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Old July 12th 19, 08:53 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

For a 2.5mm2 radial circuit supplying a washing machine (via a double 13A socket) and a boiler/pump/valves (via 3A FCU) would a 16A or 20A MCB be 'best', and why?

If the spare 13A socket might end up being used for something, e.g. an occasional iron, does that sway the decision towards the 20A MCB?

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Old July 12th 19, 11:04 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

A double socket is usually rated to 20 amps.

Do you know if it is a ring main with 2
lots of 2.5mm2 or a single 2.5mm2 or a single 4.0mm2 cable?

If it's a ring main, you can use up to a 32A MCB but clearly no point if it's one double and a spur for boiler. So a 20A MCB would be sufficient.

If it's 4.0mm2 then a 20A MCB is also ok.

If it's a single run of 2.5mm2 then you will need to check how it's been clipped.between the consumer unit and the double socket.

Depending on what it's been mounted onto and what surrounds it to determine if it's a 16A or 20A MCB.

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Old July 12th 19, 11:14 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

Mathew Newton wrote :
For a 2.5mm2 radial circuit supplying a washing machine (via a double 13A
socket) and a boiler/pump/valves (via 3A FCU) would a 16A or 20A MCB be
'best', and why?


Radial circuit in 2.5mm you can use a 20amp MCB.
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Old July 13th 19, 01:19 AM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

On 12/07/2019 20:53, Mathew Newton wrote:
For a 2.5mm2 radial circuit supplying a washing machine (via a double
13A socket) and a boiler/pump/valves (via 3A FCU) would a 16A or 20A
MCB be 'best', and why?

If the spare 13A socket might end up being used for something, e.g.
an occasional iron, does that sway the decision towards the 20A MCB?


Either would adequately protect the cable, but the 20A will give more
flexibility, so that would be my choice.


--
Cheers,

John.

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Old July 13th 19, 10:54 AM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

But would you agree with me that in certain cable run situations, the cable cross sectional area is increased if it's going through thermally insulated routes instead of surface clipped to the wall and the MCB is not uprated as a result....

Ditto for extra longer cable routes to keep the voltage drop to less than 3%?

It's not clear from the OP if this circuit was already present or whether he created this new circuit?
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Old July 13th 19, 10:34 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

On Friday, 12 July 2019 23:04:22 UTC+1, wrote:
A double socket is usually rated to 20 amps.

Do you know if it is a ring main with 2
lots of 2.5mm2 or a single 2.5mm2 or a single 4.0mm2 cable?


As mentioned it's a 2.5mm2 radial.

If it's a single run of 2.5mm2 then you will need to check how it's been clipped.between the consumer unit and the double socket.

Depending on what it's been mounted onto and what surrounds it to determine if it's a 16A or 20A MCB.


It runs loose up inside an partition wall for ~1.5m, through joist centres for ~8m and then down behind dot-and-dab skimmed plasterboard on a block wall for ~1.5m. No insulation anywhere along the run.
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Old July 13th 19, 10:37 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

On Saturday, 13 July 2019 10:54:48 UTC+1, wrote:

It's not clear from the OP if this circuit was already present or whether he created this new circuit?


Apologies; it was already present - spurred off the origin of a 2.5mm2 ring circuit inside the consumer unit and I was contemplating putting it on its own MCB.
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Old July 13th 19, 10:47 PM posted to uk.d-i-y
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Default 'Best' MCB rating for boiler + washing machine?

On Saturday, 13 July 2019 22:37:59 UTC+1, Mathew Newton wrote:
On Saturday, 13 July 2019 10:54:48 UTC+1, wrote:

It's not clear from the OP if this circuit was already present or whether he created this new circuit?


Apologies; it was already present - spurred off the origin of a 2.5mm2 ring circuit inside the consumer unit and I was contemplating putting it on its own MCB.


To clarify this further, the current spur feeds only the boiler but if I were to move it to its own MCB (turning it into a radial circuit) it was then that I'd move the adjacent washing machine on to it also. My thinking was that'd it'd help spread the current between circuits, and also help keep potentially leaky devices on their own RCD protection if I opted for an RCBO instead of the MCB.


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