Maximum distance from domestic consumer unit to Networks meter.

Andrea B.

Exploratory. Does anyone know of maximum distance or criteria for distance from consumer unit to the meter connection in a rural domestic setting?
They were considering a 100m run (which would be around 35sq cable!).

2011

I don’t believe there is a maximum distance. I can’t imagine why such a restriction would make sense. I wired and designed the wiring for some apartment blocks back in the day. All of the meters for around 50 units were installed in a central location and some apartments wold have been over 100m away. No issues.

I also did the same for an old farm yard thy was converted to around 10 holiday homes. Again no issues.

Andrea B.

Thanks. Really appreciated. They are in early stages of consideration, but does 35mm/sq seem correct for a 100m underground run for 63A(if you don't mind)?

2011

Andrea B. wrote: »

Thanks. Really appreciated. They are in early stages of consideration, but does 35mm/sq seem correct for a 100m underground run for 63A(if you don't mind)?

Not sure off the top of my head.
For a current carrying capacity it is more than enough as I’m sure you know.
From a volt drop perspective and earth you would need to check.
I would normally allow around 1.5% VD (when design current is drawn) on the mains cable and the balance on the final circuit.

Also you would need to consider earth fault loop impedance, again I’m sure you know this.

Andrea B.

Thanks!
No, there is a lot I don't know wrt to loop impedance etc. Just once they know feasibility etc, they can leave rest to contractor.

2011

Andrea B. wrote: »

Thanks!
No, there is a lot I don't know wrt to loop impedance etc. Just once they know feasibility etc, they can leave rest to contractor.

There is not a lot to know about Earth Fault Loop Impedance to be honest. It is the impedance of the entire circuit under fault conditions. So from the star point of the transformer, down the phase, to the point at which it connects to the earth (due to a fault) and back via the earth to the star point of the transformer.

I simply think of Ohm's Law (an old salty dog of an engineer taught me this many years ago).

Mathematically it is simply I = V/Z

Basically as the voltage is fixed lower impedance means higher current.
The higher the current the quicker the protective device will operate.
There is a table in the rules that tells you what the maximum loop impedance can be for a given protective device so as to ensure that the maximum permissible disconnection time is not exceeded. So if the impedance is too high the reduced fault current will mean that the protective device (such as a fuse) would take longer to operate or in extreme cases may never operate. There are a number of ways to reduce the EFLI, generally we either increase the size of the cable or reduce the length of the cable. As a rule of thumb the higher the rating of the protective device the lower the EFLI needs to be to achieve the disconnection time.

I hope this helps.

Wesekn.

The voltage drop over 100m seems high on the tails at first glance

4% of the nominal voltage is 9.2v

I think it's roughly 6.75v drop at 50amp, 100m of swa

Wesekn.

Depends on the supply quality too , proximity to transformer

Good supply I would chance it for standard but not the the 16kva

2011

Wesekn. wrote: »

The voltage drop over 100m seems high on the tails at first glance

4% of the nominal voltage is 9.2v

I’m not sure why you mean. I was suggesting 1.5% volt drop which is pretty much industry standard. Is this why you were referring to?
You can go higher but then the final circuit cabling may require larger cables.

I think it's roughly 6.75v drop at 50amp, 100m of swa

For what size SWA?

Wesekn.

2011 wrote: »

I’m not sure why you mean. I was suggesting 1.5% volt drop which is pretty much industry standard. Is this why you were referring to?
You can go higher but then the final circuit cabling may require larger cables.



For what size SWA?

35

2011

If we have a look on the last page of this.
The "r" value for a 35mm sq. 2 core SWA with a single phase supply is shown as 0.99 mV/A/m

If we use this and take the 50A value provided by Wesekn as the design current then and retain the 100m cable run the the volt drop on this section of cable can be calculated as follows:

0.99 x 50 x 100 = 4.95 volts

Note this table is from the 17th Edition of IEE Wiring Regulations.

Wesekn.

2011 wrote: »

If we have a look on the last page of this.
The "r" value for a 35mm sq. 2 core SWA with a single phase supply is shown as 0.99 mV/A/m

If we use this and take the 50A value provided by Wesekn as the design current then and retain the 100m cable run the the volt drop on this section of cable can be calculated as follows:

0.99 x 50 x 100 = 4.95 volts

Note this table is from the 17th Edition of IEE Wiring Regulations.

Don't think that 0.99 figure is accurate

Its 1.35 in et101 and online when I checked

2011

Wesekn. wrote: »

Don't think that 0.99 figure is accurate

Values differ depending on where you look. Many like to use manufacturer’s data when available as this is specific to the cable used. Nothing wrong with using ET101 either but it tends to be more conservative.

Its 1.35 in et101 and online when I checked

Looks like a good value.
Using this at 50 amps for 100m would result in a volt drop of 6.75 volts.

Wesekn.

2011 wrote: »

Values differ depending on where you look. Many like to use manufacturer’s data when available as this is specific to the cable used. Nothing wrong with using ET101 either but it tends to be more conservative.



Looks like a good value.
Using this at 50 amps for 100m would result in a volt drop of 6.75 volts.

I would be checking supply- proximity to transformer ,20kv,

Connected loads, motors, transformers

demand 12/16 kva

2011

Wesekn. wrote: »

I would be checking supply- proximity to transformer ,20kv,

Connected loads, motors, transformers

demand 12/16 kva

Yes.
I have seen heat pumps have all sorts of issues with volt drop.
Others domestic motors tend to be significantly smaller such as circulation pumps. Generally no issues with these.