Max draw on a ring?

[MattT]

Hi All,

We have just moved into a house that recently had an extension built.

Basically it seems that in the utility part of the extension, the wiring is connected to a 63a 30ma RCD in a new consumer unit.

On this single ring, there are 3 double sockets. The way I plan to use the sockets are as follows....

1) 2000w washing machine
2) 600w tumble dryer and 2400w oven
3) 2400w dishwasher

Is this too much for the circuit?

 

[Murdochcat]

Run them at different times it should be ok

Run them together and the fuse will go

 

[MattT]

Thanks, I just realised I made a mistake in my description (and have now corrected it), it is a 63a RCD, presumably this will ok?

 

[Jurassicspark]

Thanks, I just corrected it, it is a 63a RCD

Even if you do manage to overload the RCD it will not trip. The MCB will. What is the mcb rated at for the sockets? Your load (even if everything was plugged in at the same time) would nearly add up to 31A. However, in the real world it would be much less as the appliances won't be using the full rated capacity stated in the manual.

 

[MattT]

Even if you do manage to overload the RCD it will not trip. The MCB will. What is the mcb rated at for the sockets? Your load (even if everything was plugged in at the same time) would nearly add up to 31A. However, in the real world it would be much less as the appliances won't be using the full rated capacity stated in the manual.

The MCB is a 32a for that thing (sorry my dad has been relaying messages to me, and every time it changes).

So now I have looked there is a 63a 30ma RCD but the specific one for this circuit is a 32a MCB

 

[ericmark]

As said, except for the tumble dryer, the items will likely use maximum only when first switched on, as soon as the air or water is hot, the heating elements will start switching off and on to maintain the temperature, but it is unlikely they will all switch on together. And with a ring final, the 32A overload should trip before there is any damage.

As to the RCD either the main fuse (DNO) should be smaller than the RCD rating, or the total of all MCB's fed from it should be smaller than the RCD rating.

There are exceptions, in my house the DNO fuse is 60 amps, but I also have solar, so total around 90 amp. But since all RCBO's the question does not arise.

 

[Jurassicspark]

So now I have looked there is a 63a 30ma RCD but the specific one for this circuit is a 32a MCB

As long as you're NOT using all of the appliances at the same time it won't trip anything.

 

[martygturner]

Run them at different times it should be ok

Run them together and the fuse will go

No it will not...its a 32amp mcb, the total load at all appliances at 7400 watts running at full tilt is 30.83 amps. MCB's have a trip curve ie the overload required to trip it, in most domestic situations are type B so has a trip of 3-5 times instant overload. 96-160amps. Have a look at : https://studyelectrical.com/2020/04/type-b-miniature-circuit-breaker-mcb-curves.html

If you just slightly overload a circuit say at 10% then it will probably never trip.

 

[Jurassicspark]

If you just slightly overload a circuit say at 10% then it will probably never trip.

But is it suitable to do so?

 

[martygturner]

But is it suitable to do so?

Probably not, but that's not the point is it ? Oh no I have the dishwasher, cooker and tumbler dryer all working ...should I boil the kettle ?? lets just get a calculator out and work it out.

 

[Jurassicspark]

Probably not, but that's not the point is it ? Oh no I have the dishwasher, cooker and tumbler dryer all working ...should I boil the kettle ?? lets just get a calculator out and work it out.

It's better than having a mcb trip. Especially for someone who doesn't know diddly squat.

 

[martygturner]

It's better than having a mcb trip. Especially for someone who doesn't know diddly squat.

Is it not better to just tell people the truth rather than telling them otherwise...

As long as you're NOT using all of the appliances at the same time it won't trip anything.

When using all the appliances listed by the OP there is not a cat in hell's chance of the mcb tripping. Perhaps it would have been better to have advised him that he was getting close to the limit of the circuit and not to add other high loads to it...but even if he did it won't be causing a nuclear meltdown.

 

[Jurassicspark]

When using all the appliances listed by the OP there is not a cat in hell's chance of the mcb tripping.

Three sockets with four loads at the moment with a chance of two more appliances being plugged in.

Though it is pushing it to the limits. Not very civilised.

 

[Jurassicspark]

Is it not better to just tell people the truth rather than telling them otherwise...

Pushing a circuit to nearly the maximum capacity is not a very great idea mate. You've got other factors to consider such as the ring being balanced and the wiring. Assuming if it's a 2.5mm ring circuit it won't be very good running 30A through it (depending on how it is installed.)

 

[bernardgreen]

Running an MCB above it's rated current can cause the thermal sensing element to become hot enough for long enough to alter the sensitivity of the MCB and alter the current needed to trip the RCD. Worse case is the mechanism fails to trip and a fault current is not disconnected