Can this CU be modernised?
- Thread starter Vicario
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Replace it if you want rcd protection
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If you read the best practice guides issued by the electrical safety council they still say if there is a warning sticker saying not earths on lights, it is considered as satisfactory. The rules changed on lights in 1966.
So if it complied when fitted, and has not degraded or been altered, then it's OK.
However that gap at the right would have never complied, seem to remember standard finger is 12 mm and a MCB slot is 12.5 mm so missing blank is a fail, so that distribution unit, (In 1985 we did not have type tested distribution units called consumer units) does not comply, as to blank, needs to be so can't be removed without a tool, if when removed a standard finger can touch live parts, there are some boxes where the bus bar fork for the MCB could be switched off, so the blank was only to look good.
If a RCD is added, it could cause tripping of items like freezer, which clearly costs, and the more the circuits are split the less leakage on each RCD so less likely to trip, so when renewing one everything needs testing first so any faults are dealt with before the RCD causes tripping, and second you need to assess the risk v cost around £250 for all RCBO protection plus fitting, around £60 for just two RCD's since the fitting will take a day so likely another £200 for labour to my mind better to play safe and go all RCBO protection.
So there was a problem fitting RCBO because they were taller, but there have been released some short versions now, to be called a consumer unit it needs type testing so to fit any RCBO into a consumer unit which the manufacturers has not tested in that unit means no longer a consumer unit as you loose type testing, but your box is not a consumer unit to start with, so if you can find RCBO units to fit, then no problems.
The operative word is "Fit" I have found the terminals slightly higher or lower make to make, so putting a RCBO of wrong make means poor connection to bus bar, but if you swap them all then bus bar will likely be OK, however what is the point, the box, (unpopulated CU) costs around £30 so it seems pointless trying to make new RCBO's fit an old box.
The main problem is registering the work and time taken, so needs to be done before freezer defrosts, and you need to pay some one be it LABC or a scheme member electrician over £100 to do the work, to be frank likely DIY using LABC will cost more than a scheme member electrician.
In spite of being an electrician I had mine changed by a scheme member electrician, and all RCBO's. Glad I did that, as shortly after we had a roof leak, which knocked out one socket circuit, lucky I have 4 so it was simply switch it off until roof repaired, had I lost half the house that would have been very different.
I like RCD protection, be it required or not, last house it was fitted in the 90's well before required by regulations, it does not stop you getting a shock, but it does reduce the chances. So I would renew that board, and with all RCBO, but if you need to save to get RCBO or now to use twin RCD's I personally would opt to save and use RCBO's. However that's my personal opinion.
Since all new socket outlets or wiring does require RCD protection at some point it will need doing, likely you will want some new sockets at some time, but there is no rush, so do it once and do it right, using RCBO's. With that in mind may be a make which will take the RBCO needed for electric cars.
So if it complied when fitted, and has not degraded or been altered, then it's OK.
However that gap at the right would have never complied, seem to remember standard finger is 12 mm and a MCB slot is 12.5 mm so missing blank is a fail, so that distribution unit, (In 1985 we did not have type tested distribution units called consumer units) does not comply, as to blank, needs to be so can't be removed without a tool, if when removed a standard finger can touch live parts, there are some boxes where the bus bar fork for the MCB could be switched off, so the blank was only to look good.
If a RCD is added, it could cause tripping of items like freezer, which clearly costs, and the more the circuits are split the less leakage on each RCD so less likely to trip, so when renewing one everything needs testing first so any faults are dealt with before the RCD causes tripping, and second you need to assess the risk v cost around £250 for all RCBO protection plus fitting, around £60 for just two RCD's since the fitting will take a day so likely another £200 for labour to my mind better to play safe and go all RCBO protection.
So there was a problem fitting RCBO because they were taller, but there have been released some short versions now, to be called a consumer unit it needs type testing so to fit any RCBO into a consumer unit which the manufacturers has not tested in that unit means no longer a consumer unit as you loose type testing, but your box is not a consumer unit to start with, so if you can find RCBO units to fit, then no problems.
The operative word is "Fit" I have found the terminals slightly higher or lower make to make, so putting a RCBO of wrong make means poor connection to bus bar, but if you swap them all then bus bar will likely be OK, however what is the point, the box, (unpopulated CU) costs around £30 so it seems pointless trying to make new RCBO's fit an old box.
The main problem is registering the work and time taken, so needs to be done before freezer defrosts, and you need to pay some one be it LABC or a scheme member electrician over £100 to do the work, to be frank likely DIY using LABC will cost more than a scheme member electrician.
In spite of being an electrician I had mine changed by a scheme member electrician, and all RCBO's. Glad I did that, as shortly after we had a roof leak, which knocked out one socket circuit, lucky I have 4 so it was simply switch it off until roof repaired, had I lost half the house that would have been very different.
I like RCD protection, be it required or not, last house it was fitted in the 90's well before required by regulations, it does not stop you getting a shock, but it does reduce the chances. So I would renew that board, and with all RCBO, but if you need to save to get RCBO or now to use twin RCD's I personally would opt to save and use RCBO's. However that's my personal opinion.
Since all new socket outlets or wiring does require RCD protection at some point it will need doing, likely you will want some new sockets at some time, but there is no rush, so do it once and do it right, using RCBO's. With that in mind may be a make which will take the RBCO needed for electric cars.
Replacement time was a couple of decades ago.
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I favour all RCBO's. Prices are heavily dependent on make but ones from a cheaper established maker is probably a good idea. There are alternatives though. A mix of rcbo and mcb's with one or more rcd's. A popular one is 2 rcbo's for lights and mcb's plus an rcd for the rest. This way trips are likely to leave the lights on. Add another rcd to that and costs go up and all rcbo's may make more sense.
The need to replace your unit comes in when new circuits are added or a ring main altered. They are notifiable to your local building control. This just leaves spurs effectively and these days an electrician that will do this work may add rcd protection to them. Some might not do the work and want the lot upgraded. Some might even just fit a spur.
Consumer units vary as well but as far as I am aware all can be adapted to be wired the same way so in some ways the various types matter more when they come preloaded with the parts. One type is called high integrity. These have a couple of ways that bypass rcd protection. They can be used to feed armoured cable via an mcb, cable has to be armoured to avoid the use of rcd's or rcbo's could be fitted to feed ordinary cable. The armoured cable might be used for a garage sub main or for EV charging. I suspect the intent really is 2 rcbo's for lights and they may be intended for 2 rcd's on the rest as well.
There can be a need for more than one rcd as items do leak current to earth. I'd suspect this is a rare problem but may not be in unusual circumstances. I for instance have a small industrial lathe and milling machine in the house. They are old and came fitted with plugs but motors in them these days may need fixed wiring due to leakage.It would be a bit silly to mix these in with the rest of the house wiring on the off chance that all will be ok. Probably would be but ..........
The need to replace your unit comes in when new circuits are added or a ring main altered. They are notifiable to your local building control. This just leaves spurs effectively and these days an electrician that will do this work may add rcd protection to them. Some might not do the work and want the lot upgraded. Some might even just fit a spur.
Consumer units vary as well but as far as I am aware all can be adapted to be wired the same way so in some ways the various types matter more when they come preloaded with the parts. One type is called high integrity. These have a couple of ways that bypass rcd protection. They can be used to feed armoured cable via an mcb, cable has to be armoured to avoid the use of rcd's or rcbo's could be fitted to feed ordinary cable. The armoured cable might be used for a garage sub main or for EV charging. I suspect the intent really is 2 rcbo's for lights and they may be intended for 2 rcd's on the rest as well.
There can be a need for more than one rcd as items do leak current to earth. I'd suspect this is a rare problem but may not be in unusual circumstances. I for instance have a small industrial lathe and milling machine in the house. They are old and came fitted with plugs but motors in them these days may need fixed wiring due to leakage.It would be a bit silly to mix these in with the rest of the house wiring on the off chance that all will be ok. Probably would be but ..........
I had a shock from one a long time ago while working on a panel. A mad management problem - no you can't use a logic board so I did it with relay logic. I thought my hand had pressed on something sharp when it happened. This was in the days when they were trying to use low current ones though. It may have been a 30ma one but probably not.
To get an idea what these things do watch Holby City. Terrible place as people on operating tables hearts often stop and the words charging and clear are often used. The key word is charging. How much of that sets how many joules / watt seconds they run through the heart, This is effectively what the RCD's do, limit the energy to a level that wont stop the heart or supposedly interfere with it's operation. This is way way better than previous thoughts on the subject of electrocution much of which was based on experiments with pigs.
They are also used to cure live to earth shorts when installations cause problems with mcb's handling them.
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A RCBO is a RCD and MCB combined, but for a stand alone RCD it needs two slots in a consumer unit, so it makes the consumer unit bigger, in the main the single width RCBO only switches the line, neutral is only monitored, and they only detect overload on the line, double width RCBO's switch both line and neutral and monitor overload on both line and neutral, but rare to find them in a UK consumer unit, rest of EU seem to use them by not UK.
There are some single RCBO's which do switch the neutral used where there is a TT supply, but still do not sense overload on neutral.
Also RCD's do come in different flavours, AC, A, B, and F in the main we use AC, but for EV charging think in the main type F is used, as @ajohn says the cheaper RCBO are now down to around £10 each which is very little more than what you would pay for a MCB, but if you want other than type AC or want double pole switching then can't use the cheaper makes.
The regulations say we split the supply into circuits to among other things to (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit. (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation. However it defines a circuit as "An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)." and it seems many feel that since a RCD does not protect against overcurrent line to neutral that a RCD does not form a circuit, may be using English they are correct, but if you look at why circuits are formed it clearly would not help "unwanted tripping of RCDs" unless each circuit has its own RCD.
Also although you can get a RCD at £17, getting one which will take the combined load of all the MCB's then price jumps to around £21, main outlets like Screwfix jumps to £30 and a MCB is not likely less than £3 so 30/7 = 4 approx so unless the RCD is protecting over 4 circuits then unlikely to be cheaper than using RCBO's.
Also if I fit some thing in the future which needs a type A instead of type AC assuming available then just £10 to upgrade, so not a big thing to change latter.
Old RCBO's were tall
but many of the new ones are shorter
so may fit in your box, one shown is Screwfix at £24 likely you can get them cheaper than that, seem to remember that box is DIN rail so they may well fit, as to if strictly complying I am not too sure, and it may need some changes like the window cut for the switch section to stick out of may not line up, or the bus bar may not line up, so personally I would fit whole new box, I really don't care if Part P allows me to change the MCB to a RCBO but says I need a scheme member to change whole box, common sense says change whole box.
I also fitted a surge protector and an isolator before the consumer unit, health and safety rules say must isolate elsewhere and the cost was that little extra seemed prudent to fit isolator so can follow HSE rules, parts cost just over £200 for 14 RCBO's I did not pay for fitting, it took most of the day to fit, but was a rotten job as old fuse box was between ceiling and roof, so all circuits needed extending, so likely yours ½ day, not sure on what is charged now, but would expect around £400 in total. Much will depend on make used, 12 module consumer unit RCBO populated Screwfix £230 twin RCD down to £100 however noted "2 x 63A 30mA RCDs" which seems a little odd, I would want two 100A, so clearly made to be cheap.
There are some single RCBO's which do switch the neutral used where there is a TT supply, but still do not sense overload on neutral.
Also RCD's do come in different flavours, AC, A, B, and F in the main we use AC, but for EV charging think in the main type F is used, as @ajohn says the cheaper RCBO are now down to around £10 each which is very little more than what you would pay for a MCB, but if you want other than type AC or want double pole switching then can't use the cheaper makes.
The regulations say we split the supply into circuits to among other things to (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit. (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation. However it defines a circuit as "An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)." and it seems many feel that since a RCD does not protect against overcurrent line to neutral that a RCD does not form a circuit, may be using English they are correct, but if you look at why circuits are formed it clearly would not help "unwanted tripping of RCDs" unless each circuit has its own RCD.
Also although you can get a RCD at £17, getting one which will take the combined load of all the MCB's then price jumps to around £21, main outlets like Screwfix jumps to £30 and a MCB is not likely less than £3 so 30/7 = 4 approx so unless the RCD is protecting over 4 circuits then unlikely to be cheaper than using RCBO's.
Also if I fit some thing in the future which needs a type A instead of type AC assuming available then just £10 to upgrade, so not a big thing to change latter.
Old RCBO's were tall
I also fitted a surge protector and an isolator before the consumer unit, health and safety rules say must isolate elsewhere and the cost was that little extra seemed prudent to fit isolator so can follow HSE rules, parts cost just over £200 for 14 RCBO's I did not pay for fitting, it took most of the day to fit, but was a rotten job as old fuse box was between ceiling and roof, so all circuits needed extending, so likely yours ½ day, not sure on what is charged now, but would expect around £400 in total. Much will depend on make used, 12 module consumer unit RCBO populated Screwfix £230 twin RCD down to £100 however noted "2 x 63A 30mA RCDs" which seems a little odd, I would want two 100A, so clearly made to be cheap.
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I was fitting a fridge/freezer, it needed a water supply for the cold water in the door, and toilet was room above so a 12 mm water pipe was all I needed down the wall let into plaster, so a 10 mm block taped to two hack saw blades and I started making the cut in the plaster. It seems the two way cable to second light switch by the door went horizontal around 4 corners, this I had not expected, and I sawed through it, I ended up on the floor, it knocked me out, the RCD did trip and it clearly did not kill me or I would not be typing this, but even if only for less than 40 mS that was one of the worst belts I have had. There is no limit to the joules only limit is time, people seem to think limited to 30 mA this is NOT true, 30 mA trips the device but it takes in real terms around 23 mS to trip, so for 23 mS only thing limiting current is the resistance of your body.
They still work on the basis of joules by modelling a typical person. We aren't that simple when electricity runs through us. The nearest model is a capacitor and resistor circuit and the behaviour is related to the voltage. Resistance goes down as the volts goes up in an alarming fashion. It also varies from person to person.
For my sins I have drilled a hole through a cable using a corded plastic mains drill. It was really stupid of me. I didn't get a shock at all. I also once had a 10kv shock from a power supply I was building at home sitting on my bed and working on a bedside table while still living with mom and dad. Fortunately not much energy as it only needed to supply 1ma or so but had a white out and was blown back onto the bed.
I decided to build myself a desk. The white out only lasted for seconds.
For my sins I have drilled a hole through a cable using a corded plastic mains drill. It was really stupid of me. I didn't get a shock at all. I also once had a 10kv shock from a power supply I was building at home sitting on my bed and working on a bedside table while still living with mom and dad. Fortunately not much energy as it only needed to supply 1ma or so but had a white out and was blown back onto the bed.
I decided to build myself a desk. The white out only lasted for seconds.
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When I worked in the electricity industry I read an interesting paper on the design criteria for RCDs. The "30mA, 30ms" guide is an approximation of what you have a fair chance of surviving.
Interestingly, the voltage in an AC system passes through 0v in every cycle, and then up to its peak, then back through 0v, then down to the other peak, and does this 50* times a second, so the voltage passing through your body will be different depending where in the cycle the supply is when you get your shock. If you are lucky it will trip at a relatively low voltage (hence current); if you are not lucky, not. The RCD will usually trip in less than a single cycle, so fast enough for the voltage to change. It need not trip in 30ms.
*or is it 100? I usually get this wrong
Interestingly, the voltage in an AC system passes through 0v in every cycle, and then up to its peak, then back through 0v, then down to the other peak, and does this 50* times a second, so the voltage passing through your body will be different depending where in the cycle the supply is when you get your shock. If you are lucky it will trip at a relatively low voltage (hence current); if you are not lucky, not. The RCD will usually trip in less than a single cycle, so fast enough for the voltage to change. It need not trip in 30ms.
*or is it 100? I usually get this wrong
50 complete cycles per second, passing through zero 100 times per second
People could also test themselves to some extent bearing in mind that unprotected mains can kill but the isolator switch should prevent that. Main one is probably insulation. A chinese £30 one will give a good indication. When I have done this I have used the highest test voltage setting but the correct setting can be used as well. Bit of a pain as all items need to be unplugged, all light bulbs removed and lights switched on or equivalent for different styles of lighting. So effectively just the wiring is being tested. Immersion heaters have a rather low resistance so will mess readings up, Next is resistance - bit tricky as the test current used should be higher than what a multimeter uses and low ohm meters are a bit specialised. Idea here is to have short circuit currents of >= 5 times the mcb etc rating. Rings are easier to check at the consumer unit for this. Spurs are likely to need a long cable and the lead resistances has to be zero'd out. Also which socket is the last one on the spur?
More expensive - Cheaper stuff is also available to check the supply resistances. Pro test boxes crop up at times as well sometimes still in calibration. I bought one off ebay from some one who sells all sorts of used site equipment. Everything they list sells. then found I had a crap Ze. Not uncommon on TN-S supplies due to work being done on cables running down streets. We have had a lot of street light moving around and also have probably had new cables laid at some point. This is over the top in some ways but didn't cost me much and can be resold. A crap Ze means that rcd's have to be used but they do anyway. I have seen units that will do low ohms and insulation for around £130 or £160 with calibration and also cheaper than usual chinese electricians test boxes that do the lot. I decided on used so risky but quality instead. L to N Z is where it would be expected to be so the Ze reading is very likely to be correct, Volt read as they should and resistance readings also make sense.
More expensive - Cheaper stuff is also available to check the supply resistances. Pro test boxes crop up at times as well sometimes still in calibration. I bought one off ebay from some one who sells all sorts of used site equipment. Everything they list sells.
then found I had a crap Ze. Not uncommon on TN-S supplies due to work being done on cables running down streets. We have had a lot of street light moving around and also have probably had new cables laid at some point. This is over the top in some ways but didn't cost me much and can be resold. A crap Ze means that rcd's have to be used but they do anyway. I have seen units that will do low ohms and insulation for around £130 or £160 with calibration and also cheaper than usual chinese electricians test boxes that do the lot. I decided on used so risky but quality instead. L to N Z is where it would be expected to be so the Ze reading is very likely to be correct, Volt read as they should and resistance readings also make sense.
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I can't see how anyone can test the RCD trips in 40 mS using any home made tester, in the main I found proper RCD tester shows around 23 mS to trip, but 100 times a second means 10 mS per cycle so if it takes over 10 mS then 325 volt to earth, so likely you do get it at least once, but since the RCD tester does pos and neg independent 20 mS may mean only one pulse to trip as one pulse may be wrong polarity. So 40 mS is two complete cycles.
As to insulation tester think I paid £35 for replacement when could not find original, but it did not do low ohms, my problem is son also an electrician so he tends to have test gear, which I have to ask for when required. So not to hand.
We sent a PAT tester for calibration, a traceable record, and I got the boss to buy a software package to record the results, however the software package wanted me to enter the figures, but the tester just had a pair of lights, pass or fail, so rang up the software supplier, felt daft after, as the cure was so easy, get the calibration certificate and write down the figure it passes items at.
However when I got the certificate it was not recorded at what point it passed, so traceable record so no problem asked the firm I thought had done the testing, however it seems they sent it to some one else, so in the mean time sent the software back and used excel as I could then simply use the replace command so ipass would be replaced by 1MΩ or what ever else turned out to be the figure the tester passed at.
It took some time, and I started pestering the intermediate more and more, until finally I said we will stop using you as our supplier if you have not given me the new certificate within 4 weeks. Now getting to 6 month since asked for pass figures. At this point he asked if he could take the tester to be retested, they it seems could not find the traceable record, so it was returned, bit peeved, as hardly a traceable record if they can't find it.
Next the bomb shell, the tester it seems although it looked brand new, clearly not used in years, bought and left in a cupboard, the pass figure was 500kΩ which was it seems when it was built the pass mark, but the requirements had changed to 1MΩ and it could not be adjusted to that figure, so 6 months PAT testing was useless.
So from that point calibration has been compare with some one else's equipment, or select a socket and note readings, test a 1MΩ resistor out of the junk box or similar, no point sending to a calibration house when they pass some thing which passes items at half the agreed figure, OK my meter may measure 1.2 MΩ when should be 1 MΩ but that is far closer than the official calibration house. Only exception is the RCD tester, there is no way I can measure 40 mS and since it depends on when in the cycle you push the button, can't really compare one tester with another, but not convinced the calibration house tests the time either, so just cross my fingers. Not paying out for meter calibration again, once bitten twice shy.
OK if you need to submit the calibration certificate to scheme provider suppose no option, but we just had two of each meter and worked on idea unlikely both would drift at the same time.
As to insulation tester think I paid £35 for replacement when could not find original, but it did not do low ohms, my problem is son also an electrician so he tends to have test gear, which I have to ask for when required. So not to hand.
We sent a PAT tester for calibration, a traceable record, and I got the boss to buy a software package to record the results, however the software package wanted me to enter the figures, but the tester just had a pair of lights, pass or fail, so rang up the software supplier, felt daft after, as the cure was so easy, get the calibration certificate and write down the figure it passes items at.
However when I got the certificate it was not recorded at what point it passed, so traceable record so no problem asked the firm I thought had done the testing, however it seems they sent it to some one else, so in the mean time sent the software back and used excel as I could then simply use the replace command so ipass would be replaced by 1MΩ or what ever else turned out to be the figure the tester passed at.
It took some time, and I started pestering the intermediate more and more, until finally I said we will stop using you as our supplier if you have not given me the new certificate within 4 weeks. Now getting to 6 month since asked for pass figures. At this point he asked if he could take the tester to be retested, they it seems could not find the traceable record, so it was returned, bit peeved, as hardly a traceable record if they can't find it.
Next the bomb shell, the tester it seems although it looked brand new, clearly not used in years, bought and left in a cupboard, the pass figure was 500kΩ which was it seems when it was built the pass mark, but the requirements had changed to 1MΩ and it could not be adjusted to that figure, so 6 months PAT testing was useless.
So from that point calibration has been compare with some one else's equipment, or select a socket and note readings, test a 1MΩ resistor out of the junk box or similar, no point sending to a calibration house when they pass some thing which passes items at half the agreed figure, OK my meter may measure 1.2 MΩ when should be 1 MΩ but that is far closer than the official calibration house. Only exception is the RCD tester, there is no way I can measure 40 mS and since it depends on when in the cycle you push the button, can't really compare one tester with another, but not convinced the calibration house tests the time either, so just cross my fingers. Not paying out for meter calibration again, once bitten twice shy.
OK if you need to submit the calibration certificate to scheme provider suppose no option, but we just had two of each meter and worked on idea unlikely both would drift at the same time.
In spite of what Eric states most double module RCBOs do not detect overload on the neutral but disconnect it. A true double pole device (rather than switched neutral device) would be required for that, and would be needed for Reduced Low Voltage for example as there are two phase (line) conductors and no neutral.
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Shows my age, the early double pole RCBO's two modular width I used did monitor both channels, but been out of it for a good few years now.
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