Does it need rewiring?

[Karina]

Can anyone tell me what to look for in order to tell if a property needs re-wiring.

The georgian house I am going to view has been in the same ownership for 20 years and definitely not re-wired during that period (history before that is unknown). From the agent's details I can see that there are modern (ish) plastic sockets. The one I can see most clearly is mounted on some panelling below a window but does not appear to be recessed at all i.e. looks like it has just been 'stuck on'. I am assuming that when I go and view if I look at the fuse box (is this the correct terminology?) then this will give me a clue as to how old the system is. Is it possible that this might have been updated without updating the wiring itself?

Obviously there are two issues if the house does need re-wiring; firstly the cost but also the damage that will inevitably be done inserting the new wires. I am hoping this could be avoided but would clearly not want an unsafe electrical system.

 

[bower1]

Its not always easy to tell yourself the total state of wiring in a house, as it could have been modified in stages.

In general, the two really bad things you are looking for are:
1. Rubber insulated wiring - this must be replaced. It should be white or grey plastic coated.
2. Very bad (probably) DIY modifications. These are harder to spot.

The fusebox may have been replaced with a modern consumer unit, with the push up/down switched rather than the older pull out fuses (that look like dominos). That is no sign that the wiring has been updated, but will probably be safer if there is a fault.

The sockets themselves are no sign of the state of the wiring, as they can be easily replaced without changing the wiring.

If you have a survey done, they are unlikely to comment on the state of the wiring, so if you are concerned, you can get an electrical test done by an inspection electrician.

 

[MdB]

Others are more expert than I on this but here are my thoughts:

If it hasn't been touched for 20 years then it is very unlikely to meet current specifications. This won't necessarily make it particularly unsafe but it won't be as safe as it could be.

Does the fuse box / consumer unit have wire fuses in it or does it have MCBs (miniature circuit breakers - each will have its own switch)? MCBs are the modern way of doing things.

How many fuses are there? A modern system will have one for the cooker, one for the kitchen sockets, one for the rest of the sockets, one for the immersion heater, one for the lights and one per electric shower. Often there will be more, eg, one for the sockets downstairs and one for sockets upstairs, one for the fire system etc. Old systems often have far fewer and hence the protection will be less.

How many sockets are there in the house? Old properties often have very few and it is not safe to load up the system with multiple extension leads etc to increase the number of things you can plug in. In my 4 bed house, some rooms only have one socket and the whole house is run off a single ring main. Currently the house is heating is out of commission so we are using electric heating. If I put say six 3kW electric fires in the house and had them all on, they would draw 75A which is far too much for a single ring. Hopefully the fuse should blow but it may not have the correct value installed.

The lights may not have any of the ground connections connected. This is common in old houses (and is the case in mine) and allows the potential of metal light fittings going live.

Is there any cable with anything other than PVC insulation. PVC is bad for windows but required for cabling. Old cables can be made from rubber which goes brittle. This must be replaced.

As you can see, there are lots of things to consider so if at all unsure, get an expert in. They will of course tell you that an entire rewire is required as it gets them business but it probably is required anyway.

 

[Penners]

I don't think the specification for electrical wiring was much different 20 years ago from what it is today. So if your cabling was all properly installed then, it shouldn't be cause for too much concern. But you should certainly check to make sure that parts of the system are not considerably older (see other people's comments about rubber insulation).

As others have also mentioned, if your fuse box (otherwise known as the consumer unit) has rewirable fuses, then these won't give you quite as much protection as modern MCB's (miniature circuit breakers) would. This doesn't necessarily mean that you need a whole new consumer unit - you can buy plug-in MCB's to replace the rewirable fuse carriers. But if you can afford it, a new CU, with an integrated RCD breaker on certain circuits, will be the best option. If you plan to do this you will need a the services of a professional electrician who is Part P registered.

As MdB has said, you should check to ensure that the installation is properly specified for the needs of modern living - adequate numbers of sockets, a ring main for upstairs and one for downstairs (and ideally a separate one for the kitchen), lighting ditto, plus the other radial circuits that MdBmentioned.

Incidentally, the fact that a socket is surface-mounted doesn't necessarily mean that it is badly specified our out-of-date. Surface mounting is still practiced where hacking out a wall for a sunken back-box is not practical.

I am not a qualified electrician.

 

[Pford75]

One addition to the comments made by others...

Check the main fuse (the one which the main supply is connected to). If you can't tell, the electricity co. should be able to tell you what supply you have. For example, some older properties still have a 60Amp supply....which can easily be exceeded by modern requirements. In this case, an upgrade to the main supply is usually free of charge and a straightforward job...but the electricity supply company may insist on a new consumer unit if the old style is still fitted.

Secondly, if the wiring is very old, check if it is 2 or 3 phase supply. A 3-phase supply has an earth to each socket, whereas the older system relies upon an 'earth spike'. Earth spikes are not as safe as a modern 3-phase supply.

Good advice above is to have an electrician inspect. Most charge 100-200 quid for a normal size house. If you are serious about a purchase, this is a sensible investment

 

[MdB]

Secondly, if the wiring is very old, check if it is 2 or 3 phase supply. A 3-phase supply has an earth to each socket, whereas the older system relies upon an 'earth spike'. Earth spikes are not as safe as a modern 3-phase supply.

Penners mansion might have a 3-phase supply (one for each wing I guess) but normal houses only have a single phase supply. Also there is also nothing wrong with an earth spike if installed and tested properly. An earth supplied by the electricity board is a lot easier though.

 

[Pford75]

We have a 3 phase supply....

The problem with eath spikes as I see it, is that if anything interrupts the run to the spike (as happened in our case), you effectively lose the earth via the spike and the system tries to earth out via another route (again in our case, via the metal conduit, to some copper piping, into a shower and then out through cast iron downpipe...when water was running from the shower).

Many earth spikes are old and corroded...so would be worth inspecting the spike and the run of cable to the spike

 

[bower1]

There is no particular need to worry if the mains circuit is 'radial' rather than 'ring'. Many will tell you otherwise, but I have it on good authority from several people I trust that a radial is fine, as long as the cable are rated correctly.

Also, houses often have less total power use now than in the past due to electric heaters being replaced by central heating. The area defined for a ring or radial supply was defined to allow electric heaters to be plugged in.

This information might be a bit far from the original question, I just thought it might be useful against an unscrupulous electrician.

 

[MdB]

We have a 3 phase supply....

Three phase means that you have three live connections coming into the house together with neutral and earth. Five wires.

A live, neutral and earth connection is three wires but is single phase.

You get three phase in machine shops / large factories but not in homes.

Two phase is theoretically possible but I've never heard of it being used.

The problem with eath spikes as I see it, is that if anything interrupts the run to the spike (as happened in our case), you effectively lose the earth via the spike and the system tries to earth out via another route (again in our case, via the metal conduit, to some copper piping, into a shower and then out through cast iron downpipe...when water was running from the shower).

Many earth spikes are old and corroded...so would be worth inspecting the spike and the run of cable to the spike

A bad spike is not good but then neither is a broken earth wire from the electricity board, hence my comment about it needing to be tested.

 

[MdB]

There is no particular need to worry if the mains circuit is 'radial' rather than 'ring'. Many will tell you otherwise, but I have it on good authority from several people I trust that a radial is fine, as long as the cable are rated correctly.

A radial circuit can carry half the current of a ring circuit per spur but is otherwise fine. Rings are used in the UK to save copper. Radial are used in the continent I believe but they use thicker wires.

Also, houses often have less total power use now than in the past due to electric heaters being replaced by central heating. The area defined for a ring or radial supply was defined to allow electric heaters to be plugged in.

A typical ring circuit has a 30A fuse/MCB which allows two and half 3kW heaters to be plugged in and operated and nothing else.

 

[bower1]

Rings are used in the UK to save copper. Radial are used in the continent I believe but they use thicker wires.

The power sockets in the older part of our house is a 4mm radial. I had intended to replace it as it is not 'standard' these days, but I was told there was no need, and more wasteful than keeping it. I like to think of it as Period Wiring.

 

[MdB]

The power sockets in the older part of our house is a 4mm radial. I had intended to replace it as it is not 'standard' these days, but I was told there was no need, and more wasteful than keeping it. I like to think of it as Period Wiring.

I assume you mean 4mm^2 which is almost twice the 2.5mm^2 used for ring. As long as you have a 24A or less fuse then there won't be a problem. Higher ratings are also possible depending on where the cable runs go. Check the cable is PVC insulation though, you don't want rubber.

 

[Penners]

We have a 3 phase supply

I'm glad you twigged what that meant, MdB. I was trying to work it out!

 

[Flyfisher]

Yes, I think it must mean a '3-wire' supply.

Having said that, we have two phases to the house, each going to a separate meter and consumer unit (one end was originally a cottage/annexe). Since we are now combining all the living space it means we have lights and sockets on two different phases in a few rooms.

I was dubious about the legality of this and our electrician confirmed that two phases to a property is not a problem per se, but there shouldn't be different phases within a single room (his eyes also popped out when he saw the state of the fuse boards, but that's another story!).

As Pford75 mentioned, one of our supplies was only 60A but the supply company (EDF) was happy to upgrade this to 100A and they didn't mention anything about new consumer units to the latest regs.

As an aside, I'm very impressed with EDF. When our scaffolding was first erected they wouldn't finish the job until the two feeds to the house were 'shrouded' (they are overhead feeds from two unsightly poles). I was doubtful about this being necessary but I contacted EDF and they sent someone out to look. He confirmed that shrouding wasn't necessary but at the same time looked at the supply arrangements and said he would arrange to have the 3 overhead wires (2 phases + neutral) replaced by a single, insulated cable. I asked if they would put the cable underground and he said they would have to charge for the trenching and it would be very expensive, but that if I did it myself they would do everything else at no charge.

It took one man+digger and two days work to dig the trench, lay the trunking and re-fill the trench. The EDF chap came back and pushed the new supply cable through (single phase) and next week the EDF cabling team will re-wire the supply from the overhead poles to the new underground cable.

EDF are not charging anything for this work yet it means we can get rid of two rather unsightly poles from the grounds as well as the overhead wires to the house. Who says big companies don't give good service?

Mind you, the downside is that we used to receive £31 each year for ground rental for the two poles. I wonder if their internal procedures are efficient enough to realise the poles will be gone next week?

 

[Ian Bond]

Nice job - a few less overhead cables to your property will improve the appearance greatly.

I'd like to get rid of: TV aerials / Sat dishes / Telephone lines - No chance

'Lectrics in old houses can be a right old mess. I had all sorts in my house - you wouldn't believe the dangerous things some people do!!! I found examples just about every type of cable ever used in domestic installations since the 1940s...

 

[Pford75]

From our friends at Wikipedia...

Three-phase electric power is a common method of electric power transmission. It is a type of polyphase system mainly used to power motors and many other devices. A three-phase system uses less conductor material to transmit electric power than equivalent single-phase, two-phase, or direct-current systems at the same voltage.

In a three-phase system, three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at different times. Taking one conductor as the reference, the other two currents are delayed in time by one-third and two-thirds of one cycle of the electrical current. This delay between "phases" has the effect of giving constant power transfer over each cycle of the current, and also makes it possible to produce a rotating magnetic field in an electric motor.

Three phase systems may or may not have a neutral wire. A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection).

Three phase has properties that make it very desirable in electric power systems. Firstly the phase currents tend to cancel one another (summing to zero in the case of a linear balanced load). This makes it possible to eliminate the neutral conductor on some lines; all the phase conductors carry the same current and so can be the same size, for a balanced load. Secondly power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations. Finally, three-phase systems can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors. Three is the lowest phase order to exhibit all of these properties.

Most domestic loads are single phase. Generally three phase power either does not enter domestic houses at all, or where it does, it is split out at the main distribution board.

Don't claim to understand this....but as a previous farm...our property has 3 phase.

 

[Flyfisher]

Farms often have 3-phase supplies. Our outbuildings used to house a chicken hatchery and there was 3-phase for the coolstore building (big electric motors) and because of the overall load.

But I think the last paragraph of your extracted quote is the relevant point regarding houses.

Although we have two phases brought into the house, each one feeds a separate meter/consumer unit, i.e. we really have two, single-phase, supplies (although we'll be totally single-phase by the end of the month as I described earlier).

I'm not fully up on the details but 3-phase installations are very different to single phase systems, due to the potential for much higher voltages, i.e. 415V across the phases. I remember the difference being explained to me thus: 'you'd be unlucky to be killed by a 240V shock but you'd be lucky to survive a 415V shock'.

Still, 3-phase might come in handy if you want to run a big welder or some heavy machinery :wink:

 

[Pford75]

Still, 3-phase might come in handy if you want to run a big welder or some heavy machinery

Or when I finish my 'Frankenstein's Monster' :wink:

Agree with you on EDF as well....my whole experience of dealing with them was great...simple upgrade...they also lengthened the 'tails' from our meter. My wife almost fainted when their workman asked if we had a hoover he could use!!

 

[Penners]

I'm very impressed with EDF.

You can't go around saying things like that. They're French, you know.

 

[Penners]

My wife almost fainted when their workman asked if we had a hoover he could use!!

Cunning French ploy to push up your electricity bill.