RCD total load vs MCBs

[Carlos Arruda]

Hi all again.

Enough with helping my friend and back to the main thing, which is back to studying.

I am working on my final assessments (practice for my final L3 exam).

Big 2 story house with the following requirements (protected devices given accordingly and installation method C, clip direct assumed);

1 - Light Circuit 6A MCB

2 - Light Circuit 6A MCB

1 - Ring Main G.Floor = 32A MCB

2 - Ring Main 1st Floor = 32A MCB

1 - 3.0Kw I. Heater Circuit = 16A MCB

2 - Cooker (needs to be selected the given cable CSA of 4.00mm!, it doesn't make sense but these were the requirements, unless there's been a typo which I wouldn't be surprised). Having said that, that is why I selected a 32A MCB.

1 - 2.5kW P.V array = 16A MCB

2 - 8.5kW Shower = 40A MCB

1 = Total MCB amperage is 110A

2 = Total MCB amperage is 70A

My question is total RCD load 1 is 110A which is way above the 63A 30mA RCD and total RCD load 2 is 70A. Should the combined MCB load not exceed the RCD load capacity?

My house was done and commissioned 3 years ago and this also does not reflect in it as total load 1 is 73A and total load 2 is 54A.

I'm confused.

Any help much appreciated.

Regards,
Albert

 

[Carlos Arruda]

Apologies but I don't have a clue to what has happened above!

 

[trev]

Please edit that so it makes sense mate

 

[telectrix]

think i know what you mean. you're thinking of total possible load/s whereas, due to the fact that not all things will be running simultaneously, you apply diversity.

 

[Pete999]

Hi all again.

Enough with helping my friend and back to the main thing, which is back to studying.

I am working on my final assessments (practice for my final L3 exam).

Big 2 story house with the following requirements (protected devices given accordingly and installation method C, clip direct assumed);

1 - Light Circuit 6A MCB

2 - Light Circuit 6A MCB

1 - Ring Main G.Floor = 32A MCB

2 - Ring Main 1st Floor = 32A MCB

1 - 3.0Kw I. Heater Circuit = 16A MCB

2 - Cooker (needs to be selected the given cable CSA of 4.00mm!, it doesn't make sense but these were the requirements, unless there's been a typo which I wouldn't be surprised). Having said that, that is why I selected a 32A MCB.

1 - 2.5kW P.V array = 16A MCB

2 - 8.5kW Shower = 40A MCB

1 = Total MCB amperage is 110A

2 = Total MCB amperage is 70A

My question is total RCD load 1 is 110A which is way above the 63A 30mA RCD and total RCD load 2 is 70A. Should the combined MCB load not exceed the RCD load capacity?

My house was done and commissioned 3 years ago and this also does not reflect in it as total load 1 is 73A and total load 2 is 54A.

I'm confused.

Any help much appreciated.

Regards,
Albert

You need to take into account Diversity OSG Appendix A BYB Regulation311.1 may help you understand.

 

[Octopus]

& I wouldn't run PV onto a shared RCD protected circuit either!

 

[Pete999]

& I wouldn't run PV onto a shared RCD protected circuit either!

Good point

 

[Carlos Arruda]

& I wouldn't run PV onto a shared RCD protected circuit either!

Was this the regs 3 years ago?

Only asking because my house, built 3 years ago, as an RCD protecting all the sockets in the house both G. Floor and 1st Floor, almost certain that they have exceeded the 100mt sq rule for individual ring, the light circuits on 1st floor and P.V.

 

[trev]

almost certain that they have exceeded the 100mt sq rule for individual ring,

You sure your house is that big mate? There's a massive difference between 100 square metres and 100 metres square.
One thing is found in our publications, the other is not.

 

[Carlos Arruda]

You sure your house is that big mate? There's a massive difference between 100 square metres and 100 metres square.
One thing is found in our publications, the other is not.

LOL....

I meant 100 squared meters.

Opsss, sorry.

Dream come true for my wife with a house that BIG.

 

[trev]

So the ring covers an area of 100 metres by 100 metres?

 

[Carlos Arruda]

I don't have the OSG. Lost it last year and as the new edition or amendment 2015 3 rather, was due to come in this year, I just waited and never got one back.

Still haven't purchased it.

But I think this is the same as the the electricians guide to good electrical practise, page 45, there's a table for maximum demand calculations for circuits.

Am I talking about the same thing?

Many thanks,
Albert

 

[Carlos Arruda]

Trev;

I have just edited, sorry.

Lack of sleep.

 

[trev]

Come and join me in Pedant's Corner. There's always room for one more

 

[Leesparkykent]

Was this the regs 3 years ago?

Only asking because my house, built 3 years ago, as an RCD protecting all the sockets in the house both G. Floor and 1st Floor, almost certain that they have exceeded the 100mt sq rule for individual ring, the light circuits on 1st floor and P.V.

A g83 inverter can take upto 500ms to disconnect once the AC has been isolated.

 

[Carlos Arruda]

Come and join me in Pedant's Corner. There's always room for one more

I was barley holding myself up yesterday at around 21:15 on the sofa, which is so unlike me.

Still, after an episode of 12 monkeys, I still forced myself to the PC and study until 00:30, so no wonder...

This last task B on level 3 is just in a way bizarre given that C&G expect us to know all that. I see the reason why but still, in my very limited experience I am struggling a bit and feel sorry for those in the classroom that have no experience whatsoever.

Still, I am very happy I decided to do this and have a different respect/view for electricity.

Many thanks.

Albert

P.S: The worst of it is that in the end, we all will NOT be qualified electricians as we were told 3 years ago when the course started (Level 2).