Sub-main protection

[Richard]

Quick one,

Job at work, New SWA submain (60A) underground from meter position in garage to the house of about 25 meters.

I'm under no doubt that an OCPD is required in the garage end and that you can't just use the main service fuse to protect that cable.

However I'm struggling to find a reg that supports me. Any clues please?

TIA

 

[telectrix]

Ib<In<Iz is a good start.

 

[telectrix]

Ib<In<Iz is a good start. what's the DNO fuse rating?

 

[Leesparkykent]

Quick one,

Job at work, New SWA submain (60A) underground from meter position in garage to the house of about 25 meters.

I'm under no doubt that an OCPD is required in the garage end and that you can't just use the main service fuse to protect that cable.

However I'm struggling to find a reg that supports me. Any clues please?

TIA

433.2.1 and 433.2.2

 

[Deleted member 26818]

There's nothing in BS7671 about using the main service fuse to protect anything, because the main service fuse is outside of the remit of BS7671.
BS7671 only relates to Installations, not the Supply Network, as such anything that is part of the Supply Network is ignored.

 

[Leesparkykent]

I may have misread the OP...the regs I've quoted in #4 are for why you may install a switch fuse. As Spin London has said you will not find a reg which states specifically that you can't use the DNO fuse as the OCPD for the sub main because it falls out of the scope of BS7671. It is a DNO requirement.

 

[Deleted member 26818]

Bugger, someone agreeing with something I said.

 

[Octopus]

Hum... the dno's ask for a switch fuse for the tails if they are over 3m but thats not included in BS7671 either.

I would say that you have to "ignore" the DNO fuse so I would work from there!

 

[Deleted member 26818]

I always figure the Installation starts at the Consumer terminals in the Meter.

 

[Richard]

Great, thank you all for your input.

 

[Richard]

Ib<In<Iz is a good start. what's the DNO fuse rating?

I'm pretty certain it's a 60A 1361

 

[telectrix]

I'm pretty certain it's a 60A 1361

then that will protect your 60A sub-main feed. assuming the cable you use is rated for 60A or more ( allowing for any derating due to installation method). just don't tell DNO.

 

[davesparks]

There used to be something in the regulations prohibiting it. But it was far too clear cut a statement and it left no room for ambiguity, so the IET removed it from more recent editions as they don't like things like that.

 

[Richard]

then that will protect your 60A sub-main feed. assuming the cable you use is rated for 60A or more ( allowing for any derating due to installation method). just don't tell DNO.

The cable is a 25mm 3c so no worries on that front. Personally I'd always fit a switch fuse as has been suggested, however it won't be my decision unfortunately.

Thanks again

 

[Leesparkykent]

The cable is a 25mm 3c so no worries on that front. Personally I'd always fit a switch fuse as has been suggested, however it won't be my decision unfortunately.

Thanks again

Who's decision is it?

 

[Octopus]

The cable is a 25mm 3c so no worries on that front. Personally I'd always fit a switch fuse as has been suggested, however it won't be my decision unfortunately.

Thanks again

So lets go with using the DNO fuse - are you planning an isolator?

 

[Richard]

Who's decision is it?

Employers

 

[Richard]

So lets go with using the DNO fuse - are you planning an isolator?

Yes, as far as I'm concerned it needs an isolator.

 

[Octopus]

Yes, as far as I'm concerned it needs an isolator.

So add a MCB to the isolator and the cost hardly rises!:39:

 

[Richard]

So add a MCB to the isolator and the cost hardly rises!:39:

Good plan Stan!