P
puranah69
Guys,
The 2 bed flat I recently moved into is all electric. It has a Hyco Instaneous water heater (rated 12.8kW - 53A at 230v), a Shower (rated 10.5kW - 45A), Heatrae Amptec electric central heating (rated 9kW - 39A) an electric hob (rated 6kW - 25A) and double oven (rated 5.5kW - 23A) in addition to the usual array of sockets and lights . Total (not including sockets/diversity etc), 185amps!!!!
One evening last week, the central heating was on (first time this year), my gf was taking a shower and I was cooking. I turned on the hot water for the washing up and BANG! Everything went dark as all the power went off. Looking in the consumer unit, everything was fine, nothing had tripped - it was the main distribution board fuse that had blown (which was a right nuisance to get sorted out at 9pm at night).
Obvious, now, that with all those appliances running, plus the TV and a few other bits, we were drawing almost double the rating of the main fuse so not really that astonishing (all these appliances had been installed by the previous owner, but it never occurred to me that all these on simultaneously might overload the main supply. It wasn't until I investigated the current draw of each appliance and did the calcs I realised!!!!).
What DID surprise me, though, was nothing in the Consumer Unit had prevented tripped. The flat had a 16th Edition board which was very recently upgraded to a 17th Edition one.
The devices on each MCB were within their individual MCB limits, so none of them tripped (except the Hyco, which had a 45amp MCB, but didn't trip anyway).
I didn't realise until researching this that the current rating on an RCD is NOT the maximum load before it will trip, its just what the RCD is rated to take - that's very dangerous in my view, because I made the assumption it was an overcurrent rating and so did a few of my friends I spoke to.
QUESTION 1: The 100Amp Main Switch didn't trip either. Are these supposed to provide overcurrent protection and my one has a fault on it, or does nothing in a 17th Edition Consumer Unit provide overall overcurrent protection before the 100 amp main fuse?
So, to remedy this, I permanently disconnected the electric shower and installed a mixer tap. The shower now runs off the Hyco (which works marvellously, by the way - much better than the Triton, and no electrics in Zone 1 or broken knobs).
QUESTION 2: I want to reduce the load even further. Heatrae Amptec supply a relay, RL1 which cuts the boiler run circuit whilst the shower main pull-switch is energised. This is fine if you have a shower pull-switch, but is useless in my situation where I want to cut the central heating when any hot water demand is present.
a) Has anyone got any experience of the RL1 relay?
b) They're very expensive for what they are (over ÂŁ90). Is there a cheaper solution? (something from RS Components, maybe?)
c) The Hyco has a magnetic flow sensor in it which triggers a relay that energises the heater element when the hot water tap is opened. My thinking, having looked at the circuit diagram for the RL1, is that instead of connecting the coil (A1) to the demand side of the "shower pull switch", I could connect it to the live of the heater element in the Hyco and the neutral (A2) to the Hyco neutral with a 2a fuse. Thus, when the Hyco flow switch triggers the relay and energises the hot water heater element, it would also energise the coil in the RL1 relay and break the boiler control (run) signal, shutting down the Central Heating. Anyone any thoughts on this?
QUESTION 3. When upgrading my 16th Edition Consumer Unit, a second 63amp RCD was added which was fine and the load balanced. However, one of the MCB's had 3 red lives, not 2. I assumed it was a ring, plus one local spur. However, investigating further, I discovered that each cable supplied one double socket individually in the living room. I went through all the regs and couldn't see anything that would suggest this arrangement was not compliant - it was just not mentioned (I can't imagine why anyone would do this - it's extremely inefficient use of cable). I saw another thread on here in April this year with a similar issue. There was interesting to'ing and fro'ing, but no definitive conclusion. Does anyone have any definitive view on whether this is definitely compliant or not? Will it fail the inspection?
QUESTION 4. The 10mm cables to the Central Heating and Hyco are run in a large (3") plastic conduit from the consumer unit, then go through the wall into an airing cupboard where they are clipped to the wall. I can understand clipping the cables provides the lowest thermal solution, but is running double insulated cable 10mm cable clipped to the wall in the airing cupboard within regulations? In fact, what are the regulations to use plastic conduit (either surface mounted or within the plaster). I can't seem to find it in the BS7671 regs.
Finally, the cables from the CU to the ring/sockets and the meter tails have been run up inside the cavity wall. This has subsequently been filled with EPS cavity wall insulation at some point resulting in the insulation on a couple of the cables going soft and sticky. I contacted the Energy Savings Trust for their view on what I should do. Their reply was as follows, and I quote...
"cavity wall insulation materials, such as blown mineral wool, could be used and would not have caused any reaction with the older wiring, although the older wiring could still overheat. Best practice would be to replace the cables in the cavity with modern and uprated electrical cable, such that the cavity could then be filled by either EPS or mineral wool with none of the above described risks."
QUESTION 5. I didn't think it was EVER acceptable to run cable up a cavity due to the thermal issues of cables overheating, irrespective of the insulation material used. Anyone got any views on this? In any event, I'll be replacing all the cables. Can you chase meter tails into a wall (the CU is about 3m from the distribution board). Should plastic or metal conduit protect the tails? If not, is it ok to run them in plastic conduit mounted on the surface of the wall?
Final question, has anyone got any good ideas about junction boxes for extending . I plan to chop the 6 2.5mm cables where they exit from the floor and re-run them in plastic conduit up the wall to the consumer unit (instead of up the cavity). My two thoughts were either:-
- to use a 12 way junction box like this one from RS? Don't know what size connector strip this accepts - looks like 5amp only to me
J701 RS | 12 way rectangular junction box | 262-7893 | Welcome to RS Online
If I went this route or similar with a larger plastic box from RS, can I just connect only the lives and neutrals to the connection strip, and route all the earths onto an earth connection block, with a single 16mm earth back to the distribution board and another single 16mm earth to the consumer unit? I'm guessing not, because it would be nigh on impossible to do the Earth Loop Impedance tests for the final circut.
- to use individual IP20 junction boxes with 30amp connectors in each one (if they'll fit). eg. Toolstation > Electrical > Junction Boxes > Junction Box IP20
I really want to avoid having 6 ugly round 30amp junction boxes. I would much prefer them all to be in one nice box. So any suggestions that still meet the regs welcome.
Sorry, lots of questions and a long post, but I've got myself an electrical lemon with this flat so want to get it all sorted and inspected/signed-off asap.
regards
stu
The 2 bed flat I recently moved into is all electric. It has a Hyco Instaneous water heater (rated 12.8kW - 53A at 230v), a Shower (rated 10.5kW - 45A), Heatrae Amptec electric central heating (rated 9kW - 39A) an electric hob (rated 6kW - 25A) and double oven (rated 5.5kW - 23A) in addition to the usual array of sockets and lights . Total (not including sockets/diversity etc), 185amps!!!!
One evening last week, the central heating was on (first time this year), my gf was taking a shower and I was cooking. I turned on the hot water for the washing up and BANG! Everything went dark as all the power went off. Looking in the consumer unit, everything was fine, nothing had tripped - it was the main distribution board fuse that had blown (which was a right nuisance to get sorted out at 9pm at night).
Obvious, now, that with all those appliances running, plus the TV and a few other bits, we were drawing almost double the rating of the main fuse so not really that astonishing (all these appliances had been installed by the previous owner, but it never occurred to me that all these on simultaneously might overload the main supply. It wasn't until I investigated the current draw of each appliance and did the calcs I realised!!!!).
What DID surprise me, though, was nothing in the Consumer Unit had prevented tripped. The flat had a 16th Edition board which was very recently upgraded to a 17th Edition one.
The devices on each MCB were within their individual MCB limits, so none of them tripped (except the Hyco, which had a 45amp MCB, but didn't trip anyway).
I didn't realise until researching this that the current rating on an RCD is NOT the maximum load before it will trip, its just what the RCD is rated to take - that's very dangerous in my view, because I made the assumption it was an overcurrent rating and so did a few of my friends I spoke to.
QUESTION 1: The 100Amp Main Switch didn't trip either. Are these supposed to provide overcurrent protection and my one has a fault on it, or does nothing in a 17th Edition Consumer Unit provide overall overcurrent protection before the 100 amp main fuse?
So, to remedy this, I permanently disconnected the electric shower and installed a mixer tap. The shower now runs off the Hyco (which works marvellously, by the way - much better than the Triton, and no electrics in Zone 1 or broken knobs).
QUESTION 2: I want to reduce the load even further. Heatrae Amptec supply a relay, RL1 which cuts the boiler run circuit whilst the shower main pull-switch is energised. This is fine if you have a shower pull-switch, but is useless in my situation where I want to cut the central heating when any hot water demand is present.
a) Has anyone got any experience of the RL1 relay?
b) They're very expensive for what they are (over ÂŁ90). Is there a cheaper solution? (something from RS Components, maybe?)
c) The Hyco has a magnetic flow sensor in it which triggers a relay that energises the heater element when the hot water tap is opened. My thinking, having looked at the circuit diagram for the RL1, is that instead of connecting the coil (A1) to the demand side of the "shower pull switch", I could connect it to the live of the heater element in the Hyco and the neutral (A2) to the Hyco neutral with a 2a fuse. Thus, when the Hyco flow switch triggers the relay and energises the hot water heater element, it would also energise the coil in the RL1 relay and break the boiler control (run) signal, shutting down the Central Heating. Anyone any thoughts on this?
QUESTION 3. When upgrading my 16th Edition Consumer Unit, a second 63amp RCD was added which was fine and the load balanced. However, one of the MCB's had 3 red lives, not 2. I assumed it was a ring, plus one local spur. However, investigating further, I discovered that each cable supplied one double socket individually in the living room. I went through all the regs and couldn't see anything that would suggest this arrangement was not compliant - it was just not mentioned (I can't imagine why anyone would do this - it's extremely inefficient use of cable). I saw another thread on here in April this year with a similar issue. There was interesting to'ing and fro'ing, but no definitive conclusion. Does anyone have any definitive view on whether this is definitely compliant or not? Will it fail the inspection?
QUESTION 4. The 10mm cables to the Central Heating and Hyco are run in a large (3") plastic conduit from the consumer unit, then go through the wall into an airing cupboard where they are clipped to the wall. I can understand clipping the cables provides the lowest thermal solution, but is running double insulated cable 10mm cable clipped to the wall in the airing cupboard within regulations? In fact, what are the regulations to use plastic conduit (either surface mounted or within the plaster). I can't seem to find it in the BS7671 regs.
Finally, the cables from the CU to the ring/sockets and the meter tails have been run up inside the cavity wall. This has subsequently been filled with EPS cavity wall insulation at some point resulting in the insulation on a couple of the cables going soft and sticky. I contacted the Energy Savings Trust for their view on what I should do. Their reply was as follows, and I quote...
"cavity wall insulation materials, such as blown mineral wool, could be used and would not have caused any reaction with the older wiring, although the older wiring could still overheat. Best practice would be to replace the cables in the cavity with modern and uprated electrical cable, such that the cavity could then be filled by either EPS or mineral wool with none of the above described risks."
QUESTION 5. I didn't think it was EVER acceptable to run cable up a cavity due to the thermal issues of cables overheating, irrespective of the insulation material used. Anyone got any views on this? In any event, I'll be replacing all the cables. Can you chase meter tails into a wall (the CU is about 3m from the distribution board). Should plastic or metal conduit protect the tails? If not, is it ok to run them in plastic conduit mounted on the surface of the wall?
Final question, has anyone got any good ideas about junction boxes for extending . I plan to chop the 6 2.5mm cables where they exit from the floor and re-run them in plastic conduit up the wall to the consumer unit (instead of up the cavity). My two thoughts were either:-
- to use a 12 way junction box like this one from RS? Don't know what size connector strip this accepts - looks like 5amp only to me
J701 RS | 12 way rectangular junction box | 262-7893 | Welcome to RS Online
If I went this route or similar with a larger plastic box from RS, can I just connect only the lives and neutrals to the connection strip, and route all the earths onto an earth connection block, with a single 16mm earth back to the distribution board and another single 16mm earth to the consumer unit? I'm guessing not, because it would be nigh on impossible to do the Earth Loop Impedance tests for the final circut.
- to use individual IP20 junction boxes with 30amp connectors in each one (if they'll fit). eg. Toolstation > Electrical > Junction Boxes > Junction Box IP20
I really want to avoid having 6 ugly round 30amp junction boxes. I would much prefer them all to be in one nice box. So any suggestions that still meet the regs welcome.
Sorry, lots of questions and a long post, but I've got myself an electrical lemon with this flat so want to get it all sorted and inspected/signed-off asap.
regards
stu
