I'm trying to design a complete rewire for House of Multiple Occupancy (HMO), but going round in circles as there seems to be endless possibilities. I’m sure everyone will have a different view but hopefully after bouncing a few ideas around there might be a more obvious solution.
Background - it's 5 story's, basement is communal Kitchen/Dining Room/Lounge. Each floor has 3 rooms, (12 total). New central heating and DHW just gone in so no electric showers or heaters. Cooker is gas, new 100A cut-out in basement with CU. The final demand is unknown, and won't be known for a few years, so I need to build in some contingency in design. Some rooms might have combi microwave oven, Fridge, 2 ring 3kw hob. I’ll need additional circuit for hob, maybe combine with combi.
We’ll ignore communal areas as this has a known load which is unlikely to change, so straight forward design.
Room/Floor design options
Option 1: Radial circuit per floor, (12 sockets), Lights circuit per floor (3 energy saving bulbs). Advantages – simple & cheap (2 no. RCD, 8 no. MCB £68 + CU) Disadvantages – Can’t meter per room, nuisance tripping.
Option 2: RCBO Radial circuit per room (4 sockets), RCBO Lights per floor (3 energy saving bulbs). Advantages – Can meter per room, localised tripping. Disadvantages – More expensive (16 no. RCBO £320 + CU)
Option 3: Same as option 2, but with CU on each floor. Advantages – CU on each floor. Disadvantages – Much more expensive (£320 + 2 no. CU @ £48, total £416)
Core Network
Option 1: Cut-out in basement to CU. CU supplies basement and ground floor circuits, 50A MCB - 25mm SWA to 1st floor CU. 1st Floor CU supplies 1st/2nd & 3rd Floor circuits. Advantages – Cost effective, can run second feed in future using existing 25mm SWA. Disadvantages – Harder to expand in future
Option 2: Cut-Out - SP Distribution - 63A MCB to Basement CU and 63A MCB – 25mm SWA to 1st floor CU. Advantages – Better discrimination for main fuse, easier to run second feed in future using existing 25mm SWA. SP Distribution acts as REC Isolator. Disadvantages – Additional SP Distribution board about £100
Option 3: Cut-Out - SP Distribution - 50A MCB to each floor, each floor has CU. Advantages – Very scalable at ease. Disadvantages – Much more expensive, 10mm SWA £234 for 100M,
I’m not taking labour into account, clearly this will be proportional to the materials costs.
Having taken the time to write this so it’s legible has helped me get closer to a decision. My gut feeling is option 2 for both core network and floors. Once I have service to 1st Floor I am in dry riser, so very easy to change 2nd and 3rd floors as required.
Feel free to make more suggestions, did I miss something obvious?
Background - it's 5 story's, basement is communal Kitchen/Dining Room/Lounge. Each floor has 3 rooms, (12 total). New central heating and DHW just gone in so no electric showers or heaters. Cooker is gas, new 100A cut-out in basement with CU. The final demand is unknown, and won't be known for a few years, so I need to build in some contingency in design. Some rooms might have combi microwave oven, Fridge, 2 ring 3kw hob. I’ll need additional circuit for hob, maybe combine with combi.
We’ll ignore communal areas as this has a known load which is unlikely to change, so straight forward design.
Room/Floor design options
Option 1: Radial circuit per floor, (12 sockets), Lights circuit per floor (3 energy saving bulbs). Advantages – simple & cheap (2 no. RCD, 8 no. MCB £68 + CU) Disadvantages – Can’t meter per room, nuisance tripping.
Option 2: RCBO Radial circuit per room (4 sockets), RCBO Lights per floor (3 energy saving bulbs). Advantages – Can meter per room, localised tripping. Disadvantages – More expensive (16 no. RCBO £320 + CU)
Option 3: Same as option 2, but with CU on each floor. Advantages – CU on each floor. Disadvantages – Much more expensive (£320 + 2 no. CU @ £48, total £416)
Core Network
Option 1: Cut-out in basement to CU. CU supplies basement and ground floor circuits, 50A MCB - 25mm SWA to 1st floor CU. 1st Floor CU supplies 1st/2nd & 3rd Floor circuits. Advantages – Cost effective, can run second feed in future using existing 25mm SWA. Disadvantages – Harder to expand in future
Option 2: Cut-Out - SP Distribution - 63A MCB to Basement CU and 63A MCB – 25mm SWA to 1st floor CU. Advantages – Better discrimination for main fuse, easier to run second feed in future using existing 25mm SWA. SP Distribution acts as REC Isolator. Disadvantages – Additional SP Distribution board about £100
Option 3: Cut-Out - SP Distribution - 50A MCB to each floor, each floor has CU. Advantages – Very scalable at ease. Disadvantages – Much more expensive, 10mm SWA £234 for 100M,
I’m not taking labour into account, clearly this will be proportional to the materials costs.
Having taken the time to write this so it’s legible has helped me get closer to a decision. My gut feeling is option 2 for both core network and floors. Once I have service to 1st Floor I am in dry riser, so very easy to change 2nd and 3rd floors as required.
Feel free to make more suggestions, did I miss something obvious?
