could some one tell me how to work out breaker and cable size for appliances, if i had a 3249w microwave how would you wire it and so on thanks for any help
calculation
- Thread starter John-tyler
- Start date
Sponsored Links
Is this theoretical or for an actual job 
i am going to go college to be a spark and i wanna learn as much as i can before a go i like to read on this forum i have learnt a lot i just like askin and learning
Sponsored Links
Just concentrating on the circuit itself (ie not looking at mains, bonding etc) :-
Firstly decide what size/type of protective device is required to allow the appliance to function.You have the wattage, so you need to know the current that the appliance will take.
Power = Voltage x current. Transposing, current = power/voltage so
current = 3249/230 = 14.2 A
A 16A protective device should be suitable.
Then decide what wiring system you are to use T+E, conduit, SWA etc
This system needs to be suited for the conditions it will be installed in.
Then select a cable size which will carry a current equal to or greater than the rating of the protective device you have chosen, taking into account factors such as grouping, insulation, ambient temp and length of run which will, in a lot of cases, make the cable size bigger.
When installed, before energisation, the circuit needs testing to ascertain that the circuit protective conductor (earth) is continuous, the insulation is sound, you have the polarity correct (wires the right way round), that the impedance of the earth fault path is low enough to operate the protective device quickly (5 seconds for a fixed appliance) should a live fault to earth occur.
Other functional tests may need doing as well.This list is not exhautive but gives you an idea (I hope )
Firstly decide what size/type of protective device is required to allow the appliance to function.You have the wattage, so you need to know the current that the appliance will take.
Power = Voltage x current. Transposing, current = power/voltage so
current = 3249/230 = 14.2 A
A 16A protective device should be suitable.
Then decide what wiring system you are to use T+E, conduit, SWA etc
This system needs to be suited for the conditions it will be installed in.
Then select a cable size which will carry a current equal to or greater than the rating of the protective device you have chosen, taking into account factors such as grouping, insulation, ambient temp and length of run which will, in a lot of cases, make the cable size bigger.
When installed, before energisation, the circuit needs testing to ascertain that the circuit protective conductor (earth) is continuous, the insulation is sound, you have the polarity correct (wires the right way round), that the impedance of the earth fault path is low enough to operate the protective device quickly (5 seconds for a fixed appliance) should a live fault to earth occur.
Other functional tests may need doing as well.This list is not exhautive but gives you an idea (I hope
)
- Joined
- 11 Jan 2004
- Messages
- 42,733
- Reaction score
- 2,633
- Country
Mike2007 said:
You'd put a microwave in a bathroom??
Have a read: http://www.kevinboone.com/cableselection_web.html
Mike2007 said:I know nothing but like to contribute!
I would say at a guess 4mm T&E on its own radial circuit, 16amp breaker...
One elova microwave oven!
If its in a bathroom differnet again..
I love your posts..
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
