Shed power circuit

[GazaG]

I am helping an electrician do a power circuit to a shed, inside the shed there will be a lighting circuit and a power circuit.

I am assuming no more than two 100W bulbs (No fluorescents) will be used (probably lower) and there is 1 socket which will feed a clothes dryer (unknown wattage). But I am assuming the client will use this socket for power tools when needed.

Because I don't know what wattage the dryer will be I assumed it would be a 4kW meaning I need a 20A Type-B MCB for that circuit. But because I am also assuming he will use power tools in the socket when the dryer isn't used should I up this to a 32A MCB?

It is likely that the lighting circuit and socket will be on at the same time, so would I need to use a 32A Main double pole switch (or 40A if the 32A socket is used instead of the 20A)?

As for the feed from the Main DB inside the house I am planning to use an RCBO 30mA, will the rating need to match or be greater than that of the Main double pole switch inside the Shed DB? I am worried that the RCBO will cause nuisance tripping for all the shed circuits.


P.S. This was given to me as a learning task by the electrician I am working with

 

[ricicle]

Consider :-

- All domestic dryers plug in using 13A plugs so the maximum wattage would be ?

- Diversity.

- Convenience of remote RCDs

- Low energy lighting ?

- Also earthing systems, exporting them and extraneous conductive parts

- At the end of the day the electrician will (should) be signing for the design of the installation (as well as construction, inspection and testing)

 

[GazaG]

Didn't know that about dryers, the maximum wattage would be 2990W then.

Don't think diversity can be applied in this case as the two circuits are quite likely to be both on at the same time using maximum power?

The reason I don't want to put the RCD in the shed itself is because it would leave the SWA feed from the main house DB to the shed DB unprotected, except from an MCB but as I understand outside wiring requires RCD protection also. Which is the main reason for using an RCBO in the main house DB to feed to shed DB. Is this wrong?

By low energy lighting are you talking about CFL's? The reason I assumed the use of 2 100W bulbs incandescents is to have a worst case scenario. I realise it is unlikely to be that high, but either way a 6A MCB would be used as that is the lowest possible rating AFAIK.

I am unsure on the earthing systems used, I believe the mains are one of the TN sytems, but this wouldn't effect the breaker ratings would it?

Thanks for the reply and please correct anything I have been incorrect with

 

[ban-all-sheds]

P.S. This was given to me as a learning task by the electrician I am working with

There are two important things you need to learn:

1) You need to ask your clients what their requirements are, not make assumptions, or at least not make them without telling the client what they are.

2) If you've been given a learning task it's SFA use you getting other people to do it for you, and going back to the person who gave it to you thus misleading him into thinking that you did it.

 

[ericmark]

The cost at over 3kW or 13A to under 3kW or 13A is quite a lot. So one has to consider if it will work within the 13A limit. Likely you can work below 13A.

So below 13A a RCD FCU can be the termination in house with a FCU and 1A fuse for shed lights if there is not a fuse in the unit.

Above this limit then RCBO/or MCB with RCD need space in consumer unit and second mini consumer unit in shed.

So likely the price will double once over 13A.

Which means first job is to work out which side of the 13A limit it will be.

 

[GazaG]

I like the reply, but I have one concern with using RCD FCU's.

I am not familiar with using them but the ones I have seen don't look like they can be used to isolate and lock off to perform maintenance on their respective circuits. Which means I will require seperate MCB's for each circuit anyway is this right? I think having to isolate both the socket and lighting circuit together goes against the regs regarding devision of installation (314)?

 

[davelx]

I like the reply, but I have one concern with using RCD FCU's.

I am not familiar with using them but the ones I have seen don't look like they can be used to isolate and lock off to perform maintenance on their respective circuits. Which means I will require seperate MCB's for each circuit anyway is this right? I think having to isolate both the socket and lighting circuit together goes against the regs regarding devision of installation (314)?

What would you say about a normal domestic installation then, where the only means of ISOLATION is the double-pole main switch, which will turn off both socket and lighting circuits together? (537.1.4. applies so a normal single pole MCB cannot be used for isolation)

 

[GazaG]

I like the reply, but I have one concern with using RCD FCU's.

I am not familiar with using them but the ones I have seen don't look like they can be used to isolate and lock off to perform maintenance on their respective circuits. Which means I will require seperate MCB's for each circuit anyway is this right? I think having to isolate both the socket and lighting circuit together goes against the regs regarding devision of installation (314)?

What would you say about a normal domestic installation then, where the only means of ISOLATION is the double-pole main switch, which will turn off both socket and lighting circuits together? (537.1.4. applies so a normal single pole MCB cannot be used for isolation)

Not sure if I fully understand what your saying, according to Table 53.2 a circuit breaker can be used for isolation?