32 amp breakers in consumer units.

[thaibeachlovers]

When I went to Global House recently to buy a new consumer unit, I noticed that most of them had several 32 amp breakers installed. If lights are 10 amp, plugs 16 ( not many had 10 or 16 amp breakers ) and presumably 20 for AC etc, what are the 32 amp breakers for?

Thanks.

[yankee99]

32 amps is going to protect your wire coming(from drawing too much current) from your meter also from overloading the actual box. The boxes here are very small most only handle about 8-10 breakers which if your house is wired properly would barely handle ones kitchen and bathrooms....

[Crossy]

I don't see the logic either.

To be honest I see few things that would require 32A breakers, on-demand water heaters (up to 7kW), electric cooktops (both on 4mm² wire) and that's about it. Even pretty big aircons are going to be OK on 2.5mm² and 20A.

Put your outlets on 20A and 2.5mm² wire, lights on 10A and 1.5mm² and you're good to go.

[thaibeachlovers]

Thanks.

Can't put the plugs on the 20 amp breaker- I've dedicated that to the water pump, and the only other breakers are 10 ( lights ), 16 and 32. It's OK for the plugs on 16 though, as EVERYTHING was on a single 10 amp breaker before I got started!

[Crossy]

This is one of the reasons not to buy pre-configured consumer units, if you buy empty (or at least without breakers) units you can configure as you want and need.

[bankruatsteve]

If you need a dedicated breaker for the pump, you could probably get away with that on the 32a as it's very unlikely to overload even 10a - and any size breaker will trip on like a short circuit. Then you could use the 16a and 20a breakers to divide up your sockets.

[IMHO]

If you need a dedicated breaker for the pump, you could probably get away with that on the 32a as it's very unlikely to overload even 10a - and any size breaker will trip on like a short circuit. Then you could use the 16a and 20a breakers to divide up your sockets.

Not so sure about that... if I had a 50M run of 1.5mm2 THW, would it trip a 32A breaker with and end of line short?... before it turned into a fire that is

[Crossy]

If you need a dedicated breaker for the pump, you could probably get away with that on the 32a as it's very unlikely to overload even 10a - and any size breaker will trip on like a short circuit. Then you could use the 16a and 20a breakers to divide up your sockets.

Not so sure about that... if I had a 50M run of 1.5mm2 THW, would it trip a 32A breaker with and end of line short?... before it turned into a fire that is

Exactly, with a fixed load it's not necessary to provide overload protection, but it is vital to provide short circuit protection.

Breakers are not expensive, simply remove some or all the 32A units and replace with some of sensible size.

[bankruatsteve]

It sounded like he had a Safe-T-Cut box which, I thought have fixed breakers which cannot be replaced. (?) Anyway... I'm pretty sure 150m of 1.5mm2 would trip a 32a breaker on short circuit.

[Crossy]

It sounded like he had a Safe-T-Cut box which, I thought have fixed breakers which cannot be replaced. (?) Anyway... I'm pretty sure 150m of 1.5mm2 would trip a 32a breaker on short circuit.

1.5mm² copper has a resistance of about 12.1 milli-ohms / metre, so your 150m run (assuming that's 75m out and back) will have a resistance of .0121 * 150 = 1.8 ohms.

Worst case scenario, dead short at the far end, supply at the low end of the 220V +-10% (198V), short circuit current = 198/1.8 = 110A , about 3.5 x rated current. A 'C' curve MCB will take between 2 and 10 seconds to open at that current. Most codes expect a short to open the breaker in 0.4 seconds so in this case, fail!

[thaibeachlovers]

Thanks for the replies.

Didn't have time to be buying individual beakers. Trip to the village came up at short notice and had to do a flying visit to Global House. The nearest supply of breakers to the village is over 2 hours away, and not doing that just for a couple breakers. What is there will have to do, and it's all better than the single 10 amp breaker for the whole house, especially as they have built a whole new extension ( which is what I've been wiring up ).

The consumer unit is a Bi Tek. It does have replaceable breakers but see previous.

Anyway, going back to the world tomorrow, so what is there is what they get.