consumer unit schematics for the outbuilding

[Airiasas]

Hi everyone,

I am looking for some advice regarding getting power to one of the outbuildings, it will be used as a small workshop. (around 20 sqm, lights, sockets, solar (over 3kw), some welding equipment, power tools). On schematics, this is marked as Outbuilding 2. (This is not yet built).

The current Outbuilding that Power goes to from the house is around 5.76 sqm and is mainly used to store garden tools, it has a light inside and outside, a couple of power sockets inside and I plan to add an external socket. On schematics, this is marked as Outbuilding 1.

The house has 100 AMP DNO fuse, no electric shower or cooker, a solar array of 3825W, a 5kw hybrid solar inverter, and 14.7kw battery storage, currently, the house is heated via a combi boiler, but in the distant future, I might fit an air source heat pump & tank, tank would probably be fitted to Outbuilding 1 (this would have to be extended slightly or rebuilt with adequate insulation.) and finally, once the move to EVs happens single phase 7.4 kW electric car charger...

Currently Outbuilding 1 is connected via a 32A breaker, when I decide to build Outdoor Building 2 this breaker will be changed to a 50A and a 10mm cable will be used to connect CU in Outbuilding 1 & Outbuilding 2.

House is on Single Phase supply.
Schematics:

Questions:

1. I am better off just running another shielded cable from the house consumer unit from another breaker. As Outbuilding 1 would not be used a lot or barely used (apart from future air source heat pump installation) if Outbuilding 2 is used, to keep the installation tidy I thought just to run both buildings of 1 shielded 10mm cable.
2. Would using sometimes welding equipment, and power tools in the workshop cause issues with the power load assuming ASHP is installed?
3. I assume I am on TNS Supply (see the image below), can someone confirm that? Does that DNO main cable look in OK condition, as shielding or whatever it's covered/wrapped in seems rough?
4. Would I potentially have to upgrade to 3-phase supply in the future based on my plans? Thank you.

 

[SUNRAY]

I suggest you ask the electrical installer these questions.

 

[JohnW2]

3. I assume I am on TNS Supply (see the image below), can someone confirm that?

To my relatively inexperienced eye, something seems a little odd. .... it does, indeed, look like TN-S. However, there is a sticker which says "Earthing Terminal PME System", which would usually imply TN-C-S.

What do others think?

Kind Regards, John

 

[Murdochcat]

You really need eyes on site rather than random internet advice by people who think they know better

 

[flameport]

1. I am better off just running another shielded cable from the house consumer unit from another breaker. As Outbuilding 1 would not be used a lot or barely used (apart from future air source heat pump installation) if Outbuilding 2 is used, to keep the installation tidy I thought just to run both buildings of 1 shielded 10mm cable.

Two cables, one for each building would be a much better design.
It's a poor choice to supply them from an RCBO in the existing consumer unit, and so is having them looped from one consumer unit to another one and then to a third.
Via an MCB would be better, and from a fuse better still.
Having a consumer unit in the outbuilding(s) may not be the best choice either.

Much further consideration is required before any choices are made.

2. Would using sometimes welding equipment, and power tools in the workshop cause issues with the power load assuming ASHP is installed?

Power tools not a problem. Welding will be a problem, regardless of whether an ASHP is installed or not.
Welding puts a very large intermittent load plus a pile of interference onto the supply. Such things may not be permitted on a domestic supply as it may cause problems for other customers nearby.
Heat pumps require DNO approval, as does EV charging.

3. I assume I am on TNS Supply (see the image below), can someone confirm that? Does that DNO main cable look in OK condition, as shielding or whatever it's covered/wrapped in seems rough?

Doubtful due to the presence of the PME sticker. Cable is typical of older supplies. Cutout may need to be replaced as that yellow label could be covering up damaged parts. Further investigation required.

4. Would I potentially have to upgrade to 3-phase supply in the future based on my plans? Thank you.

Exceptionally unlikely.
Heat pumps use far less electricity than most people think (assuming that it has been sized and installed correctly)
Car charging would normally be configured to be reduced in power or disabled if total loads were high, and most people would charge from the solar if they have it, or overnight when other loads would be at a minimum.

 

[securespark]

I have seen something similar, where the sheath of a PILC cable has broken down and the supply has been made PME by the DNO.

 

[JohnW2]

I have seen something similar, where the sheath of a PILC cable has broken down and the supply has been made PME by the DNO.

Yes, even I have seen that, but the PME sticker is on a Henley-like block which is separate from the cutout and seems to be connected only to the sheath of the incoming cable. In other words, if it has been converted to TN-C-S, it's not clear (at least, not to me!) where the 'earth' connection to the CNE conductor is.

Kind Regards, John

 

[Airiasas]

if it's PME that would mean there should be an earth rod outside which would have to be connected up to CU? that earthing cable from that block goes into CU and it does not seem like there is an earth rod outside

 

[securespark]

Yes, even I have seen that, but the PME sticker is on a Henley-like block which is separate from the cutout and seems to be connected only to the sheath of the incoming cable. In other words, if it has been converted to TN-C-S, it's not clear (at least, not to me!) where the 'earth' connection to the CNE conductor is.

Kind Regards, John

Could the braid be connected, not to the PILC sheath, but the neutral in the cutout?

 

[JohnW2]

if it's PME that would mean there should be an earth rod outside ...

Eh? There seem to be some flaws in your understanding !

 

[JohnW2]

Could the braid be connected, not to the PILC sheath, but the neutral in the cutout?

Possibly. As has been said, 'investigation' would be required to provide a definite answer (if a definite answer is actuallyt needed) - without opening the cutout, we are inevitably just guessing.

As I said (and flameport seems to agree), it would seem very odd that a PME sticker would have been put on anything had it not been converted to TN-C-S. Whether or not it 'matters' whether it is TN-S or TN-C-S is perhaps a different question.

Kind Regards, John

 

[Jurassicspark]

if it's PME that would mean there should be an earth rod outside which would have to be connected up to CU? that earthing cable from that block goes into CU and it does not seem like there is an earth rod outside

No, that would be TT then.
PME: Protective multiple earthing, combined conductor is earthed at multiple points along the network.

 

[ebee]

The only way to know properly is to ask the DNO, things that actually were true TNS are getting rarer by each year and often you can only assume what it originally was by the way it presented itself. Often it has become TNC-S or effectively TNC-S like

 

[JohnW2]

The only way to know properly is to ask the DNO, ...

I suppose that depends upon what you mean by "only". As I said, in my version of an "!only" statement, in a situation such as we are talking about ()i.e. per the photo we have seen) a definitive answer can 'only' be achieved by someone' looking inside the cutout.

In my limited experience, DNOs are not usually able to answer such a question 'from their records' {which many people seem to think they can} - so even the DNO would have to look inside the cutout in a situation such as we are talking about..

Kind Regards, John

 

[Murdochcat]

This type of work definitely DIYNOT