The earth will be available in the consumer unit. He connects to that, not in the meter box.
You can see in the consumer unit what is available. In this case, one 100A 240V conductor.
Which is in the consumer unit.
Wrong, wrong and wrong.
Have a look at an electrical installation certificate.
All of that information may well be available at the "fuse box" (consumer unit), without needing to visit the master fuse and meter. In my present house it's difficult to distinguish because both are in the same place, but in my last house which had separate meter and consumer unit locations, the RCD (protective device) was part of the consumer unit - unless for all electrical installation certificates the electrician also needs to inspect the master fuse (a wire fuse rather than an MCB or RCD). Is house earthing usually via the meter installation rather than via the consumer unit? I
*think* I remember a fat green-and-yellow wire coming from the CU and going to the cold water rising main under the sink.When we had a new electric shower fitted in our present house, I don't remember the electrician going to the meter/CU area - rather trustingly he relied on me saying "I've turned off the master switch" - and yet he gave us a certificate of installation.
I hadn't realised that certificate of installing a device involved doing a sanity check on the rest of the electrical installation in the house that is not specific to the device being installed. It's good if this is the case.
Would the electrician actually need to know that there was a three-phase cable of which one phase was connected to a meter and the other two were "blind ends", and distinguish that from the more normal case of one phase supply?
In the case of three-phase supply where the customer only now uses one, is the disconnection only at the customer's end, or do they also disconnect at the overhead pole in the street? Assuming overhead rather than underground. And if the wire every needed replacing would it tend to be replaced with a two-core rather than three-core pole-to-house cable?
Our house is a terrace of three with three cables from the pole to the end of the terrace, but three cables are fastened to the house wall from our neighbours to us (middle of three) and one goes into our house but two continue to our neighbour on the other side, whereas I'd expect two cables on the incoming side and one on the outgoing side.
What is the normal arrangement for the number of adjacent houses which are fed from the same phase? Do they tend to alternate phases with every house or do they tend to feed several (eg three) houses from one phase, then feed the next three from the next phase, etc.
I remember at work when our lab was rewired, every bench was fed from a different phase and there were warnings not to connect equipment on one bench (eg by RS-232, Ethernet, USB or other low-voltage data cable) to equipment on another bench, which caused us horrendous problems.
That's a weird idea, you'd think they'd at least have each room on its own phase.
Although I can't see the problem. USB for example would have its ground the same as the appliances earth, which remains constant for all the phases.
ox. From what he's told me there is the normal arrangement of master fuse, meter, then into the house to the consumer unit. The house was built in 1
985ish and is detached. I've never seen inside the meterbox myself, only t he consumer unit, which looked like a normal run of the mill row of circuit breakers with one master at the end, 100A. If there were three phases in the meterbox I'd expect his description to include a lot more. Now the pre vious owner did have an ironwork hobby with "high powered equipment", but h e was a very frugal sort and I doubt he would have got three phases install ed if he didn't absolutely have to - mind you I believe he was the first ow ner of the house and designed it himself, so maybe it's just as cheap to ge t three phases when building the property? The reason this has come up is they've just had a 10kW electric shower fitted (used to run from the hot wa ter tank, but that onewith an electric one, which the electrician fitting the shower warned would require a relay to switch off the boiler so it didn't run at the same time as the shower as he'd run out of juice. When he saw 415V he was wondering if he infact had more phases available.
to peek around and use a multimeter. But at the moment it's just a matter of interest for a possible future electric boiler installation. I was jus t wondering if houses ever had more than one phase installed or if you had to ask for it.
Some houses were supplied with three phases if there was an abnormally high load or a workshop attached with maybe three phase motors or welders. In some cases if there were electric storage heaters. But his was for quite big houses.
But quite unusual. You need to see if there are four wires entering the premises or two. The cutout will have three fuses if it is a three phase supply.
The one previous owner did have an ironwork hobby with large equipment in the double garage with adjoining workshop.
I'm not there, but I was told what it looked like. There are no extra fuses or evidence of where they used to be. There is only one cable coming into the meter box through one hockey stick, and it's the same width as my single phase one. This leads to the master fuse, then two wires go through the meter from that, and an earth straight into the house. If there used to be three phases, it's been very well tidied up.
Yes I thought the restrictions seemed draconian considering that all signal cables have a signal ground which may be connected to a common mains earth ground through the equipment or else will be floating wrt mains earth and so will be no worse for two pieces of equipment on the same phase compared with equipment on two different phases. It meant that if we took any portable equipment into the lab, we had to be careful to plug it into the same bench as the equipment, even if that meant unplugging something else to free up a mains socket. (*) They even supplied little opto-isolators if we ever needed temporarily to connect a server on one bench by Ethernet to a router on another bench when setting up a private LAN.
Maybe the worry is that if mains-live gets onto a signal wire separately on both pieces of equipment (**) then there's phase-to-phase voltage between the two whereas there's no voltage between equipment on the same phase, so you wouldn't get a shock if you touched signals on both devices (providing you weren't earthed) in the latter case.
I remember our department manager called site services when he became aware of the operational problems it was causing us, and got them to cost out rewiring the lab onto a single phase, with SS covering the cost, given that the change was something that site services had taken it upon themselves to introduce when we'd not asked for it. Sadly the whole department was made redundant before the matter could be taken any further... So all the building/rewiring work was a complete waste of everyone's time and money, given that no other department with similar need for a lab moved onto that floor - but such is life!
(*) What they didn't consider was that some of us had old VT220 terminals on our desks connected by RS232 to servers in the lab, and no attempt was made to ensure that the desk was on the same phase as the bench in the lab. It didn't take some of long to see that unwitting loophole in the regulations.
(**) Unlikely for one piece of equipment, let alone two, to fail in this way, but you've got to cover the worst-case scenario.
Where I used to work (and I'm sure plenty large buildings are like this), there were three phases throughout the building, and ethernet connections throughout the building. There was no attempt made to isolate anything from anything.
As for your **, you'd only need one to cause severe damage, two wouldn't be any worse.
This thread has just been transformed.
on it! I definitely only have one phase. Very strange. Why would a maste r fuse need a 415V rating? If I had three phases, surely I'd have three fu ses, one on each phase, so they'd still only need to be rated at 240V each.
Many electrical items are marked with the MAXIMUM voltage they are suitable for. That doesn't mean that they are actually running at that voltage.
that only applies to overhead wiring. Here there is multicore cable coming out of the ground and terminating in a cutout.
It just seemed odd that it happened to be the voltage of 3 phase. I guess it's for the reason I posted afterwards, in case you have three phases and short two together.
Yes, I have never understood why people get so worked up about appliances connected to multiple phases in close proximity or even connected to each other. I can't think of a plausible single failure which would be made more dangerous by two adjacent or connected appliances being on different phases.
Nobody seems to worry about using uninterruptible power supplies, even though (depending on the type) they may be delivering an output which has a random phase relationship to the mains and which therefore could have a hgher phase to phase voltage than a 3-phase supply.
John
relationship to the incoming
I have an American Power Conversion UPS. It gives out -110 0 +110V, where 0 is the earth, -110 is the neutral, and +110 is the live. I've always assumed it's because it's American, a British one would tie the neutral to the earth. The computer, monitors, printers, stereo, lighting, etc connected to it doesn't seem to care, but I would have thought some devices might expect neutral to be about 0.
I think in a roundabout way you have answered your own question.
What you have described in your last paragraph seems to be an ordinary everyday single phase supply.
You will only know for sure either when you see it yourself or more likely if your relative enquires for 'load acceptance' for an electric boiler or similar connection to the DNS (Distribution Network Supplier) and they check it out.
The 415v sticker could be a remnant from a previous 3 phase supply installation.
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If the supply cable is alraedy 3 phase and nuetral and still connected as such to the street cable, the cost would negligible as the extra fuse and meter would be provided by the DNS.
If the DNS deems a 3 phase supply to be required for the installed capacity in a property they will weigh the cost of any work against the revenue stream from that installation .
Meter cost are normally recovered through the tariff daily standing charge by the ESCO, the customers chosen electricity supply provider, which is different from the DNS (the Distribution Network Supplier)
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The sticker on the fuse I can understand, mine has it too. But he said there was a sticker on the cable, which suggests he must have a 3 (or 2) phase cable already there, substantially reducing the cost of giving him a 2nd phase.
I don't see that he would find out, would the installer not just assume he has no extra phases available and fit the switch to shut the boiler off while the shower is operating?
All these fuses will say 415V and are generally 100A, although sometimes le ss. This doesn't mean it's three-phase, unless there are three of them ;)
The 415V is just the voltage the component is rated to ? fuses oper ate on Amps alone, the voltage is not relevant. A 100A fuse will blow just beyond 100A whether it's at 12V or 1200V.
The same way appliance mains cables are rated to 300V or even 600V; it just refers to the insulation resistance or safety factor of the cable.
es less. This doesn't mean it's three-phase, unless there are three of t= hem ;)
operate on Amps alone, the voltage is not relevant. A 100A fuse will bl= ow just beyond 100A whether it's at 12V or 1200V.
just refers to the insulation resistance or safety factor of the cable.=
I guess it's so they can be used in 3 phase setups. A short from L1 to = L2 could put 415V across one of the fuses.
-- =
During the weekly Lamaze class, the instructor emphasized the importance= of exercise, hinting strongly that husbands need to get out and start w= alking with their wives. From the back of the room one expectant father inquired, "Would it be o= kay if she carries a bag of golf clubs while she walks?"
Thank God. I?ve been waiting three years for someone to answer. Oh, hang on, they did three years ago.
Try this link...
Tim
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