Can i use a 13A plug for a 3.6kW connected load combi microwave oven?

[Adam_151]

I usually tell people to imagine that the conductor in each terminal was not joined, but a continuous loop.

But it's not a loop, the cable is jointed in the terminal, and the joint needs to be suitable for the load that's flowing through it. Unless the manufacturer says the the input terminals on an accessory are rated to carry more current than the headline rating of the accessory, then we can only presume that they are are rated the same as the accessory, we can't go guessing that they look like they can handle more than accessory with nothing to back that up.

 

[JohnW2]

Can you apply diversity to this and use a 13 amp plug?

It's not conceptually different from "applying diversity and then using an X amp MCB". I think you'll find that at least some cooking appliances which come supplied with fitted 13A plugs are relying on diversity.

It's been observed that anything over 2.5 kW shouldn't really have a 13 amp plug, though I think it's a bit of grey area.

That's at least one of my electric kettles out, then, and probably some of my power tools!

I would say hardwiring is better.

I suspect that most of us would probably agree with that.

Kind Regards, John

 

[JohnW2]

But it's not a loop, the cable is jointed in the terminal, and the joint needs to be suitable for the load that's flowing through it. Unless the manufacturer says the the input terminals on an accessory are rated to carry more current than the headline rating of the accessory, then we can only presume that they are are rated the same as the accessory, we can't go guessing that they look like they can handle more than accessory with nothing to back that up.

The point is that, unless the conductors have not been terminated correctly, only a tiny proportion of the 'through current' will go through the material of the terminal - and the terminal won't even 'know' what through current there is.

Kind Regards, John

 

[Adam_151]

I get what you are saying John.

But would it be correct if I jointed a ring final in an adaptable box using 15A connector blocks provided I ensured both conductors were laid together through both terminals and both screws tightened. As opposed to sticking on cable in each side under a single screw.

It would probably be perfectly fine, but I would not consider it compliant with BS7671 as I had not selected the correctly rated materials to do the job and would be using them beyond the rating at which the manufacturer has deemed them safe to operate on.

 

[JohnW2]

I get what you are saying John. But would it be correct if I jointed a ring final in an adaptable box using 15A connector blocks provided I ensured both conductors were laid together through both terminals and both screws tightened. As opposed to sticking on cable in each side under a single screw.

All true - but the situations of the cables being 'joined' in the terminal of an accessory (which is what we are talking about) is analogous with the former of those scenarios (hence 'OK'), not the latter (in which current does, indeed, flow through the connector block material).

It would probably be perfectly fine, but I would not consider it compliant with BS7671 as I had not selected the correctly rated materials to do the job and would be using them beyond the rating at which the manufacturer has deemed them safe to operate on.

I don't think it's really quite as straightforward as that. I have never seen a domestic electrical accessory whose specification says anything explicitly about a rating for 'through currents' in the terminals, so one is really left having to make one's own decision, based on knowledge and electrical common sense, as to whether one has "selected the correctly-rated materials". For example, if you look at the Technical Data Sheet for an MK single socket or FCU, it gives the 'Current Rating' as 13A (with no qualification). Even though it doesn't say so explicitly, I think we all know what that 'means', and also know that it does not mean that such accessories cannot be wired into a 32A (ring or radial) circuit, in which there theoretically could be a 32A 'through current' in conductors connected to its terminals.

Kind Regards, John

 

[stillp]

Based on the fact a 13 amp plug with a 3 kW load can melt easily

I think you need to buy better plugs!

 

[JohnW2]

Based on the fact a 13 amp plug with a 3 kW load can melt easily

I think you need to buy better plugs!

He probably does. However, although I have no real experience of long-term 3kW loads, with a 2kW load (e.g. fan heater) even a brand new good quality plug with a brand new fuse can sometimes get surprisingly (well, at least, surprising to me!) 'warm'.

Kind Regards, John

 

[EFLImpudence]

yes, it all depends but I don't know on what.

I have seen an immersion wired with a plug with a plug-in timer that has been there "for ever" - perfectly fine condition.

Other times ...

 

[kai]

Some people say that an immersion heater rated at 3kW should never be wired via a Switched-Fuse-Connection unit. There was one situation that it was essential that the 13amp fuse was included in the past. If the circuit earth loop impedance was too high to operate a C50 type C15 breaker , the 13amp fuse was used as a solution to the problem. (Yes I have seen domestic installs fitted with Crabtree C50 type breakers, those distinctive brown bakelite ones of yesteryear!).