10mm T&E for Consumer unit supply

[sparksburnout]

Re: 10mm T&E for Consumer unit supply

An RCD up front and then another in the board?! Ah yes good point, each room would have to have it's own RCD or it would take out the whole lot. Could you not use a 100mA time delay RCD in a CU after the meter, and then 30mA in each individual CU, that way protecting the T&E?

Dunno where you get your SWA from but I get it cheaper that T+E.

I must check my supplier then, that seems mad!!

 

[Zebra Stripe]

Well, evidently thats far too expensive and you'll never in a month of sundays win the job, cos I'm priceing to have one shower unit RCD CU in the basement and just split off this 40amp MCB with 4mm flex for each flat clipped direct to the stairwell walls using metal clips with a 13amp FCU in each flat for 1 socket and, further fused down with an 3amp FCU for lights :wacko:

 

[D Skelton]

Re: 10mm T&E for Consumer unit supply

Could you not use a 100mA time delay RCD in a CU after the meter, and then 30mA in each individual CU, that way protecting the T&E?

Additional protection for a T+E cable buried less than 50mm in a wall can only be afforded by a 30mA RCD

I must check my supplier then, that seems mad!!

Not really, SWA is far cheaper to produce than T+E

 

[nickblake]

And you've just priced yourself out of the work!

Probably ,lol

 

[sparksburnout]

Re: 10mm T&E for Consumer unit supply

Can you explain what you actually mean? So are you saying put a front end 30mA RCD on each supply to each flat with T&E submain burried?

No, I didn't make myself very clear I admit. I was initially suggesting only one RCD in a CU that would then feed each individual CU, but I now realise after giving it more than 10 secs thought that this would be crap. However, could you not use the method i suggested in my reply to D Skelton? I was not advocating having a buried T&E with no RCD protection!

 

[Zebra Stripe]

Re: 10mm T&E for Consumer unit supply

No, I didn't make myself very clear I admit. I was initially suggesting only one RCD in a CU that would then feed each individual CU, but I now realise after giving it more than 10 secs thought that this would be crap. However, could you not use the method i suggested in my reply to D Skelton? I was not advocating having a buried T&E with no RCD protection!

Well thanks for the offer of your method, Im sure its a very good method, but its not my job or thread.

 

[Zebra Stripe]

That only applies to fuses. What you don't want to have is a situation where a circuit tripping a downstream device causes the upstream fuse to have to 'prepare to trip' to use a phrase. Pre arcing is a state where the fuse is subjected to the fault current but has not yet tripped. The more this happens the more damaged the fuse becomes.

Say for example you have a DB where the highest rated MCB is 50A and you plan to supply this via a sub main. If for example you choose a 63A fuse and it has a prearcing current of 45A (it won't have, this is purely an example) then this is bad design. You would need to uprate the supply fuse or, if possible, downgrade the downstream device.

A very simplistic explanation I know.

I think I shall do some reading up, if I ever get some time and can stay off the booze. Do you know of any good reading material in relation to this? No worry's if not, its just I tend to get a bit side tracked when researching something on the web. (Im mean Im lazy)

 

[D Skelton]

I think I shall do some reading up, if I ever get some time and can stay off the booze. Do you know of any good reading material in relation to this? No worry's if not, its just I tend to get a bit side tracked when researching something on the web. (Im mean Im lazy)

http://www.cooperindustries.com/con...-datasheets-a/Bus_Ele_DS_4131_HRC_Form_II.pdf

 

[sparksburnout]

D Skelton, iv'e just noticed your signature, it's fantastic. I know this is going off topic but i saw a program revisiting the miners strike the other night. I had forgotten they even took benefit off their families. Lower than vermin indeed......

 

[Jimmyb]

Answer me this; when you're taking a feed for a garage DB, do you HRC that or do you take it from the existing DB?[/QUOTE]

I normally use c40 or c32

 

[D Skelton]

I normally use c40 or c32

Same problem then, no matter what curve the protective device is.