Having received some excellent advice about the best way to service a small number of individual services form an emergency generator on this forum last week, further investigations have thrown up a question and I am looking for a "best practice" solution.
The house has a 3ph supply, presumably because it used to have electric storage heaters in every room.
Electric heating long gone, and previous occupant has clearly "added" or "extended" services without any thought to the regs - or as far as I can see common sense.
There is no RCD protection of any kind.
The phases are mixed up - so a room may have lights on one phase, with sockets on another - which I assumed was bad practice, because you should avoid having access to mixed phases in order to avoid lethal voltages being accidently encountered. I have tried to rectify this as far as possible by simply moving the MCBs onto different slots, so that upstairs is one phase, downstairs another, and outside the third. However, I still have oddities - such as the boiler control stat on the heat store is on one phase, with the overheat control stat on the same heat store on another (its OK though - its only a large copper tank full of water!!!).
I am in the process of working out best options, and following advice I was going to put separate CUs on each phase, with essential circuits on one unit so that I can power that single phase in the event of a power failure. I want to retain the three phase supply, because I may be installing an electric vehicle 3ph charger at some point. However, this makes the phase mix-up situation even worse.
Options - proceed as planned, placing warning notices in any installation where an engineer would need to realise there were different phases present - is this sufficient?;
Partially re-wire to ensure that this cannot happen - a very awkward job due to the design of the house, and location of key components such as heat stores and boilers;
Can the whole idea, switch all supplies to a single phase on a single CU, and take a separate CU (eg a garage CU unit) off the main CU for the essential services, and power this smaller CU from the emergency generator via a manual changeover.
The last option is starting to look better, and was one of the options proposed by the forum. However, I am unsure as to the safety of this - I cannot prove the state of the individual services within the house, so I might end up with a shared neutral somewhere of which I am unaware. So, here is the scenario - power fails, and I switch the small CU to generator - fully isolated, now working from the generator supplied LNE. Power is restored, and the main CU is energised - but smaller CU still running from the generator. In theory, no problem. However, if somewhere in the house there is a shared rabbit run neutral from one of the circuits running from the generator supplied CU with one of the circuits now powered by the main CU, will I be presented with a loud bang and lots of sparks - or worse? This is a T-N-CS PME installation.
Cheers
D4
The house has a 3ph supply, presumably because it used to have electric storage heaters in every room.
Electric heating long gone, and previous occupant has clearly "added" or "extended" services without any thought to the regs - or as far as I can see common sense.
There is no RCD protection of any kind.
The phases are mixed up - so a room may have lights on one phase, with sockets on another - which I assumed was bad practice, because you should avoid having access to mixed phases in order to avoid lethal voltages being accidently encountered. I have tried to rectify this as far as possible by simply moving the MCBs onto different slots, so that upstairs is one phase, downstairs another, and outside the third. However, I still have oddities - such as the boiler control stat on the heat store is on one phase, with the overheat control stat on the same heat store on another (its OK though - its only a large copper tank full of water!!!).
I am in the process of working out best options, and following advice I was going to put separate CUs on each phase, with essential circuits on one unit so that I can power that single phase in the event of a power failure. I want to retain the three phase supply, because I may be installing an electric vehicle 3ph charger at some point. However, this makes the phase mix-up situation even worse.
Options - proceed as planned, placing warning notices in any installation where an engineer would need to realise there were different phases present - is this sufficient?;
Partially re-wire to ensure that this cannot happen - a very awkward job due to the design of the house, and location of key components such as heat stores and boilers;
Can the whole idea, switch all supplies to a single phase on a single CU, and take a separate CU (eg a garage CU unit) off the main CU for the essential services, and power this smaller CU from the emergency generator via a manual changeover.
The last option is starting to look better, and was one of the options proposed by the forum. However, I am unsure as to the safety of this - I cannot prove the state of the individual services within the house, so I might end up with a shared neutral somewhere of which I am unaware. So, here is the scenario - power fails, and I switch the small CU to generator - fully isolated, now working from the generator supplied LNE. Power is restored, and the main CU is energised - but smaller CU still running from the generator. In theory, no problem. However, if somewhere in the house there is a shared rabbit run neutral from one of the circuits running from the generator supplied CU with one of the circuits now powered by the main CU, will I be presented with a loud bang and lots of sparks - or worse? This is a T-N-CS PME installation.
Cheers
D4