Main switches at residential property

This includes types of overcurrent, Short Circuit and RCD protection
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tumeke
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Main switches at residential property

Post by tumeke »

Hi Guys - just a question about main switches and overcurrent protection of mains at a residential property. I have asked some of the guys I work with but don’t totally trust their answers.

1) How do you know the fuse size that has been used by supply authorities before the meter box? The company I work at maximum demand done by limitation often seems to assume this is 63 amps, is this a standard size or is it a dangerous assumption being made?

2) Is there a reason that main switches are used instead of a 63 amp (or suitable) MCB? Is it something to do with a main switch being double pole operating in the supply and hot water single core? A single pole MCB may not be able to achieve this as by not isolating the hot water single it does not “isolate the supply of electricity to the electrical installation” as per 1.4.82?

Thanks
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gregmcc
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Re: Main switches at residential property

Post by gregmcc »

1) Generally speaking 63A is the size supply authorities give for domestic installation. but without physically checking the fuse size in the pillar/pole there is no way to be 100% sure

2) No particular reason i know of for a switch been used instead of a MCB, no reason why a 2 pole MCB could not be used instead of a 2 pole main switch
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DougP
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Re: Main switches at residential property

Post by DougP »

1. Yes 63A is the usual size, but best to double check with your network if you want the absolute answer for your location.

2. The supply fuse is a requirement for fault protection (ESR 32). It doesn't have to provide overload protection, although the HRC fuses used generally do provide overload protection. But, your network connection standard, or supply rules might specify that it is not to be used for overload protection and that overload protection must be provided on the consumer side.

Usually, you would do a maximum demand and work out what is required. 2.2.2

You could use an MCB as a main switch for the installation, and you can also have more than one main switch if necessary.
2.3.3 is the clause relating to the requirements for main switches, not the definition at 1.4.82 which only explains the meaning of the words.

One issue might be, that if you're using a 63A circuit breaker for current limitation, how do you wire it to include the hot water service within that 63A? Once again, you might need to check your network connection standard for the usual wiring method.
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