Ok to add socket for microwave?

[Boilerman2020]

Hello Everyone,

I just want to make sure I'm ok adding this new socket for a microwave.

I plan on putting in a single socket on a 13A fused switch and linking it as a spur from the existing radial circuit. It will be in 2.5mm2 T+E, running from a circuit which is protected by a 20A circuit breaker. The cable will be run in surface trunking over tiles vertically and across in to a cabinet, all sealed safely. On the board, it shares a 63A RCD with four other 20A fuses.

I have attached a diagram showing what is already on it.

 

[EFLImpudence]

Yes, that's fine.

The fuse and switch aren't really needed.

 

[Boilerman2020]

Thanks for your reply! I guess it's better to put a FCU on it because if it has a problem, it won't affect the whole line I don't think? i.e if it trips for some reason, the boiler and fridge etc stay on? It is a 1000W microwave so would require a double pole FCU I believe.

 

[EFLImpudence]

Thanks for your reply! I guess it's better to put a FCU on it because if it has a problem, it won't affect the whole line I don't think? i.e if it trips for some reason, the boiler and fridge etc stay on?

True - but just a 20A switch is required for that - although they cost more than the FCU.

It is a 1000W microwave so would require a double pole FCU I believe.

I think they are all DP.

 

[flameport]

! I guess it's better to put a FCU on it because if it has a problem, it won't affect the whole line I don't think? i.e if it trips for some reason, the boiler and fridge etc stay on?

Unlikely.

If the RCD trips, the whole circuit and several others are off.
If the circuit breaker trips, the whole circuit is off.
If the fuse in the FCU blows, then only the microwave is affected - but it already has an identical fuse in the plug. You don't need another one.
If there is some problem with the microwave, it can be disconnected by unplugging it.

 

[Boilerman2020]

It's a built in microwave though

 

[Taylortwocities]

As above. Connection-wise its ok.
But I would worry about a 20amp MCB being man enough for Fridge/Freezer + microwave + dishwasher + whatever else is plugged in to the 4 x 13A double sockets.

 

[Boilerman2020]

That's my worry Occasionally we have had a heater plugged at Christmas when using a lot of sockets and the breaker has tripped.

But it might be a big job to remedy it. We would have to put in a new circuit and corresponding MCB, that could take some of the load. Too big a job to change to a 4mm ring. I've thought about putting some of the load on to the 6mm/ 32A hob/oven circuit. I think the hob is about 5-6kw and is wired in 2.5mm to a 13A FCU, which goes to a switched 45A FCU via 6mm which also has the (4.4kw) oven. Maybe an opportunity there somewhere?

Edit: I mixed up the hob and oven .. it's late

 

[AndyPRK]

See if a 25A Mcb is available for your cu

 

[Taylortwocities]

Occasionally we have had a heater plugged at Christmas when using a lot of sockets and the breaker has tripped

In that case, the circuit is already at its limit. A new circuit would be best.

Too big a job to change to a 4mm ring.

Why 4mm ring?

The current circuit is a radial probably wired in 2.5mm. It could be turned into a ring and the MCB uprated to 32amp.

 

[Boilerman2020]

See if a 25A Mcb is available for your cu

That seems like a great idea. There are currently 5x B20s protected by a 63A RCD so I could ask to have one upgraded. It's not much, should handle it.

In that case, the circuit is already at its limit. A new circuit would be best.

Why 4mm ring?

The current circuit is a radial probably wired in 2.5mm. It could be turned into a ring and the MCB uprated to 32amp.

Also a great idea, pushing it though unless changing out the 63A RCD for a 80? A 25A swap for the 20A might be easiest (and cheapest!).

 

[DetlefSchmitz]

pushing it though unless changing out the 63A RCD for a 80?

Well changing the MCB doesn't mean you are taking more current than at present (well, apart from the microwave). Are you likely to be taking 230 x 63 = 14.49kW at a time on those circuits?

 

[Taylortwocities]

Also a great idea, pushing it though unless changing out the 63A RCD for a 80?

And what would you expect that to achieve?

 

[Boilerman2020]

Well changing the MCB doesn't mean you are taking more current than at present (well, apart from the microwave). Are you likely to be taking 230 x 63 = 14.49kW at a time on those circuits?

No I can't see it unless a lot of big electric heaters plugged in at the same time. With diversity in mind also it would be just fine.

And what would you expect that to achieve?

The existing 63A should be fine then, I was thinking about overcurrent protection rather than residual.. think that would be an RCBO not a RCD.

 

[AndyPRK]

Yeah an RCD won’t trip at 63A or 80A. It’s just the thickness of the internals are rated to handle that current.

In practice your main fuse may only be 60 or 80A and circuits maybe split across 2 RCDs

What brand is your consumer unit? Got a pic? B25 aren’t available for all brands.