Correct Breakers For Different Kind Of Circuits

[Khun Jean]

A new airconditioning is installed and it has its own circuit. I pulled three wires 2.5mm for live and neutral and 4mm for earth.

The sticker on the back says it is using about 1500W. I presume that is when it starts up and when the compressor is running fully.

The circuit breaker in the CU is 32 Amps. I changed it into a 10Amps as that seems more than enough and closer to the max power used by the airconditioner.

As the CU has room enough for 10 circuits i wired the small shop with many circuits. Some circuits have only a few lights, maybe about 100W. I took out the 32 Amp breakers for that too and changed them into 10Amps, but still wonder why there are no 1Amp or 2Amp circuit breakers available.

The wires for the light circuits are 1mm. That wire should be able to handle 1.5Amps, is that correct?

I would like the circuit breaker to break instead of the wire melting.

Is 10Amp the lowest value for a circuit breaker?

I would prefer lower amps.

What kind of wires are sufficient for wall sockets, i would like to pull wires to one place and then split it to two double wall sockets about 2 meters from the 'split'.

It would be used for a light and something like an electric pan (1800W) or grill (2000w).

That would be 4100w maximum for both double wall sockets. I bought 2.5mm for that, is that sufficient?

All wires (2 times 2.5mm and 1 time 4mm) are in electric tube and have some wiggle room, but this means the maximum is lower then free in the 'air'.

How much lower is the maximum?

Edited December 23, 2012 by lopburi3

[Khun Jean]

Could not edit my post but i missed a period in this sentence. Pretty important period.

The wires for the light circuits are 1mm. That wire should be able to handle 15Amps, is that correct?

should be:

The wires for the light circuits are 1mm. That wire should be able to handle 1.5Amps, is that correct?

[Artisi]

Why do you want lower amp. breakers is more the question?

[Khun Jean]

I feel 10 Amps is way to much for a circuit having a maximum power used of 300w some even less.

The wiring to those is done with 1mm wire and 10 Amps is way to much for that circuit.

In that case there is a possibility that the wire will melt before the circuit breaker breaks the circuit.

Am i wrong in that thinking.

Some of the circuits are more 'dirty', like lights outside. I don't want them to be part of a safety cut as then it will cut all other circuits too.

The best 'other' way is to have low Amps circuit breakers to protect the wiring. Those 'dirty' circuits are out of reach and isolated from conducting materials, even for adults so i do not worry about someone getting a shock.

Edited December 23, 2012 by Khun Jean

[lopburi3]

Below is a link to chart designed for various wires in voltage used here (believe you may be thinking 120 volts with your concerns for size) or simple chart attached (size over amps).

http://www.elecsa.co...-of-Cables.aspx

Table 1: Cables enclosed in an insulated wall: Method 1

Cable size

Rating in Amps

1mm

11

1.5mm

14

2.5mm

18.5

4.00mm

25

6.00mm

32

10.00mm

43

Table 2: Cables which are clipped direct: Method 2

Cable size

Rating in Amps

1mm

15

1.5mm

19.5

2.5mm

27

4mm

36

6mm

46

10mm

63

[Crossy]

The MCB (breaker) is intended to protect the cable, so its maximum size is dependant upon the cable in use, nothing to stop you using smaller breakers if it makes you feel better. If the manufacturers instructions recommend a smaller breaker then do use one.

You can get MCBs down to 1A, they're just not common, you electrical wholesaler may be able to get them, we have our lighting on 6A.

If your wiring is 1mm protect it with a 10A (or smaller) breaker.

You're chancing it with a 1500W motor load on a 10A breaker, not hazardous but you could get nuisance trips on start. A 2.5mm cable should be protected by a 20A breaker, no real point fitting a smaller one, but 32A was indeed too large.

For outlet circuits wire in 2.5mm2 with a 1.5 or 2.5 earth and protect with a 20A breaker. In your kitchen run two circuits if you have a lot of big loads.

EDIT What possessed you to pull a 4mm earth on a 2.5mm circuit? Common wisdom says same size as your live conductor, in reality one size smaller is OK.

EDIT 2 In reality very few fires are caused by overloads in fixed wiring, the ratings used for cables are very conservative and even a 200% overload won't cause things to get hot enough to cause a fire. However, poor joints with their associated overheating are a significant cause of conflagration. Twist-n-tape is a major no-no, as a minimum use correctly sized wire-nuts, better screw type tunnel connectors or 'Wago' connectors.

[Khun Jean]

Thanks guys.

Lopburi, your google <deleted> is better than mine. Good charts and other info.

Crossy i ran a 4mm ground wire as that is what i had lying around. I was under the impression that there is only a minimum size for an earth wire (same as the live wire) but making it bigger would not introduce problems.

Is that information correct?

I used screw tunnel connectors and wire-nuts corresponding to the wires diameters. No tape allowed.

Is soldering wires when they are twisted together and then a wire-nut an allowed procedure? I did not do that just curious.

[Crossy]

KJ. No issue whatever with a larger ground wire, since you had it around there was no cost penalty

Soldering of power wiring is not a good idea, it's difficult to do well in-situ (you need a much larger iron than most people own) and there are certainly issues with the solder wicking up inside the insulation and introducing a potential hidden weak spot.

[electau]

The rating of a protective device is based on the current rating of the cable in use.

IEC ratings 6/10/16/20/32/40/50/63/80/100.

[canopy]

For outlet circuits wire in 2.5mm2 with a 1.5 or 2.5 earth and protect with a 20A breaker.

I was under the impression and also see in lopburi's chart that 20A is too big for 2.5mm2. Is it possible to clarify this? One other thing is if a light switch or outlet has 16A stamped on the back, would that mean it should not be on a breaker that exceeds 16A?

[Crossy]

For outlet circuits wire in 2.5mm2 with a 1.5 or 2.5 earth and protect with a 20A breaker.

I was under the impression and also see in lopburi's chart that 20A is too big for 2.5mm2. Is it possible to clarify this? One other thing is if a light switch or outlet has 16A stamped on the back, would that mean it should not be on a breaker that exceeds 16A?

It's actually down to the installation method, buried in insulation 2.5 is rated at 18.5A according to L3's table, but clipped direct it can handle 27A. If you go to the Bangkok Cable website it's much simpler for the layman to understand the stuff most of us use is here http://www.bangkokca...LOG/VAF2EN.HTML or here for singles http://www.bangkokca...ALOG/THWEN.HTML

In reality for a domestic installation where it's highly unlikely to get near its rating for an extended period, stick it on 20A and all will be just fine. The ratings / de-ratings are very conservative anyway.

Your 16A rated outlet or switch should not have a load greater than 16A (3,500 W) attached. Nothing to stop the circuit being on a 20A breaker, it's there to protect the cable not the switch / outlet, you could have two outlets on one circuit pulling 10A each with no issues.

[T_Dog]

Circuit breaker maximum capacity should be set by wire size, but it is good practice to use a smaller sized breaker based on expected load so Khun Jean is trying to do the right thing. We had an extension cord start to arc and the 16 amp breaker never tripped as the connections and plastic melted down. A 10 amp breaker may have tripped as the power being dissipated had to be fairly high to cause the corona and melting.

[electau]

Cable rating of a cable depends on the method of installation, individual single circuit, bunched( over 50% of the route length), in free air, in conduit, underground, unenclosed and enclosed in conduit ot duct.

It is required to derate cables under certain circumstances, eg when enclosed in thermal insulation( over 50% of route length).

Derating may apply to very long circuit runs to comply with impedance requirements under fault conditions.

For domestic installations, single circuit rating to IEC/AS/BS requirements is all that is required.