I Self built my bungalow back in 1981,and updating is necessary,in those days you could diy and get the electrics passed by electricity board,now I will sub the work but wish to specify what is required.I have read through pages of questions on this forum and screwfix forum,and have gained some knowledge of modern requirements.dwelling is out in the sticks,so earth is TT ,between the meter and fusebox there is a generator change over switch and a Chilton current operated earth leakage circuit breaker rated at 500ma.My plan is to use a split load 16 way MK csu,the with the ring main sockets protected by 30ma rcd,to protect the whole system I gather a 100ma ,rcd is now common practice but not essential,would it be ok to retain the 500ma breaker or is this now considered to be of too high a rating? External lighting query 3 gang switch in kitchen controls kitchen light and two external lights one on outside wall the other on garage 30 feet from dwelling,should these lights be on a 30ma rcd controlled circuit or on the higher rating rcd ? Freezers/fridges I gather rcd tripping (30 ma) can be a problem with these appliances but the dwelling has just two ring mains and supplies to appliances come off 13 amp sockets in kitchen and utility which must be 30 ma protected,3 out of four appliances are free standing so could be repositioned in future,is there an easy way over this problem as the only way I can see to solve this problem would be to add spurs to the ring with a wall mounted unit similar to an immersion heater connection (13 amp dp) for each appliance, Generator,the switch was the only unit which i had professionally fitted, as the mains had to be disconnected, but I have noticed that the switch is not earthed,I would have thought that it should be earthed , should I earth the generator direct to the earth rod,the generator is a small 1800 watt Honda or earth the switch to the earth busbar in the consumer unit?
updating domestic wiring and csu
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I Self built my bungalow back in 1981,and updating is necessary,in those days you could diy and get the electrics passed by electricity board,now I will sub the work but wish to specify what is required.
I have read through pages of questions on this forum and screwfix forum,and have gained some knowledge of modern requirements.dwelling is out in the sticks,so earth is TT ,between the meter and fusebox
there is a generator change over switch and a Chilton current operated earth leakage circuit breaker rated at 500ma.
My plan is to use a split load 16 way MK csu,the with the ring main sockets protected by 30ma rcd,to protect the whole system
I gather a 100ma ,rcd is now common practice but not essential,would it be ok to retain the 500ma breaker or is this now considered to be of too high a rating?
External lighting query 3 gang switch in kitchen controls kitchen light and two external lights one on outside wall the other on garage 30 feet from dwelling,should these lights be on a 30ma rcd controlled circuit or on the higher rating rcd ?
Freezers/fridges I gather rcd tripping (30 ma) can be a problem with these appliances but the dwelling has just two ring mains and supplies to appliances come off 13 amp sockets in kitchen and utility which must be 30 ma protected,
3 out of four appliances are free standing so could be repositioned in future,is there an easy way over this problem as the only way I can see to solve this problem would be to add spurs to the ring with a wall mounted unit similar to an immersion heater connection (13 amp dp) for each appliance,
Generator,the switch was the only unit which i had professionally fitted, as the mains had to be disconnected, but I have noticed that the switch is not earthed,I would have thought that it should be earthed ,
should I earth the generator direct to the earth rod,the generator is a small 1800 watt Honda or earth the switch to the earth busbar in the consumer unit
I have read through pages of questions on this forum and screwfix forum,and have gained some knowledge of modern requirements.dwelling is out in the sticks,so earth is TT ,between the meter and fusebox
there is a generator change over switch and a Chilton current operated earth leakage circuit breaker rated at 500ma.
My plan is to use a split load 16 way MK csu,the with the ring main sockets protected by 30ma rcd,to protect the whole system
I gather a 100ma ,rcd is now common practice but not essential,would it be ok to retain the 500ma breaker or is this now considered to be of too high a rating?
External lighting query 3 gang switch in kitchen controls kitchen light and two external lights one on outside wall the other on garage 30 feet from dwelling,should these lights be on a 30ma rcd controlled circuit or on the higher rating rcd ?
Freezers/fridges I gather rcd tripping (30 ma) can be a problem with these appliances but the dwelling has just two ring mains and supplies to appliances come off 13 amp sockets in kitchen and utility which must be 30 ma protected,
3 out of four appliances are free standing so could be repositioned in future,is there an easy way over this problem as the only way I can see to solve this problem would be to add spurs to the ring with a wall mounted unit similar to an immersion heater connection (13 amp dp) for each appliance,
Generator,the switch was the only unit which i had professionally fitted, as the mains had to be disconnected, but I have noticed that the switch is not earthed,I would have thought that it should be earthed ,
should I earth the generator direct to the earth rod,the generator is a small 1800 watt Honda or earth the switch to the earth busbar in the consumer unit
Thanks Pensdown, a lot more readable
I won't claim expertise here, I'll have a bash based on my understanding of the On Site Guide:
'Where an RCD is fitted only because the earth loop impedance is too high for shock protection to be provided by an overcurrent device, for example in a TT system, the rated residual operating current should not be less than 100mA"
i.e. the RCD is there to ensure disconnection times are met and your 500mA should meet that (depending on how old it is, if it is working correctly etc.)
However, you also need to consider the situation where the product of operating current (A) and earth-fault loop impedance exceeds 50V - That would mean that your Ze (Earth electrode resistance) should be less than 100Ohm, which is quite achievable with earth rods I believe.
Assuming those things apply (and the usual disclaimer) then the 500mA would be ok, although you are right that a 100mA would be used commonly. If the RCD is old then it may be time to replace it anyway.
However, if it is used effectively as a main switch (A diagram of the setup would help) then it should be a time delayed RCD.
It also suggests that RCBOs will minimise inconvenience, and I know that someone on here will be along shortly to suggest that
It also points out that in a TT insulation the consumer unit should be all insulated or Class II, so go for a plastic MK rather than a metal one.
Regarding the outside lights - the requirement is for 0.4 disconnection time , not that it is on a 30mA rcd (although this is one way of meeting the disconnection time).
Fridges/Freezers can cause rcd trips (though mine never has).
A spur added to a ring that is rcd protected will still trip the rcd if it is going to. One way of doing it would be to run a radial circuit from the CU for such appliances, although you should then connect them directly with flex outlets and not use sockets, which would have to be rcd protected anyway.
RCBOs would mean only the relavent one would trip, although they are an expensive option.
You don't say if the generator switch is metal - if it is then it should be earthed (to the earthing point in the CU will be fine if its convenient).
I'm unsure if you are also saying that the generator is not earthed, so I will ask for clarification and leave that to someone else.
Hope all that helped, but feel free to ask if you are unsure, and I am sure someone else will be along to add wiser words.
Gavin
I won't claim expertise here, I'll have a bash based on my understanding of the On Site Guide:
'Where an RCD is fitted only because the earth loop impedance is too high for shock protection to be provided by an overcurrent device, for example in a TT system, the rated residual operating current should not be less than 100mA"
i.e. the RCD is there to ensure disconnection times are met and your 500mA should meet that (depending on how old it is, if it is working correctly etc.)
However, you also need to consider the situation where the product of operating current (A) and earth-fault loop impedance exceeds 50V - That would mean that your Ze (Earth electrode resistance) should be less than 100Ohm, which is quite achievable with earth rods I believe.
Assuming those things apply (and the usual disclaimer) then the 500mA would be ok, although you are right that a 100mA would be used commonly. If the RCD is old then it may be time to replace it anyway.
However, if it is used effectively as a main switch (A diagram of the setup would help) then it should be a time delayed RCD.
It also suggests that RCBOs will minimise inconvenience, and I know that someone on here will be along shortly to suggest that
It also points out that in a TT insulation the consumer unit should be all insulated or Class II, so go for a plastic MK rather than a metal one.
Regarding the outside lights - the requirement is for 0.4 disconnection time , not that it is on a 30mA rcd (although this is one way of meeting the disconnection time).
Fridges/Freezers can cause rcd trips (though mine never has).
A spur added to a ring that is rcd protected will still trip the rcd if it is going to. One way of doing it would be to run a radial circuit from the CU for such appliances, although you should then connect them directly with flex outlets and not use sockets, which would have to be rcd protected anyway.
RCBOs would mean only the relavent one would trip, although they are an expensive option.
You don't say if the generator switch is metal - if it is then it should be earthed (to the earthing point in the CU will be fine if its convenient).
I'm unsure if you are also saying that the generator is not earthed, so I will ask for clarification and leave that to someone else.
Hope all that helped, but feel free to ask if you are unsure, and I am sure someone else will be along to add wiser words.
Gavin
Thanks PCBOFFINUK
MK unit is plastic its been in stock for a couple of years,re outside lights
what is normal practice to achieve 0,4 disconnection time? will the feed for
the outside lights have to be separated from the kitchen light circuit?
Ref generator,the change over switch is plastic ,the incoming feed cable
from the generator has an earth wire but there is no connection from this
earth to the earth system of the dwelling so basically the geny is not
earthed .re fridge circuit I made error I should have said fit a new ring main
just for the appliances,
MK unit is plastic its been in stock for a couple of years,re outside lights
what is normal practice to achieve 0,4 disconnection time? will the feed for
the outside lights have to be separated from the kitchen light circuit?
Ref generator,the change over switch is plastic ,the incoming feed cable
from the generator has an earth wire but there is no connection from this
earth to the earth system of the dwelling so basically the geny is not
earthed .re fridge circuit I made error I should have said fit a new ring main
just for the appliances,
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lampstart said:
The generator frame earth is one thing. The means of referencing the generator output to earth is another thing.
If the 230 volt supply from the generator is not referenced to earth, ( in otherwords completely floating ) there is no return path for current should a generator "live" to earth fault occur. The symptoms are that a fault will trip the RCCB when the supply is from the network but the same fault will not trip the RCCB when the supply is from the generator.
I am not offering a answer, just suggesting it is not straightforward.
Bernard
Sharnbrook
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