Can you please check my cable calculation.

[L Plate]

Good evening all,

Can you please have a look for my cable calculation if I am doing the right one, it's our project this year.

Bathroom

A 10kw shower has been installed by the plumber in the bathroom, only the water supply to the shower has been installed. the shower unit is 24m from the CU,The bathroom does not have a window and the loft space is insulated with 150mm insulation ..

Here is my calculation ,

To find Ib

Ib= 1000w / 230v

therefore Ib= 43.48A

In = 45A

Establish the following to select protective device.

Ca = thermoplastic = 70C @ 30C

Cg= N/A

Ci = N/A

therefore :

It=

It = In/Cg = 45Amps

Table 45D IEE Page 282

Note **** for full installation refer to to page 262 Regbook Table 4A2 method 20

From table 45D IEE with the reference method C ( clipped direct )

therefore I can prove that the 47A current carrying capacity reqiures 6.00mm

twin and earth .

Voltage drop for this installation

( Mv/A/M) x l x lb

---------------------

1000

Although the given lenght for this installaion is only 24m , I added 1.5 meter for dressing and termination .

therefore

7.3x25.5x 43.48

-------------------= 8.9 V

1000

Vd=8.09V and this is acceptable reading for this installation

nominal voltage = 230x%5

--- - ----------= 11.5V

1000

2) the costumer has asked for a double socket-outlet and a light in her shed, which at the bottom of the garden, 39m from cu . It is used for storing small gardening tools and plant seeds . the power point will be used to run her " Flymo type mower.

Demand

16A socket

6A lightings

Ib = 22A

In= 30A

Establish the following to select protective device .

Ca = 0.77 ( IEE page 267 table 4B2 @70c thermoplastic

Ci =none

Cg = none

therefore

IT= In 30A

----------------= -=------ = 39.8amps

CgxCixCa 0.77

Refference method 4D4A ( IEE page 280 )

for Vd.. I add another 1.5m for cable dressing and termination

Vd = 7.3x40.5x22

--------------- 6.50 v

1000

therefore , I can prove that this installation needs a 6.0mm 3core armored cable to supply 22amps demand in the shed.

thank you all for your time and help

regards,

Lplate

 

[Apache]

2) the costumer has asked for a double socket-outlet and a light in her shed, which at the bottom of the garden, 39m from cu . It is used for storing small gardening tools and plant seeds . the power point will be used to run her " Flymo type mower.

Demand

16A socket

6A lightings

Ib = 22A

In= 30A

Establish the following to select protective device .

Ca = 0.77 ( IEE page 267 table 4B2 @70c thermoplastic

Ci =none

Cg = none

therefore

IT= In 30A

----------------= -=------ = 39.8amps

CgxCixCa 0.77

Refference method 4D4A ( IEE page 280 )

for Vd.. I add another 1.5m for cable dressing and termination

Vd = 7.3x40.5x22

--------------- 6.50 v

1000

therefore , I can prove that this installation needs a 6.0mm 3core armored cable to supply 2amps demand in the shed.

thank you all for your time and help

regards,

Lplate

I think you are overcooking demand. Just because all the MCB's add up to 22A doesn't mean they will draw that.

What 2 amp supply do you refer to [i made bold]?

 

[L Plate]

I think you are overcooking demand. Just because all the MCB's add up to 22A doesn't mean they will draw that. What 2 amp supply do you refer to [i made bold]?

uppss sorry apache .. that is 22 amps .. bit :yawn sorry

 

[kme]

`pache picks up on a valid point there - your shed loading.

It is highly probable to be a short term, low current load. If you allowed for a 13A load max, and were intending to utilise a 15 or 16 A OCPD, then you could downrate your cable, possibly to 2.5/2 core (I haven`t calculated, just hypothesized), which is a huge cost saving materials wise.

Even if this is a question from college; you would still be expected to apply diversity.

KME

 

[L Plate]

`pache picks up on a valid point there - your shed loading.It is highly probable to be a short term, low current load. If you allowed for a 13A load max, and were intending to utilise a 15 or 16 A OCPD, then you could downrate your cable, possibly to 2.5/2 core (I haven`t calculated, just hypothesized), which is a huge cost saving materials wise.

Even if this is a question from college; you would still be expected to apply diversity.

KME

Thanks KME,

the assignment that has been given to us says that , " the supply to the shed is to be run in SWA and supported by a cable tray "

BUT , we were advised that we can pick what reference method we going to use , and I choice reference method D ( direct in ground ) I think the college just want us to do it in cable tray to find out how we run the armoured cable in a tray . BTW we need to do the installation in a small cubicle only ( Bay ) as long as we have the right calculation then I think thats what the college want ..

but any suggestion from all of you guys is a big help .. I will take all of those , in this way I can gain more knowledge and idea ..

thanks

 

[oldtimespark]

Good luck with you assignment nice to see someone doing the work then asking for comments not asking for the answers

 

[PC Electrics]

Good evening all, Can you please have a look for my cable calculation if I am doing the right one, it's our project this year.

Bathroom

A 10kw shower has been installed by the plumber in the bathroom, only the water supply to the shower has been installed. the shower unit is 24m from the CU,The bathroom does not have a window and the loft space is insulated with 150mm insulation ..

Here is my calculation ,

To find Ib

Ib= 1000w / 230v

therefore Ib= 43.48A

In = 45A

Establish the following to select protective device.

Ca = thermoplastic = 70C @ 30C

Cg= N/A

Ci = N/A

therefore :

It=

It = In/Cg = 45Amps

Table 45D IEE Page 282

Note **** for full installation refer to to page 262 Regbook Table 4A2 method 20

From table 45D IEE with the reference method C ( clipped direct )

therefore I can prove that the 47A current carrying capacity reqiures 6.00mm

twin and earth .

Voltage drop for this installation

( Mv/A/M) x l x lb

---------------------

1000

Although the given lenght for this installaion is only 24m , I added 1.5 meter for dressing and termination .

therefore

7.3x25.5x 43.48

-------------------= 8.9 V

1000

Vd=8.09V and this is acceptable reading for this installation

nominal voltage = 230x%5

--- - ----------= 11.5V

1000

Manufacturers still quote the ratings for showers using 240volts. This is because it gives the marketing boys a higher figure to put on the box / advert etc.

So, 10kW at 240V = 41.66amps

The equivalent rating at 230volts is 9580W (or 9.6kW)

the Triton catalogue even has a tablke at the back showing the equivalent ratings at both voltages.

You've also put for a 45A device. Few manufacturers make a 45A MCB (mores the pity), so you'll probably end up with a 50A. This will force 10mm cable.

 

[PC Electrics]

2) the costumer has asked for a double socket-outlet and a light in her shed, which at the bottom of the garden, 39m from cu . It is used for storing small gardening tools and plant seeds . the power point will be used to run her " Flymo type mower.

Demand

16A socket

6A lightings

Ib = 22A

In= 30A

Establish the following to select protective device .

Ca = 0.77 ( IEE page 267 table 4B2 @70c thermoplastic

Ci =none

Cg = none

therefore

IT= In 30A

----------------= -=------ = 39.8amps

CgxCixCa 0.77

Refference method 4D4A ( IEE page 280 )

for Vd.. I add another 1.5m for cable dressing and termination

Vd = 7.3x40.5x22

--------------- 6.50 v

1000

therefore , I can prove that this installation needs a 6.0mm 3core armored cable to supply 22amps demand in the shed.

thank you all for your time and help

regards,

Lplate

If you take a tour round the mower section of your nearest DIY shed, you'll find that even a large Flymo only has a 1500W motor. So lets say the load is 2kW max (for good measure).

A 6 foot florry will pull 100W in round figures.

So, Ib = 11 amps

Ca = 0.77 ??

You installing in the Sahara?

Outdoors, UK ambients will rarely touch 30C, which is design, so Ca = 1.0

Now recalculate. Cable will defo drop to 4mm, maybe 2.5mm.

Don't forget to work to max Vd = 3% for lighting.

 

[L Plate]

Manufacturers still quote the ratings for showers using 240volts. This is because it gives the marketing boys a higher figure to put on the box / advert etc.So, 10kW at 240V = 41.66amps

The equivalent rating at 230volts is 9580W (or 9.6kW)

the Triton catalogue even has a tablke at the back showing the equivalent ratings at both voltages.

You've also put for a 45A device. Few manufacturers make a 45A MCB (mores the pity), so you'll probably end up with a 50A. This will force 10mm cable.

PC. thank you for the info ... I am bit confused now of which one am I going to do as you've mentioned about 240V, is this a new power rating for the shower?? or should I stick to the wiring reg. ??

thanks a lot PC

 

[PC Electrics]

PC. thank you for the info ... I am bit confused now of which one am I going to do as you've mentioned about 240V, is this a new power rating for the shower?? or should I stick to the wiring reg. ??thanks a lot PC

No. In the 'good old days' of pre-17th, the official UK mains voltage was 240 volts. So all devices were rated at 240 volts. Now that the official voltage is 230 volts, that same device has a lower wattage rating (it's recieving 10 volts less now). But, the manufacturers of showers (and maybe other items) still quote their 240 volt rating because the figure is higher (the marketing boys no doubt believe it gives them an 'advantage').

 

[L Plate]

If you take a tour round the mower section of your nearest DIY shed, you'll find that even a large Flymo only has a 1500W motor. So lets say the load is 2kW max (for good measure).A 6 foot florry will pull 100W in round figures.

So, Ib = 11 amps

Ca = 0.77 ??

You installing in the Sahara?

Outdoors, UK ambients will rarely touch 30C, which is design, so Ca = 1.0

Now recalculate. Cable will defo drop to 4mm, maybe 2.5mm.

Don't forget to work to max Vd = 3% for lighting.

Thanks PC.

I was not so sure at first about my Ca 0.77 TBH, what is in my mind is, maybe it will get hotter on the summer. So yea , correction accepted about Ca 0.77, and also did you mean I have to show my calculation on the lighting for the shed as well ? my calculation is 6.9v acceptable for the lightings..

thanks

 

[PC Electrics]

Thanks PC. I was not so sure at first about my Ca 0.77 TBH, what is in my mind is, maybe it will get hotter on the summer. So yea , correction accepted about Ca 0.77, and also did you mean I have to show my calculation on the lighting for the shed as well ? my calculation is 6.9v acceptable for the lightings..

thanks

No, I simply mean that when a single circuit such as this supplies lighting and other devices, the most onerous design condition is the 3% for lighting rather than the 5% for other. Thus, design to 3%.

 

[L Plate]

edited new calculation in the shed.

from the info of PC that the large flymo has only 1500w ( 1.5kw ) but to make sure , just incase I will have 2kw for the flymo mower max.

So, 2000/230 = 8.6V ( 9v rounded )

therefore demand for the shed

9v for the mower

6v for the lightings

so total demand is 15A

Ib=15A

In=20A

Ca= 0.89 ( IEE page 267 table 4B2 @ insulation 70C thermoplastic )

It= 20

------ = 22.5A

0.89

Vd = 15x40.5x20

_________ = 12.15 A

1000

this is the 2.5mm 3 core armoured cable but the Vd for this is to high.

therefore

for 4mm 3 core armoured cable

Vd= 9.5x40.5x20

___________= 7.7V

1000

so therefore I will use 4.0mm 3 core armoured cable to supply the shed.

Can anyone check it again pls

thanks all

Good evening

Lplate

 

[Apache]

edited new calculation in the shed.from the info of PC that the large flymo has only 1500w ( 1.5kw ) but to make sure , just incase I will have 2kw for the flymo mower max.

So, 2000/230 = 8.6V ( 9v rounded )

therefore demand for the shed

9v for the mower

6v for the lightings

so total demand is 15A

You have confused volts and amps there!

You don't need 6A for light, as PC says 100w or 100/230 = 0.4A!

Add a 150W security light and you are still around 1 amp!

 

[L Plate]

You have confused volts and amps there!You don't need 6A for light, as PC says 100w or 100/230 = 0.4A!

Add a 150W security light and you are still around 1 amp!

Good morning Apache,

thanks for more info .. I will work it out again tonight . In the meatime, have a nice weekend ... >>> gone fishing