10A MCB protecting a Radial in a Garage.

[vwes59]

This should have been a straight forward install, and maybe it should be and I'm just being an a***, so be interested to know what you would have done if presented with the same thing.

Got called out to quote for an Outdoor Double Socket to go on the back of a garage. The house is reasonably new, built in the late 90's. The Garage has power. There is a DB in the garage with a 6A and a 10A MCB. 6A feeds the lights, the 10A feeds a single double socket on the back wall of the garage. This DB is fed by an SWA back to the main house DB and connected to a 16A MCB.

I've said to the client, before I can add the outdoor double socket to the garage radial, the 10A MCB needs to be changed to a 20A MCB, and the 16A changed to a 32A. This is to agree with the 18th edition regs which I believe states that socket radials need to be protected by a 20A MCB. The SWA cable and existing wiring are fine and need no alteration.

No surprise that I didn't get the job, but another sparky did who just put in the new double socket.

Was I wrong or right ?

 

[Pete999]

This should have been a straight forward install, and maybe it should be and I'm just being an a***, so be interested to know what you would have done if presented with the same thing.

Got called out to quote for an Outdoor Double Socket to go on the back of a garage. The house is reasonably new, built in the late 90's. The Garage has power. There is a DB in the garage with a 6A and a 10A MCB. 6A feeds the lights, the 10A feeds a single double socket on the back wall of the garage. This DB is fed by an SWA back to the main house DB and connected to a 16A MCB.

I've said to the client, before I can add the outdoor double socket to the garage radial, the 10A MCB needs to be changed to a 20A MCB, and the 16A changed to a 32A. This is to agree with the 18th edition regs which I believe states that socket radials need to be protected by a 20A MCB. The SWA cable and existing wiring are fine and need no alteration.

No surprise that I didn't get the job, but another sparky did who just put in the new double socket.

Was I wrong or right ?

What size SWA is feeding the Garage?

 

[ChipFanDave]

What regulation states that radial sockets must have a 20A OCPD ?

 

[vwes59]

They have 4mm SWA which can take 43A burried, and as for the regs, its Fig 15B in Appendix 15 which references 433.1, which states 20A for 2.5mm, 30 or 32A for 4mm. Also Appendix H in the OSG

 

[Pretty Mouth]

They have 4mm SWA which can take 43A burried, and as for the regs, its Fig 15B in Appendix 15 which references 433.1, which states 20A for 2.5mm, 30 or 32A for 4mm. Also Appendix H in the OSG

App 15 is a design guide. It is very useful, but doesn't have to be adhered to 100% - there's nothing stopping you from installing BS1363 sockets on a circuit protected by a breaker less than 20A, and in fact they can be put on lighting circuits (559.5.1(v)).

As far as 433.1 is concerned, the only reg that might be an issue is 433.1.1 (i):

433.1.1
The operating characteristics of a device protecting a conductor against overload shall satisfy the following conditions:
(i) The rated current or current setting of the protective device (In) is not less than the design current (Ib) of the circuit

If your client was planning to use it for a 3kW heater, this would fall foul of the above reg - the design current (~13A) would be greater than the 10A protecting it. But if it was going to be used for say a freezer, battery charger, or other low load, then it would comply.

 

[Strima]

Not an ideal circuit design but not unsafe.

 

[Baddegg]

Rcd protection anywhere in that setup?...

 

[Dave OCD]

The MCB sizes in the garage and at the supply end make me think someone has used a 1.5mm SWA , it does happen with new builds, penny pinching !

 

[vwes59]

They are planning to use a patio heater, which is what made me think the install wouldn't be up to spec, oh and yes there is an RCD...one on the whole house which is in the main DB, which I know isn't ideal. I suppose I could have spec'd a 20A RCBO for the garage DB. All the "new" housing estates near me were built around the same time, mid 1990's and they all have near identical installs.

 

[EricMark]

My son was wiring up some houses back in early 90's and it had 2.5 mm inside the house and 4 mm SWA to garage, and today we would not dream of wiring like that, but in the 90's that was the plan he was given to follow.

Back then no one considered electric car charging or patio heaters, or hot tubs, I would not have changed the overload protection, 10 amp is ample for lawn mower, etc. Had an electrician come to my house and said he wanted to upgrade the MCB's like that without doing a loop test first, he would be shown the door and told never to return.

 

[Dave OCD]

A patio heater ffs ?! Is there a more ridiculous waste of electricity ?

 

[DPG]

A patio heater ffs ?! Is there a more ridiculous waste of electricity ?

I'm no eco warrior, but surely they shouldn't be allowed in this day and age. Heating the outdoors - really??

 

[Dave OCD]

I think it's just another example of the idiocy that surrounds us these days sadly.

 

[Sparkgap]

So, the protective device is rated lower than the cable/outlet it's protecting and presumably higher than the prospective load? I don't see a problem.

 

[pc1966]

Given the feed is on a 16A MCB you might as well feed the sockets directly (or put in any MCB 16A+ in the garage CU) and keep the 6A MCB (or 3-5A fuse in FCU) to protect the lights.. You won't get any meaningful selectivity between a 16A and 10A MCB anyway!

It is far from ideal, but also it is not unsafe in any real way.