Don't you think that a failure of single RCD could put whole neighbourhood in danger with this 1 ?I don't. How I see it working is that the supplier provides each customer a ~10 A or so rated, simple, robust, reliable differential current trip in the same assembly as they currently provide a fuse, and a second backup unit at the substation. (..) Of course it'll never happen, too much installed infrastructure exists, and nor do I claim to have "invented" it.
You are aware that current IEC regulations prohibit use of any switchgear on PE? I mean, zero. No switches, disconnectors, isolators, fuses. You would have to install sth that disconnects phases and neutral only (so you need 4-pole RCD). So the failure of this one RCD would have tripped whole area, finding nuisance tripping of this fault in a city would have been an experience very close to horror story.
[...]fusing arrangements at the customer incomer. [...]
[...]fusing arrangements at the customer incomer. [...]
I'm trying to understand what you're saying, and failing.
Can you tell me how UK differs from how we do it here in DK ?
[...]fusing arrangements at the customer incomer. [...]
I'm trying to understand what you're saying, and failing.
Can you tell me how UK differs from how we do it here in DK ?
At the 10kV/400V trafo, each distribution cable (4x400mm² typically) is fused with Nx100A. Those almost only blow when a backhoe does something stupid. The neutral is grounded at the trafo. No PEN in the distribution cables.
Each installation is fused at the point where it connects to the distribution cable, typically in a small road-side cabinet or at the top of a mast.
For a house 3x25A is normal. They are in peril when preparing for X-mas evening, but usually make it through.
From there it goes underground, or in a few straggling cases via overhead wire, (typically 4x4mm², but 4x16mm² for longer runs) to the house, through the meter, which is mounted on the outside of the building these days, then to the distribution panel where, it hits the HPFI first. Each building has its own PEN electrode.
A more up to date and hopefully more representative / clearer TNC-S installation (situated in integral garage). Although the service head and incoming supply cable date back to the early 1980s.
The 3-phase street cable is paper insulated, so presumably the individual house branches are too. Each house is connected to one phase with PEN to the outer sheath. These connections are buried underground and inaccessible. If you look at the cable boot on the feed cable entry into the service head, you can see that the cable is coaxial with the PEN conductor forming the outer sheath. You can also see a Yellow disc on the back board, signifying that the house is on the Yellow phase of the street cable (old colour coding).
As richard.cs says, the service head contains the electricity company cartridge fuse of up to 100A. A PFC of up to 10kA sounds too high for a domestic situation though, as it would exceed the 6kA maximum breaking capacity of the main switch and breakers (MCB / RCD / RCBO) in a normal domestic consumer unit.
Lots of photos covering a range of construction types and voltages here:
https://www.spenergynetworks.co.uk/userfiles/file/scottishpower_cables_equipment_metal_theft.pdf
Basically that UK houses typically have high-current single phase supplies. This is not really a very good idea, but the vast majority of domestic supplies, old and new, are single phase.
Basically that UK houses typically have high-current single phase supplies. This is not really a very good idea, but the vast majority of domestic supplies, old and new, are single phase.
Basically that UK houses typically have high-current single phase supplies. This is not really a very good idea, but the vast majority of domestic supplies, old and new, are single phase.
Ohh, wow...
Now I understand why the UK plugs have built in fuses!
The detail which makes my hair stand on end is that the customers feed cable is only fused by the substation fuse.
Basically that UK houses typically have high-current single phase supplies. This is not really a very good idea, but the vast majority of domestic supplies, old and new, are single phase.
Ohh, wow...
...
This picture shows the road-side cabinet where my house is connected, they had to upgrade it to find space.
The main distribution cable in+out 4x150mm² go on the unfused blue clamps.
Usually the distribution is run in a sort of two-string zig-zag pattern along a residental road, this allows them to isolate one or two of these cabinets, while keeping power on the rest of the road. The unconnected cable on the right is one such fused "diagonal" connection, probably 4x100mm².
The white plugins hold three fuses or six fuses, and supply one or two cables.
The "drop" cables to the nearby installations are 4x6mm²
Because our house is 200m from this cabinet, they ran a 4x75mm² to another cabinet about halfway, that holds our 25A "mast-fuse" and the cable from there is 4x16mm².
One benefit of this system, is that the fire-brigade can pull the fuses when a house is on fire.
Now I understand why the UK plugs have built in fuses!
The detail which makes my hair stand on end is that the customers feed cable is only fused by the substation fuse.
I don't believe that the supplier equipment is a significant cause of domestic fires (as badly installed (loose connections) older plastic consumer units can be. I think this is probably due to careful installation, but the small risk is there.
Meter installers yanking on the tails is a significant cause of fires in otherwise perfectly good CUs, for which they take no responsibility whatsoever..
Now I understand why the UK plugs have built in fuses!That.. has absolutely nothing to do with it being a single phase supply.
25A is such small current that 3x25A requires careful balancing acts for many households and even then it's quite common to accidentally blow the main 25A fuses.
But yes, adding an electrical car would require 3x35A, but that is just a one-time fee here in DK, so I dont consider it a problem?
But yes, adding an electrical car would require 3x35A, but that is just a one-time fee here in DK, so I dont consider it a problem?
Just so I understand, you are saying that a typical home only has 25 amp service on a three phase circuit? Also, for some reason, EV charging it typically done with a 35 amp, three phase circuit?
I know in the UK they use 9 amp tea kettles. It would seem a 25 amp circuit for a whole house means limited usage of electricity for heating, either the home or water. My hot water heater is on a 30 amp, 240 volt circuit actually drawing 18 amps and over 4 kW. Instant on hot water heating must draw more current since my heater won't keep up with taking a shower.
I know in the UK they use 9 amp tea kettles. It would seem a 25 amp circuit for a whole house means limited usage of electricity for heating, either the home or water. My hot water heater is on a 30 amp, 240 volt circuit actually drawing 18 amps and over 4 kW. Instant on hot water heating must draw more current since my heater won't keep up with taking a shower.
I know in the UK they use 9 amp tea kettles. It would seem a 25 amp circuit for a whole house means limited usage of electricity for heating, either the home or water. My hot water heater is on a 30 amp, 240 volt circuit actually drawing 18 amps and over 4 kW. Instant on hot water heating must draw more current since my heater won't keep up with taking a shower.
Two things: The fuses we are talking about, are slow fuses. It will take 25A sustained forever, and brewing a cup of tea, even if it puts you at 34A for a few minutes, will not blow the fuse.
Your 240V/18A hot water heater would claim 18/(3*25) = 24% of the available continuous capacity, but it runs only every so often and the chances that it, the oven, the dishwasher, the washer, the dryer and the hair-dryer all being on a the same time is practically non-existent, and even then, it would only be for a few minutes.
The trouble is when you add a huge "base-load" like EV-charging: That constant hour-long load steals the head-room, and means that the probability of intermittent loads may push the fuse to blow increases a lot.
A number of EV chargers have options for incomer current transformers, this way they can back-down the charge current to limit the peak load. I haven't seen this done often in domestic UK installs.
I think it is important for the discussion that we all understand how much this is "per-country" due to political and technological history.
Even between the nordic countries there are huge differences, for instance in EV uptake or how much resitive heating is used, it has been almost outlawed in DK since 1973, whereas I belive it is still pretty much the norm in NO and FI (not sure about SE).
...
But yes, adding an electrical car would require 3x35A, but that is just a one-time fee here in DK, so I dont consider it a problem?