new supply needed for granny annex?

[sparks1664]

I've been asked to quote for wiring a granny annex and i'm in two minds whether it needs a second supply or not, i know the on site guide is only a guide and you have to do whats practical but because there's a real possibility of cookers, kettles dishwashers etc.. being used at the same time i'm thinking it would be better on a separate supply, wiring as follows

x2 - 32A cookers
x3 - 32 rings
45A garage/shower (used daily)
15A immersion
6A lights
6A lights

I get about 153A after diversity

what would you do?

 

[westward10]

60/63A. Are you loading this on an existing supply.

 

[LankyWill]

Out of interest what is the heating system? If you could swap that shower to a mixer it would help improve the loading situation.

I'd weigh up the cost of an extra supply to that of changing the plumbing.

I still reckon the single supply will more than cope with that demand anyway. How did you calculate the shower and cooker? Seems high

 

[sparks1664]

heating's on a combi , one cooker is 4.5kw the other 10.5kw. first 10A plus %30 of rest. i calculated shower as 100% with a few sockets/lights in garage, i have suggested changing shower, how did you get 60A?

 

[sparks1664]

new 32A cooker, ring and lights

 

[sparks1664]

i see you divided it all by 0.4 i already did that??

 

[Octopus]

NO property would EVER draw 163 a...

The diversity calcs in the OSG are so old hat and take absolutely no account of the reality these days....

Even multiplying by 0.25 will give you 58A but that is too high.... IMHO

 

[mhar]

6 bed holiday cottage, 3 electric showers, cooker etc. First I was suprised when the seals fell off, second I was suprised when the fuse fell out, third I was really suprised to find that it had all been running quite happily for over 10 years on a 60A fuse. I worry a lot less about maximum demand these days and would agree with all the others

 

[sparks1664]

Ok thanks for the help guys, you would think amendmant 3 would have a relevant method for calculating diversity

 

[Resu]

There is a 12 bedroom guesthouse local to me with an electric shower in each room. The property is fed with a standard single phase supply and the client assured us he had never had an issue! Was tempted to pull the fuse carrier and see if there was actually a fuse in there!

 

[DPG]

That's nothing. I know of a 32 bedroom old people's home that is powered using an extension lead from a nearby house with a 13A fuse in it. In fact no, it's a 3A. So there.

 

[Dave OCD]

There is a 12 bedroom guesthouse local to me with an electric shower in each room. The property is fed with a standard single phase supply and the client assured us he had never had an issue! Was tempted to pull the fuse carrier and see if there was actually a fuse in there!

They serve breakfast by room numbers at ten minute intervals so only a couple of showers at most can ever be on simultaneously.

 

[Resu]

They serve breakfast by room numbers at ten minute intervals so only a couple of showers at most can ever be on simultaneously.

Possibly! They take a lot of these minibus tours so most, if not all rooms being filled at the same time of evening. Can only be luck that they've managed so far.

 

[telectrix]

run shower from combi boiler. existing supply will cope.

 

[Resu]

I've been asked to quote for wiring a granny annex and i'm in two minds whether it needs a second supply or not, i know the on site guide is only a guide and you have to do whats practical but because there's a real possibility of cookers, kettles dishwashers etc.. being used at the same time i'm thinking it would be better on a separate supply, wiring as follows

x2 - 32A cookers
x3 - 32 rings
45A garage/shower (used daily)
15A immersion
6A lights
6A lights

I get about 153A after diversity

what would you do?

As mentioned if new shower was mixer type then you can cross off the shower and immersion, then you're sorted.

 

[davesparks]

That's one heck of a big granny flat if it needs two cooker supplies and three ring circuits!

 

[davesparks]

heating's on a combi , one cooker is 4.5kw the other 10.5kw. first 10A plus %30 of rest. i calculated shower as 100% with a few sockets/lights in garage, i have suggested changing shower, how did you get 60A?

If they are having a combinboiler then why have you allowed for an immersion heater?

 

[DPG]

I think he's included the two ring mains from the main house, and I'm assuming the immersion is in the main house. Could be wrong.

 

[sparks1664]

As DPG said