Understanding the electricity supply to my house...

[DIYNotIan]

Partly cos I like to know everything... Partly because I'm a geek... And partly because we're going to have some electrical work done on the house which has made me curious.... I'd like to know more about the feed to my house...

The power lines come to us through the garden and reach a pole with transformer. From there the supply comes to us underground. Because the ground is lower at the back of the house, you can see the main cable going into the wall of the house. I'm guessing it then travels under the house to the meter box which is on the front of the house. The meter box has two fuses. The house has three consumer units. As we're having the consumer units changed and a partial rewire amongst other things, I'm not too worried about comments on the photos of the consumer boxes (but feel free to make them if you wish)...

... What I am more eager to know is anything you can tell me about the pole, transformer, underground line and meter box. Some of the things of particular interest...:

1. Earth/ground. How can I tell what the set up is for that? A sparkly told me there was a supplied earth, but there's only two overhead cables. But there are three cables running down the side of the pole and going into the ground.

2. Earth/ground - is there any way to test it? (I'll be running a music studio in the house which I've been told needs a low impedance path to ground)

3. I'd love to know what's what on the pole and how it works, so any explanations or links would be fantastic.

4. The diagonal "cable" with the yellow cover coming from the pole. Is that purely just a support or does it have something to do with the earth/ground?

5. Why two fuses in the meter box?

6. Can anyone tell me roughly how old those two fuses are?

7. How often are the power companies maps wrong? I was in touch with them today and they sent me a map which shows the cable running underground from the pole to the front of the house. But I can see a power line going into the back of the house (see photos). Odd...

8. Anything what you want to enlighten me with!

I've got no broadband at home and so it takes an age to upload anything. I'll therefore link to a folder on Google drive that has all the photos. Let me know if that's a problem and I'll upload the photos to the site when next at the library.

Sorry for such a long thread. Any thoughts most welcome. Cheers

https://drive.google.com/folderview?id=1-5SRqpupjqCplW9hDkE06pA9UjCL1hU9

 

[JohnW2]

5. Why two fuses in the meter box?

You've also mentioned this in the other thread ... a photo or two would be helpful.
Edit: Ah - I didn't read right to the end of your message. I'll have a look at the photos!

Kind Regards, John

 

[JohnD]

The meter box has two fuses.

I can only see one company fuse. Where can you see two?

Are you looking at the two Wylex boxes? They are your switchfuses which send the power to something else within your installation. Perhaps one goes to the house and one to an outbuilding, or maybe you have two consumer units. Turn each off in turn and you will find out what it supplies. Maybe one is no longer needed. The really ought to be labels identifying their purpose.

It looks to me like the upper one is supplying power to the lower one, which is pointless. The upper one has undersized tails.

 

[JohnW2]

I can only see one. Where can you see two?

I imagine he is referring to the two switch-fuses (which are, as he said, 'in the meter box'), rather than cutout fuses.

Kind
Regards, John

 

[mattylad]

4. The diagonal "cable" with the yellow cover coming from the pole. Is that purely just a support or does it have something to do with the earth/ground?

That's the support cable.

6. Can anyone tell me roughly how old those two fuses are?

Probably older than you.

7. How often are the power companies maps wrong? I was in touch with them today and they sent me a map which shows the cable running underground from the pole to the front of the house. But I can see a power line going into the back of the house (see photos). Odd...

I would imagine that company maps can often be wrong, changes get made but not updated on the maps.
You have to assess and take the situation that's there.

 

[aptsys]

Not much to know really about the supply, on the LV side, the neutral is tied to earth, there'll be a conductor buried in the mass of earth to reference the earth to terra firma, usually another HV earth going to the mass of earth in the opposite direction.
There's a fuse on the pole for the LV side which then feeds the split concentric cable going to your cut-out. The supply is TN-S

The cable you took a picture of is SWA, so probably going to a building or some outdoor lights.

 

[Taylortwocities]

Earth/ground - is there any way to test it?

You will need a tester that is capable of measuring the Earth Fault Loop Impedance. Any electrician will have one of these.

 

[gman76]

I have a pretty poor understanding of these things, but I will tell you what I know in the hope that someone will come along & correct me if I'm wrong as this stuff interests me too.

The incoming HV supply is 2 phase, or split phase 11kV, this enters the transformer via the two big insulators on the top. The single phase LV 230V exits on the side we cant quite see, the neutral output is tied to earth via one of the wires coming down the pole.

The transformer converts the high voltage to lower voltage via two coils of wire of differing lengths & gauge that are isolated from each other & works by induction.

The LV 230V feeds come down the pole, through a fuse then join to your cable.

Your earth is then joined to the suppliers neutral.

I will cower & wait to be corrected!

 

[DIYNotIan]

Amazing, fantastic replies. I really do appreciate it. I've had to go away for the weekend so will revisit this next week at some point. Just wanted to say thanks in the meantime.

 

[Adam_151]

I have a pretty poor understanding of these things, but I will tell you what I know in the hope that someone will come along & correct me if I'm wrong as this stuff interests me too.

I'd say you've got most of it right just a couple of bits where terminology is probably not quite right.

The incoming HV supply is 2 phase, or split phase 11kV, this enters the transformer via the two big insulators on the top. The single phase LV 230V exits on the side we cant quite see, the neutral output is tied to earth via one of the wires coming down the pole.

I's say that thats 1 phase, 2 wire. (But it is two phase conductors of the system [so you can see why it might seem sensible to call it two phase] but you can only access one phase via them - Its distributed as delta at HV).

I'd also say its not split phase, that would have the same single phase of HV into the transformer, but would utilise a centre tapped transformer to give 230-0-230, whereas the transformer only appears to have a single secondary winding, or at the very least, only one that is in use

 

[gman76]

Thanks Adam - the HV was the part I was most unsure about.

 

[DIYNotIan]

Hi all

I'm back home now, and a couple of replies before bed....

A) SWA... The total diameter of the swa at the back of the house is around 18mm. The black sheath says 600 - 1000V. It seems to be exactly the same as what comes into the meter box (bottom left). Also, there are currently no external electrics, so if it does feed anything outdoors it's no longer there. There's no sign of the cable inside the property. In fact, where it enters the wall is roughly 30cm below the current floor level. Everything to my very untrained eye and mind would still suggest that this is what goes to the meter box... Although at the same time I'm happy to admit I might be wrong!

B) The two fuses (switchfuses) in the meter cupboard... The white one controls the c/unit in the lobby. The black one controls the other two c/units - the understairs and cow shed mezzanine ones. These two consumer units do work independently though. If you turn one off the other still works.

I'll be back later with further questions, but in the meantime massive thanks for all the help.

 

[DIYNotIan]

Any further thoughts chaps?

Also...

The supply is TN-S

If you get a moment would you mind explaining why so? It's just that I've been told by others that it's TN-C-S.

Cheers

 

[DIYNotIan]

Hi again

Along with the questions in my last 2 posts, I do have a couple more to add if anyone would be so kind?

C) In the meter box, someone commented that the cutout ground connection block is corroded and I should maybe speak to the DNO about replacing it. What do you guys think?

D) Should I look to have the two switchfuses replaced for something with trip protection, so that the cables from the meter box to c/units are safe?

E) Looking at the wooden pole in the garden again there is one wire coming down on one side and two on the other side, and all of them go down and into the ground. Why three??? I've taken some photos and put them in the same google drive folder. Link above but here it is again to save scrolling:

https://drive.google.com/folderview?id=1-5SRqpupjqCplW9hDkE06pA9UjCL1hU9

The additional photos are labelled 3h, 3i, 3j and 3k.

Thanks a million for all the help.

 

[aptsys]

Hi again

Along with the questions in my last 2 posts, I do have a couple more to add if anyone would be so kind?

C) In the meter box, someone commented that the cutout ground connection block is corroded and I should maybe speak to the DNO about replacing it. What do you guys think?

D) Should I look to have the two switchfuses replaced for something with trip protection, so that the cables from the meter box to c/units are safe?

E) Looking at the wooden pole in the garden again there is one wire coming down on one side and two on the other side, and all of them go down and into the ground. Why three??? I've taken some photos and put them in the same google drive folder. Link above but here it is again to save scrolling:

https://drive.google.com/folderview?id=1-5SRqpupjqCplW9hDkE06pA9UjCL1hU9

The additional photos are labelled 3h, 3i, 3j and 3k.

Thanks a million for all the help.

HV and LV ground, plus a ground from the over voltage arrestors on the HV side