Parallel Switching - Light fittings

willmoac · 6 Dec 2020

So a strange request I have had to help someone out.

Basically they want to be able to switch all the lights on in a building at once, regardless of the position of the wall switches. They want to also turn them all off (or at least return to the previous state when they turn the central control off.

To me it seems the only way to do this would be parallel switching, basically take 2 lives from the same MCB, run one live through the wall switch to the light fitting and take the other live feed it via relay to the light fitting. So you would have 2 live wires at the fitting.

I have tried to find reference to parallel switching in the regs and can't! Part of me says you can't do it, but part of me is struggling to find a reason not to if you put a 3 pole isolator beside each light fitting to isolate it for servicing purposes. My background is electronic engineering and in the past I did used to specify some electrical systems within my job, but it's long before the latest regs.

It's essentially going to be like the systems you see if movies for switching all the lights on in a fire station, when the callout alarm sounds.

Any thoughts? Or at least where in the regs it states you cannot parallel switch the live?

Thanks

bernardgreen · 6 Dec 2020

Each switch has a normally open relay contact connected across it, if ten switches then ten sets of relay contacts.

The relay contact sets can all be on one multipole relay or distributed over a number of relays. It will depends on the existing wiring layout which will be the most cost effective design,

The central control switch supplies power to all the relay coils to energise them and thus close the normally open contact sets.,

Bear in mind that turning on a lot of lights at the same instant will create a large inrush current that may be enough to trip the MCB for the lighting circuit. Using multiple relays would allow the switch on to be sequential and reduce the single inrush current to be several much lower inrush currents thus reducing the risk of the MCB tripping

SUNRAY · 6 Dec 2020

willmoac said:
So a strange request I have had to help someone out.

Basically they want to be able to switch all the lights on in a building at once, regardless of the position of the wall switches. They want to also turn them all off (or at least return to the previous state when they turn the central control off.

To me it seems the only way to do this would be parallel switching, basically take 2 lives from the same MCB, run one live through the wall switch to the light fitting and take the other live feed it via relay to the light fitting. So you would have 2 live wires at the fitting.

I have tried to find reference to parallel switching in the regs and can't! Part of me says you can't do it, but part of me is struggling to find a reason not to if you put a 3 pole isolator beside each light fitting to isolate it for servicing purposes. My background is electronic engineering and in the past I did used to specify some electrical systems within my job, but it's long before the latest regs.

It's essentially going to be like the systems you see if movies for switching all the lights on in a fire station, when the callout alarm sounds.

Any thoughts? Or at least where in the regs it states you cannot parallel switch the live?

Thanks

Depending on the size of the installation relays are not required and the way it's currently wired, it can be done with 2 way switches [or an intermediate for 2 way]:

'Overide' wiring shown red and 2 way 'Strappers' shown purple.

However Bernards comment about inrush needs to be considered if it's a large prperty.

This takes me back to a large commercial property with a really horrible and frequently modified version of this for occupied/unoccupied use.

willmoac · 6 Dec 2020

Thanks everyone for your comments, my initial thought was doing something with 2 way switches but couldn't work out what!

MCB inrush current shouldn't be too much of an issue as all the lights are LED, and there is only 4 or 5 rooms.

Thanks SUNRAY for the diagram, I won't need the additional 2 way stappers.

The relays are going to be controlled by software driven by a Raspberry Pi.

Cheers

SUNRAY · 6 Dec 2020

willmoac said:
The relays are going to be controlled by software driven by a Raspberry Pi.

Cheers

In that case have you considered smart switches?

willmoac · 6 Dec 2020

Yeah, thnaks, they have considered Smart Switches, but the on site wifi is provided by a 4G modem which drops in and out. So using anything that needs a cloud connection can be problematic, it's easier to trigger the raspberry pi with a simple command and then drive the relays. They have a guy who is very capable of getting the software side to run, most of it works currently even with the 4G modem, but it makes sense to limit how much needs to go into the cloud.

bernardgreen · 6 Dec 2020

willmoac said:
MCB inrush current shouldn't be too much of an issue as all the lights are LED, and there is only 4 or 5 rooms.

The inrush current to some LED drivers can be high as the 230 Volt mains is rectified to DC to charge a capacitor with minimal is any effective current limiting in the design.

In defence of the relay method.

The control voltage to the relay coils can be ELV ( Extra Low Voltage ) and can be wired to relays using small wires both in terms of voltage rating and current carrying capacity. For retro fitting to an existing installation this is a great advantage.

endecotp · 6 Dec 2020

Can anyone work out how to do it with diodes?

Would be easy with DC.....

SUNRAY · 6 Dec 2020

willmoac said:
Yeah, thnaks, they have considered Smart Switches, but the on site wifi is provided by a 4G modem which drops in and out. So using anything that needs a cloud connection can be problematic, it's easier to trigger the raspberry pi with a simple command and then drive the relays. They have a guy who is very capable of getting the software side to run, most of it works currently even with the 4G modem, but it makes sense to limit how much needs to go into the cloud.

The WiFi/LAN is only a network and one port of the network happens to be an interface to the WWW.

Assuming the WiFi coverage is adequate for the smart switches, Idon't see any need to to access the cloud at all, unless you require remote control.

I intended to raise the same comments about ELV [Been out working] it's also possible to run a control signal over the mains supply but the cost of interfaces will probably exceed that of smart switches.

bernardgreen · 9 May 2021

SUNRAY said:
Idon't see any need to to access the cloud at all, unless you require remote control.

What happens if the connection to the cloud is lost ? ( or the sun comes out and the cloud(s) disappear ).

SUNRAY · 9 May 2021

bernardgreen said:
What happens if the connection to the cloud is lost ? ( or the sun comes out and the cloud(s) disappear ).

Wouldn't that be blamed on global warming?

flameport · 9 May 2021

Standard switch in each room, with a Shelly1 behind each switch for the remote on/off options.
Cloud is optional.

bsr · 10 May 2021

Hi, this is a feature I have seen in a number of Building Management Systems (BMS) to turn on all lights to max when the fire alarm sounds.

This would normally be done by the light switches being ethernet connected to the BMS which then switches the relays for the lights.

bernardgreen · 10 May 2021

bsr said:
This would normally be done by the light switches being ethernet connected to the BMS which then switches the relays for the lights.

Before Ethernet the simple system in SunRay's post was used in Fire Stations, simple effective and reliable in operation. Probably still is used.

SUNRAY · 10 May 2021

bernardgreen said:
Before Ethernet the simple system in SunRay's post was used in Fire Stations, simple effective and reliable in operation. Probably still is used.

I vastly prefer to keep things simple, despite the amount of technical stuff I have done. My system only works if everything is on the same RCD/RCBO.
I installed something similar in a sports facility and to avoid a massive inrush delayed each circuit by about 1/2 second. It looked just like films where we hear the big switches/contactors clunk in. Originally it was part of the BMS system but after a panel burnout on Christmas day (not one I built) they asked for it to be independant and fail safe on.

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Parallel Switching - Light fittings

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