Double Pole Ciecuit Breaker

Code.

Look at your local building codes.

IF you are in the US or a country with similar power THEN the only time I have seen double pole breakers is for 230V circuits. In the US a home does not have a 230V line but has two 115V lines that are 180 degrees out of phase.

Q2: If 60A or 100A is enough then the builder and power company were probably cost sensitive and only provisioned as required.

Exception to your rule - let an European designer do the schematics for the panel you are building for USA use, and you'll have double pole circuit breakers and fuse blocks with the one fuse a brass dummy on 120V circuits - and yes they know the one side is connected to N as evidenced by the dummy fuse. Been there and done that. I have redesigned more than a few European designs in the past three years to make them more acceptable for use here.

It's economical, the higher the voltage the lower the amp draw, the smaller the wire size required, the cheaper the cost of installation....

Q2 - If the incoming CB was rated at 300A, all the wiring to the next protective devices would also have to be rated at 300A. That's chunky wire in a little DB.

If both conductors are ungrounded, the CB must interrupt both poles.

There is no such 60 or 100A limitation if the bus bars are sized for greater current, except for the vagaries of local codes.

Switching a neutral is prohibited under British Standard 7671. So the question is a non-starter.

Should the main disconnect(isolator,cb,lbs) in a switchboard/load centre/consumer unit have neutral disconnect together with phase disconnect?.

Even if you are on ship?

Friend,

It's hard to answer your question with details when we don't know the location you refer to. As you can see from posts already, CR4 has membership around the world.

With typical residential or small commercial installations, the power is single-phase. If it is brought in as a single-voltage (such as 120VAC), one of the two wires is grounded/earthed for safety (and is called the neutral) and the other one requires a fuse or CB to provide short circuit or overload protection (and is called the hot). However, by adding one more hot wire from the source, with voltage opposite to the first hot wire, you can double the amount of power with only the addition of 50% more wires. You then would need a double-pole CB, because safety requires that both wires be de-energized if either one has a short or serious overload.

Therefore the answer to Q1 is add 50% more wires and get 100% more power capacity. A pretty economical move.

Regarding Q2, many have answered it well already. Generally you are balancing the anticipated load with the cost of providing power to it. In the USA: 100 years ago, the typical service was 30A @ 110V single-pole and two circuits branching from it. More uses for electricity have become common, so the typical service size rose to 60A @ 220-240V, double-pole. More recently, the minimum size is 100A @ 240V, double-pole. During all these years, there have been exceptions for people planning a long-ways ahead or having larger homes. [My father rewired the family home in 1952 and went from 30A/120V to 200A/240V; the only way the utility could sell him electricity was with a small business rate, because nobody else had a home with that large a service. Of course, 60-years later, that home still has plenty of power available.]

--JMM

In UK when they disconnect power to a premises(home/industry)by the main switch/breaker in switchboard/consumer unit does the neutral remain connected?.

Pnaban,

I work in the USA and don't know the UK rules on this. Someone out there???

--JMM

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