Maximum diversity and Garage DB

[Mo Fard]

Hi

We are doing some refurbish work at my house and I am planning to run a new feed to the garage and install a DB. Mainly because I don’t trust the exciting wiring in there and I have no idea where its supplies from. Plus I would like a separate DB as I use a lot of tools in the garage and I would like to allow for future lights or power I may install in the garden.
I am having two problems.

1. I have calculated the maximum demand for the house and after considering diversity we are using around 130A. I know we don’t come nowhere near that, as there is only 4 of us in the house. I am not sure how much power we can use before it becomes a problem.
2. I don’t know if I should install a MCB in the main DB an take the feed from there or take the feed after the main isolator.

Thank you
Mo

 

[Darkwood]

Welcome to the forum MO ...

Firstly as we seem to have a error in your demand for your premises, can you show us how you arrived at 130Amps then we can guide you and/or correct your sums then work from there.

 

[davesparks]

When you have an existing installation the easiest way to assess the max demand is to measure it.

What exactly do you mean when you say take the feed after the main isolator?

 

[Mo Fard]

Lighting: 22 lamp holders at 100w each. 2200W / 230V = 9.56A / 100 x 60 = 5.73A lighting after diversity at 60% of total demand.

8.5kw shower 36.95A

Power: 32A 32A 20A 16A.
32+ 40% of remaining circuits (32 + 20 + 16) = 59.2A

Cookers: 0ne 20A one 32A. Both 10A + 30% of the remaining. 16.6A + 13A = 29.6A

5.73 + 36.95 + 59.2 + 29.6 = 131.51A


ps I forgot to mention that we have two kitchens.

Hope I have made a mistake

 

[Mo Fard]

I Just mean taking the supply before the main distribution board.

 

[snowhead]

Lighting: 22 lamp holders at 100w each. 2200W / 230V = 9.56A / 100 x 60 = 5.73A lighting after diversity at 60% of total demand.

8.5kw shower 36.95A

Power: 32A 32A 20A 16A.
32+ 40% of remaining circuits (32 + 20 + 16) = 59.2A

Cookers: 0ne 20A one 32A. Both 10A + 30% of the remaining. 16.6A + 13A = 29.6A

5.73 + 36.95 + 59.2 + 29.6 = 131.51A


ps I forgot to mention that we have two kitchens.

Hope I have made a mistake

Your electricity bill will confirm you have made a mistake.

I assume each person only eats 1 meal at a time?

 

[Mo Fard]

Both kitchens sometimes gets used at the same time!

 

[Mo Fard]

Welcome to the forum MO ...

Firstly as we seem to have a error in your demand for your premises, can you show us how you arrived at 130Amps then we can guide you and/or correct your sums then work from there.

Do you think I have made a mistake? Should I be multiplying my diversity figure by 0.4?

 

[Darkwood]

It was the initial 130amps for a domestic - the diversity we are taught to use covers most situes in the domestic arena but not all, tbh if your not planning on having any heavy loads in the garage then I wouldn't worry about running a supply for a few lights and hand tools.

If your are concerned about heavy loads for your garage then list them out (Electric heating, machinery, welding sets etc)

 

[telectrix]

130A would give you a leccy bill of about £1136/ quarter. divide this figure by your average bill, then divide the 130A by the result. that will give you a more sensible demand.

 

[Mo Fard]

It was the initial 130amps for a domestic - the diversity we are taught to use covers most situes in the domestic arena but not all, tbh if your not planning on having any heavy loads in the garage then I wouldn't worry about running a supply for a few lights and hand tools.

If your are concerned about heavy loads for your garage then list them out (Electric heating, machinery, welding sets etc)

There will be a welding machine and a large air compressor.

 

[Risteard]

There will be a welding machine and a large air compressor.

But will you be using the welder and compressor whilst in the shower, and simultaneously cooking multiple meals in multiple kitchens?

 

[Mo Fard]

But will you be using the welder and compressor whilst in the shower, and simultaneously cooking multiple meals in multiple kitchens?

There are 4 of us in the house so there is possibility that some of the high powered equipment could be used at the same time. How ever unlikely this maybe I don't want to assume that it will never happen.

I do really want to learn the correct steps taken to calculate the maximum demand for a CU. Appendix A of the onside guide doesn't seem to give a realistic value.

 

[shanky887614]

But will you be using the welder and compressor whilst in the shower, and simultaneously cooking multiple meals in multiple kitchens?

at home have the induction hob (40amp), two showers 40amp each and a lot of other things running and dont have a problem on 100amp service head.

to open your eyes have a search to see what max demand is allowed per property.

compressors will use hardly any power cause they will cycle to keep the tank upto pressure.

unless this is an industrial welder it will be plugged into a wall with the max of a 13amp fuse and the same with the compressor.

go to screwfix and buy a clamp meter they cost say £40-50, clamp the main tails and start turning things on and you will be suprised at how low the draw is

 

[DPG]

I think the idea of a separate DB in the garage is a good idea if large compressors/welders etc. are going to be used. Saves any worry about overloading existing circuits. Daz