Is a 35mm cable big enough for a 3-phase domestic installation with...

[davesparks]

But in theory if they install a 35mm cable, I should be good whatever I need to plug in within reason, right?

You said earlier in the thread that they are installing an 80Amp 3 phase supply. So whether they install 35mm or 300mm cable your supply will still be 80Amps.

 

[Lucien Nunes]

they're planning on putting in a 35mm cable

Who is the 'they' in this case? The DNO or your electrical contractor?
If it's the DNO, what cable they use is out of your control. They will size their equipment according to their regulations and specs, to meet your agreed requirements which should have been calculated by the electrician before the application was made. The methods they use to size cables are different to the ones electricians use within an installation, as they have different performance specifications to meet under the ESQCR, for example.

If it is your electrician installing the said 35mm², then they should be able to calculate the cable to meet the requirements of BS7671 for whatever you have asked them to install either now or in the future. The worst case will be all demand or all generation - i.e. the maximum power that can flow in either direction. From what you have stated, the demand will significantly outweigh the generation, but is likely to be within 69kVA.

As mentioned above there are many factors built into the cable calculations, not just the load. Without all the information from a site survey, it's difficult to give a definitive answer to whether a particular cable size is suitable. 35mm² is in the right ballpark.

 

[Spinball]

Who is the 'they' in this case? The DNO or your electrical contractor?
If it's the DNO, what cable they use is out of your control. They will size their equipment according to their regulations and specs, to meet your agreed requirements which should have been calculated by the electrician before the application was made. The methods they use to size cables are different to the ones electricians use within an installation, as they have different performance specifications to meet under the ESQCR, for example.

If it is your electrician installing the said 35mm², then they should be able to calculate the cable to meet the requirements of BS7671 for whatever you have asked them to install either now or in the future. The worst case will be all demand or all generation - i.e. the maximum power that can flow in either direction. From what you have stated, the demand will significantly outweigh the generation, but is likely to be within 69kVA.

As mentioned above there are many factors built into the cable calculations, not just the load. Without all the information from a site survey, it's difficult to give a definitive answer to whether a particular cable size is suitable. 35mm² is in the right ballpark.

The 'they' is the DNO, National Grid who are doing the install. The cable in the street coming to my property is 95mm according to the DNO engineer. That's about as much as I know.
Thanks for the advice.

 

[IAmSparkytus!]

It's not the size of the cable you yourself need to worry about. You need to tell them how many amps/kva you require and then let them worry about what size cable they need to install to be able to safely provide you with that.

If you have a 3phase 80amp supply and they install a 35mm cable, you'll be able to use 3phase 80amps. If they install a 70mm cable, you'll still only be able to use 3phase 80amps.

 

[pc1966]

What the DNO can give you depends on many factors, not just the cable to your property. For example, the local substation might be close to max capacity based on all other property's loads in which case they might not offer new connections, or if they do it might not be 100A but instead fused down to 80A or 63A protect their system from overload.

 

[Spinball]

To follow up on this, they installed their normal cable knowing the power I was getting and it was all fine. I was fretting over nothing.
Thanks to those who replied.