DIY Doctor

2nd Consumer unit

Postby remelad » Fri Jan 09, 2009 10:12 pm

Hi all
went to a friends today to connect an electric cooker, when i arrived i found it was to be connected to a second consumer unit. The 2nd consumer unit is supplied from the main c/u with 10mm t&e at a distance of at least 15 meters,it is 6 way and fully used. There is a ring circuit on it that feeds the kitchen a lighting circuit and a couple of radial circuits. For these reasons i did not connect the cooker and advised my friend that we should fit a modern c/u and run a new supply.My question is would 25mm steel armour be suitable for this.

I am part p, just need a little help to confirm this to be okay or any sugestions.

Many thanks in advance
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Postby BLAKEY1963 » Sat Jan 10, 2009 12:19 pm

YES 25mm2 , if 2 core , run at least 16mm2 earth with it.

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Postby securespark » Sat Jan 10, 2009 10:48 pm

How big a cooker?
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Postby remelad » Sun Jan 11, 2009 7:22 pm

Hi Mr B,
thanks for your response, is 25mm2 the smallest size of cable to use or would it be possible to go smaller. As you will be aware 25mm2 is quite a size and anything smaller would be easier to get to 2nd c/u.

Have looked at table 4D4A and see that a 2 core 10mm2 armoured cable will take 67 amps method 1, would this be acceptable,if not could i use 16mm2.

Hi Securespark ,its not the size of the cooker that is the problem,but the amount of circuits being feed from 2nd c/u. In original post i stated that the 2nd c/u is fed with a 10mm2 t&e which is only capable 0f 43amps looking at table 4D2A which is to low as the 2nd c/u has several circuits

The input received is much appreicated
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Postby ericmark » Sun Jan 11, 2009 11:01 pm

The current that cable can take depends on reference method. Table 4D5 does allow 45 amp for 10mm for Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness). But 64 amp Reference Method C* (Clipped direct).
The same applies with SWA with thermal setting (90 deg) 16mm is rated at 110 amp Ref method C clipped direct Table 4E4A do remember that even if you use 3 core cable when using core as earth you still use the 2 core bit on table.
The only problem is heat affecting other items near to the cable 90 degs is quite hot there is no table for thermal setting twin and earth I would use Table 4E2A which still gives clipped direct as 107 amp for 16mm which I think would be smallest you could use because of earth size needing to be min of 10mm.
If you want it neat then how about mineral insulated that's a lot smaller in physical size.
You seem to be using old book may help but no guarantee it's 100% correct.

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