Lighting Circuits......

[Toneyz]

Without going into calculations, at what length of the main run from the D.B. on a lighting circuit do you get a gut feeling that it needs to be upgraded from 1.5 to 2.5 cable more referring to singles than T & E. 6/10A type C mcb LED lighting low design current so more of a V.D max loop etc.

 

[westward10]

Without calculation it is impossible to say as you have to consider vd and fault protection requirements.

 

[telectrix]

Without going into calculations, at what length of the main run from the D.B. on a lighting circuit do you get a gut feeling that it needs to be upgraded from 1.5 to 2.5 cable more referring to singles than T & E. 6/10A type C mcb LED lighting low design current so more of a V.D max loop etc.

when the end comes off the reel and it won't stretch to the last light.

 

[Toneyz]

Without calculation it is impossible to say as you have to consider vd and fault protection requirements.

The only reason asking was we all get an experience view after doing in practice. The electrical consultant has worked out 1.5 but in most cases the run is not always in practice.

 

[Toneyz]

when the end comes off the reel and it won't stretch to the last light.

It wasn't that long Tel, more the main run feed to 1st light.

 

[telectrix]

assuming that the load is irrelevant ( i.e well within the ccc of 1.5mm) , then all you need to consider is VD.

 

[Toneyz]

Not making this a technical question too much but if you are pulling just over half a drum in to the first light then you have the lights as pre-flexed leads between fittings just looking for an view from a gut feeling/past experience.

 

[Pete999]

Without going into calculations, at what length of the main run from the D.B. on a lighting circuit do you get a gut feeling that it needs to be upgraded from 1.5 to 2.5 cable more referring to singles than T & E. 6/10A type C mcb LED lighting low design current so more of a V.D max loop etc.

Domestic, Commercial or industrial?

 

[Toneyz]

Domestic, Commercial or industrial?

commercial

 

[Pete999]

Not making this a technical question too much but if you are pulling just over half a drum in to the first light then you have the lights as pre-flexed leads between fittings just looking for an view from a gut feeling/past experience.

Have you worked out the VD ?

 

[Toneyz]

As I posted ,as experienced electricians and with years of experience of installing circuits we all must stand there looking at the practical run and thinking this run is a bit too long it needs to have a increased cable size more safe than sorry.

 

[Strima]

One method is to transpose the volt drop calculation.

(Max Volt Drop x 1000)/(current x mV/A/M)=Max length in meters.

One I use quite often for 6mm SWA on a 32 amp distribution circuit is:

11.5 x 1000/32 x 7.9=45.49m

Then you need to take into account installation methods and derating factors etc but this gives you a figure to work from.

 

[Pete999]

As I posted ,as experienced electricians and with years of experience of installing circuits we all must stand there looking at the practical run and thinking this run is a bit too long it needs to have a increased cable size more safe than sorry.

If you were to opt for 2.5mm2, how do you intend to connect the lighting flexes to the larger size cable, might be a bit more expensive but has bus bar trunking been considered? or will it be cost prohibitive?

 

[Toneyz]

If you were to opt for 2.5mm2, how do you intend to connect the lighting flexes to the larger size cable, might be a bit more expensive but has bus bar trunking been considered? or will it be cost prohibitive?

Not relevant to the question that I am asking sorry Pete to be blunt to you Pete ( with respect). We are not all robots to what something is calculated off site getting a cable A to B is not always a straight line as it is on paper we must all get to have a experienced view when looking at a practical run.

 

[Ian1981]

If my gut feeling was that the first light was a bit of a stretch then I’d install say 2.5mm singles to the first point then perhaps 1.5mm to the other points however I’d be estimating the run and writing down some design calcs as well , as quite often it’s the max zs you need to watch when installing long runs especially if it’s a type c mcb.

If you take what the iet design guide says then if the load is evenly distributed along the circuit the voltage drop is reduced.
A lighting circuit with evenly distributed luminaries the average current is half the total load current
Max volt drop
6.9x1000/(Ib/2) x (mV/A/m)