2365 Design Project - May need some advice.

[RDB85]

Hello Everyone,

As many of you know I am doing my Design Project. I am working on Q4. I have had a go, but I am unsure of some of the questions. I was just wondering if it would be possible to get some advice on what I have done, whether it's correct or not.

Also for Q1, we need to draw a Vehicle Charging Point. It is supplied from a TNC-S System. I have done it 3 phase, then the EV Charge point is TT System. I just need to draw the Main Fault, is the only place that could occur be on the Casing of the CCU.

I will probably need some more advice but for now, I am working on Q4.

 

[RDB85]

Just so I am on the right path. The first question asks for the design current on each final circuit. So for now I am going to do the lighting circuits first.

Pool lighting I have 24 lights around the pool. The voltage is 240v. The wattage is 29w. So would I be right in thinking it’s

24x29 divided by 240v to get my design current for that lighting circuit? Or I’m i way off?

 

[Richard Burns]

The vehicle charge point diagram needs the earth fault path, therefore this is a fault to earth, which can be shown easily by a line conductor connecting the casing, this is the most likely fault but others are possible.

Regarding the lighting because they are all likely to be on whenever the pool is in use then the design current is the total lighting load as you have shown.

 

[RDB85]

The vehicle charge point diagram needs the earth fault path, therefore this is a fault to earth, which can be shown easily by a line conductor connecting the casing, this is the most likely fault but others are possible.

Regarding the lighting because they are all likely to be on whenever the pool is in use then the design current is the total lighting load as you have shown.

Thanks for that. I will try and do a drawing to see if I’m on the right path. Then upload it.

 

[Bobster]

Not your scenario, but something to push you in the correct direction

 

[RDB85]

I am just working through the calculations and I am unsure on the last point:

Earth Fault Loop Impedance:

In BS7671 the calculation is

Zs =UoxCmin divided by Ia = Amps

Would the Ia be the protective device in this case 6A

Uo=230V Cmin=0.95

As I have given that a go and got 36.416 ohms

But the Zs for 6A BS EN60898 is 7.28 ohms

 

[Richard Burns]

In Bs7671 below the Zs formula it gives Ia as the current causing disconnection of the protective device within the time required.
For a type B bsen60898, that will disconnect "instantly" in 3 to 5 times its rating, the worst case is 5 times i.e. 30A.
This is the minimum current that can be guaranteed to disconnect within 0.4s/5s.
Therefore use 30A in the equation.
Note that your result of 36.416 divided by 5 gives 7.28 ohms.

 

[RDB85]

In Bs7671 below the Zs formula it gives Ia as the current causing disconnection of the protective device within the time required.
For a type B bsen60898, that will disconnect "instantly" in 3 to 5 times its rating, the worst case is 5 times i.e. 30A.
This is the minimum current that can be guaranteed to disconnect within 0.4s/5s.
Therefore use 30A in the equation.
Note that your result of 36.416 divided by 5 gives 7.28 ohms.

I see what you mean. That makes sense, I was concerned about the calculation, but it now makes sense.

 

[RDB85]

I have done my Lighting Circuits. I am pretty happy with them, but I may need someone just to check them if that is okay? I am now working on the Power for the Pool.

I have two Circuits:

• Circuit 1: 32A 5 core 90 degrees SWA cable clipped direct. I should be okay with that.
• Sockets. Would you recommend a Ring or Radial, as I have the CCU in the Pump Room.

I will upload the diagram, so you have an idea.

 

[RDB85]

Ive decided that I will include a Ring Circuit in the Kitchen Area. So it will be 32A. As they are General Sockets.

In the Changing Rooms, there are Sockets I was thinking of running them as a Radial so 16A. Would this be correct? I have attached the drawings above.

 

[Pete999]

Ive decided that I will include a Ring Circuit in the Kitchen Area. So it will be 32A. As they are General Sockets.

In the Changing Rooms, there are Sockets I was thinking of running them as a Radial so 16A. Would this be correct? I have attached the drawings above.

16 Amp Radial is not a standard circuit! according to 7671.

 

[RDB85]

16 Amp Radial is not a standard circuit! according to 7671.

Would it be 20A. I’m not sure where I got 16A from. That’s another circuit. Sorry.

 

[Richard Burns]

For a cafe even a small one try to think about what appliances would be used and how often to give you an idea of the likely current drawn when the cafe is open.
You might even want to split down your circuits further.
I would generally suggest making the best use of the cables being installed whilst also ensuring that they are not close to overloaded.
A 16A radial is a common occurrence but is not making best use of the available current carrying capacity.
Rings have the advantage that the volt drop experienced on a ring is lower than that on a radial so if you are covering a large area with a single circuit a ring can be useful.

 

[Bobster]

16 Amp Radial is not a standard circuit! according to 7671.

It may not be a standard circuit, but there is certainly nothing wrong with it.

 

[RDB85]

I’m just thinking what would be best. As we are limited to 30m of cable. The same drawing is 1:50. So I may even use a ring for the Cafe and a ring for the Kitchen.