Multiple Exterior Lighting Circuits

[Danny124]

Hi all,

Having a brain fart...

Looked at a job today, have multiple exterior lighting circuits (4x MCB'S). Can see why there is multiple, as previous electrician was worried about cable lengths etc as the property is quite large.

But seem to have multiple Photocells and timers controlling, with outside switch for over riding specific lights.

Client doesn't like 4 photocells on side of his house, and having to reset/change times on 4 timers.

Any ideas how to incorporate these 4 circuits into one timer switch, possible PIR's and over ride switch.

I'm thinking contactors, but can't get my head to think properly on this one.

Thanks in advance guys.

Cheers

 

[radiohead]

You've answered your own question, 4 pole contactor with the coil controlled by whatever the client wants, you'll have to re-jig/disconnect existing PIR's and PC's to suit the new arrangement. Alternatively if the load permits feed all four lines on one mcb, then becomes a single circuit

 

[Danny124]

I would like to put them on one MCB, but we are talking possibly many hundreds of meters of cable there are quite a few lights.

I want to still comply with VD etc.

Would the best way to seperate supply the PIR, PC, Over ride SW and timer, then making sure that each lighting system has its own isolator for future protection if worked on etc.

thanks for your reply

 

[westward10]

Run the four circuits through a four-pole contactor. The control circuit (coil) of the contactor would only require a single PIR and timer.

 

[radiohead]

I would like to put them on one MCB, but we are talking possibly many hundreds of meters of cable there are quite a few lights.

I want to still comply with VD etc.

Would the best way to seperate supply the PIR, PC, Over ride SW and timer, then making sure that each lighting system has its own isolator for future protection if worked on etc.

thanks for your reply

I don't see your logic with this, if all four circuits originate from the same DB then converting them to one circuit from one device will not affect the length of run or volt drop in any way.

 

[freddo]

I'd also go the 4 pole contactor route, when a fault appears you don't lose all the lights.

 

[Danny124]

I don't see your logic with this, if all four circuits originate from the same DB then converting them to one circuit from one device will not affect the length of run or volt drop in any way.

I have 4 circuits all in 1.5mm SWA and some T&E. One of the circuits is approx 80 meters.

If i join these all up, i'm probably looking at 300 meters of cable.

I'm worried that if i join them all up to one MCB, although most of the circuit is LED and odd low voltage lighting, my Voltage Drop will still exceed the 3% (11.5v).

Rough calculation say i have 300m of cable, 460watts (2Amp) lamp (approx total)

1.5mm mA/A/L = 29

29x2ax300m/1000 = 17.4v (7.57%)

Unless I've taken Voltage drop out of context and misunderstood it some where, then thats what my logic is.

Thanks for your reply

 

[westward10]

Leave them as four circuits controlled by one four pole contactor and one control circuit.

 

[Baddegg]

I think what @radiohead is getting at is if all four single radial circuits originate at one db at present on 4 x mcbs then you’d still have 4 x radial circuits just with one mcb so the length for each circuit won’t change in regards to volt drop....or am I lost here?

 

[Danny124]

I think what @radiohead is getting at is if all four single radial circuits originate at one db at present on 4 x mcbs then you’d still have 4 x radial circuits just with one mcb so the length for each circuit won’t change in regards to volt drop?....or am I lost here?

Hmmm,

I think i am lost too. The blue bible is not very helpful. But starting to think VD is based on longest cable run is thats what Radiohead is getting at.

So if all 4 are supplied from one MCB,

say;

Original circuit 1 = 80m
Original circuit 2 = 70m
Original circuit 3 = 60m
Original circuit 4 = 50m

All joined up with one MCB, is VD calculated from the longest 80m ?

Always thought it was from circuit in total.

But then max lengths based out of OSG give you max length for lighting i believe 88m


If i keep scratching my head, I'm going to go bald!

 

[Baddegg]

Volt drop would still be calculated for each radial...they’d just be protected by one device.....again that’s assuming they are all originated from the same consumer unit/distribution board?

 

[Danny124]

Volt drop would still be calculated for each radial...they’d just be protected by one device.....again that’s assuming they are all originated from the same consumer unit/distribution board?

Yes all external lighting is fed from the same DB

 

[westward10]

Why do you want to create a single circuit?

 

[Baddegg]

So you’d only calculate for volt drop at the furthest point of each leg.....not add them up.....ideally though youd be better of leaving em on they own breakers and going down the contactor route....but that’s over my head ?

 

[Danny124]

thanks guys.

I think i stay with the contactor route.

 

[radiohead]

The contactor route is preferable, not least because as already stated you wont lose all the lights with a single fault. The point I was making on the single circuit is as stated above, the volt drop would be calculated on each separate line and the highest would apply, not all four added together. Either system could be used, conversion to a single circuit or a contactor, a contactor having the advantage.