What is the incoming Voltage Before and After the Service Fuse?

[James1985]

I know that after the Henley Block which houses the Service Mains fuse, the Voltage is 230v

If we was to remove the fuse and Measure the incoming Live wire, would the Voltage still be 230v?

 

[James]

In short, yes the voltage will be the same.
However, there may be other terminals available inside the service head that provide other phases and the voltage between them will be around 400v
also a fuse that is running close to its current limit will have a small but measurable voltage drop across it.

 

[littlespark]

I hope that picture on the OP is a textbook example and not a board being worked on….

And what you doing asking questions at 4 in the morning?

 

[timhoward]

@James1985 can you clarify if your picture is the setup you are asking about? If so there are a couple of things to make you aware of about it.

 

[pc1966]

For most purposes they are the same.

Typically such a fuse might dissipate around 6W at full load so if you were running at 60A (what looks like the maximum for your picture) then there would be about 0.1V drop over the fuse. You are unlikely to be able to measure that in practice as no access to the fuse terminals while live!

 

[James1985]

Hello guys, thanks for the answer.

​

james
1) is the service head the more square box with the 2 cylinders on the side under the two henley blocks?
2) if this is a common residential single phase, wouldn't the line incoming always be around 240v give/take 5%?

littlespark and timhoward
The board isnt my own, I am trying to study and take in as much as I can, and nuanced questions seem to bring some knowledge... 4am is a time I can silently focus.

tim, can you shed light on what I should be aware of?

pc1996
thanks, I was concerned with potential for much higher.


My reasoning for this question was, its commonly mentioned that the incoming phase is 60A, 80A, 100A, but apparently under the fuse the connection back to the sub can go to 400A - 800A, So I wanted to confirm if something similar occurred with the voltage... Apparently not.

 

[timhoward]

tim, can you shed light on what I should be aware of?

Two main things came to my mind when I saw that.
That service head design is a type that could incorporate a fuse on the Neutral as well as on the incoming phase. These haven't been allowed since the mid-1950s according to my notes. The main danger being that if a N fuse pops then everything Neutral in the installation becomes live (in simple terms as there is no way 'back' for the current)

It's highly likely by now that it has a solid link inside and not a fuse, but if it was a supply that hasn't been touched for a while I'd be mentioning it to the DNO to cover myself.

The other thing is that the way the main earth is connected is not a permitted method, those clamps are designed for bonding pipework and should not be used for creating a TNS earth connection.

I'd also be checking if the tails are single insulated just in case.

 

[Lucien Nunes]

That service head design is a type that could incorporate a fuse on the Neutral as well as on the incoming phase.

IMO that is a dedicated neutral block that cannot take a fuse. On these Series 3's they are similar in style but different shapes; the neutral block is flatter.

In any case I think this is a mock-up, not a real live intake. Neither the head nor the meter are sealed, there's no test sticker on the meter, the chipboard looks newish but the service cable couldn't have been threaded through a hole (and cable-tied from the other side) without disconnecting and then that head (and Wylex board) would likely have been replaced. And the cable itself looks like a piece of SWA wrapped in S/A tape. It's all a bit artificial.

 

[ipf]

It is a mock up. How old is the photo?
It seems like an example of a 50's or 60's job, except for the cable earth connection.
The earth bar is new, still find those small bars with bolts and cables shaped round for fixing.

As well as everything else, poking about with an uninsulated driver isn't a good example for students.

 

[ipf]

I hope that picture on the OP is a textbook example and not a board being worked on….

And what you doing asking questions at 4 in the morning?

Oh no! Not that Faron Young song...!!!