Am I using the correct size MCB?

joedonnelly1

I'm installing a 2.8kW fan assisted oven (no hob) I done some cable sizing calculations and voltage drop calculations and added 50% overload in aswell and I found I could use a 2.5mm cable to supply it. I also found I could use a 20A MCB, a friend said that he would use a 32A to be safe but didnt give me any other reasons why? Is this better or would it stop it from tripping under fault conditions? Is it also acceptable to use a 20A double pole switch to isolate it?

Thanks for any feed back

rjniles

I assume you are in Europe(or another area using similar electrical standards) based on terminology.

2800 watts (2.8 KW) at 220 volts is approx 13 amps. #12 wire with a 20 amp breaker will carry that load unless the cable length is very long (under 75 feet or 25 meters I would not be concerned)

2.5 MM is #10 cable

2.05 MM is #12 cable

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joedonnelly1

I'm in the UK!

Ye I think i worked it out at about 12amp and then added 50% overload which came to about 18/19Amps

The run is only 15 meters so i'm right in saying a 20 MCB and a 20 doublr pole switch would take this ok?

kbsparky

"... doublr pole switch ..."

Do you switch the neutral over there?

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joedonnelly1

Double even sorry and yes dp switch line and neutral

rjniles

KB
I think he means a breaker.

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joedonnelly1

No you've got the 20A MCB breaker at the main board and then a seperate double throw (double pole) switch beside the oven to isolate it

rjniles

Sorry for my confusion. This is primarily a North American based forum and most of us are not familiar with UK requirements.

Based on the load 20 amp devices should be fine.

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joedonnelly1

Didn't even realise :o is there a UK section? Thank I thought that but I always like a second opinion!

frenchelectrican

Let me step in here due I do live in France and I should know some of the UK / Mainland European codes.

First of all .,

rjniles.,

Just a small correction on metric cable sizing the 2.5mm2 is about the same size as 14 AWG so the 4.0mm2 is the same as 12 AWG size while 6.0mm2 is little bigger than #10 AWG size.

They will have differnt ampcapitcy rating than North Americian side so we have little more leeway with rating but all it depending on type of conductor we used.

joedonnelly1.,

You can use the 4.0mm2 Twin et earth if your area do allow it and use the 20 amp breaker ( don't get 24 amp breaker otherwise they will overheat the 4.0mm2 T&E which I have see it before )

For the 32 amp breaker as someone mention to ya the answer is don't go there it is not legit in France which I know but UK it may be a doable but I doubt it due you can not have any major fixed appalice or cooker on ring circuit which it is a no-no what I heard.

Of course you may have to put a double pole switch for your local disconnecting means if your area do use the 17Th edition of regulations.

IIRC you may want to get a 20 amp MCCO breaker ( avce RCD )


Hope that clear up some of the confusing parts between North Americian side and European side.

Merci,
Marc

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rjniles

FrenchElectrican

Thanks for the correction on the wire size conversion. My mistake is thst I used a table that converted to metric diameters and I see you use the cross sectional area in mm's.

Question on European voltage standard. I know the voltage is 220. Is that an ungrounded 220 and a grounded neutral from a single pole breaker?

Rj

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diyjohn1234

I agree with this. Technically it should be fine.

frenchelectrican

Rjniles.,

I will clear that question up for ya for the voltage in European area right now we are running 230 to 240 volts line to netural just the same as your 120 volts line to neutral system you have in state side.

However let me throw this in the mix it will get your attetion we do have 240 volts three phase as well in few area but it is not super widespread used but the most common three phase voltage we have in Euroepan side is 380 to 415 volts depending on which grid you are on in France where I am now it is 415 volts line to line on three phase system.

I will post the metric listing as well.

1.5mm2 = 16 awg
2.5mm2 = 14 awg
4.0mm2 = 12 awg
6.0mm2 = 10 awg
10mm2 = 8 awg
16mm2 = 6 awg

If you want more let me know I will post it later.

Merci,
Marc

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itsnotrequired

one of the reasons the IEC world uses 400V for three phase is that it works out to 230V for single-phase loads. convenient! i remember looking at some motor control center schematics and asking where the control power transformer was for the starters. response was that they simply went line to neutral.

rjniles

To the OP

Here is a link to a UK electrical forum

http://www.electriciansforums.co.uk/

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