything that conducts electricity offers its own resistance to the circuit, wire is no exception, in fact over distance it is the biggest contributor.
The hapless characters in the image illustrate perfectly the effect over the entire length of a wire. The simplest analogy is with plumbing, if you want to deliver more water use a bigger pipe! Volts relates to water flowing through the pipe, Amps (or current) the volume of water flowing through it. So, Resistance (measured in Ohms) is the limiting factor- the diameter of pipe or in our case, wire.
Application
Above all, for safety we recommend that all handrail wiring is installed according to Safety Extra Low Voltage (SELV) regulations. This is to protect the handrail user from electrocution.
In order to comply, most of our installations operate at 24v D.c. This is provided by a power supply known as an LED Driver which transforms high voltage AC (110 / 240v mains) to this much lower D.c. voltage.
Higher voltages can transmit power over longer distances with smaller cables. An extreme example is of Power Transmission Lines (UK National Grid) which operate at up to 400,000 AC volts in order to carry power across the entire Country.
Alternating Current (AC ) plays a major role in transmission efficiency, the opposite is true of Direct Current (Dc) which has to be used in handrail wiring
Handrail Wiring for Constant Voltage Circuits
So, we seem to have everything stacked against us from the outset, the factors of extra low voltage and Direct Current mean that cable losses are much greater.
One of the driving factors in the design of our Handrail Lighting Projectors was to provide the most efficient and powerful lighting package available. Simply, less power per metre.
In fact, our Handrail Projectors consume only 1watt of power (350ma operation), even including the power losses of the 24v Dc -Dc converter in circuit this only increases to 1.3watts. In typical installations our Projector spacing are between 800 – 1500mm so, that is only 1.6 – 0.9 watts per metre!.
Because we like to make life easy, we recommend using one of the many online cable sizing calculators (please note these are for guidance only):
Cable sizing calculators
Useful on-line cable calculator click here>
In order to use the water resistant and efficient Gel Crimp Connectors we are ideally looking to use a 1mm² wire
The core is Copper
Temperature does have a significant effect on resistance, for external use in the UK use 25º C
For calculation purposes the wiring is enclosed in a conduit
Maximum permissible voltage drop for lighting is 3%
Cable size examples for two different lengths of handrail with Projectors at 800mm centers.
8 metre handrail = 9* projectors at 1.3watts = 11.7 watts
11.7watts/24v=0.49 Amps
Maximum permissible voltage drop for lighting is 3%
Cable calculator result = <1mm² wire
40 metre handrail = 41 projectors* at 1.3 watts = 53watts
53watts/24v= 2.2Amps
Maximum permissible voltage drop for lighting is 3%
Cable calculator result = 4mm² wire
*Assuming first projector is half distance from the end of the handrail.
Results
Results for the 8 metre handrail are perfect, even using a 0.5mm² wire the voltage drop would be only 1.13%, however, the 40metre handrail is proving more difficult. A 4mm² (x2) wire is going to be quite difficult to install and interconnect and so alternative options would be preferred.
Such as:
Using 2 x Drivers (1 at each end)
Or, installing two circuits from one end, one for the first 20 metres another for the last. Although the distance for the second circuit is the same, the Load (Amperage) is halved.
As a result our handrail wiring can use more manageable 2.5mm² wires with a voltage drop of only 2.54%
These examples assume the LED Driver is installed at the handrail, however, the driver may have to be sited remotely so the cable run to the handrail will also
Constant Voltage Circuit – Parallel read more>
Constant Voltage Circuit – Series / Parallel read more>
Wiring for Constant Current Circuits
SELV regulations allow for the Dc voltage to be higher than 24volts. The maximum permissible voltage in the UK is:
48 volts Dc in Dry conditions
30 volts Dc in Wet conditions.
Please note regulations vary according to Country-please check
When installing a Series / Constant Current Circuit the voltage required increases proportionally to the number of Handrail Projectors. This means there is a limit to the number of fixtures but also the installation may operate up to 48volts, which reduces the problem of cable loss.
Operating at 350ma (current) our Projectors require 2.85volts Dc so, up 16 can be installed in a handrail in dry conditions. If
Example:
If we use the calculator above and to make the installation and connections easier we use a 1mm² the calculation is:
16 x 2.85volts = 45.6 volts (within regulation)
Dc current = 0.35 Amps x 45.6 volts = 16 watts
Calculated results mean the 16 Projectors can be installed in a handrail 110 metres long (2.94% Voltage Drop)
Please contact us for more information or if however, you would like us to provide cable size calculation for your project.
Constant Current Circuit – Series read more>