Endpoint circuit breakers, radial circuit current, and cowboy electricians

[Morakot]

Two main issues, but a bit of context up front. The "electrician" who did the wiring is a plumber, but he's not a real plumber; his wife merely owns a shop that sells plumbing supply...

[1.]

What is the point of these "endpoint" circuit breakers? In the utility room, I have a dedicated socket for the washing machine. This socket connects to a circuit, with a proper 20A MCB in a D-Square box. Before the socket there is a 20 A circuit breaker/ isolator (see picture). Similar situation, in some rooms there is 20 A circuit breaker/ isolator before the aircon. Here the breaker is right next to the light switch, as I one were to operate the A/C unit with a breaker. The 20A breaker connects to a 32A circuit.

I am in the processes of rebuilding some part of the house that includes altering door openings. I need to rewiring some parts of the lights switches and sockets. Why would I need these breakers? And if I do, should they not be installed out of sight.

[2.]

My current distribution unit has a main breaker (with RCBO) of 43A. The circuits are protected with either 32A or 20A MCBs. The 32A circuits are for various A/C units and water heaters (7KW). The 20A circuits are combined lighting and socket circuits. 20A and 32A seems ridiculously high. Standard socket take only 16A max, for example.

I assumed that one would protect radial circuits for sockets with 16A, light circuits with 10A, and heavy duty wired-in appliance with 24A. How common and how safe is this 20A/32A arrangement with combined lighting and sockets circuits?

Edited June 12, 2016 by Morakot

[bankruatsteve]

Circuit breakers protect over-current for the wire and as such should never exceed rating for the wire. If your circuits go into a CU protected with properly sized breakers, then there is no need for endpoint breaker. If an isolator is needed, a simple switch is all that is necessary (in most cases).

If you want to under-size a breaker (IE: put a 10amp breaker on 2.5 mm2 wire), go ahead but that is totally unnecessary.

[Morakot]

Thanks Steve, that's very useful! Now I understand.


I just saw Crossy's table (see below). So I think there is definitely a problem, as I have come across plenty of 1.5mm² wire. I might replace the 20A breakers in the CU with 15A if I can separate the power circuit from the lighting.

I already suspected that these endpoint breakers are nonsense.

1.5 mm² cable - 15 amp maximum circuit breaker.
2.5 mm² cable - 20 amp maximum circuit breaker.
4 mm² cable - 25 amp maximum circuit breaker.
6 mm² cable - 32 amp maximum circuit breaker.
10 mm² cable - 40 amp maximum circuit breaker.

Edited June 12, 2016 by Morakot

[Crossy]

Indeed, in a modern installation the endpoint units are pointless. There are however still many homes with very basic electrics where installing these does add to the safety, at least slightly. It would of course be better if they were RCBO's rather than plain MCBs.

We have a box full of the things from our aircon installation and even one from when we got a new washing machine. The installation chaps say "you paid for them, you keep them", ok by me they'll find a use one day.

You'll likely get away with reducing your breakers to 15A apart from, possibly, the kitchen. Our overall consumption rarely goes above that anyway except when the water heaters are on or Wifey is watering her plants (5HP of irrigation pumps).

[Morakot]

Thanks Crossy!

In the kitchen there is a combined fridge-frezzer, dishwasher, microwave, kettle, rice cooker, and extractor hood. Do you think it may exceed 15A?

Also looking at the homepro website, the MBCs by Schneider for D-Square CUs are actually 16A for some reason. Only B-Ticino and Panasonic are 15A which I'm not sure will fit the D-Square.

Edited June 13, 2016 by Morakot

[Morakot]

Another question about the current/ cable ratio. Is this table for air?

Would we have different ratios for cables inside walls: i.e. plastered over or in conduits inside a wall cavity?

1.5 mm² cable - 15 amp maximum circuit breaker.
2.5 mm² cable - 20 amp maximum circuit breaker.
4 mm² cable - 25 amp maximum circuit breaker.
6 mm² cable - 32 amp maximum circuit breaker.
10 mm² cable - 40 amp maximum circuit breaker.

[bankruatsteve]

Thanks Crossy!

In the kitchen there is a combined fridge-frezzer, dishwasher, microwave, kettle, rice cooker, and extractor hood. Do you think it may exceed 15A?

Also looking at the homepro website, the MBCs by Schneider for D-Square CUs are actually 16A for some reason. Only B-Ticino and Panasonic are 15A which I'm not sure will fit the D-Square.

Your kitchen will definitely exceed 15A if all or most of your stuff is on at the same time. If you are in the construction phase, you should have two 20-24A circuits on 2.5 mm2 wire to your kitchen with the idea being to load balance your stuff between the circuits.

[Morakot]

On 6/13/2016 at 5:10 AM, Crossy said:

Indeed, in a modern installation the endpoint units are pointless. There are however still many homes with very basic electrics where installing these does add to the safety, at least slightly. It would of course be better if they were RCBO's rather than plain MCBs.

 

This is a old topic, but I just to update these breakers are now available as RCBOs.

 

Saw them in Thai Wadsadu yesterday for 415 THB per 32A unit. Exactly the same size and design as regular MCBs.

 

 

Edited October 9, 2017 by Morakot

[KhunBENQ]

3 hours ago, Morakot said:

This is a old topic, but I just to update these breakers are now available as RCBOs.

Available for longer.

I have replaced two 20A breakers with RCBO types (shower heater and complete external shack with water pump and washing machine).

[Morakot]

1 hour ago, Arjen said:

I should have choosen a switch.

 

 

Order from Ebay send to your house in Thailand for a few baht...

 

May look OK in a utility room out off site.

 

 

http://www.ebay.com/itm/AC380V-3-7KW-Cutting-Machine-On-Off-Push-Button-Switch-230B3-/172347087666?epid=1949345786&hash=item2820afdb32:g:tvEAAOSwmfhX3z0I

 

 

 

1 hour ago, Arjen said:

In the main distribution panel all circuits are secured with their own ELCB.

Good. This is how it should be.