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Hi. please can you tell me if i use
a 45a 30ma. or 45a 300ma. for an instant water heater 9.8kw. Many thanks

What is the earthing system, type of installation, installation method, cable type etc etc?

On its own, as a fixed appliance, BS7671 doesn't require an instantaneous water heater to have RCD protection, however other factors may mean the circuit requires it.
 
Depends on the circuit design, location of installation, earthing arrangement. Quite a lot of missing information.
 
What is the earthing system, type of installation, installation method, cable type etc etc?

On its own, as a fixed appliance, BS7671 doesn't require an instantaneous water heater to have RCD protection, however other factors may mean the circuit requires it.
16mm 2. Cable. Live. Neutral and an earth. Direct from water heater in a cupboard to mains box. Water heater is for hot water to shower and 1 basin...
 
what clown specified 16mm? that's 80A CCC.
 
16mm 2. Cable. Live. Neutral and an earth. Direct from water heater in a cupboard to mains box. Water heater is for hot water to shower and 1 basin...
Is the W/H in a room, containing a Bath or Shower??.
 
This is a predominately UK based forum so you may not receive correct advice in respect to the local Regulations/Codes where you are undertaking these works.
 
In the UK a 300ma rcd is suggested where environmental factors give increased risk of fire from faults. A 30ma rcd is generally employed for additional protection.
 
The rating of the RCCB isn't crucial - so long as its above the design current of the circuit. It does not provide overcurrent protection. You will need a device that does.
 
and imo, 10mm would suffice. VD = 3.9V over 20m.@ 9.8kW
 
The rating of the RCCB isn't crucial - so long as its above the design current of the circuit. It does not provide overcurrent protection. You will need a device that does.
The rating of the RCCB isn't crucial - so long as its above the design current of the circuit. It does not provide overcurrent protection. You will need a device that does.
fixed load. may only need s/c protection.
 
Serious question. Can you omit overload protection on fixed loads in this way and be compliant with regs? I know there is sometimes provision for it, but I tend to have a problem with it when it's wholly unnecessary.

In effect the only protective device other than the RCCB could be the suppliers cut out fuse. That just seems wrong to me. What about a line-neutral fault. This shouldn't trip the RCCB so is potentially dangerous. C2 if I find this imo.

Slightly different is the situation I found today doing an EICR. 2x single sockets fed from the same 32A MCB - both radials. 2.5 T&E. Technically not dangerous as it's impossible to overload the cables. C3 for me though as it could be improved and is unnecessary in my opinion.
 
Serious question. Can you omit overload protection on fixed loads in this way and be compliant with regs? I know there is sometimes provision for it, but I tend to have a problem with it when it's wholly unnecessary.

In effect the only protective device other than the RCCB could be the suppliers cut out fuse. That just seems wrong to me. What about a line-neutral fault. This shouldn't trip the RCCB so is potentially dangerous. C2 if I find this imo.

Slightly different is the situation I found today doing an EICR. 2x single sockets fed from the same 32A MCB - both radials. 2.5 T&E. Technically not dangerous as it's impossible to overload the cables. C3 for me though as it could be improved and is unnecessary in my opinion.
You still need to provide over current protection. Overload is a slightly different matter.
 

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