How many Amp circuit breakers do I need?

[Cyrus123]

I've never given these things much thought back home and have no idea what to do with it.

So I open up my main electric box today in the condo and find four circuit breakers of 20, 40, 40 and 32 Amps. Now there is no way i'm using that much power, so should I install smaller breakers?

My Shower heather is 3500Watts and we have 220v here. Now I divide 3500w by 220v = 15.91 Amps. Apparantly a circuit needs 125% protection so I need a 1.25 x 15.91 = 19.88 Amps breaker for my shower heather. First available size would make this a 20 Amp breaker.

Looking at my box the shower heather is on a 40Amp breaker so this is wrong to start with...

So this one was easy because I know exactly what is connected to it but what kind of circuit breaker do I need for my regular electrical outlets? Today I only have a fan and a fridge connected but tomorrow I might buy a 500W pc or plugin a 600W powertool like a drill, perhaps do some electric cooking?

Should I buy a circuit breaker with so many Amps as I would possibly ever expect to connect to my outlets together? In this case what's the use of the breaker in the first place?

For example:

Fans 100w

pc 500w

drill 500w

cooker 1300w

fridge 100w

=2500w x 1,25 = 3125

so I'd need a 40Amp breaker for the circuit but right now I only use the fridge (0.5Amp)and a fan (0.5Amp) so what's the use?

I hope this post isn't confusing. I'm trying to determine which kind of Amp breakers I should install and then I wonder what a 40Amp breaker will protect when most of the time only 1Amp of devices will be actually connected.

[Keesters]

You should also take into account the load rating of your meter. I would say that ideally the main breaker should not exceed the maximum overloaded capacity of the meter. I'm no expert, but that's what the electrician who rewired my house said. He, the third one I tried, had a brain, had been to tech college, and knew how to calculate amps from volts and watts. None of the others did but still called themselves electricians.

Please also consider ELB (Safety Cut) and/or earthing especially for the bathroom and kitchen areas.

Keep safe.

Edited September 22, 2014 by Keesters

[Crossy]

You need an electrician.

Your shower should have a 20A breaker although the 40A would be fine if the cable was 4mm² or bigger.

For your outlets, they should be wired in 2.5mm² cable and protected with a 20A breaker. If you have lots of outlets they may be split between two or more circuits.

How are your lights wired? Own breakers or on the power circuits?

Do you have aircon? How is it connected?

MOST IMPORTANTLY Do you have any form of earth leakage protection (RCD or Safe-T-Cut) installation of this is the number one priority if you don't have already. If you don't know what you have the presence of a "Test" button is a dead give-away, no test button, no RCD.

[bankruatsteve]

Just to add... protection from circuit breakers is for over current. IE: too many amps for the wire size in use. For that reason, circuit breakers must be sized in amps no more than the rated capability of the wires used in the circuit. Then, it doesn't really matter if you only draw, for example, 1 amp on a 40a circuit - everything is cool. Chances are your water heater is on 40a breaker and 4mm2 wire for the possibility that a larger heater might be installed in the future.

[Cyrus123]

MOST IMPORTANTLY Do you have any form of earth leakage protection (RCD or Safe-T-Cut) installation of this is the number one priority if you don't have already. If you don't know what you have the presence of a "Test" button is a dead give-away, no test button, no RCD.

I don't think there's a propper earthing line to start with so I don't see what these could do for me.

Just a box with 4 circuit breakers. No propper earthing line as far as I know yet.

I live in a condomium, electricians other than the one's working here wouldn't be allowed to mess with the wiring and my thai is very bad.

But I got the point that the breaker protects the line, that's what I wanted to know!

[bankruatsteve]

MOST IMPORTANTLY Do you have any form of earth leakage protection (RCD or Safe-T-Cut) installation of this is the number one priority if you don't have already. If you don't know what you have the presence of a "Test" button is a dead give-away, no test button, no RCD.

I don't think there's a propper earthing line to start with so I don't see what these could do for me.

Just a box with 4 circuit breakers. No propper earthing line as far as I know yet.

I live in a condomium, electricians other than the one's working here wouldn't be allowed to mess with the wiring and my thai is very bad.

But I got the point that the breaker protects the line, that's what I wanted to know!

FYI: RCD's will protect against current faults over (usually) 30ma. They do not require "proper earthing". What can they do for you? Save your life.

[Cyrus123]

Well I have two slots left in the circuit breaker box, from the pictures I see on google an RCD might fit next to them?

So how do I properly install an RCD? Should it be in between the main line going out the room and my circuit breakers or in between my devices and the breakers?

[bankruatsteve]

You should check with condo mgmt. if they can install a "Safe-T-Cut" box at their cost since that is now (I think) the requirement. If not, you could buy one yourself at Home Pro or the like and have your condo electrician replace.

Just to confirm... The main (larger) breaker usually on the far left in your box does NOT say "RCBO" or have a "Test" button, right?

[Cyrus123]

No it doesn't. Thanx, I need some rewiring done anyway so I'll buy one today and have it all done together.