AM2

[LeeH]

I must be missing a trick here Matt.

The reason why you take the nameplate figure to set your overload is because the kW rating is the shaft output not the electrical load.

You need to use powerfactor and efficiency in the equation don't you?

A 3 phase motor is around 6 amps IIRC, a single phase will be more.

So the 4.78A makes no sense to me.

Did the tutor not explain why?

 

[Matthew terry]

I must be missing a trick here Matt.

The reason why you take the nameplate figure to set your overload is because the kW rating is the shaft output not the electrical load.

You need to use powerfactor and efficiency in the equation don't you?

A 3 phase motor is around 6 amps IIRC, a single phase will be more.

So the 4.78A makes no sense to me.

Did the tutor not explain why?

Nope, no explanation just a sum which was ÷3 ÷230 x1.1... they dont really explain stuff he just said ' make sure you note the equation down on the paper provided' if they explained everything the 2 days wouldn't be enough in dont think!

 

[Wilko]

Hi Matthew - can I ask where you did your prep, and any thoughts? Thanks

 

[Jamchiv01]

Hello, the formula I was given for setting a motor overload is as follows:

(Motor current / 1.73) + 30%

So take the Motor rating; in Your case its 3kW


using I = P / V
I = 3000W / 400V = 7.5A

Now you divide the motor current by 1.73 (Square root of 3) to get the current per phase.

7.5A / 1.73 = 4.34A

Take 30% of the above and add it to the existing value for max operating current to be achieved without the overload tripping.

4.34A * 1.3 =5.64A

You would set your overload to 5.64A




The way the formula you have been given is as follows:

The Value of motor is 3Kw, Convert this into watts.

3kW = 3000W

Now divide the value by 3 as there are 3 phases giving you 1kW per phase

3000W / 3 =1000W

Divide the 1000W by the voltage to give you the current per phase

1000W /230V = 4.35A

Now Multiply the current given by 10% to allow for max operating current to be achieved without the overload tripping.

4.35A x 1.1 = 4.79A


The difference between the 2 is: My formula applies A 30% Addition, Yours applies a 10% Addition.


Hope that Helps you understand it a little better.

 

[Matthew terry]

Hello, the formula I was given for setting a motor overload is as follows:

(Motor current / 1.73) + 30%

So take the Motor rating; in Your case its 3kW


using I = P / V
I = 3000W / 400V = 7.5A

Now you divide the motor current by 1.73 (Square root of 3) to get the current per phase.

7.5A / 1.73 = 4.34A

Take 30% of the above and add it to the existing value for max operating current to be achieved without the overload tripping.

4.34A * 1.3 =5.64A

You would set your overload to 5.64A




The way the formula you have been given is as follows:

The Value of motor is 3Kw, Convert this into watts.

3kW = 3000W

Now divide the value by 3 as there are 3 phases giving you 1kW per phase

3000W / 3 =1000W

Divide the 1000W by the voltage to give you the current per phase

1000W /230V = 4.35A

Now Multiply the current given by 10% to allow for max operating current to be achieved without the overload tripping.

4.35A x 1.1 = 4.79A


The difference between the 2 is: My formula applies A 30% Addition, Yours applies a 10% Addition.


Hope that Helps you understand it a little better.

So if my motor is 4.5kw

I have 4500 ÷ 3 ( for each phase) = 1500

1500 ÷ 230 ( should this not be 400 if its three phase) = 6.52

6.52 x 1.1 ( for 10% overload ) = 7.15a?

Im getting confused as why is it ÷230 if its a three phase motor? Or is it becsuse each phase is 230?

Thanks for your help though.

 

[Jamchiv01]

If your motor is 4.5kW using your method you would do the following:

4.5kW in Watts = 4500W

4500W / 3 = 1500W (This is where you divide the power of the motor by 3 for the 3 phases)

1500W / 230V = 6.52A (This gives you the current per phase)

6.52A * 1.1 = 7.15A (This applies the 10% for max operating current to flow without overload)

 

[Matthew terry]

If your motor is 4.5kW using your method you would do the following:

4.5kW in Watts = 4500W

4500W / 3 = 1500W (This is where you divide the power of the motor by 3 for the 3 phases)

1500W / 230V = 6.52A (This gives you the current per phase)

6.52A * 1.1 = 7.15A (This applies the 10% for max operating current to flow without overload)

Appreciate that mate, thank you very much!!

 

[Jamchiv01]

No Problem, if you need help with anything else, just ask.

Good Luck Tomorrow!!!

 

[Matthew terry]

No Problem, if you need help with anything else, just ask.

Good Luck Tomorrow!!!

Im pretty good with everything else, safe isolation and risk assesment im okay. Install okay as far as im concerned only the s plan heating I think will throw me off as i know I will over complicate it!! Testing im quietly confident and fault finding will be me hoping for 7 faults on the data.... lol!

Cheers though, ill let you know!

 

[Jamchiv01]

Study this:

Simplified S-Plan Wiring Diagram

 

[Matthew terry]

Study this:

Simplified S-Plan Wiring Diagram

Surely it cant be as easy as taking a single cable from room stat terminal 2 to the main wiring centre terminal 5?

 

[Jamchiv01]

You would run 3 core + cpc from the roomstat back to the wiring center. Sleeving all cables appropriately. My drawing just shows how it needs to be connected.

 

[Leesparkykent]

Just remember the order it switches. programmer to thermostat, thermostat to valve, valve to boiler and pump.

 

[Matthew terry]

You would run 3 core + cpc from the roomstat back to the wiring center. Sleeving all cables appropriately. My drawing just shows how it needs to be connected.

You would run 3 core + cpc from the roomstat back to the wiring center. Sleeving all cables appropriately. My drawing just shows how it needs to be connected.

Oh yes, my bad! But surely some will require just a single core no? The orange for instance?

 

[Jamchiv01]

No , The Valve comes with a 5 core cable pre-attached.

Grey = Perm Live
Blue = Neutral
Green / Yellow = Earth
Orange = Boiler call (SW)
White / Brown = Valve Call (Just noticed on my diagram I didn't label the brown from the valve as white as both colors can be used depending on the manufacturer)

I will update that now