Double Phase MCB used as Single Phase MCB with Neutral

Thanks for the reply, i got it,what i understood is it will give protection for neutral also. so there is nothing wrong is using it. i will go head to install it.

Thank you

It depends on where it is to be installed. Switchable neutrals in panels and distribution boards are prohibited under British Standard 7671, for instance. One usually uses links instead.

Why cannot a single pole breaker be used instead?

i didnt get you about the contex "where"

you mean "geographic location"...??

its in the Asia continent and in the Country India. and its for Home Application. particularly for running Washing machine ,water heater and other normal home appliances.

I dont know about the "British Standard 7671", but in India, i hope we follow "Bureau of Indian Standards" (http://www.bis.org.in/index.asp). i dont have much knowledge about it, because i am not a Electrical-technical Person.

The reason why i went for Double pole is to cut off the neutral also when phase trip off to be in safer side. and i have all ready brought the Double pole MCB.

There is no need to pass the neutral through it.

Some arrangement which is to code for one country is not necessarily appropriate for an installation in another and this is a global forum. If in doubt, consult a qualified local Electrician, who will install to the local code.

The only problem you might have is: Suppose that the that the pole used for Neutral becomes faulty, like the O/Load device, inside, goes open circuit, then you are in danger of receiving a shock since the Phase line will remain connected!

Better to connect the phase and Neutral as you plan, but bypass the neutral by connecting the in and out of the neutral pole (selected) with a bridging wire. this way, it will be neat.

I spoke with a local electrician and he told 'it is OK to use a 2-pole MCB'. but i didnt ask him about the pors and cons. And i also observed in one of the friend house they have used the 2-pole MCB for single phase with neutral.

I agree with PWSlack regarding use of N-link for neutral side. In that case, you can use the DP MCB by connecting both the poles in series for the phase and an N-link or direct connection to the Neutral wire in your home for the neutral of your appliance.

And to PWSlacks point, in some areas it might be ILLEGAL to disconnect the neutral. A local qualified electrician in your country will (should) know that. Disconnecting the Neutral has little effect on safety by the way.

<...Disconnecting the Neutral has little effect on safety...>

Were the neutral to be disconnected and the line conductor left energised, then touching the neutral conductor downstream of the isolation will result in an electric shock.

"i dont have much knowledge about it, because i am not a Electrical-technical Person."

And there we have the real issue, get someone local who is qualified to do this work and live just a little bit longer.

In industrial lighting circuits where 415/ 230 V lighting transformers are used, the secondary winding is sometimes centre tapped and earthed to reduce the shock voltage (115 V instead of 230V). In this case both the terminals of the secondary circuit need to be isolated in case of fault. As such DP (double pole) MCB should be used instead of SPN (single pole and neutral) MCB in such applications.

As you state it's single phase with neutral. Double pole switching should incorporate an early make / late break neutral.

Contact the manufacturer and get the correct MCB.

Sorry PWS, it's covered in BS7671 rev 2.

Good stuff.

The key thing is breaking the neutral after the line conductor breaks and making it again before the line conductor makes.

GA

Ive gotta agree with JRaef and PW and go a step further - if switching the neutral is not illegal in your local code, it is in US code and BS for a good reason = safety. This is simply not a good idea.

Loosing a neutral in some circuits can cause all sorts of spurious and dangerous situations. For this reason in the UK the neutral was always solid with protection only on the live. Neutral links came about as a means of electrical isolation during maintenance in more industrial situations - remove the fuse and the fuse link.

Although the UK still has the protected live and solid neutral you don't need to go further than the double switched sockets which have progressed from single pole switching to switching both the live and neutral. This is for good reason because with respect to earth there is more stray voltages imposed on the neutral from the non linear equipment - computers etc - we are now using.

Don't know whether your sockets are switched are not but as long as the live and neutral poles are mechanically locked together which yours are then your system is safe and safer than single pole.

The IEE regs are a good (ish) document but you only need to see how many times they have got it wrong and had to change it to realise it needs to be used with care.

If the 2nd live wire (neutral) is tied to earth it CAN be isolated by an MCB so long as the Neutral breaks at the same time or after the other live conductor. It must not re-make on closure after the other live conductor (at the same time or before for making).

ie the one in the first picture.

PS it is not against the rules to not break the neutral either.

If the 2nd live of a centre tapped transformer is to be broke, it is recommended to break both poles simultaneously, ie a 2 pole MCB, ie the second picture.

The first unit is usually cheaper as (previously pointed out) there is no current detection in the neutral pole. It may be that its a sales rumble...