calculation sanity check please

[Penance]

Hi All,

Been away for a few weeks but now starting planning on a job.

I will be installing a sub main for a single room office area in a house extension.

The sub main will be run in SWA protected by a 63a MCB. The run is 7 meters to a CU that will have 3 circuits on RCBO's
Circuits are
1x 32a ring for office area
1 x 20a A3 radial for small kitchen area within office. Kitchen area is just a microwave and kettle.
1 x 6a lighting

So my calcs have been -

Max demand
((20 + 6)/0.4) + 32 = 42.4
installation method is clipped direct so Lt is 42.4
Calculated VD is 1.49 using 10mm XLPE SWA

Does this all look OK?

 

[Engineer54]

More like 22A and even that would be conservative!!!

 

[Penance]

for max demand?

did you add all breaker values and divide by 0.4?

 

[VoltzElectrical]

for max demand?

did you add all breaker values and divide by 0.4?

did you read the post?

 

[Penance]

did you read the post?

Yes, am I being dim and missing the obvious?

 

[yellowvanman]

Way over spec'ed. Office equipment will be minimal in terms of ampage. How many people are going to be there?

Even on the ring in a house you would rarely get anywhere near 32A, and if you did it would be there for a few minutes (whilst the kettle boiled).

 

[Penance]

3 maybe 4 people, mostly using laptops and desk top printers.

Do you mean the SWA is overspec?
Reason for it being armoured is that customer doesn't want office boss needing to access house if there's an rcd trip.
10mm cuz I'm old fashioned and can't get head round smaller for a sub main.

 

[yellowvanman]

Laptops are small consumers or power, so are printers. No problem with using SWA if you don't want to protect it with an RCD, but I'm sure 6mm will be more than adequate with a 40A MCB, if the installation method permits, or even with a 32A MCB!

 

[telectrix]

agree^^^

 

[Penance]

Yea see your point.
Well over spec is better than under!

 

[telectrix]

10mm xlpe would be right if there was going to be a shower installed as well.

 

[Penance]

10mm xlpe would be right if there was going to be a shower installed as well.

A clean worker is a happy worker?

 

[nikmet]

When it gets colder the portable fan heaters will appear 3kw each lol