Advice needed on expanding electrical consumer unit

[cybertek]

Hi,

I need on advice on wheher it would be possible to expand my existing electrical consumer unit which currently has a 100ma and 80ma RCD which supplies power to the house and detached garage.

We've purchased a whirlpool bath which is comsumes 4800w and requires a 25amp C rated 30ma RCD connection supply.

I'v taken a look at the consumer unit and cannot see any spare slots to accomodate an MCB.

Can anyone advise me if it would be possible to upgrade the consumer unit to a larger one to accomodate the new mcb or if it would be easier to somehow add another smaller consumer unit to service just the whirlpool bath which would feed of the existing consumer unit's 100ma or 80ma mcb block.

Thanks in advance cybertek

 

[ban-all-sheds]

It will be much easier to add a separate mini-CU for this.

Unless you have a particular reason to want your existing CU replaced, that is what you should ask your electrician to do.

 

[Steve]

If you have 2 lighting circuits, run a 20A radial (2.5mm²) from the existing CU to 2 FCUs with 5A fuses, connect the lights to these FCUs.

This frees up one space in the CU! Run a 32A radial from the new spare to your bath. The protective device will be a 32A RCBO rated at 30mA trip.

 

[Spark123]

Do they really make a 80mA RCD?

 

[andy]

Do they really make a 80mA RCD?

not that im aware of

 

[kai]

If you have 2 lighting circuits, run a 20A radial (2.5mm²) from the existing CU to 2 FCUs with 5A fuses, connect the lights to these FCUs.

Surely a 10amp circuit would do the job just as well?

 

[Spark123]

I think what crafty is suggesting is to use use two fcu units for inconvenience purposes i.e. so you shouldn't lose both lighting circuits at once. Good idea in theory, although then you end up with having to replace 5A fuses instead of just having an MCB to reset.
I personally don't like the idea of providing domestic lighting at 10A as there is no way of controlling what type of light fittings are used, SBC and SES are rated for a max fuse of 6A.
I'd personally go with bans idea of a mini cu with 30mA RCD incomer and 25A MCB.

 

[Steve]

I think what crafty is suggesting is to use use two fcu units for inconvenience purposes i.e. so you shouldn't lose both lighting circuits at once. Good idea in theory, although then you end up with having to replace 5A fuses instead of just having an MCB to reset.
I personally don't like the idea of providing domestic lighting at 10A as there is no way of controlling what type of light fittings are used, SBC and SES are rated for a max fuse of 6A.
I'd personally go with bans idea of a mini cu with 30mA RCD incomer and 25A MCB.

yes. Also, a 20A MCB and 5A fuse combo would be less likely to nuisance trip/blow when a filament lamp blows (i think). I suppose you could use a 10A MCB, keeping the 2 FCUs.

And my method of freeing up an MCB slot is a (competent) DIYers job. adding a new CU with henley blocks isnt. Only trying to help the OP

 

[cybertek]

Hi All,

Thanks for the replies.

Just another query. I've looked at the mini consumer unit in my garage which has a which as a 100ma main fuse with a 5 and 16 amp MCB in the unit which has 2 spare slots.

I was thinking it would be possible to add the 25amp C rated RCD in the garage's mini conumber unit and run a amoured / sheilded cable from the unit to the outside wall of the bathroom and connect to the whirlpool bath.

I welcome anyone's thoughts on this.

Thanks

Cybertek

 

[plugwash]

If you have 2 lighting circuits, run a 20A radial (2.5mm²) from the existing CU to 2 FCUs with 5A fuses, connect the lights to these FCUs.

Surely a 10amp circuit would do the job just as well?

yeah if the cuircuit is in spec at 10A and doesn't have any SES or SBC fittings.

and if feeding two FCUs you may as well make the breaker feeding em 20A to improve the chances it'll discriminate.

 

[Steve]

cybertek, where does the garage cu take its feed from? Is it from the main cu in the house? or has someone split the meter tails? If its from the main CU, what rating MCB is it on? What size cable feeds it? i'm only thinking, it was probably not installed with expansion in mind.

The main switch in the garage CU - is it an RCD? What are its exact ratings? (mA and A)

 

[ebee]

Do they really make a 80mA RCD?

NO 80A 30mA

 

[Spark123]

I thought it was a bit of an odd size....