Supply to a 63A RCB

[spike47]

Hi

I need to put a 63A RCB 6 way weatherproof consumer unit ( Garage unit ) with 2x6A , 2x20A , 1x32A MCB's, in my workshop at my farm , now the supply to it, comes from the Main 83A 3 phase fuse box on the other side of the wall where I want to mount this unit , the length of cable would be around 500mm max .

Question , with it being such a short length of cable for the feed could I use a 6mm2 cable ! , as I have loads of it, but no 10mm2 .


cheers


spike

 

[EFLImpudence]

I take it you mean RCD.

If so, the 63A is just its Current Carrying Capacity and has no bearing on anything else nor does it limit the current.
As the MCBs in the Garage CU amount to 84A you will have to determine the actual maximum load and account for it in the design.
You can get 100A or 80A RCDs.

However, 10mm² cable only has a maximum CCC of 64A so may not be large enough and 6mm² cable definitely would not.

 

[Iggifer]

back in a minute.

going on holiday?

 

[EFLImpudence]

No. Misread the OP. Going to shop now.

 

[spike47]

I take it you mean RCD.

If so, the 63A is just its Current Carrying Capacity and has no bearing on anything else nor does it limit the current.
As the MCBs in the Garage CU amount to 84A you will have to determine the actual maximum load and account for it in the design.
You can get 100A or 80A RCDs.

However, 10mm² cable only has a maximum CCC of 64A so may not be large enough and 6mm² cable definitely would not.

Sorry yes I mean RCD , I understood that the 63A RCD is to take the full load of the MCB's it supplies , however it also protects the cable feeding it from its source , no! , there will never be a time that all the MCB's will be on full load .

 

[spike47]

I could use 2x16A instead of the 20A and use a 20A instead of the 32A ! .

 

[securespark]

Going to shop now.

Could you get me a loaf, please?

 

[spike47]

Does the supply cable have to take a 83A load , not the 63A ! .

 

[spike47]

Attached BS7671

 

[EFLImpudence]

I understood that the 63A RCD is to take the full load of the MCB's it supplies ,

It has to do that, yes. So, you may as well buy a 100A one.

however it also protects the cable feeding it from its source , no! ,

No. it doesn't protect against overload.

there will never be a time that all the MCB's will be on full load .

No, that's normally the way but had to check.

So, the supply cable is only protected by the 83A ? fuse.
10mm² is not technically big enough.

 

[John D v2.0]

If it's normal PVC t&e then the insulation won't handle 90c.
I think first you need to know your load, if you down rate the MCB you have to be sure you won't leave yourself with a small overload.
If it's only half a metre, it's only going to be a small percentage of your overall cost to use 16mm2 tails.
The length doesn't matter, if a 50cm cable or a 50m cable is overloaded it'll still melt the insulation and short.

 

[EFLImpudence]

That's right. You have the wrong table, Spike.

 

[Spark123]

Table 4D5 is for normal twin and earth.
Also if you are in a workshop using power tools it isn't a good idea to have lights on the same 30mA RCD (assuming that's what your 6A MCBs are for), if the RCD trips you may end up in darkness. What type of lights are you looking to use?
Is this on the same supply as a dwelling?

 

[EFLImpudence]

SS - are you going to pick up this loaf or not?

 

[spike47]

OK , guys got it now , will get some 16mm tails , and a 100A RCD and use the MCB's that I first was going to use .

Table 4D5 is for normal twin and earth.
Also if you are in a workshop using power tools it isn't a good idea to have lights on the same 30mA RCD (assuming that's what your 6A MCBs are for), if the RCD trips you may end up in darkness. What type of lights are you looking to use?
Is this on the same supply as a dwelling?

Hi

Thanks for your feedback , the lights (lights 60W ) are only for the Tack room x1 and grain store x1 , chicken room x2 , the sockets are for these rooms only , they are part of the main workshop ( but they are separated ) it all was the Cow shed !.

The Main workshop wiring is fine ( off the blue phase ) , anyway what I have done is :

Have changed the Main supply fuse feeding the 63A RCD from 83A to a Lawson 63A ,( this is off the Yellow phase , house is off the Red phase ) and used a 10mm2 cable to supply the 63A RCD , yes I know I really should put in 16mm2 tails ! , needed it doing today

ps: I would not do anything until I was 100% sure it was right , that is why I am asking the questions , maybe stupid questions but if I get the correct answer at the end that is what I will do ! , not before .
I am not a Electrician as you have guessed , I am a time served mechanic so I do have a bit of savvy about me , not a lot but a bit ! , as they say in my trade you learn something everyday ! .

spike