Cg derating query

To answer the specific question, ERA 69-30 only goes up to 60cm c-c. Greater than that I think you would need to calculate it directly using BS EN 60287. We use Cableizer for that but there are other tools out there, with varying pricing.

However, I might suggest think a trench 3m wide (with room for bedding etc) between a transformer and its LV feeder pillar is not likely to be a cost-effective or practical approach in most circumstances. Worth considering also that the horizontal distance is often around this length and the gland plate at each end force "pinch points".

You will also need to be mindful of imbalanced current sharing as the lengths and reactance are likely to differ.

I assume you've looked at larger conductors? Is the soil exceptionally warm or load large? Could you install the cables in air (a trough)?

If you genuinely are stuck, you could extend the LV spill box from the transformer. Definitely not a cheap option if it's already on site of course (not least you'd have to get it to the factory), but if it's still at the factory or in design it can be done.

Hi Jam, 

would you recommend Cableizer for sizing LV circuits between transformers and feeder pillars / switchboards? 

It'll do it (I've done similar) but it could be a bit sledgehammer vs nut. The user interface is slow, as it's web based, and it does assume you know what you're doing (although the documentation is very thorough). You do need to know more details of the construction of the cable than typically appears on datasheets; ideally you'll have a good idea of your answer and be using this to confirm or check a limited set of solutions. If I recall correctly you can set up a project without carrying out any calculations before paying so you could have a play to see whether it's a realistic prospect.

You will still have to do adiabatic for faults, impedance calcs etc etc... It just does the current carrying capacity and a few bells and whistles.

For the record, I'm not affiliated with it except as an occasional user. There are others out there, and do check the contract with your Client in case it specifies particular calculation methods.

I do prefer to use the more common BS7671 appx 4 or ERA 69-30 where they are appropriate though. Not least, the arrangements described by the standard tables are the most common solutions for a reason, i.e. if you can't use them you've gone off-piste: Fine if intentional, but stop and think first!

PS - Their server does seem to be flaky this week, which is not ideal

It'll do it (I've done similar) but it could be a bit sledgehammer vs nut. The user interface is slow, as it's web based, and it does assume you know what you're doing (although the documentation is very thorough). You do need to know more details of the construction of the cable than typically appears on datasheets; ideally you'll have a good idea of your answer and be using this to confirm or check a limited set of solutions. If I recall correctly you can set up a project without carrying out any calculations before paying so you could have a play to see whether it's a realistic prospect.

You will still have to do adiabatic for faults, impedance calcs etc etc... It just does the current carrying capacity and a few bells and whistles.

For the record, I'm not affiliated with it except as an occasional user. There are others out there, and do check the contract with your Client in case it specifies particular calculation methods.

I do prefer to use the more common BS7671 appx 4 or ERA 69-30 where they are appropriate though. Not least, the arrangements described by the standard tables are the most common solutions for a reason, i.e. if you can't use them you've gone off-piste: Fine if intentional, but stop and think first!

PS - Their server does seem to be flaky this week, which is not ideal