Lighting Question

[Lc1]

We have a 3 ph DB. I am a little confused with the cable sizing that has been carried out and would like to verify it for my self.

A 4core 16mm (3 ph and N) goes from this DB to a jb in the field, through an underground cable route. At this JB the cable splits. One cable goes off and feeds 14 400W HQI lights and another cable feeds 12 400 W HQI Lights and three street lights.

From a sizing point of view is this treated as one three phase circuit with 29 lights on it?

Thanks

 

[Leesparkykent]

We have a 3 ph DB. I am a little confused with the cable sizing that has been carried out and would like to verify it for my self.

A 4core 16mm (3 ph and N) goes from this DB to a jb in the field, through an underground cable route. At this JB the cable splits. One cable goes off and feeds 14 400W HQI lights and another cable feeds 12 400 W HQI Lights and three street lights.



From a sizing point of view is this treated as one three phase circuit with 29 lights on it?

Thanks

Its 1 circuit as they are all on one OCPD. From a sizing point of view the 16mm cable before it splits would obviously have to be sized to cope with the load of all 29 lights.

 

[HandySparks]

Its 1 circuit as they are all on one OCPD. From a sizing point of view the 16mm cable before it splits would obviously have to be sized to cope with the load of all 29 lights.

...taking into account how the various loads are distributed across the three phases.

 

[Lc1]

Thanks for the replies. I am struggling a little with this. We are not sure at this stage what lights are on what phase so to verify this cable size I will assume there are 10 per phase.Does anyone have any worked examples of this type of calculation?

thanks

 

[Andy78]

Thanks for the replies. I am struggling a little with this. We are not sure at this stage what lights are on what phase so to verify this cable size I will assume there are 10 per phase.Does anyone have any worked examples of this type of calculation?

thanks

Measuring current draw at the TP MCB with all lights activated would be my starting point. If possible I would be doing the same at the JB so I could verify the load on the smaller cables and look at their size and suitability.

 

[Lc1]

Does anybody have any worked calculations that have a 3ph source that splits into single phase loads such as the lights above. Just to I can get my head around it. Am I missing something really simple?

Thanks

 

[Richard Burns]

If each light is single phase then the load on each phase is P/V = I where P is the total light wattage on that phase.
The maximum current on a phase is then the highest loaded phase.
With the lights as evenly distributed as possible (9*400W + street light) then the load would be ~16A per phase.

 

[Lc1]

ok thanks. I understand the lights on single phase from the jb. I am not sure of the sizing from the db to the jb which is 3 phase. Do we just treat this a 3 single phases?

thanks again

 

[telectrix]

ok thanks. I understand the lights on single phase from the jb. I am not sure of the sizing from the db to the jb which is 3 phase. Do we just treat this a 3 single phases?

thanks again

yes, because you need to know the load per phase. that's what the cable size and OCPD ratings are determined from.

 

[Lc1]

Good morning,
to follow on from my question above.
The 29 lights mentioned above are on way 1 of a 3 phase db
way 2 has a further 3 400 w lights
way3 is spare
way 4 is double poled and feeds a further 3 400 w hqi lights
way 6 feeds a further 4 400 w hqi lights

I have been told that these are controlled by a photo cell and a contractor. So when the photo cell activates can the lights on these ways energise at once ? After speaking to a colleague they say there is no way this can happen. I am not quite sure as to why ?

thanks

 

[snowhead]

If it's a single contactor fitted on the incomer to the 3 phase DB then yes 1 contactor could control all lights.

 

[Lc1]

Thanks Snowhead,

would it it be possible if it was a 3 phase contractor on the incomer to the Db ?

thanks

 

[ipf]

Thanks Snowhead,

would it it be possible if it was a 3 phase contractor on the incomer to the Db ?

thanks

Is this 3 ph contractor self employed?

 

[snowhead]

Is this 3 ph contractor self employed?

He'd be on a good earner turning the power on and off every day if he was.

 

[snowhead]

Thanks Snowhead,

would it it be possible if it was a 3 phase contractor on the incomer to the Db ?

thanks

Yes a Single 3 phase contactor on the incomer OR multiple contactors or relays on the outgoing feeds to the circuits.