Street lighting wiring / electrical questions

[Nomad]

Hi,
I am not familiar with the last bs7671 and have never carried out street lighting design.
I am trying to carry out calc for a street lighting system using 9 nos 150 w hit/hst lamp per radial circuit. Each run of the circuit length is approx 150m.
I have optd for 16Amp type D mcb for each circuit, 3 core 6sqm cable.
Volt drop for the circuit is within the limit.
The feeder pillar is likly to be connected to clients LV panel.
Can anyone tell me that it is a standard practice to have fuse (6amp) for each pole?

Problem:
Amtech is generating errors
1.exceeding 5 sec disconnection time
2. Fault current is high

Solution
1.Rcd for each circuit
2.But unable to reduce the fault level. Does this mean I need to replace the 16amp mcb with bs88 fuse.

Is there any other way I can address the both or I simply ignore the high fault current.

 

[Richard Burns]

You do not say which device is not meeting its disconnection time, if it is the 16 Type D (I assume this is selected based on the manufacturers specifications for the lighting) if it is near the origin it should be possible, but presumably this is pushing the fault current too high for the MCB.
(though I am not sure why, if the fault current is high then the R1+R2 should be low))
Managing the fault current (how high is it?) can only be covered by current limiting devices upstream or changing the type of protective device.
If you change to a BS88 will it meet the requirements for the protection of the lighting circuit.
For street lighting you are likely to have each pillar fused but it does depend on the actual application whether you can safely have banks of lights failing from a single fault.

 

[Darkwood]

Call me confused here but you say your not familiar with the current BS7671 and your designing Electrical circuits .... Hello McFly!!!! .. You should have to hand a copy of the lastest regulation if designing or carrying out any Electrical work and any other standards if applicable, we are happy to help but Im stopping short of telling you how to do your job because your years behind the regulations.

Your profile says Electrical , Electronics Engineer, with all respect a software program should only be a guide and a way to speed things up, but they are generalised and a good grasp of the regulations is needed before relying on any software hence you have become stuck.

 

[Plonker 3]

There are plenty of ways to get around the 5s disconnection time not being met, the first thing you need to do is check what the max value is in BS7671 not what some software is telling you on a PC.

Secondly what do you mean the faulty current is too high? You need to expand on this statement.

 

[telectrix]

could always install gas lamps.

 

[snowhead]

Is this an Exercise or planning for a real install?

All the lighting columns I see in Private car parks have 2amp fuses in Lucy blocks, or similar.
And some of the cable sizes get up to 10mm with only half a dozen lights on.

 

[Guest111]

Is this an Exercise or planning for a real install?

All the lighting columns I see in Private car parks have 2amp fuses in Lucy blocks, or similar.
And some of the cable sizes get up to 10mm with only half a dozen lights on.

sounds like it's an excercise in getting someone else to do the difficult bit for you,after all anyone can bury a few cables,it's getting the sizes and everything else right thats the tricky bit.

 

[Hobsoni]

One presumes that the fault current your referring to must be at the Origin? MCCB's have a higher kA rating than standard MCB's. So if for example you have 3 radials consisting of 9 lights per circuit ( presumably balanced over 3 phases? 1 radial per phase) then you will most likely require a contactor panel with a photocell control circuit? I would utilise your MCCB's within here for over current and to overcome excessively high Fault currents. Down stream with 150m using 6mm, I doubt high fault currents will be an issue which would enable you to use 6amp MCB's at each pole?


gents feel free to correct me if I'm wrong.......but with a loop reading of 0.03 ohms the greatest fault current one could expect (single phase) is circa 7.5 kA?? I have seen MCB's with short circuit rating of 10kA, not exactly specialist.