Garage Feed from House

[apprentice87]

Hi Beety,

Ok, so I will point out the errors for you....

When it comes to cable sizing it is obvious you have not got a clue. Online calculators will not help you either.. It is not as simple as you think..

For a start off, you do not size a cable according to the load, so it is not as simple as you think. You size a cable according to lots of things.

What is the load on the circuit??

What size, and TYPE of OCPD [Overcurrent protection device] are you going to use?

Next there are a load of "correction factors" for such things as ambient temperature, cable grouping, thermal insulation the cable might pass through, and type of OCPD too.

You calculate these factors, and apply them to the rating of the OCPD. You will find that the cable very often has to be rated for a substantially larger current than the rating of the OCPD itself.....

Then you have to decide what "disconnection times" are applicable to the type of circuit in the event of an earth fault.

Next you need to figure out the max figure for "earth fault loop impedance" allowable for the OCPD you have selected, in order to achieve the disconnection times you require.

You then need to figure out Ze for the supply, and then the value of R1 + R2 for your circuit, and then see if the resultant figure for Zs complies with the above, bearing in mind that the resistance of conductors increases with heat, and you have to make sure that it will be within permissible limits at the cable temperatures reached during a fault, NOT at room temperature..

Now you have to decide if the cable is suitable from the point of view of VD.

Next you have to see if the cable CPC is sufficient from the point of view of thermal effects in the event of a fault. Google the "adiabatic equation"

Oh, and if the cable CPC has to double as a bonding conductor there is another whole lot of fun to be had..

If your circuit is to comply, than ALL this needs to be checked..

Oh, and if you do all this, and the cable is the wrong type for its environment it will still not comply

See any of this in your "online calculator"????

As you can see, it is a piece of piss to be an electrician, anyone can do it... [NOT!!]

john..

 

[Slowhand]

Don't bite, you're only giving whoever it is oxygen.

The MO is somewhat reminiscent of neil from Essex.

Well known for sitting under a bridge waiting for billy goats if you catch my drift.

 

[Magnet]

Hi Beety,

Ok, so I will point out the errors for you....

When it comes to cable sizing it is obvious you have not got a clue. Online calculators will not help you either.. It is not as simple as you think..

For a start off, you do not size a cable according to the load, so it is not as simple as you think. You size a cable according to lots of things.

What is the load on the circuit??

What size, and TYPE of OCPD [Overcurrent protection device] are you going to use?

Next there are a load of "correction factors" for such things as ambient temperature, cable grouping, thermal insulation the cable might pass through, and type of OCPD too.

You calculate these factors, and apply them to the rating of the OCPD. You will find that the cable very often has to be rated for a substantially larger current than the rating of the OCPD itself.....

Then you have to decide what "disconnection times" are applicable to the type of circuit in the event of an earth fault.

Next you need to figure out the max figure for "earth fault loop impedance" allowable for the OCPD you have selected, in order to achieve the disconnection times you require.

You then need to figure out Ze for the supply, and then the value of R1 + R2 for your circuit, and then see if the resultant figure for Zs complies with the above, bearing in mind that the resistance of conductors increases with heat, and you have to make sure that it will be within permissible limits at the cable temperatures reached during a fault, NOT at room temperature..

Now you have to decide if the cable is suitable from the point of view of VD.

Next you have to see if the cable CPC is sufficient from the point of view of thermal effects in the event of a fault. Google the "adiabatic equation"

Oh, and if the cable CPC has to double as a bonding conductor there is another whole lot of fun to be had..

If your circuit is to comply, than ALL this needs to be checked..

Oh, and if you do all this, and the cable is the wrong type for its environment it will still not comply

See any of this in your "online calculator"????

As you can see, it is a piece of piss to be an electrician, anyone can do it... [NOT!!]

john..

Most of the info you are saying has already been mentioned by the op  ( all info for a 4mm2swa cable from house to garage that is it ! ) , load 16A , 16/20A mcb c , 63A RCD 30mA , 4mm2 to 2.5mm2 , run 4mm2 13Mtr run 2.5mm2 12Mtr , see there pics for bonding ( would think 10mm2 ! )  , the op is  talking about cable clipped direct , most of it outside and in a garage , all this info I fed into the program to give the results I posted , you can not see all that is fed into it , it just produces a chart , but not all the readings given are shown , can not tell you what the program is sorry . 

 

[Supersparks1234]

Most of the info you are saying has already been mentioned by the op  ( all info for a 4mm2swa cable from house to garage that is it ! ) , load 16A , 16/20A mcb c , 63A RCD 30mA , 4mm2 to 2.5mm2 , run 4mm2 13Mtr run 2.5mm2 12Mtr , see there pics for bonding ( would think 10mm2 ! )  , the op is  talking about cable clipped direct , most of it outside and in a garage , all this info I fed into the program to give the results I posted , you can not see all that is fed into it , it just produces a chart , but not all the readings given are shown , can not tell you what the program is sorry . 

https://www.youtube.com/embed/kgUDJ9lr_qc?feature=oembed

 

[apprentice87]

Oh, nearly forgot, there is the little matter that you do not use 240V in your calculations either..

If you want to come on here and ask sensible questions, everyone will try and help, but if you come on here and think you know everything, you will not get far..

I know a little teeny bit. The others are proper "boffins" but they will all help others, and most of all, none of them claim to know everything..

john..

 

[Magnet]

Oh, nearly forgot, there is the little matter that you do not use 240V in your calculations either..

If you want to come on here and ask sensible questions, everyone will try and help, but if you come on here and think you know everything, you will not get far..

I know a little teeny bit. The others are proper "boffins" but they will all help others, and most of all, none of them claim to know everything..

john..

It is all based on 230V 50Hz

 

[apprentice87]

Not according to your calculator it is not. Explain what difference this would make to cable calcs and why??

john..

 

[Magnet]

14 hours ago, Supersparks1234 said:



https://www.youtube.com/embed/kgUDJ9lr_qc?feature=oembed

Cool  :signthankspin: !!!!

 

[Magnet]

Not according to your calculator it is not. Explain what difference this would make to cable calcs and why??

john..

Don't understand your question !.

 

[apprentice87]

Hi Beety,

Your calculator says it based it findings on 240v I was just asking 1, why this was, and 2, what difference would voltage make to cable calcs. Just to test your understanding!! Not in a nasty way, just to try to see "where you are" and what bits you need helping with. Trying to help really..

john..

 

[Magnet]

Hi Beety,

Your calculator says it based it findings on 240v I was just asking 1, why this was, and 2, what difference would voltage make to cable calcs. Just to test your understanding!! Not in a nasty way, just to try to see "where you are" and what bits you need helping with. Trying to help really..

john..

Hi John

Again not sure what you are asking me , you quoted " Oh, nearly forgot, there is the little matter that you do not use 240V in your calculations either.. " , I answered that , now you are asking me quote "  what difference would voltage make to cable calcs " ! , the program is for domestic voltage @ 230/240v , it is set for that , it is not possible to put in any other voltages ,  because it is built into the program , so I can not tell you what the program would come up with,  using different voltages ! .

 

[Murdoch]

Hi John

Again not sure what you are asking me , you quoted " Oh, nearly forgot, there is the little matter that you do not use 240V in your calculations either.. " , I answered that , now you are asking me quote "  what difference would voltage make to cable calcs " ! , the program is for domestic voltage @ 230/240v , it is set for that , it is not possible to put in any other voltages ,  because it is built into the program , so I can not tell you what the program would come up with,  using different voltages ! .

Hi John

Again not sure what you are asking me , you quoted " Oh, nearly forgot, there is the little matter that you do not use 240V in your calculations either.. " , I answered that , now you are asking me quote "  what difference would voltage make to cable calcs " ! , the program is for domestic voltage @ 230/240v , it is set for that , it is not possible to put in any other voltages ,  because it is built into the program , so I can not tell you what the program would come up with,  using different voltages ! .

And the name of the programme is?

 

[apprentice87]

There you go then, Just for your information NO electrical calculations are based on 240V because that is NOT the voltage used here. Do not know where you got the programme as you will not say, but it is a piece of junk....

As to the question as to what difference would the voltage make to the cable calcs, this was just to test your knowledge and understanding a bit, problem is you have no idea at all... I will give you a hint "disconnection times" Write an essay on that and factors related to it and publish it on here..

Without being rude, it also appears that you do not what to learn, and think that you "know it all"

Good luck...

john..

 

[Lurch]

it also appears that you do not what to learn, and think that you "know it all"

I think has already been established many times over.

 

[a3]

So you don't all become confused, Magnet and Beetyboop44's accounts have been merged and are now Magnet

It is against forums T&C's to have more than one account.

Many Thanks

 

[apprentice87]

Ahhhhhh.....

All becomes clear......

john..

 

[Lurch]

That raises more questions than it answers.

 

[apprentice87]

I think someone is about to be blocked......

john..

 

[Slowhand]

Was there any point to this?

If there was I've missed it.

 

[Blue Duck]

An exercise in trolling I believe.