going 3phase from single (residential)

[virgilns]

I have a piece of equipement I want to run on 3phase in my garage.

My new house already has all 3 100amp phases presented in the utility cupbaord but only one phase taken to the meter and on to the CU. My energy company can add in an addition 3phase meter but it'll incur a £50/yr standing charge or they can swap the meter for a 3phase free of charge).

What I'd like to do is keep the existing house CU (currently on phase 1) and run a 3phase feed to the garage to feed my metal working lathe and feed all the other garage electrics from (say phase 2)

So...

L1 to existing single phase house CU
L1/L2/L3 to 3phase CU >>armour cable >> Garage 3phase CU and distribute L2 to Garage sockets/lights

The only issue with this is that I need to add in isolation/protection in the house utility cupboard for the 3phase cable running to the Garage.

Can I do this or would I need to repalce the house single pahse CU with one big 3phase distribution board in the utility cupbard and just branch off the single phases (L1 for house, L2 for Garage) and run L1/L2/L3 to the workshop for the Lathe?

Thoughts?

Is there any benefit of 3phase distribution in the house (as oposed to the safety down side of having 415v) dist in the house?

Ultimately whilst the house is being renovated most of not all cabling will be replaced/renewed.

Cheers,

V.

 

[JohnD]

how big is the house and why has it got a 3-phase supply?

 

[virgilns]

1912 built 6 bed (2,500 sqft) over 3 floors (built like that, not extended). Electrical upgrade work undertaken between say 10-20 years ago...so MCB style CU but some evidence of antique wiring in house still.

No idea why it has 3phases run in...presume that's just what the power co did when they laid up the cable?? Not been able to test L2 and L3 so don't know for sure they're live...is a private spark allowed to test the unmetered tails or is this a job for the power company only (they're wire sealed)?

 

[plugwash]

You need to speak to your electrician so you can get a setup you are both happy with.

Ideally you should balance loads across the phases, particually if you have multiple large single phase loads loads but also ideally you should try and avoid having equipment on multiple phases in the same room.

I would definately fit a three phase board in the garage as I suspect it's not unlikely you will end up with more than one three phase machine once you've done the work of puttting the supply in. Either a four or six way board depending on how much expansion room you want to leave.

For the house end I see a few options:

Option 1 use a three phase board in the house. A 6-way board is probablly appropriate here. Imo this is the best option but also the most expensive as you will have to use RCBOs (though IMO you should be using RCBOs anyway).

Then put upstairs on one phase, downstairs on another and single phase loads in the garage on the remaining phase.

Option 2: Use a switchfuse for the supply to the garage and keep the existing CU, this is probablly the cheapest option but it is messy and means your load is unbalanced among the phases. I would NOT do this if you have both an electric cooker and a shower,

Option 3: Use a switchfuse for the supply to the garage and use two seperate CUs in the house, this will let you get a good phase balance and will probablly be cheaper than a three phase board but IMO it's a rough as hell way of doing things.

 

[dhutch]

Or another option, which you may or may not have explored, is to get an inverter controler to run the three phase motor from a single phase.

Not that I wouldnt like to have three phase in my garage if I could do it for free.


Daniel

 

[JohnW2]

...For the house end I see a few options:
Option 1 use a three phase board in the house. A 6-way board is probablly appropriate here. Imo this is the best option but also the most expensive as you will have to use RCBOs (though IMO you should be using RCBOs anyway). ... Then put upstairs on one phase, downstairs on another and single phase loads in the garage on the remaining phase.

How appropriate that approach is will depend on the actual physical size and layout/arrangement of the house. I don't think it would be a sensible option in my house ...

Mine is very large, 3-story (plus cellar and roofspace). One phase directly supplies a ground floor CU. Sub-mains via switch fuses feed the other two phases to CUs in the two upper floors, cellar and a detached garage. To run all final circuits back to a single CU/DB would result in some uncomfortably long final circuit lengths, which could well result in the need for 'fatter than usual' cables - e.g. a ring final to the top floor could well end up >100m, and a lighting circuit to the roofspace would also be very long, as would some shower circuits. With the distributed system I have, no final circuits are 'any longer than usual' and the loading is reasonably balanced across the phases.

Kind Regards, John

 

[jeepmadmike]

You lucky man having a 3 phase supply available.

I would fit a 3phase DB in the house and another in the man cave

House loads can be evenly split between phases and it keeps it simple

 

[JohnW2]

You lucky man having a 3 phase supply available. I would fit a 3phase DB in the house and another in the man cave House loads can be evenly split between phases and it keeps it simple

Yes, a single 3-phase board for the whole house is an option but, as I said, in my case that would result in some of the final circuits being extremely long, which introduces various problems. My arrangement doesn't do too badly at balancing the phases. The ground floor, which has more than its fair share of larger loads, gets a phase to itself, whilst the other two phases serve the four other areas (including water heating and showers - although they very rarely get used). Another advantage is that it enables me to DP isolate individual areas when I so wish. I did contemplate having 3-phase supplies to garage and cellar (partially workshop) but I've managed fine for ~25 years without it.

Kind Regards, John

 

[virgilns]

Or another option, which you may or may not have explored, is to get an inverter controler to run the three phase motor from a single phase.

Not that I wouldnt like to have three phase in my garage if I could do it for free.


Daniel

Got one of those now, which is how I ran it before I moved...not ideal though as quite often requires a little 'nudge' of the chuck to turn the motor slightly to get it started...

 

[Bungle4x4]

have you considered changing the motor to cap start single phase? might be a cheaper option.

but i would love the 3phase option

 

[virgilns]

You need to speak to your electrician so you can get a setup you are both happy with.

Ideally you should balance loads across the phases, particually if you have multiple large single phase loads loads but also ideally you should try and avoid having equipment on multiple phases in the same room.

I would definately fit a three phase board in the garage as I suspect it's not unlikely you will end up with more than one three phase machine once you've done the work of puttting the supply in. Either a four or six way board depending on how much expansion room you want to leave.

For the house end I see a few options:

Option 1 use a three phase board in the house. A 6-way board is probablly appropriate here. Imo this is the best option but also the most expensive as you will have to use RCBOs (though IMO you should be using RCBOs anyway).

Then put upstairs on one phase, downstairs on another and single phase loads in the garage on the remaining phase.

Option 2: Use a switchfuse for the supply to the garage and keep the existing CU, this is probablly the cheapest option but it is messy and means your load is unbalanced among the phases. I would NOT do this if you have both an electric cooker and a shower,

Option 3: Use a switchfuse for the supply to the garage and use two seperate CUs in the house, this will let you get a good phase balance and will probablly be cheaper than a three phase board but IMO it's a rough as hell way of doing things.

Thanks.

For option 1, out of interest why do you consider a TP distribution box so expensive ?

Also not sure 6way would be anywhere near enough mcbos?? Three floors of lights 3 floors of sockets (I'd rather keep them on separate rings for later work...) Oven(s), Garage 2 phase...and 3 phase to lathe...got to be at least 10? No shower though....

Kind of like your option 3 but if it's considered a hodge then I'd steer clear..

Like the sound of the cu per floor as in later reply...but might be a little over kill for my 3 floors...they're not THAT big...

 

[virgilns]

have you considered changing the motor to cap start single phase? might be a cheaper option.

but i would love the 3phase option

briefly, before I bought the inverter but I'd lose the two speed function and have to hodge the wiring in the lathe to get reverse. I'd rather keep it as un-molested as possible, spend the few quid to get TP into the garage and sell the inverter to cover the cost.

As said above, TP opens up a new little world of bargains on ebay...all the little industrial kit industry doesn't want and the diyer can't use

 

[JohnW2]

Also not sure 6way would be anywhere near enough mcbos?? Three floors of lights 3 floors of sockets (I'd rather keep them on separate rings for later work...) Oven(s), Garage 2 phase...and 3 phase to lathe...got to be at least 10? No shower though....

The secret is in the terminology A "6-way" 3-phase DB has 6 sets of 3-phase 'positions', each of which you can think of as 3 single-phase 'ways' for single-phase circuits. Hence, a 6-way 3-phase board has space for installing 6 x 3-phase circuits, 18 x single-phase circuits, or intermediate situations between those two extremes (e.g. 2 x 3-phase circuits plus 12 x single-phase ones).

Kind Regards, John.

 

[Iggifer]

Also not sure 6way would be anywhere near enough mcbos?? Three floors of lights 3 floors of sockets (I'd rather keep them on separate rings for later work...) Oven(s), Garage 2 phase...and 3 phase to lathe...got to be at least 10? No shower though....

A 6 way TPN board effectively gives you 18 SP ways

1L1
1L2
1L3
2L1
2L2
2L3 etc etc

Obviously if you're going to have a TPN board in the garage that reduces you to 15 ways. If you dont think 6 is enough, go for an 8, or a 12 or 16 (that's getting a bit ridiculous though).

edit: damn too slow

 

[jeepmadmike]

You lucky man having a 3 phase supply available. I would fit a 3phase DB in the house and another in the man cave House loads can be evenly split between phases and it keeps it simple

Yes, a single 3-phase board for the whole house is an option but, as I said, in my case that would result in some of the final circuits being extremely long, which introduces various problems. My arrangement doesn't do too badly at balancing the phases. The ground floor, which has more than its fair share of larger loads, gets a phase to itself, whilst the other two phases serve the four other areas (including water heating and showers - although they very rarely get used). Another advantage is that it enables me to DP isolate individual areas when I so wish. I did contemplate having 3-phase supplies to garage and cellar (partially workshop) but I've managed fine for ~25 years without it.

Kind Regards, John

It's a house the circuit lengths arnt going to be that long it's not usual for industrial circuits to be hundreds of meters long.