SWA into ground

[ban-all-sheds]

Yes, I thought it curious that the regs would actually address this topic, and then be a bit vague, rather than reference the Electricity Supply Regulations Act 1989. The regs were revised in June 2001 - if there was an actual law in force at that point which explicity stated what you must do, then surely its existence should have been referenced, or its requirements quoted?

 

[Big_Spark]

Chowbasa, you need to find the cable type and use the correct table for that type to get the maximum permissable current capacity, then you need to look up the correction factor for it being buried in the ground.

The table for the current carrying capacity is table 4D4A for standard 70C armoured cable.

Here is the Data you need.

1.5 = 21A 29mV/A/m correction factor = 0.98
2.5 = 28A 18mV/A/m correction factor = 0.95
4.0 = 38A 11mV/A/m correction factor = 0.93
6.0 = 49A 7.3mV/A/m correction factor = 0.92
10 = 67A 4.4mV/A/m correction factor = 0.91

So, to work out the cable you require you do this.

Vz = Ib x Vd x m x Ci / 100

Where,

Vz is the calculated votage drop
Ib is the design current of the circuit (not the size of the protective device)
Vd is the Volt drop
Ci is the correction factor

Example:

Ib = 22A
Vd = 18mV
m = 28 meters
Ci = 0.95

So... 22x18x28x0.95 / 100 = 10.53V

In this case 2.5mm2 SWA would not do the job as the maximum permisable Volt drop must not exceed 4% of the nominal supply which is 9.2V.

 

[BR]

FWL, although i can find no fault in what you are saying, it is important to remember that this is a domestic installation, not an industrial one. I think as you have already stated somewhere, (even though you may have been referring to something else) an 'on-site' decision has to be made here. And in my opinion, the running of cable in circumstances such as these has to be taken on a case by case basis, by suitably skilled personnel of course.

 

[ban-all-sheds]

Yes, but as someone once said, ye cannae change the laws of physics.

Industrial or domestic, business or pleasure, amateur or professional, fish or fowl, red or white, it makes no odds. You will get the same voltage drop in the same circumstances, and you need to do the same sums.

 

[breezer]

Yes, but as someone once said, ye cannae change the laws of physics.

Mr Scott "Scotty" Starship Enterprise, year not arrived yet?

 

[Big_Spark]

FWL, although i can find no fault in what you are saying, it is important to remember that this is a domestic installation, not an industrial one. I think as you have already stated somewhere, (even though you may have been referring to something else) an 'on-site' decision has to be made here. And in my opinion, the running of cable in circumstances such as these has to be taken on a case by case basis, by suitably skilled personnel of course.

BR, as Ban has stated, electricity is electricity, volt drop is the same for a given circuit whether it is in your home, your garden, in a factory or on Mars. This must be taken into account when designing any electrical circuit or installation and failure to do so is nothing short of criminal negligence in my opinion. If you do not account for something as fundermental as the volt drop, then who is to say you have taken into account other things...

Further, and more importantly, the volt drop has a DIRECT bearing on the disconnection time of the protective device, get it wrong and the device may not operate as intended or required, that is when people die, hence it being criminally negligent.

 

[chowbasa]

Thanks for the replies, Its getting clearer every day.

 

[securespark]

That's as maybe, but can you see all obstacles in your way?

 

[ban-all-sheds]

Only once the dark clouds have passed away..

 

[securespark]

I love being silly!

 

[Big_Spark]

I love being silly!

Well not a lot changes then

 

[securespark]

My missus says I'm still 11 inside my head

 

[Big_Spark]

My missus says I'm still 11 inside my head

Age or IQ ??

 

[masona]

Age or IQ ??

What's the difference ?

 

[ChrisRogers]

Further, ducting also prevent accidental damage caused by persons digging in the ground, they hit the marker tape and duct first, not the cable. If you only have the marker take above the cable, it is still possible to damage the cable before you realise that a cable is there.

does anyone know of an internet supplier of this ducting?