MCB's Protecting Spur

[ban-all-sheds]

I've asked my electrician to make the system safe for a tumble dryer and washing machine to be used in the garage. His solution:

Garage consumer unit with RCD fed by the 2.5mm spur

He's a twit.

1. Does this adequately protect the 2.5mm spur cable to the junction box

No.

2. Is this work notifiable

Yes, as it involves a CU. But as you're using an electrician it's irrelevant.

3. Would connecting both washing machine and tumble dryer to one of the 16A MCB's be OK, assuming tumble dryer and washing machine are unlikely to draw more than 16A long-enough to trip the MCB, and that 2.5mm is OK to handle max. 16A

Hmmm - a B16 will pass 18A indefinitely, and will trip in 1 hour at 23.2A.

Tumble driers pull their rated current for the whole time they're on, or almost if they have an anti-crease finish.

4. If none of the above are OK, are there any other alternatives other than new ring or radial from the main house consumer unit

What's wrong with extending the ring?

 

[ban-all-sheds]

( need ban or sparks me think)

I won't take that personally

Nor I....

 

[ban-all-sheds]

A double socket is not rated at 26A.

I can't comment on other manufacturers but MK twin sockets are rated at 13A per outlet, 26A total.

http://www.mkelectric.co.uk/PDF/technical/LOGIC_PLUS_tech.pdf[/QUOTE]
BS 1363:1984 requires a double socket to pass 20A without overheating.

I don't have a copy of BS 1363-2:1995 so I don't know if the requirement has changed.

 

[GaryMo]

A double socket is not rated at 26A.

I can't comment on other manufacturers but MK twin sockets are rated at 13A per outlet, 26A total.

http://www.mkelectric.co.uk/PDF/technical/LOGIC_PLUS_tech.pdf[/QUOTE]
BS 1363:1984 requires a double socket to pass 20A without overheating.

I don't have a copy of BS 1363-2:1995 so I don't know if the requirement has changed.

Thanks though it seems MK have designed their product above the minimum standard of BS1363-2:1984 as it's rated at 13A per outlet which can only mean 26A in total.

EDIT - typo, changed 1995 to 1984

 

[ban-all-sheds]

Dunno - is the 1995 standard unchanged from 1984, i.e. it still only requires a twin outlet to be rated at 20A?

 

[GaryMo]

Sorry Ban, I meant 1984 as per your findings but the 1995 in your reply caught my eye.
I haven't seen any of the standards, just going by what you've read from the 1984 standard.

 

[securespark]

]My question is if the spur is from a junction box with no other load on the junction box, can it supply more than 13A.

In practice yes. But in theory, the maximum load from a spur from a RF circuit is 13A.

A 20A CB will indeed protect your 2,5 cable from overload, but drawing 20A from a spur off a RF circuit is not allowable.

 

[sparkyspike]

You could always split the ring to create two equally loaded radials and fit two 20A mcbs in the CU.

What else is on the circuit though? You may end up with the whole kitchen sockets on one of the 20A MCBs.

I was being midly sarcastic. Best thing is to extend the ring. You don't want to start loading spurs with more than 20A.

 

[OBB7]

Thanks everyone. All very useful.

For now I think I'll protect the spur cable with 16A MCB and run two seperate single sockets from that for washing machine and tumble dryer.

I reckon both appliances running together will draw about 15.5-16A, and so shouldn't trip the MCB even taking some peak currents at start-up into account. 16A MCB should provide sufficient protection for the 2.5mm spur - with some safety margin.

I'm happy total load on that part of the ring is OK as total number of appliances hasn't changed and I've never had any issues with CU MCB's trippping for the 10 years since the property was first built.

Trip characteristics of 16A MCB should make it just as safe (probably safer) than if both sockets were fed from a 13A FCU with a cartridge fuse. Would you agree?

Thanks again.

OBB7

 

[Pensdown]

2. Is this work notifiable

Yes, as it involves a CU. But as you're using an electrician it's irrelevant.

I agree that if it were allowed within the current regs, fitting a CU to a ring circuit would be notifiable because the sub circuits would technically be new circuits.

However, I was referring to the options I suggested which are not notifiable.

 

[ban-all-sheds]

Sorry - I guess I misinterpreted this sequence...

Garage consumer unit with RCD fed by the 2.5mm spur
2 x 16A MCB's in the garage consumer unit, one feeding a socket for the washing machine and another feeding a separate socket for the tumble dryer
.
.
Is this work notifiable

No it's not notifiable because you're altering existing and your garage is attached.

 

[Pensdown]

but drawing 20A from a spur off a RF circuit is not allowable.

Because an unfused spur fed in 2.5mm to a double socket is allowed, surly 26amps is the maximum allowed?

As long as the conditions of 433.1.5 are met, which is this case they probably are, I can't see a problem with installing an MK double socket fed in 2.5mm T&E as an un-fused spur.

 

[ban-all-sheds]

Because an unfused spur fed in 2.5mm to a double socket is allowed, surly 26amps is the maximum allowed?

Good question.

Is the assumption that you will not draw more current than that which BS1363 requires a twin socket to support, even if some manufacturers make their sockets to a higher standard?

 

[GaryMo]

It's down to the designer and the consideration they give to the circuit arrangement.

Page 362, Appendix 15

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable. This can be achieved by:
(i) locating socket outlets to provide reasonable sharing of the load around the ring.

If socket 1 on the ring will be subject to two large appliances that may be used for long periods of time then a twin socket shouldn't be spurred from that point.

 

[Spark123]

I reckon both appliances running together will draw about 15.5-16A, and so shouldn't trip the MCB even taking some peak currents at start-up into account. 16A MCB should provide sufficient protection for the 2.5mm spur - with some safety margin.

Have you read the rating plates on the washing machine and the tumble drier?