safety device for distribution circuit!

[IQ Electrical]

hi nickblake, do you agree with mart that SWA is enough with distribution cable, as long as there is 17th edition board in the shed?

It's not about whether we agree with each other, it's about the requirements of BS7671:2008-do you not have a copy to refer to?

 

[Deleted member 9648]

RCD is not required on a distribution circuit.
an earthed SWA should be used and this is all you would need.
if the house is on a tt system then there must be a 100mA RCD protecting the whole installation. thats the only requirment.
it doesn't matter if its a BS 60898/3871/88..... thats your protection!! your disconection time is 5sec for distribution so just cjeck yor cable size ect.

If it was a TT it would be 1 second for a distribution circuit.....411.3.2.4

 

[bluesky]

It's not about whether we agree with each other, it's about the requirements of BS7671:2008-do you not have a copy to refer to?

i do have one, but cannot find the reference, thinking ask someone who knows it, and poeple could have different understanding, the codes cannot say everything clearly, do you agree?

 

[nickblake]

I wouldnt like to comment unless i have more information regarding the installation , like IQ has said why are you going to all this trouble after just changing the light bulb

 

[bluesky]

I wouldnt like to comment unless i have more information regarding the installation , like IQ has said why are you going to all this trouble after just changing the light bulb

i am newly qualified, i would like to learn everything on site, even some small jobs, i found it is good practice, surely i wont do any suggesstions to the client, but next time i would be prepared when i see it again, i really appreciate that i have got lots of patient help here...

 

[bluesky]

in my opinion, really need a rcd or a circuit breaker at the origin of the distributiion circuit, but at the moment there is only a 100A main swith there...

 

[mart8235]

Can you point me to that regulation please?

In a '17th edition' consumer unit why would you use a 100mA RCD?

are you really asking why i would use a 100mA RCD on a TT system????

 

[bluesky]

are you really asking why i would use a 100mA RCD on a TT system????

hi mart, do you think a 100A main switch is enough at the origin? because the main switch will never trip anyway, so it wont satisfy the 5s disconnection time? at least it is a breaker, sorry cannot find the reference in red book...

 

[mart8235]

Im with IQ on this one you cant say that the disconnection time is 5 seconds as you dont know the size of the protective device !!! all circuits up to 32 amps have a disconnection time of 0.4 seconds ,above 32 amps is 5 seconds , and again if you have a 17th addition board installed as IQ has stated there is no need for a 100ma RCD

All final circuits up to 32A are 0.4s, all circuits above 32A AND DISTRIBUTION CIRCUITS are 5s, therefore all distribution circuits reagrdless of size are 5s......... have look at the table.
only mentioned a 100mA RCD incase it was a TT system, and that would be the only reason you must have an RCD protecting the distribution circuit....... and yes i know the disconnection time is not 5s for TT.

 

[mart8235]

hi mart, do you think a 100A main switch is enough at the origin? because the main switch will never trip anyway, so it wont satisfy the 5s disconnection time? at least it is a breaker, sorry cannot find the reference in red book...

A 100A main switch is a switch and not a circuit breaker. the distribution circuit must be on a circuit breaker/fuse of some sort at the appropriate size to protect the cable. the armourings must be earthed and then no RCD is required.
if the suppliers fuses are 100A or less then diversity is satisfied and there is no reason to consider changing the main switch.

 

[IQ Electrical]

are you really asking why i would use a 100mA RCD on a TT system????

No, I'm not interested in why YOU would use a 100mA RCD, I asked you to point me and anyone that subsequently reads this mess of a thread to the regulation that requires it...

 

[Deleted member 26818]

411.5.3 indicates that an RCD is the prefered protective device in a TT system, and that it can be ommited if a suitably low value of Zs can be permanently and reliably assured.
Not aware of a particular Regulation that states the rating of the RCD, other than that it must meet the requirements of Table 41.5 for the apropriate values of Zs.

 

[IQ Electrical]

411.5.3 indicates that an RCD is the prefered protective device in a TT system, and that it can be ommited if a suitably low value of Zs can be permanently and reliably assured.
Not aware of a particular Regulation that states the rating of the RCD, other than that it must meet the requirements of Table 41.5 for the apropriate values of Zs.

That's all correct Spin but here is my original question:

Can you point me to that regulation please?

In a '17th edition' consumer unit why would you use a 100mA RCD?

 

[mart8235]

That's all correct Spin but here is my original question:

Can you point me to that regulation please?

In a '17th edition' consumer unit why would you use a 100mA RCD?

Please define a '17th Edition' edition consumer unit, as I am unaware the IEE have designed a particular CU.
But no, I will not tell you where regulations are in the book. Its up to you to find them yourself!!! besides, my regs are in work!!!!

 

[Deleted member 26818]

That's all correct Spin but here is my original question:

Can you point me to that regulation please?

In a '17th edition' consumer unit why would you use a 100mA RCD?

You are well aware IQ, that there is no Regulation that requires 100mA RCD protection.
It might be desirable to use a time delayed 100mA RCD to provide discrimination, where there are a mixture of circuits some provided with 30mA RCD protection and others without.