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Postby diyderek » Fri Nov 30, 2012 9:26 pm

I will be installing a 4.5kw double oven in a couple of weeks.
I already have 10 metres of 6sq mm cable most of which will be needed to install by the "clipped direct method"from the fusebox via the 45amp socket to the cooker and a spare 32amp mcb .
Would you consider both the 6sq mm cable and the 32amp fuse to be oversized or can they be safely used anyway?
Am i right in assuming that "clipped direct method" means securing cable to the joists by plastic clips?

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Postby stoneyboy » Sat Dec 01, 2012 7:05 pm

What you propose will be well oversized for the double oven so I suggest you have a look at the cooker instructions and see if they specify a fuse rating. Clipped direct is as you describe providing the cable is not run in insulation.
I guess you already know that this work comes under Part P of the building regulations so should be checked and certified by either a registered installer or your local building inspector.
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Postby ericmark » Wed Dec 05, 2012 6:37 pm

It would seem 32A is a standard size for ovens and hobs and with duel fuel cookers even when the oven does not need 32A the manufacturer often stipulates 32A as the requirement.

Although stoneyboy is correct with what he says I would consider it unlikely that a oven which requires over 13A can't be supplied from a 32A supply. In general the sizes are 3A, 13A, 16A, 32A, 63A, 128A and since your oven is over the 16A then normally one would expect it to go to the next which is 32A. It comes down to the fact it could be plugged in and the sockets are 13, 16, 32 so there is no socket outlet generally used between 16 and 32A. Clearly hard wired one could have 20 or 25 amp but if used in a commercial kitchen likely it would be plugged in.

As to clipped direct (ref method C) the idea is that heat can be dissipated from the cable by the item it is clipped to as well as surrounding air. Ref method 100, 101, and 102 are also where clipped to a beam but without free air around the cable as well. As a result 6mm cable is rated between 27 and 35 amp not the 47 amp of ref method C. When using Ali-tube or other XLPE (Cross-Linked Polyethylene) or LSZH (Low Smoke Zero Halogen) cables the ratings are higher and one has to be careful to stipulate 70 deg C thermoplastic or 90 deg C thermosetting cables when working out what current they can take.

I am frankly dismayed when I walk into B&Q to see current ratings stated for a cable only flex has a fixed current rating as that has to be visible so installation method is always the same.

As already said building regulations mean LABC need notifying either direct or using a scheme member electrician but more to the point all installation should be tested. The test equipment is expensive even to hire around £75 which means most DIY guys take a chance. I do have the test gear and I have been surprised on how many times installations fail. Often just a lose screw or dropped link but with out testing it would be missed.
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