How much to replace old consumer unit

[JamesHughes]

There is no cabling in to the garage at the moment, but if 3ph is available then I would want that (lathe and milling machine both 3ph). Cable could be run around out side of house, then jump the 1.5m gap to the garage, if that would be cheaper than underground.

Supply cab serves only the house AFAIK. Unless there is some sort of underground bunker I don't know about!!!

James

 

[Steve]

If you just want 3 phases in the garage, you really ought to use all 3 in the house too. Otherwise, you could end up overloading one of the phases, though its unlikely.

You'd have a 3ph DB in the house, a smaller version of the one adam showed you, probably 4 or 6 way (12 or 18 single phase ways). And from that would come all the house circuits, and the garage 3ph circuit.

Then in the garage, to save costs you could just use a stripped down CU with your breakers in a row. You will probably only have one 3ph circuit and a couple of 1ph circuits, so a DB would be a waste. I'm not sure if a single point of isolation is required for a garage though.

Given 3ph DBs dont have the capacity to split the load with an RCD, you'll probably need to use RCBOs, for the circuits that need it. This, again, is extra cost.

My thoughts!

3phase is also the ideal fuel for heat pumps, a 500% efficient way of heating your home. Google heat pump, research it. I'll bet its cheaper to run than oil.

 

[plugwash]

i'd think you could adapt a CU (even a split load one) to allow a single 3 phase circuit pretty easilly by the following method.

replace the incomer with a four pole one.
put the 3 phase MCB at the end of the non-rcd section with one of its poles fed by the last position on the bussbar.

add wires from the other poles of the 3 phase MCB direct to the incomer.

but i tend to agree in the house at least you want a 3 phase DB to allow you to spread the load between phases and frankly if you have more than one three phase load in the outbuilding you probablly want one there too.

 

[JamesHughes]

First off, thanks for all the replies - its obviously a lot more complicated than I originally imagined!!

I've had a look at prices for 3ph DB's (Screwfix), and they are not outrageous, so will probably look to go that way, but will need to get a quote in. I estimating about 2.5x the price of a CU.

Would I be right in thinking (not to do myself, just for own knowledge)

Put in a DB inb house, spreading the phases around - for example upstairs one phase, downstairs one phase, cooker/showers one phase type of thing to balance things.

Runs a three ph cable to garage where I have a smaller DB, powering lights and sockets, with couple of 3ph sockets for the equipment.

James

 

[Steve]

Yes. In the garage you might not even need a 3ph DB, just a large domestic consumer unit with the devices individually wired.

Alternatively, put the SP circuits next to the mainswitch, and feed them using a busbar, from the last pole of the mainswitch.

 

[JamesHughes]

Cheers Crafty,

top notch explanation.

James