2365 L3 Design Project

[Pops1]

Hello,

I am just starting my Design Project. I am just looking for advice regarding Q4 which asks you to Determine, for every final circuit in the cafe/pool each of the following:

• Design Current
  
• Nominal Rating and Type of Protective Device
  
• Method of Installation
  
• Rating factors that apply
  
• The minimum cross-sectional area of live conductors for current capacity and volt drop
  
• Actual Volt Drop
  
• Maximum disconnection time for each circuit
  
• Earth Fault loop impedance
  
• Maximum earth fault loop impedance.
  

Some Specs

Pool Lighting 1: https://www.osram.com/ls/ecat/Floodlight%2020%20midi%20LED%20power-projectors%20and%20floodlights-Outdoor%20Luminaires/com/en/GPS01_3037987/PP_EUROPE_Europe_eCat/

Pool Lighting 2: https://www.collingwoodlighting.com/index.php/en/products/downlights-halers-range/item/new-h2-pro-550-uk

Cafe Lighting: https://www.collingwoodlighting.com/index.php/en/products/downlights-halers-range/item/new-h2-pro-550-uk

Kitchen Lighting: https://www.kellwoodlighting.co.uk/product-range/high-output-led-batten-fittings

I am just looking for advice on how to work out the design current for the lights on each circuit. Also for the design current, for example, the dishwasher, which is 230V 16A 3 core SWA, how would you work that out. Just so I have an idea, please.

Thanks

 

[Sidewinder]

Taking your last question with regard to the dishwasher.

You need to look at the specification for the dishwasher.

Post that, with how you think you would work out the design current for it and we can work you through the calculation.

 

[Pops1]

Taking your last question with regard to the dishwasher.

You need to look at the specification for the dishwasher.

Post that, with how you think you would work out the design current for it and we can work you through the calculation.

Okay so for the Dishwasher its 16A and the Voltage is 230v. Its fed from a 3 core SWA 70 degrees C. 

So if I did 16 x 230 I get 3680w but then I would need to apply diversity? 

 

[Sidewinder]

So it's a 16A load, do you think that it is viable or suitable to apply diversity to a single point load?

Do you have the full spectrum of load characteristics?

Is it worthwhile spending time designing a 16A circuit to the n'th degree to reduce cost with the risk that on full load it could trip?

 

[Pops1]

So it's a 16A load, do you think that it is viable or suitable to apply diversity to a single point load?

Do you have the full spectrum of load characteristics?

Is it worthwhile spending time designing a 16A circuit to the n'th degree to reduce cost with the risk that on full load it could trip?

I would say that it's not viable to apply diversity to a single point load. You would apply it to a final circuit, such as a Lighting Circuit or a Ring Main. 

The only specification we were given was that it was a 16a load, wired with 3 Core SWA. 

 

[Blue Duck]

Just do everything in 4mm FP rings on 20a breaker then nothing could possibly go wrong!

Just being silly but see it a lot on commercial jobs where the designer can't be arsed. (2x4mmFP in 25mm tube anyone) ?  :shakehead

Dishwasher is fixed load, so just design a circuit capable of safely delivering that.

 

[Pops1]

As an example. I have in the Pool 24 lights. The wattage of each light is 29w. 

So Ib would be: 24x29 divided by 230v. which gives me: 3.02a

Just do everything in 4mm FP rings on 20a breaker then nothing could possibly go wrong!

Thanks for the suggestion. But I am afraid I need to show my workings out, as its a design project for college. 

 

[Pops1]

So I have had a go with the Pool Lighting.

Ib = 24 lights x 29w divided by 230v = 3.026A.

In would then be Ib > In = 6A circuit breaker.

Then apply diversity:

6A x 230v = 1380w

24 x 29w = 696w

Table A2 in OSG using 90% of total current demand I get 626.4w divided by 230v = 2.72A

Would that be correct?

 

[Sidewinder]

You can only apply diversity across circuits, not within circuits.

The way you have done the pool lights here, suggests that they will not all be in use at one time.

Whereas the likelihood is that they will be on a single switch, and all on/off at the same time.

 

[Pops1]

You can only apply diversity across circuits, not within circuits.

The way you have done the pool lights here, suggests that they will not all be in use at one time.

Whereas the likelihood is that they will be on a single switch, and all on/off at the same time.

Right okay. I am just new to all of this.

 

[Pops1]

You can only apply diversity across circuits, not within circuits.

The way you have done the pool lights here, suggests that they will not all be in use at one time.

Whereas the likelihood is that they will be on a single switch, and all on/off at the same time.

The pool lights would only be on when the pool is in use. They would be controlled by a single switch. I was just concerned whether or not that I had the right idea when trying to work out the Design Current. Shall I list the circuits? Would that be better? 

 

[Ardet R]

When you are working out the design current for a circuit you are attempting to ascertain the expected current draw in normal use on that circuit.

If you have a domestic house with only one lighting circuit then you would generally expect that say in the early evening downstairs lights will be on and upstairs off, then late evening the other way around so perhaps only half the total load being used at any one time.  This does assume a lot of people who do not turn off lights as generally only perhaps two or three rooms would be lit at any one time. However if there are 20 x 15W lights in the house then that is 1.3A and you could perhaps assume the design current might be only 0.65A.

In your case you have one circuit for all the lights in the pool, therefore when the pool is in use it is likely that all the lights would be on at the same time so your design current would be the total load of the lights.

It is only when there are diverse draws on a circuit across different areas or pieces of equipment that you could apply diversity.  In most commercial applications the majority of lighting and heating would be on during working hours so there is less chance to apply diversity,  However there may be pieces of equipment that are used separately and not at once. for example in a pool perhaps the pump for draining the pool would not be in use at the same time as the water heater for the pool.

 

[Sidewinder]

Right okay. I am just new to all of this.

You should have been taught all the theory required between your previous courses and this course.

 

[Pops1]

When you are working out the design current for a circuit you are attempting to ascertain the expected current draw in normal use on that circuit.

If you have a domestic house with only one lighting circuit then you would generally expect that say in the early evening downstairs lights will be on and upstairs off, then late evening the other way around so perhaps only half the total load being used at any one time.  This does assume a lot of people who do not turn off lights as generally only perhaps two or three rooms would be lit at any one time. However if there are 20 x 15W lights in the house then that is 1.3A and you could perhaps assume the design current might be only 0.65A.

In your case you have one circuit for all the lights in the pool, therefore when the pool is in use it is likely that all the lights would be on at the same time so your design current would be the total load of the lights.

It is only when there are diverse draws on a circuit across different areas or pieces of equipment that you could apply diversity.  In most commercial applications the majority of lighting and heating would be on during working hours so there is less chance to apply diversity,  However there may be pieces of equipment that are used separately and not at once. for example in a pool perhaps the pump for draining the pool would not be in use at the same time as the water heater for the pool.

Thanks for that, so the way I have done it is incorrect?

So, for example, the Design Current for the Pool lights on that 1 Circuit would be:

24 lights x 29w divided by 230v = 3.026A. so the Design Current would be just over 3A? 

As these are the main pool lights, so I would assume they are on when the pool is in use, for ease we could say they are on 100% of the time. 

 

[Sidewinder]

Basically yes.

 

[Pops1]

Basically yes.

Okay, could you explain where I am going wrong, maybe with a calculation?

 

[Sidewinder]

You are correct for the pool lights.

As Ardet R has said, you can only apply diversity for circuits where not all the load is in use at the same time, though for some more complex loads that is difficult and will require considerable design analysis or physical measurement of the load profile.

You need to work out the loading for each final circuit, then at the distribution board level you can look at some diversity once you know how the installation is to be used.

You might for example as you say allow for the pool lights to be on at all times the pool is open.

There may be outside lights that only come on when it's dark, but the pool is never open when it's dark outside (humour me it's just an example), so the DB would never see both loads, just one, or the other.  There you could apply diversity and ignore the smaller load.

There are some examples of diversity allowances in the OSG.

 

[Pops1]

You are correct for the pool lights.

As Ardet R has said, you can only apply diversity for circuits where not all the load is in use at the same time, though for some more complex loads that is difficult and will require considerable design analysis or physical measurement of the load profile.

You need to work out the loading for each final circuit, then at the distribution board level you can look at some diversity once you know how the installation is to be used.

You might for example as you say allow for the pool lights to be on at all times the pool is open.

There may be outside lights that only come on when it's dark, but the pool is never open when it's dark outside (humour me it's just an example), so the DB would never see both loads, just one, or the other.  There you could apply diversity and ignore the smaller load.

There are some examples of diversity allowances in the OSG.

Right okay. You would only apply Diversity on say the other Lighting Circuit in the Pool as that is for the Changing Rooms, Pump Room, Plunge Pool etc.

I have a Power Circuit for the Pool:

Circuit 1 400v 32A 3 phase - an SWA 5 core 90 degrees C thermosetting clipped directly.

Circuit 2 Sockets

I have added some files:

https://ufile.io/t61nkqup

https://ufile.io/m1fgw5r5

https://ufile.io/8tfa30c7

 

[Sidewinder]

Possibly, that depends on whether those lights would be utilised 100% of the time that the main pool lights were.

Who are you studying with?

 

[Rob.]

Circuit 1 400v 32A 3 phase - an SWA 5 core 90 degrees C thermosetting clipped directly.

Why are you using this cable?

You know that unless the accessory termination points are rated to 90dec C you have to de-rate the cable.